Physics and Instrumentation Study Guide - Comprehensive overview
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Patient Handling and Safety
Study Guide Menu

  • Patient Education and Preparation 

  • Patient Screening

  • Radiation Safety 

  •  Radiation Dose and Important Factors

  •   Overview of Contrast Media                                                                                                                                              

        

Patient Education and Preparation

All patients should be informed as to the nature of the CT examination and how to prepare for the CT appointment. The more the patient understands the more cooperative and calm they will remain. The type of clothing they are currently wearing should be discussed and the fact that they may be required to change into a hospital gown. The removal of metal such as zippers, buttons, snaps, dentures, eyewear and jewelry from the area of interest should be addressed.


The patient should also be informed of the use of contrast media prior to the scan. Explain how the contrast media improves the visualization of pathology and outlines the vascular and bowel structures so the patient will understand the reason for administering contrast. A review of reactions resulting from contrast administration must be discussed with the patient before the procedure begins.


The patient must receive precise instructions, based on the individual practice of the facility, as to the drinking schedule of oral contrast media.  This could be instructions to begin drinking the night before and/or the morning of the exam.  If the prep includes any dietary or fasting requirement the patient must be informed.  It is common in some CT exams to require the patient to fast for several hours before the scan. Depending on the patients history it may be determined that the patient needs to be pre-medicated with antihistamines to decrease the chance of a severe allergic reaction.


Patients who are taking the diabetes drug Glucophage (Metformin) must understand the need to stop the use of the diabetes drug for 48 hours following a procedure involving the use of contrast media.  Glucophage use should resume only after the reassessment and determination of adequate kidney function.

Important Concept

Remember that Glucophage and Metformin are both names of diabetic drugs and the use of these drugs is stopped for a period of 48 hours following a CT procedure using contrast media.


Patients should be told what to expect once placed in the CT scanner. They should be aware the CT gantry will move around them and the patient table will move through the gantry aperture. It is also very important to emphasize the need for the patient to remain still during the scan in order to produce diagnostic images. If necessary, the CT tech should use pads and straps to aid in the immobilization of the patient.  Patients also need to have any special breathing instructions explained to them before the procedure begins.


Before an exam begins the CT tech must determine if the patient is capable of holding their breath the necessary amount of time. When an ill and/or elderly patient is involved a shorter helical study may be substituted for a longer extended study.  When a patient is unable to hold their breath the tech should give instructions on breathing slow and shallow to minimize movement.


Some individuals experience claustrophobia when placed in the CT scanner.  If reassurance from the CT tech does not eliminate this, most facilities request the patient receive a prescription for a sedative from the referring physician before the scheduled exam is to take place. When the time is taken to educate the patient on what to expect before, during and after the CT exam the resulting CT images will be of the best possible quality.
A note on signed consent forms.


Most facilities require that patients sign a consent form prior to the CT scan being performed. Consent forms indicate the patient has received adequate information and understands the procedure and possible complications involved with the exam, IV contrast and sedation. Written consent forms arenot required by law in every state.  The patient’s consent is needed to perform a biopsy or drainage, as these are invasive and considered a surgical procedure.  Another use of consent forms is to ensure that facilities receive payment for the procedure performed.

Important Concept

Some states do not require a consent form.
Often technologists overlook the fact that the patient is anxious to know the results from their CT exam.  By providing an estimate as to when the results will be available for the referring physician the level of patient anxiety can be reduced.


Patient Screening

Four Key Screening Topics:

  • Reason for the exam

  • Possibility of pregnancy

  • Patient’s medical history

  • Lab test values

Reason for the Exam

Great emphasis must be place on why the patient is having a CT examination. If the patients order does not match the reason the patient gives, confirmation that the requested study is the correct exam must be determined first and foremost before performing the exam.

 Pregnancy

Female patients of child-bearing age must be certain there is no chance of pregnancy. If the patient is not 100% sure she is not pregnant a pregnancy test needs to be ordered or the scan rescheduled until the patients next menstrual period.  Although ionizing radiation is potentially harmful to the human body at all ages it is particularly detrimental to the human embryo/fetus.  Radiation exposure has been linked to a considerable increase in prenatal abnormalities and even death during the first trimester.  Pregnant patients that must have a CT exam should wait, if possible, to the second trimester before undergoing the scan.

Which trimester(s) of pregnancy are considered the greatest risk for a CT examination?
Patient’s Medical History

The inquiry about a patient’s medical history involves questions about surgery, allergies and any prior conditions. Two parts of information are needed. First, does anything in the patient’s history indicate a condition or tendency to be intolerant to the contrast media? Second, a complete list of all surgeries and treatments that would change a patient’s anatomy (e.g. removal of the gall bladder, surgical clips, scar tissue). Treatments such as radiation therapy could account for scarring in the lung that might be mistaken for lung disease. 
To determine a patient’s tolerance to contrast media three areas must be discussed:

  • Any reaction to previously given contrast media.

  • Any allergies to iodine or barium

  • Any of the following conditions:

  •     

Hypertension
Heart disease
Asthma
Sickle cell anemia
Renal impairment
Diabetes


One of the most important questions to ask is if the patient has ever experienced an adverse reaction to contrast media during a previous diagnostic study of any kind.  Next, determine if the patient is allergic to iodine or barium which are the two most widely used CT contrast media. It should be noted that at one time it was believed if a patient had allergies to shellfish it was a possible indication the patient may be allergic to contrast media. It has since been established that a potential allergy to CT contrast agents is not indicated by an allergy to shell fish. Patients with hypertension, heart disease, asthma, sickle cell anemia, renal impairment, diabetes should not receive ionic contrast agents. Patient born with one kidney or who have had a kidney removed are at a greater risk for contrast reaction than those with both kidneys. 
Lab Tests

Two types of lab results are important to CT:

  • Tests for renal function

  • Test to determine the blood’s coagulation ability

Renal function is the ability of the kidneys to clear toxins from the body.  The kidneys must be functioning properly before the administration of contrast media in order to clear the IV contrast from the patient’s body.
The two most common lab tests ordered to determine kidney function include:

BUN – 5 to 25 mg/dl is considered within normal limits

Creatinine – 0.6 to 1.7 mg/dl is within the normal range BUN

Blood urea nitrogen provides an indication of the kidney’s ability to remove toxins/impurities from the blood. Elevated BUN levels indicate the kidneys are not removing impurities properly from the body and the patient may have renal disease.  A patient with elevated BUN levels should not receive CT intravenous contrast agents.  Each facility determines what is considered within normal limits but typically a range of 5 to 25 mg/dl is acceptable for BUN values.


Creatinine

During muscle contraction creatine, a waste product stored in the muscle as creatine phosphate, is turned to creatinine.  In normal functioning kidneys creatinine is removed from the blood stream by the kidneys.An elevated creatinine level may indicate impaired kidney function and patients exhibiting this should not receive CT intravenous contrast agents. Each facility interprets the normal range somewhat differently. The commonly accepted values for creatinine are in the range of 0.6 to 1.7 mg/dl.
Tests used to determine blood clotting ability are:

INR –A standardized ratio that attempts to present the results of a PT test and method used independently of the method. Normal INR is approximately 1.

PT
Prothrombin time determines the blood’s ability to clot and is considered normal within 10 to 14 second range.

PTT
Partial thromboplastin time is another test to determine the  blood’s clotting ability. Normal range is within 20 to 40 seconds.
The PT and PTT are tests used to calculate the series of chemical interactions required to form a blood clot in an individual’s blood.

Platelet Count
The small cell fragments responsible for the formation of the plug at the site of a puncture are the platelet. A value in the range of 150,000 to 400,000/mm3 is considered the standard.


Radiation Safety

To provide the patient with the safest environment during their visit to the CT department we cannot overlook the fact that x-rays when absorbed are damaging. We must measure the radiation dose absorbed by the patient so that exposure can be regulated and the damage limited.
There are two “types” of measurements of radiation. First, when dealing strictly with radiation from x-rays the measurements used are the rad or Gy. The second is the Sv and rem which are used to measure any kind of ionizing radiation.

  • X-ray radiation measurements

 

  • Measurement of all types of radiation

X-ray radiation measurements


The rad is the common unit for measuring the absorbed radiation dose.  One rad is equal to 0.01 joules of energy per kilogram of matter.  The gray (Gy) is the second unit of measurement for `x-rays, where 1 Gy = 100 rads.
Measurement of all types of radiation

The rem (rem-equivalent-man) and a sievert (Sv) are used to measure all types of radiation, where 1 Sv is equal to 100 rem. The rem and Sv are use to measure the effective dose or dose equivalent of all types of ionizing radiation. The measurements take into account the dose absorbed by each organ of the body plus the radiosensitivity of each irradiated organ. The measured radiation dose from x-rays only is 1 rad is equal to 1 rem.

Important Concept

It is important to remember rad and Gy are used to measure the radiation dose. Rem and sievert (Sv) all types of radiation. What do all these measurements of radiation dose tell us about patient absorbed dose? 

To put it in perspective the greatest naturally occurring exposure to radiation in the United States is from radon.  Each person in the United States receives an annual radiation dose equivalent of 2 rem. Now, compare this exposure to that of a typical CT examination of the head which is 1-5 rads (remember rad and rem are equivalent when speaking of radiation from x-rays). A CT scan of the abdomen results in a radiation dose of 2-6 rads.


CTDI and MSAD

Most CT exams used today are multi-slice studies. It is important to compare how the radiation exposure from a single slice differs from that of multiple contiguous slices are scanned. Due to the way collimation affects the x-ray beam the amount of radiation from a single slice is not uniform. Collimation increases the radiation in the center of the slice and radiation intensity decreases as it reaches the outside edges. Due to a phenomenon known as penumbra the radiation actually extends outside the slice into adjacent tissue. Penumbra is an undesirable consequence of collimation limitations that cannot be avoided. Penumbra will increase as the slice thickness decreases.

Important Concept

Remember, as slice thickness decreases penumbra will increase.
When computing the radiation dose received by the patient from a multi-slice scan, the dose calculation will include the dose from each slice as well as the dose from the penumbra. For contiguous slices (with no overlap or gap between them) the cumulative dose will be equal to the sum of the radiation dose from the actual slices and the sum of the penumbra around each of the slices.  The radiation dose is measured by a factor called the CT dose index or CTDI.

Important Concept

FORMULA:  CTDI = radiation dose from intended slices + radiation penumbra of each slice.
When an overlap or gap occurs between adjacent slices the CTDI measurement is not accurate.  CTDI can not account for the extent of slice overlap, and the resulting increase or decrease in dose due to the spacing of CT slices. A second measurement of radiation dose is needed.

The MSAD or multiple scan average dose equals the CTDI times the ratio of the slice thickness to patient table increment.

Important Concept

Formula: MSAD = CTDI x (slice thickness/patient table increment)
An example:

If the CTDI = 3 rads, the slice thickness is 5mm and the table increment is 3.5 mm (resulting in overlapping slices), the MSAD will equal (3rad) x (5mm/4mm) or 3.75 rads.

MSAD= 3 rad x 5mm/4mm = 3.75 rads
The MSAD will be greater than the CTDI when the adjacent slices overlap, but the MSAD will be less than the CTDI when there are gaps between adjacent slices. When no overlap or gap exists between adjacent slices the CTDI will be equal to the MSAD.

Take a little time to let this sink in and do a couple more problems!!


Review question 1.
If the CTDI = 4 rad, the slice thickness is 5mm and the table increment is 5mm the MSAD will equal?
(4 rad) x (5mm/5mm) = 4 MSAD. In this equation the CTDI and the MSAD are equal due to there being no overlap or gap between adjacent slices.


Review question 2.
If the CTDI = 2 rad, the slice thickness is 3mm and the table increment is 5mm the MSAD will equal?
(2 rad) x (3mm/5mm) = 1.2 MSAD. This time the CTDI is greater than the MSAD indicating a gap between adjacent slices.
It is important to understand the following concepts:

  • When the MSAD is greater than the CTDI there is an overlap in adjacent slices.

  • When the MSAD is less than the CTDI there is a gap between adjacent slices.

  • When the MSAD and CTDI are equal there is no overlap or gap between adjacent slices.

There are a multitude of varying views related to how much risk is associated with a CT scan. One thing is certain, each time a patient is exposed to ionizing radiation there is some risk of cellular damage and this increases with each additional exposure (at least in theory).
At this time there is no federally imposed limit for the amount of exposure a patient may receive. The medical community has placed its own limitations to radiation exposure and strives to strictly adhere to them. This concept is based on ALARA, and simply states the radiation dose should be “AS LOW AS REASONABLY ACHIEVABLE.”  To fully appreciate what is involved in limiting the radiation dose absorbed by the patient we must first understand the many factors that affect the dose. The dose received from a CT exam is affected by scanner design and hardware, scan parameters and the number and type of scans used to make a clinical diagnosis.

 
Scanner design and Hardware factors

Scanner design plays an important function in patient dose.  One such design factor is the placement of the CT x-ray tube distance from the patient. The greater the distance between the patient and the x-ray tube the lower the absorbed dose will be. Does this remind you of the Inverse Square Law learned in basic x-ray? Another design factor that affects patient dose is the filtration used. Filtration removes the low energy photons from the x-ray beam. These photons do not pass through the patient but are absorbed increasing dose and contributing nothing to the image because they never reach the detectors.


A third factor is the pre-patient collimation, which is responsible for the slice thickness. By controlling slice thickness scatter radiation is reduced reducing patient dose. 


The last and an important factor in how the hardware and scanner design affects patient dose is the number of slices the CT scanner acquires in a single rotation.  Most scanners used today are multi-row detector scanners which have the ability of collecting four or more slices in one rotation of the gantry. Multi-row detector scanners provide important benefits to diagnostic imaging such as shorter scan times, but the downside is a higher rate of dose inefficiency when compared to single row detector scanners.


The greater the number of slices collected per rotation the greater the radiation dose received by the patient. Manufacturers of CT scanners are developing “dose-optimizing software” to overcome this problem.

 
Scan Parameters Affecting Patient Dose

Scan parameters are predetermined protocols used with each type of CT examination.  Although these scan parameters come pre-set either by the manufacturer, or the medical facility, it is up to the technologist to adjust the parameters for a patient who does not “fit” the parameter criteria. An example of this could be patient size where a CT protocol for an adult abdomen can be adjusted to accommodate the small size of a pediatric patient. Another example is scanning only the area of interest in a patient with a known mass in the abdominal area instead of the entire abdomen. The technologist should adjust scan parameters that affect patient dose by applying the ALARA principle.


The scan parameters that can be adjusted include:

  • mAs

  • kVp

  • Anatomical coverage

  • Slice thickness

  • Table incrimination

  • Pitch

The mAs is used in the production of the x-ray photons and determines the number of photons produced. The relationship between mAs and radiation dose is linear.  When the mAs is doubled the dose is also doubled. Likewise, when mAs are halved the dose is also reduced by half. The lowest mAs values that result in a quality diagnostic image should be used to ensure the patient is receiving the lowest radiation dose possible.  Decreasing mAs can be achieved by decreasing either the tube current (mA) or the scan time (sec).

  • Remember, mA x time = mAs

A decrease in the mAs increases the noise in the CT image. Due to this, the mAs value used must be sufficient to minimize the apparent noise level. An image with noise may have important diagnostic details obscured resulting in a compromise in the diagnostic value. A general rule to the appropriate mAs is the mAs should be enough to keep the apparent noise in the CT image at an amount that will not negatively affect the diagnostic integrity of the CT image.


The kVp or peak kilovoltage provides the energy at which the photons travel. When the tube current remains unchanged, a decrease in the kVp will to some extent decrease the dose to the patient. In average sized patients the decrease in dose resulting from lowering the kVp is so minimal that it is considered insignificant in CT. Only in CT studies of small or pediatric patients who have less tissue to penetrate would it be advisable to decrease the kVp. The kVp is important in maintaining the proper tissue contrast so important in quality CT images. For this reason kVp is not normally considered an option in reducing radiation dose.


A reduction in radiation dose can be achieved by scanning less anatomical area of the body. This is only true if the slice thickness remains the same.  When scanning a smaller anatomical area fewer slices are needed exposing less of the patient’s body to ionizing radiation. By carefully evaluating the anatomical landmarks on the localizer image the CT technologist can ensure that only the area of interest is included in the CT exam.

Important Concept

Keep in mind that although kVp can decrease patient dose it is NOT regularly decreased in CT imaging. Lowering kVp is only considered when scanning a small patient.


Slice thickness is somewhat confusing because a single slice results in a different patient dose than does a multi-slice study. To understand this first consider that with a single slice as the slice width increases so does the volume of irradiated tissue. When the area of tissue increases within the slice so does the dose for that slice.

The opposite is seen in multi-slice scans. As the slice thickness increases, the dose to the total volume of irradiated tissue is decreased because fewer slices are needed to cover the tissue area. Also, remember when fewer slices are scanned the radiation penumbra is decreased this decreases the total dose to the patient.


Table incrementation involves the movement of the patient table through the CT gantry to scan the desired number of slices.  When the table increment is increased (while the slice width remains the same), a reduction in the number of slices needed to cover the area of interest will result.  The reason less slices are needed is because the increase in table increment either reduces the over-lap of slices or increases the space between adjacent slices. Fewer slices result in a decrease in patient exposure, reducing patient dose. For this reason it is important to use a table incrementation speed that allows for the least amount of CT slices while retaining the diagnostic quality of the CT image.

Important Concept

To apply the inverse square law in a clinical setting, the technologist can simply increase the table increment and the patient dose is decreased.


Pitch is similar to table increment in that it is used during the helical CT study to move the patient table through the CT gantry as the x-ray tube rotates around the patient.  By increasing the pitch for a given volume of tissue the x-ray helix will be stretched, covering a greater area of interest in fewer rotations. Think of the x-ray helix as a child’s slinky toy, with one end held in each hand, as the slinky is pulled apart the distance between the loops widen.

This is the same concept as increasing pitch and results in a decrease in the number of x-ray photons needed to image the anatomical area of interest. As with table increment an increase in pitch will reduce the patient dose.
To ensure that the CT exam exhibits diagnostic CT images most facilities have pre-programmed protocols for pediatric and adult patients with small body habitus.  These protocols should incorporate lower values for the mAs and kVp needed to image the decrease in tissue density exhibited in the smaller patients.

It should be noted if the kVp used on a small or pediatric patient is the same as that used on an average sized patient the resulting CT image will be severely degraded in image quality. Therefore the CT technologist must be capable of adjusting the scan parameters to optimize each scan based on patient size.  In the absence of pre-programmed pediatric protocols these changes can be saved to the CT scanner protocol list and used again in the future for small patients.


Minimizing patient dose:

  • Avoid repeat scans

  • Reformat instead of re-scanning

  • Reduce multiple scans

The need to avoid repeat scans cannot be over-emphasized. Repeat scans result in additional exposure to radiation and most times can be avoided. Patient motion is a cause of numerous repeats in CT examinations. The CT technologist must ensure the patient is comfortable and understands the need to be still during the scan. 

Positioning aids such as pillows, head holders and Velcro straps can assist a patient who cannot hold still on their own. The use of helical scanning in place of conventional or serial imaging will minimize patient motion. Also the use of motion correction algorithms when available can remove motion artifacts.


Another cause of repeats is artifacts such as zippers, eye glasses, body piercings, and jewelry to name a few. Artifacts are an error on the part of the Technologist and can be avoided by following strict dressing codes for all patients. Before each scan begins the technologist should question the patient to ensure all potential artifacts have been removed from the area of interest. Reducing the area repeated can also reduce patient dose.
An example

A CT exam of the abdomen has been performed and it is found to include a belly ring in the CT image. Instead of repeating the whole exam only the area that included the belly ring should be rescanned. This will result in 8-10 mores slices but far fewer slices than a complete CT of the abdomen which can include 40 to 60 slices or more. Being ever diligent in the desire to avoid repeating a CT scan the technologist can significantly reduce the radiation dose to the patient.

This is truly an example of “cause no harm.”


With the advancement of computer programs repeat scans can be avoided by using the computers reformatting program to enhance and reformat details within the CT scan.  Reformatting the anatomical data requires no additional ionizing radiation.

One such program, retrospective reconstruction, is used to better see small pathologies found between contiguous slices. This program uses data from a helical image to generate overlapping slices eliminating the need to re-scan the area of interest with a thinner slice width.


A reduction in the number of multiple scans performed on the patient is an appropriate means to decrease dose. Often, at the request of the radiologist, CT studies that include the use of contrast media are required to be scanned prior to contrast injection, during contrast injection and after contrast injection.

When the diagnostic information will not benefit from the additional scans the pre-contrast and/or delayed scans should be minimized or eliminated. This will ensure patient dose is kept to a minimum.
Patient Monitoring

The patient’s well being should be of upmost concern during a CT scan. The CT technologist should monitor the patient both visually and verbally throughout the patient’s visit to the CT department. Visually assessing the patient’s breathing and watching for signs of a reaction to the contrast media will potentially avoid a life-threatening situation in the patient. The intercom located on the gantry console of the CT machine should be used to maintain communication with the patient during scanning. This assures the technologist the patient is well and calms the patient during the exam.


During routine CT scans most patients do not require the use of monitoring devices such as a pulse oximeter. It is recommended to use the pulse oximeter for the patient who has been sedated for a CT exam. An in-patient who is already connected to monitors or life-support equipment and is scheduled to have a CT exam should have this equipment transported to the CT department with them so that monitoring can continue.


Code Procedures

As a CT technologist it is crucial to know what to do and who to contact in the event a patient has complications.  Medical facilities are required to have a strict code of procedures that employees are trained in. The following steps should be followed if complications arise while the patient is in the CT scanner.
Code Procedures

  • First, move the patient couch out of the gantry and remove any restraining devices.

  • Second, check the patient’s airway to ensure it is clear, take the patient’s vital signs and be prepared to begin CPR if needed.

  • Third, the technologist should follow the facilities procedure and contact the correct persons. This is usually the radiologist on duty, nurses and possibly the emergency room physicians. The CT technologist must be able to distinguish between acute cares situations to provide the patient with the best care.

A few of the most common conditions

Shock is caused by a lack of blood flow to the vital organs and surrounding tissues. Shock caused from a loss of blood volume could be a result of trauma or surgical complications. A sudden substantial vasodilatation can also induce shock.

Anaphylactic shock can result from a severe reaction to CT contrast media. Signs of shock include grayish-blue skin color, restlessness and tachycardia.


The patient exhibiting symptoms of shock should be kept warm and if there is no bleeding in the upper body and head, the legs should be elevated. Epinephrine should be administered to the patient with anaphylactic shock from a reaction to IV contrast.


Stroke results from a lack of blood flow to the brain. This is a severe condition that requires quick response to minimize the damage to the brain. Signs of a stroke include, the inability to speak, numbness and or paralysis on one or both sides of the body, difference in pupil size, incontinence and hypertension. The CT technologist should assess vital signs frequently and the patient should be readied for airway ventilation, suction, intravenous fluids, and possibly CPR.


Cardiac Arrest results from a complete loss of heart function. CPR must be started immediately on cardiac arrest victims to decrease damage from a lack of oxygen.  The symptoms include no pulse, no respirations, vomiting, seizures, damp blue-gray skin color, and incontinence or defecation.


A seizure indicates an underlying medical condition in which the patient has periods of unconsciousness and convulsions. A patient exhibiting symptoms of a seizure should have all restraints and any objects that could cause harm removed. It is best to move a seizure patient into a resting position on the patient table, the floor or a chair. Signs of a seizure include: muscular contractions, twitching of the face, lack of motor activity, difficulty breathing, confusion and loss of facial expression.


Vital signs

There are four important vital signs that must be monitored during the patients visit to the CT department: blood pressure, pulse, respiratory rate and temperature. Some of these vital signs can be performed in more than one area of the body. It is important that the CT technologist document the location and method used to perform the measurement.


Measuring blood pressure is one of the most common vital signs taken and can be an important indicator of a problem in the patient. The blood pressure is measured by two numbers, the systolic pressure and the diastolic pressure. The systolic pressure represents the force of the ventricular contraction. The diastolic pressure represents the lowest pressure of the ventricle between heartbeats, also called the resting period.  The systolic pressure is written over the top of the diastolic pressure, as a fraction is written.

Important Concept

Hint: Remember that the systolic pressure is over the diastolic pressure when written!
A person’s blood pressure can be measured sitting, standing or lying down. Normally the blood pressure is measured in the patient’s brachial artery, found near the bend of the elbow. The blood pressure cuff is placed against the patient’s skin and then a stethoscope is place over the brachial artery. It is important that the stethoscope be place directly over the artery to ensure that the Technologist can hear the sound accurately. When sitting or standing the arm with the cuff should be placed level with the patient’s heart.

The blood pressure cuff is inflated using the bulb until the gauge reads at least 180 mm of mercury. As the pressure screw is released it is important for the technologist to listen carefully with the stethoscope for the first sound of the pulse, this is the systolic pressure. The technologist should continue to monitor the sound from the stethoscope for the pulse sounds to end. The diastolic pressure will be the point when no rhythm is heard.
Normal blood pressure

  • Adult

  • Systolic 90-140                                        Diastolic 60-90

  • Children

  • Systolic 85-130                                        Diastolic 45-85

The patient’s pulse can be taken in several sites beginning at the head and ending at the feet they are as follows: temporal, carotid, apical, radial, femoral, popliteal and pedal. Most medical facilities use the radial site found at the patient’s wrist. The radial pulse is measured by placing the index and second finger on the lateral side of the patient’s wrist and counting for one minute.  In the event the pulse cannot be detected lift the technologist’s thumb from the patient’s arm to avoid feeling the technologist’s pulse instead of the patients.


The practice of counting the pulse for 15 or 30 seconds and then multiplying by a factor of 4 or 2 respectfully is common but it should be stated this is not as accurate as counting for the full minute. The adult pulse rate range is from 70 to 100 beats per minute (BPM). However, in the athletic adult the normal range can be as low as 45 to 60 BPM. For a child the pulse rate is between 95 to 110 BMP and for an infant the range is between 100 to 180 BPM.
Respiratory rates should be monitored for a period of one minute in the patient. Also the patient’s breathing should be evaluated and noted as normal, labored or shallow.

Respiratory Values

  • Adults 12 to 20 respirations/minute

  • Children 15 to 30 respirations/minute

  • Infants 25 to 50 respirations/minute

The temperature is not always monitored in the CT department but it is a good idea to know where and how to measure temperature. There are three locations on the patient’s body to measure temperature: the mouth, the axilla and the rectum.  It is important to record the temperature to the nearest tenth of a degree and also note skin temperature, moisture and skin color. 

Normal temperature for each area:

  • Oral               97° to 99°

  • Axilla             96.5° to 98.5                         

  • Rectal            97.5° to 99.5°

Contrast Media

The use of contrast media is found in many diagnostic imaging modalities, including CT imaging. The contrast media used in CT imaging includes intravenous, oral and intrathecal. The CT technologist must be proficient in the administration, contraindications and possible reactions contrast media may pose in each patient. Contrast media (also called contrast agents) are produced from pharmaceutical compounds found to “highlight” specific areas of interest in the patient’s body.


Contrast media is introduced into a patient’s body to help delineate abnormalities and differentiate adjacent anatomical structures. The contrast media improves visual sensitivity and results in more precise clinical diagnosis. Intravenous contrast (IV) agents are injected directly into the patient’s bloodstream. The IV contrast media is used to infiltrate or penetrate the blood vessels, organs and vascular lesions. 


There are many CT examinations performed that include the use of contrast media. These CT studies include the brain, soft tissues of the neck, the chest, the abdomen, the pelvis and the vessels.


Iodine contained in the IV contrast media increases the attenuation of the x-ray photons during the CT scan. Tissue scanned with an IV contrast agent will have a higher CT number assigned to the tissue on the CT image as a result of the increased attenuation.  The increased CT number is reflected in the image as a brighter area due to the enhancement by the CT contrast agent.  Also, the perfusion rate for each anatomical and pathological structure affected by IV contrast media varies. This allows the radiologist to differentiate between correct anatomy and possible pathology on a CT image.

There are many manufacturers of IV contrast media, each with unique properties but all contain one common ingredient = iodine. The IV contrast agents produced by various manufacturers contain other properties individual to their compound which affect how the patient will tolerate the IV contrast when administered. One important property of contrast agents is whether it is an ionic or non-ionic contrast agent.
The ionic agents when placed in solution (like the patient’s bloodstream) divide into charged particles called ions. The dissociation of ionic agents into ions once it is introduced into the bloodstream results in many particles entering the blood. The more an agent breaks down into charged particles the less the patient will be able to tolerate the contrast agent.
Non-ionic contrast media do not divide into particles in the bloodstream but rather remain intact as an entire molecule when injected into the patient’s bloodstream.  The non-ionic contrast media remains in the bloodstream until it is excreted in its original form by the kidneys.  Non-ionic agents are much safer and result in less reaction in the patient.  Conditions requiring non-ionic contrast media include: diabetes, kidney disease, loss of a kidney, and liver disease.

Important Concept

Hint:  Ionic agent’s breakup into particles in the blood, non-ionic agents remain intact.
Osmolality refers to the concentration of molecular particles found in the IV contrast agent and is a predictor of how well an agent will be tolerated by the patient.  There are two categories of contrast media based on osmolality: low osmolar contrast media (LOCM) and high osmolar contrast media (HOCM). Non-ionic contrast media is in the LOCM category containing comparatively lower concentration of particles (about 500 to 800 mOsm/kg). Contrast agents containing the lower osmolalities are generally better tolerated by the patient. With that said it is somewhat surprising to find that all ionic contrast media, with the exception of one not found in CT imaging, is considered high osmolar with approximately 1300 to 1600 mOsm/kg of particles.


Generally all IV contrast media have greater osmolality than blood plasma which is approximately 285 mOsm/kg. Therefore the IV contrast agents are considered hyperosmolar or hypertonic solutions when compared to blood plasma. Hypertonic solutions when placed in the bloodstream cause fluid from within the vascular space to increase. This can result in dehydration in the patient. Because of this it is crucial that the patient be well hydrated before the exam. The patient should be encouraged to drink fluids after the exam to hydrate the body and aid in removing the IV contrast agent from the body.


Another aspect of the contrast agent is its viscosity. Viscosity refers to how thick a substance is, and can vary depending on the temperature of the liquid. The more viscous the solution the larger the particles become. Viscosity affects how the contrast media is administered. Greater force is required for the injection as the viscosity increases.  Also the patient’s tolerance decreases as viscosity increases due to the difficulty of removing the large molecular particles from the blood into the kidneys.


Most CT departments store the contrast media in a warming box designed to maintain the desired temperature of the contrast media. The desired temperature is body temperature. The use of the contrast media warmer found with the power injector unit at the CT scanner continues to maintain the temperature of the contrast agent until injection begins. Warming results in a thinning of the contrast media, which slightly decreases the force of injection. This is important especially in patients whose veins cannot tolerate the increased pressure required to inject the thicker solution.  A very viscous (thick) contrast agent can cause discomfort at the injection site that usually goes away after the injection is complete. The application of warm compresses to the patients arm can aid in the discomfort.


Oral Contrast Media

During examinations of the abdomen and pelvis, oral contrast media is often used in conjunction with IV contrast media. The oral contrast agents pacify the gastrointestinal tract. The opacifications of the gastrointestinal tract allow the radiologist to distinguish between air in the bowel and possible pathology such as a lesion, abscess or fluid.  A lesion is found on the external portion of the bowel and can be hard to evaluate without the use of oral contrast. The two most common types of oral contrast agents are barium sulfate and iodinated solutions. The package insert provided with each media must be referenced when determining indications, contraindications, safety, dose and precautions.  The use of air and water as a type of negative contrast agent is sometimes used in addition to the iodine or barium solutions.


The barium sulfate used in CT is similar to that used in radiography the difference being the amount of barium concentration is typically 1 to 3 %.This is due to the streak artifacts that would result from the higher concentration of barium found in conventional radiograph۔


One problem with barium contrast is it moves through the GI tract at a slow rate. By adding iodinated oral contrast media to the barium sulfate solution the speed at which it progresses can be increased.  Barium is insoluble therefore it is not absorbed or metabolized in the patient’s body as the barium moves through the gastrointestinal tract the density remains the same resulting in the same opacity in the distal intestines as found in the upper GI tract. The lack of absorption or metabolism of the oral contrast media results in few adverse reactions and are usually minor in nature.


The most common adverse reactions include diarrhea and abdominal cramping.  In rare cases colon impaction, barium appendicitis, barium granuloma, intestinal perforation and peritonitis have resulted.  Since the possibility of a reaction is always a concern the patient should be monitored closely.
The following are considered contraindications for the use of barium sulfate solutions:

  • Colon obstruction

  • Colon perforation

  • Pyloric stenosis

  • Obstructing lesions of the small intestine

  • Tracheosophageal fistula

  • A patient who is hypersensitive to barium sulfate

 The administration and dose of barium sulfate used is determined by the area to be scanned. For the stomach the patient should be instructed to drink 300 ml of the contrast solution approximately 15 minutes prior to the CT scan. When all of the gastrointestinal tract is to be studied the patient is usually instructed to drink 300 ml the night before and then an additional 300 ml 15 minutes before the start of the exam. When the rectum and lower bowel require opacification the barium sulfate solution can be administered as an enema and then the patient should be instructed to roll 360 degrees to thoroughly coat all areas with the barium solution.


Iodinated Oral Contrast Agent

Iodinated oral contrast media is commonly used in patients with contraindications to barium sulfate solutions. This includes hypersensitivity to barium sulfate solutions, patients with bowel perforation, partial bowel obstructions or a patient who is at risk of aspiration of the contrast media. Iodinated oral contrast moves through the GI tract more rapidly than barium. Therefore eliminating the need for administration the night before or long waits to allow proper coverage of the GI tract.


Iodinated oral contrast agents contain the same type iodine as intravenous iodinated contrast media. When compared to intravenous iodinated contrast media the iodinated oral contrast media is a diluted solution of 6 to 9 mg /ml. The lower concentration of iodine found in oral solutions results in better tolerance by the patient than the intravenous iodinated contrast media.


One disadvantage of iodinated agents is the slight absorption that occurs within the gastrointestinal tract. There is approximately slightly less than five percent absorption of the total amount of contrast media administered. This results in a decrease in opacification of the distal intestines. Also the fluid located in the bowel causes considerable dilution of the contrast media as it passes through. The same precautions must be followed when administering oral iodinated contrast media as followed with intravenous iodinated contrast media. The risk of an adverse reaction is much less due to the lower concentration of iodine found in oral solutions. Also it should be noted when oral solutions are administered to patients with diabetes great care must be taken due to the flavoring agents used to make them more palatable.


Intrathecal Contrast

Patients who have received a myelographic study of the spine in the radiographic imaging department may be sent to the CT department for a post-myelographic CT study. The post exam is performed to enhance and/or clarify the findings of intradural and extradural abnormalities. The use of an intrathecal contrast agent is required. The patient will arrive at the CT department with the contrast agent already administered. Therefore it is not necessary to discuss how to administer the contrast agent but the care and positioning of the patient needs to be addressed. The patient’s head should be maintained in a slightly elevated position to reduce the potential for headaches and seizures.


Before scanning the patient several things must be considered. Scanning should be performed one to four hours after the administration of the intrathecal contrast media to allow proper integration of the contrast media with the cerebral spinal fluid. Scanning performed more than four hours after injection with contrast media may result in a decrease in contrast agent resulting in decreased image quality. Due to the delay between administering the contrast media and the CT examination most patients have been in the supine position for several hours, this results in the separation of the contrast agent and the CSF.


Just prior to scanning most facilities request the patient roll 360 degrees to mix the contrast media with the cerebral spinal fluid (CSF). Another technique is to place the patient in the prone position for the spinal examination which will eliminate the layering effect of the contrast media. When scanning begins one slice should be scanned then evaluated to ensure the contrast agent is not too dense, otherwise it will cause streak artifacts on the CT image.

Important Concept

Post-Myelographic CT Imaging considerations

  • Place patient head in elevated position

  • The delay should be 1 to 4 hours from the time of injection to the time of scan

  • Rolling the patient eliminates the layering effect of contrast agent and  the CSF

Reactions to Contrast 

Each year, in the United States, more than ten million patients receive contrast media. Of these approximately 10% will experience some type of reaction. All reactions no matter how insignificant should be documented in the patient’s record. The longer it takes for an adverse reaction to occur in the patient the less severe the reaction will be. Most severe reactions occur quite rapidly and as a result patients must be monitored carefully during CT contrast injection. Generally, the higher the injection rate, the larger the total volume of contrast media given and the higher the iodine content in the IV contrast the greater the chance of an allergic/adverse
reaction.  In patients who have had a prior allergic response to IV contrast media, but will benefit from the CT study, the imaging facility radiologist may order pretreatment with anti-histamines or steroids.


The best medicine is prevention when it concerns the patient’s well-being. Since many chemical compositions and properties are used in contrast agents it is the CT technologist responsibility to review the package insert for each agent and establish the possible allergic reactions.  Every facility has predetermining criteria to decide which contrast media ionic or non-ionic should be administered to the patient.

There are three levels of reactions:

  • Minor reactions

  • Moderate reactions

  • Acute reactions

Minor reactions usually last only for a brief time and require no treatment. Usually reassurance from the technologist to the patient will relieve minor reactions. When itching or hives become generalized it is an indication of a systemic reaction which can lead to a more severe reaction.  The administration of a mild antihistamine may be ordered by the attending physician to counter the allergic response.

Minor reactions include:
Nausea and/ or vomiting 
Chills and /or flashes of warmth
Itching and/or minor hives (urticaria)
Metallic taste in the mouth
Dizziness (vertigo) and/or headache
Trembling
Perspiring
Change in skin color (pallor)
Moderate reactions may require some type of treatment and close observation by the CT technologist to ensure the reaction does not progress into an acute reaction. The physician should be notified immediately when a patient has an allergic reaction. All allergic reactions should be recorded in the patient’s history.
Moderate reactions include:
Moderate hives (urticaria)
A change in the patients pulse rate
Wheezing (asthmatic attack)
Swelling or spasms of the bronchial and laryngeal area
Swelling of the face
Fainting (syncope)


Although an acute reaction to IV contrast is rare they do happen. Many acute reactions can be avoided by closely monitoring the patient and by having a physician available to assist. Acute reactions happen quickly and require immediate intervention to alleviate the allergic reaction. Every facility should have a procedure “code” in place designating how such emergencies are to be handled. Each CT technologist must follow these procedure codes and document any reaction in the patient’s record.


Acute reactions include:
Shock
Cardiac arrest
Diabetic crises
Respiratory distress
The Administration of Contrast Agents

Each state mandates who is allowed to administer the IV contrast media. For instance some states allow only a registered nurse or physician to perform the injection.  Other states allow the CT technologist to perform the injection under the supervision of a physician, should complications arise.


The injection of contrast media is considered an invasive procedure and requires sterile techniques to be used. Most facilities use disposable butterfly needles or catheters to inject the contrast media.  Should a question arise concerning whether the contrast media, catheter/needle or IV tubing sterility has been compromised it must be disposed of. The package insert should be reviewed for specific procedures of preparation, proper handling and verification of the date to be used by. Should the contrast media show any visible signs of contamination, tampering or problems inform the radiologist and discard.


The injection of contrast requires an 18-22 gauge lumen size. For higher rates of injections (approx. 4-5cc per second) such as CT angiography studies, an 18 gauge catheter would be used. The use of the plastic sheathed catheters allow for greater rates of injection compared to the butterfly needles. One reason for this is the longer length of the plastic sheath tends to remain in the vein better decreasing extravasations (the injection of contrast media into the surrounding soft tissue). During high rate injections the risk of an adverse reaction increases, this can be reduced by decreasing the viscosity of the contrast agent to allow better flow. Warming the contrast agent to body temperature will reduce the viscosity.

Important Concept

As the gauge number decreases the lumen size increases. An 18 gauge needle will have a larger lumen size than a twenty gauge needle.
Due to accessibility the hand and forearm are the most common sites of injection. There are several vessels located in the anterior portion of the arm called the cubital fossa, which is just below the elbow. The vessels include the cephalic vein, brachial artery, basilic vein, deep venae comitantes and the venous anastomosis. The basilic vein is the most common injection site due to its location in the cubital  fossa.  This is because of two reasons.  First, the basilic vein is more proximal to the axillary vein when compared to the cephalic vein. Second, due to anastomosis located between the basilic and cephalic veins results in less “roll” in the basilic vein.
Most CT scans require the patient’s arms be raised above their head once the catheter has been inserted, the basilic vein allows the best flow of contrast with the hands in this position. The cephalic vein originates in the arm and forearm crossing the elbow and running between the pectoral is major muscle and the deltoid muscles to drain into the dorsal portion of the hand. Although the cephalic vein can be used it is less suitable due to the circuitous route it travels. The veins located on the dorsal side of the hand should be considered only when there is no access found at the patient’s cubital fossa. This is because the veins of the hand “roll” in the subcutaneous tissue and are more easily “blown” from the pressure of the injection. When inserting a catheter into the hand the veins must be stabilized. Also a smaller catheter and slower injection rate are recommended to reduce injury to the patient’s vein.


All equipment needed for catheter insertion should be gathered and placed on a clean sterile tray easily accessed by the technologist. This should include tourniquet, catheter, alcohol square packages, tape to stabilize the catheter once inserted and sterile gloves. It should be noted that in most facilities the use of gloves by the CT technologist is mandatory, this is often ignored. Some CT technologists have the opinion that the vein cannot be felt through the gloves. With consistency and practice the use of gloves will not interfere with catheter insertion. The need to protect both the patient and the CT technologist from infection and communicable diseases cannot be emphasized strongly enough.


To best visualize the vessels during insertion of the catheter a tourniquet made of elastic or rubber is applied to the patient’s arm. Once the tourniquet is applied the patient should be instructed to open and close the hand several times. If no vein is seen slight slapping of the vein can be done to increase the size. When the vein is slapped it enlarges to almost double due to reflex vasodilation. Also, applying heat to the site will enhance vasodilation making the vein more visible. 

To distend the vein:

  • Apply elastic/rubber tourniquet

  • Patient open and closes hand

  • Slightly slap the injection site

  • Apply a warm compress to injection site

Once the vein has been located and properly dilated for injection cleansing must be performed. An alcohol or beta dine solution is used to thoroughly cleanse the area. This should be done with several small cotton squares or cotton balls. Most facilities provide individual prepackaged ready to use products for this purpose. With a small amount of cleansing solution applied to the square begin at the center of the injection site wiping in a circular motion.


A spiral rotation from the center of the injection to the outer edges of the site should be made then discard the square and repeat with at least one more sterile square. The area is now considered clean and ready for injection.


The tip of the needle/catheter is the placed against the skin at the site of insertion into the venous wall. With gentle pressure push the tip of the catheter at a 45° angle upward into the vein. A slight sensation of a “pop” should be felt and blood return will appear in the catheter. Once approximately three millimeters of the catheter is inserted the plastic catheter is advanced as the needle portion is removed. This eliminates the risk of puncturing the vessel wall with the needle tip. Before removing the tourniquet pressure should be applied over the tip of the catheter to avoid blood from seeping out. Once the tourniquet is removed the IV tubing can be attached and the catheter secured with tape. 

During the CT examination the catheter and insertion site should be monitored closely, especially during the first few seconds of the IV injection. Usually extravagation will occur rapidly. If this should occur the injection flow must be stopped to avoid a large volume extravasations. Most extravasations involve a small volume of contrast agent and are not clinically noteworthy. The patient may have discomfort and slight swelling in the injection area, this usually passes rather quickly. The application of warm compresses can relieve the pain. Large volume extravasations are more serious and should be brought to the attention of the attending physician. All extravagation issues and treatment should be noted in the patient’s file.
Three Phases of Enhancement

  • Bolus Phase

  • Non-equilibrium Phase

  • Equilibrium Phase

  • The timing of contrast media injection used in various CT examinations is extremely important due to the three phases of enhancement. If the scan is initiated too soon after injection the organs will not be enhanced properly. If the scan is delayed too long the organs and lesions will both enhance. In both cases, early or late, the contrast media will be unproductive in properly enhancing the structures and pathology could be overlooked.

The three phases of tissue enhancement are based on the contrast media as it travels through the circulatory system. The total time that each phase requires is affected by the injection rate, the contrast media volume, and the rate of the patient’s blood flow.

Important Concept

Total time of each phase is affected by injection rate, the contrast media volume and the rate of patient’s blood flow.
The first is the bolus phase which follows immediately after the injection. After injection the bolus phase travels through the veins to the right side of the heart. From there it continues through the lungs is oxygenated and then returned to the left side of the heart and into the aorta (arterial system). It is during this phase that the contrast media moves as a bolus away from the heart and through the arteries distally. An example of an examination requiring the bolus phase of enhancement is CT angiography (CTA). When the contrast media returns to the heart through the veins the contrast bolus is fairly well distributed.

Important Concept

Bolus phase begins immediately after contrast injection.
Next, the non-equilibrium phase can be recognized by a 10 to 30 Hounsfield Unit density difference between the inferior vena cava and the abdominal aortas. The non-equilibrium phase begins to distribute the contrast bolus through the capillaries and then into the veins. 
When the bolus reaches the capillaries and veins the contrast density difference found between the inferior vena cava and the abdominal aorta decreases. Most often the best soft tissue structural differences are obtained during the non-equilibrium phase of IV contrast media injection.

Important Concept

Non-equilibrium phase offers the best soft tissue structural differences.
The equilibrium phase is the last phase of enhancement recognized by a 10 – 30 Hounsfield Unit density difference between the inferior vena cava and the abdominal aorta. The concentration of contrast media between the veins and the arteries becomes more equal resulting in a diminished differentiation of soft tissue structures.

Important Concept

Equilibrium phase is characterized by a diminished differentiation of soft tissue structures.
The CT technologist must control the exact time the scan is initiated. The scan start time is correlated with the time of the contrast media injection to ensure the specific phase of enhancement is captured. This is very important when imaging specific anatomy such as the liver with its dual blood supply.


The delay time to be used can be quite challenging to calculate and are based on several factors. Scan delay will differ depending on whether a conventional (serial) scan or helical scan is performed. The conventional, serial scans take longer to scan the area of interest when compared to helical scanning. When serial scanning is performed the scans are often begun immediately after the injection occurs to ensure proper enhancement when the scan reaches the area of interest. With helical scans the delay factor must be adjusted to allow the non-equilibrium phase of enhancement to begin as the scan is run.


Each manufacturer programs standard delay times in the scan programs based on normal cardiac output. If desired these delays can be refined by individual facilities using the scanner. Most often these preprogrammed delays work adequately and produce quality images. However, the patient who has a compromised blood flow, resulting from injury or shock may need delay times adjusted to produce suitable images. Most CT scanners in use today offer software programs that sense the onset of the contrast bolus in a predetermined slice. Or, the CT scanner may use a “test bolus” to factor the time required for the IV contrast to reach the area of interest. When using the test bolus method a single slice is repeatedly scanned over the same anatomical area until the contrast media is detected. It should be noted that it usually takes no more than 2-3 slices to detect the test bolus; therefore the radiation dose to the patient is minimal.  Once the delay time is established the actual IV contrast injection and scan can be performed.


End of Patient Care Study Guide

 

 





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