During post-contrast CT imaging of the abdomen, the degree of hepatic parenchymal enhancement depends on:
1) the iodine concentration of the contrast agent
2) the rate if contrast agent injection
3) the osmolality of the contrast medium
1 & 2
After initiation of rapid bolus administration of an iodinated contrast agent, the hepatic venous phase of contrast enhancement occurs at approximately:
60-70 seconds
Hepatic venous phase is the period of peak hepatic parenchymal enhancement. approx. 60-70 seconds after initiation of rapid bolus administration.
Which of the following may be used to reduce metal streak artifact on coronal-plane CT images of the orbits?
1) retrospective reconstruction of targeted images with reduced display field of view [DFOV]
2) metallic artifact reduction [MAR] software to improve image quality
3) construction of coronal multiplanar reformation [MPR] images from the acquired axial-plane images
2 & 3
Manufacturers may offer metallic artifact reduction [MAR] software in an effort to reduce streaking artifact from metal substances. Targeted reconstructions would not remove unwanted streak artifact appearing through the area(s) of interest.
During CT colonography, acquisitions are performed with the patient in at least two positions for the purpose of:
differentiating polyps from feces/fluid
A patient is required to have the following radiographic examinations: CT of the abdomen, GI series, and a barium enema. The correct order for the scheduling of these procedures would be:
CT of the abdomen, barium enema, GI series
Dense barium causes a streak artifact on the CT images. CT first. Barium administered during a GI series could interfere with interpretation of enema study. Barium enema, then GI series.
Following the injection of intravenous contrast media during a CT examination of the brain, which of the following anatomic areas does not enhance?
B) posterior horn of lateral ventricle
It contains cerebrospinal fluid and does not enhance following the intravenous administration of contrast material.
The technique that provides the detail of the outer portions of the 3D model while maintaining the typical CT detail of the lungs inside is called:
surface rendering
Computer programs are capable of constructing 3D models of anatomy with several different types of rendering techniques. This provides excellent surface anatomy while maintaining the normal cross-sectional anatomy appearance of the volume inside the model.
The CT imaging plane that is parallel to the metatarsals, approximately 20 to 30 degrees caudal from the direct axial plane, is called the:
oblique axial plane
oblique axial plan is located parallel to the metatarsals, approx. 20 to 30 degrees caudal from the direct axial plan. This plane is used to assess the tarsal-metatarsal joint.
Each 1.0% in contrast between adjacent objects amounts to a difference in pixel value of approximately:
10 HU
MDCT systems are typically capable of differentiating adjacent objects with attenuation differences as small as 3 HU.
For a given CTA examination of the pulmonary arteries, 100 mL of a low-osmolar iodinated contrast agent is administered at a rate of 4 mL/sec. Peak pulmonary artery opacification should occur at approximately:
B) 20-25 sec
Empiric scan delays for CTA of the pulmonary arteries cary between 20-25 seconds. Peak contrast opacification of the pulmonary arteries depends heavily on the rate of the injection and the cardiac output of the patient.
Which of the following laboratory value may be used to assess the renal function of a patient prior to the IV administration iodinated contrast media?
BUN and creatinine are routinely used to assess renal function. GFR is a more accurate measure calculated using the patient's measured serum creatinine level and taking into account the patient's age, sex, and race.
The blocking of a pulmonary artery by a thrombus that has migrated from a distal vein is referred to as:
pulmonary embolism
This occurs when a thrombus (blood clot) breaks free from elsewhere in the venous system (usually lower extremities) and migrates into a pulmonary artery.
Patients whose posterior descending artery branches from the right coronary artery, and whose left posterior ventricular branches arise from the left circumflex artery, are said to be:
codominant
7% of the population is said to be codominant, meaning that the posterior descending artery [PDA] is supplied by the right coronary artery [RCA], and the left posterior ventricular branches arise from the left circumflex artery [LCX].
In an effort to reduce radiation exposure to the orbits during a CT examination of the brain, the gantry may be angled:
15 degrees superior to the infraorbital-meatal line (IOML)
Brain CT may be performed at an angle 15 degrees above the IOML, parallel to the skull, to reduce orbital radiation dose and minimize beam-hardening artifact.
In patients who are left dominant, the posterior descending artery branches from the:
Left circumflex artery
8% of the population is said to be left dominant, meaning that the posterior descending artery (PDA) branches from the left circumflex (LCX)
Which of the following is a typical protocol for a CT study of the brain for a patient with a history of dizziness?
C) 2.5-mm x 2.5mm sections through the posterior fossa, 5 mm x 5 mm to vertex
Patients with histories of headaches and/pr dizziness should be evaluated for abnormalities of the inner ear. Thin sections (1-3 mm) are required through the posterior fossa in order to best demonstrate the small anatomic structures and improve image quality.
A patient demonstrates diffuse urticaria shortly after the intravenous administration of iodinated contrast media. Correct treatment would include:
administration of an antihistamine drug
Administration of an antihistamine drug is the usual treatment for the development of urticaria (hives) following the injection of iodinated contrast media.
Assuming a bolus injection of iodinated contrast agent at a rate of at least 4 mL/sec, an appropriate scan delay for a CTA examination of the mesenteric vasculature would be in the range of:
20-30 seconds
Dual-phase imaging including the arterial phase (20-30 sec) and portal venous phase (60-70 sec) is typically performed for complete evaluation of the mesenteric vasculature. The use of bolus-tracking software of test bolus technique is recommended to ensure appropriate scan timing.
In which of the following cranial nerves would an acoustic neuroma be found?
eighth
An acoustic neuroma (schwannoma) arises from Schwann cells of the eighth cranial nerve, or the vestibulocochlear nerve. This type of cranial mass may be imaged with CT examinations of the internal auditory canals.
The ability of a CT scanner to image a small high0density object is controlled by the ___________ of the scanner.
spatial resolution
The spatial resolution of a CT scanner controls its ability to image small structures.
The approximate CT density of the unenhanced spleen is:
between +40 and +60 HU
The CT density of the unenhanced spleen is between +40 to +60 HU. The unenhanced spleen CT density is approximately 10 HU less than that of the unenhanced liver.
The general practices necessary to obtain a sufficient medical history prior to a CT procedure include:
1) asking open-ended questions
2) encouraging the patient to provide maximum information
3) repeating and summarizing the information to assure accuracy
1, 2, and 3
All three practices should be employed during the taking of a detailed and accurate medical history. In addition, any required follow-up questions should be focused to acquire the most appropriate information possible.
Which of the following correctly describes the patient position relative to the gantry for a CT study of the brain?
Supine, head first
The patient is usually placed in the supine position so as to move head first into the gantry for a CT examination of the brain.
An MDCT image is reconstructed using a 512² matrix and a display field of view of 44 cm. IF the detector collimation is set to a section width of 2.5 mm, what is the volume of each voxel?
2.15 mm³
The linear dimension of the pixel must first be calculated by dividing the DFOV, in mm, by the matrix. This linear pixel dimension is squared to yield the pixel area, in mm². The volume of the voxel may be calculated by multiplying the pixel area by the section width.
Which of the following units is used to quantify absorbed dose?
grays (Gy)
Absorbed dose describes the amount of x-ray energy absorbed in a unit of mass. It is measured in grays (Gy).
In a female patient, gonadal shielded may be applied during which of the following CT examinations?
1) chest
2) abdomen
3) brain
1,2, and 3
Gonadal shielding may be used whenever the gonads do not lie within the area of clinical interest. Gonadal shielding in the female patient is most difficult during CT scanning of the pelvis.
Which of the following types of contrast material may be used during CT evaluation of the pelvis?
1) an intravenous iodinated contrast agent
2) low dense barium sulfate solutions
3) oil-soluable contrast material
1 and 2 ONLY
During CT examination of the pelvis, both intravenous and oral contrast agents are commonly administered. An intravenous contrast agent is important in differentiating pelvic blood vessels from lymph nodes. An oral contrast agent serves to opacify the small and large colon and greatly improves their visualization. Oil-based contrast media are not commonly used for CT procedures.
CT scanning of the liver for tumor evaluation should NOT be performed during which of the following phases of contrast enhancement?
Equilibrium phase
Contrast enhancement is at its lower point during the equilibrium phase. This phase is apparent when the aorta and inferior vena cava differ by less than 10 HU. It is during this phase that hepatic lesions may become isodense with the surrounding hepatic parenchyma. Non-contrast scanning of the liver is actually preferred to scanning during the equilibrium phase.
A patient has a severe vagal reaction to iodinated contrast material that includes bradycardia. Initial treatment may consist of:
atropine
Patients suffering from vagal reactions to iodinated contrast agents present with hypotension and bradycardia. Treatment includes increasing blood pressure with IV fluids and intravenous administration of atropine to block vagal stimulation of the heart.
Which of the following places the listed butterfly needles in decreasing order in terms of bore dimension?
A) 19, 21, 23
The gauge of a needles increases as its lumen size decreases. Therefore, 19-gauge needle has a larger lumen than a 23-gauge needle.
The normal range of cerebral blood flow (CBF) through 100 g of the brain's gray matter is:
50-60 mL/100 g/min
The normal range of CBF in gray matter is 50-60 mL/100 g/min.
The articulation between the distal tibia and fibula is called the:
Syndesmosis
The syndesmosis is the articulation between the distal tibia and fibula.
Iodine is commonly used in radiopaque contrast media because of its:
High atomic number
Iodine's high atomic number causes it to attenuate a large portion of the primary beam. Introducing iodine into tissue changes the subject contrast of the enhanced anatomic area.
A CT scanner with a limiting resolution of 15 lp/cm can resolve an object as small as:
0.3 mm
The minimum object size that a CT scanner can resolve may be calculated by taking the reciprocal value of the scanner's limiting resolution. The reciprocal of 15 lp/cm is 1/15 lp/cm. This is equivalent to 10/15 lp/mm, which equals 0.6 mm/lp. Because a line pair (lp) is equivalent to a line and the space adjacent to it, this value may be divided in half to provide the minimum object that this scanner can resolve: 0.3 mm.
The image was produced with a 1.0-mm aperture size and was displayed using a 512² matrix and a 15-cm DFOV. The voxel dimension for this image would be:
C) 0.29 mm x 0.29 mm x 1.0 mm
The pixel dimension may be calculated by dividing the DFOV by the matrix size. This two dimensional pixel size is then multiplied by the length of the voxel.
The interaction between x-ray and matter than is responsible for the production of the scatter radiation absorbed by the patient and detectors is:
Compton effect
Compton effect, an x-ray photon ejects an outer-shell electron of an atom. The photon loses some of its energy in the collision and the continues on in a different, scattered direction. This interaction is the major source of the scatter radiation involved in the formation of the CT image.
Which of the following types of the image noise can be most easily reduced by the CT technologist?
B) quantum noise
The quantum or statistical noise of a CT image can be reduced by increasing the number of x-ray photons absorbed by the detectors for each voxel of tissue. This can be accomplished with increases in technique (mAs) and with increases in the pixel and voxel dimensions.
The largest deterrent of a CT scanner's contrast resolution is:
noise
The largest enemy of contrast resolution is noise. Noise appears as a graininess that can obscure the outline and delineation of structures, thus limiting the scanner's ability to separate them.
The primary indication for a non-contrast cardiac MDST examination is:
Coronary artery calcium quantification
The primary clinical indication for non-contrast cardiac MDCT is coronary artery calcium (CAC) quantification for the assessment of atherosclerotic disease.
Cerebrospinal fluid (CSF) is produced in the:
Choroid Plexuses
The cerebrospinal fluid is secreted by the choroid plexuses that are located in each of the four ventricles of the brain.
Which of the following laboratory values is used to measure the coagulation ability of a patient prior to an invasive CT study?
1) PTT
2) hematocrit
3) PT
1 and 3
The coagulation capabilities of a patient may be evaluated with the measurement of prothrombin time (PT) and partial thromboplastin time (PTT). Each of these laboratory values attempts to detect deficiencies in the various clotting factors. Hematocrit is the concentration of red blood cells within the total volume of blood; it may be used to evaluate the hydration status of a patient.
The term beam hardening is used to describe which of the following physical phenomena?
B) the increase in average photon energy of a heterogeneous x-ray beam
Beam hardening occurs as the x-ray beam traverse the patient. The x-ray beam used in CT is composed of x-ray photons with numerous different energies. The heterogeneous beam undergoes an increase in average photon energy as it passes through the patient and the lower-energy photons are absorbed.
The grainy appearance of the pelvis image is commonly referred to as:
Noise
Noise degrades the CT image, giving it a grainy, mottled appearance. The terms quantum mottle and noise are often used interchangeably.
Which of the following is not a category of isolation technique?
C) gram-negative isolation
Categories of isolation technique are:
- drainage-secretion precaution
- enteric precautions
- acid fast bacillus isolation
- respiratory isolation
- contact isolation
- strict isolation
The presence of outpocketings in the wall of the colon is referred to as:
Diverticulosis
It is the presence of small pouch-like openings in the wall of the colon.
Important characteristics of a quality control program in CT include:
a) consistent testing frequency
b) prompt corrective actions when necessary
c) accurate record-keeping
a,b, & c
Hallmarks of a superior QC program are routine frequency of testing, prompt corrective actions as needed, and accurate record-keeping.
Advantages of automatic power injectors in comparison with the manual bolus method of intravenous contrast administration include:
1) increased tissues enhancement due to faster injection times
2) uniform administration of contrast agent over the entire length of the study
3) decreased incidence of adverse reaction to contrast agent
1 & 2
Adjustable-flow-rate automatic injectors improve overall enhancement levels and offer consistency both throughout an exam and between individual patients.
In patient who are right dominant, the posterior descending artery branches from the:
Right coronary artery
85 % of the population is said to be right dominant, meaning that the posterior descending artery (PDA) branches from the right coronary artery (RCA).
The approximate radiation dose measured during a scan of a 100-mm pencil ionization chamber is termed the:
CTDI
CTDI is a fixed measurement taken with a 100-mm-long pencil ionization chamber inserted into an acrylic phantom. The CTDI standardizes the dose measurement from a single axial scan and can be used to compare doses from different scan techniques.
Which of the following is not an iterative method of CT image reconstruction?
Fourier transform
The iterative methods of CT image reconstruction include simultaneous reconstruction, ray-by-ray correction, and point-by-point correction. The Fourier transform method is an analytic method of CT image reconstruction.
In a modern CT system, the total number of possible Hounsfield values that may be assigned to any pixel is approximately:
4096
CT computer system is typical capable of displaying 12 bits of data per pixel and is therefore able to display any of up to 4096 Hounsfield values for each pixel. (2¹²=4096)
Examples of moderate adverse reactions to iodinated intravenous contrast media are:
1) shock
2) faintness
3) severe vomiting
2 and 3 only
Examples of moderate or intermediate reactions to iodinated intravenous contrast agents are severe vomiting, dyspnea, faintness, chest pain, and seizures. Shock is an example of a severe reaction.
The water-soluable oral contrast agents used for CT scans of the abdomen and pelvis should contain approximately _________ iodine.
2-5%
A solution of 2%-5% iodinated water-soluable contrast agent and water provides sufficient bowel opacification for CT studies of the abdomen and pelvis. Some institutions may use a flavored contrast agent or add a flavoring agent to the solution for ease of consumption. Common water-soluable contrast media include Gastrografin and Hypaque.
The technique that allows the user to select the range of pixel values used in a 3D CT reformation is termed:
Thresholding
The selected threshold allows the user to select the range of pixel values rendered in the 3D model. For example, the higher, bone threshold (>300 HU) can be chosen to build a skeletal model of the patient's skull. Decreasing the threshold to include voxels with lower attenuation values results in a 3D model with the patient's soft tissues included.
Coronal imaging through the paranasal sinuses is typically performed with the plane of imaging:
Perpendicular to the hard palate
Imaging plane should be positioned perpendicular to the hard palate for coronal evaluation of the paranasal sinuses.
A CT images of a homogeneous material contains variations in CT number from pixel to pixel. This image is said to have:
Noise
A CT image of a homogeneous material should have pixels with the same CT number. Any variation in CT number between pixels indicates that noise has entered the system causing a loss in accuracy.
An injury to the brain at a location opposite to the site of traumatic impact is referred to as:
contrecoup
The contrecoup type of acute brain injury occurs at a location on the opposite side of the head from the point of impact. As the moving skull rapidly decelerates prior to impact, the portion of brain opposite to the impact site temporarily pulls away from the skull before forcibly recoiling back into its original position, resulting in traumatic injury. In comparison, coup injuries to the brain occur at the actual site of traumatic impact.
In an MSCT system, the detector array is composed of multiple rows if individual detector elements along the:
z-axis
A multislice CT (MSCT) system utilizes a third-generation curvilinear detector array with multiple rows of individual detector elements segmented along the longitudinal axis, or z-axis.
The viscosity of a contrast material may be decreased through:
increase in temperature
The viscosity of a contrast material can be reduced by heating it to body temperature. The decrease in viscosity allows for easier administration of the contrast agent.
Which of the of the following contrast media may be used during a CT examination of the chest?
Diatrizoate meglumine is an ionic intravenous contrast material, and iopamidol is a nonionic one. Both may be used for soft-tissue enhancement during CT of the chest. A barium sulfate contrast agent, usually in the form of a paste, may also be used to outline the esophagus, when necessary.
A high-osmolar contrast material has an average osmolality of:
1000-2400 mOsm/kg water
The osmolality of a contrast material is a measure of the number of particles per kg of water. Osmolality is a factor in determining the potential for adverse reactions to iodinated contrast material. Ionic contrast media, which dissolve into a large number of anions and cations in solution, have an average osmolality between 1000 and 2400 mOsm/kg.
During a coronary artery CTA, single segment reconstruction of a 400-msec rotation scan results in a temporal resolution of:
200 msec
During single-segment, or half-scan reconstruction, data from only half a gantry rotation is used, resulting in a temporal resolution equal to one-half the gantry rotation time.
The propensity of a contrast agent to cause fluid to move from the extravascular space to the intravascular space is called:
Osmolality
An important characteristic of iodinated radiopaque contrast media, osmolality describes the propensity of the agent to cause fluid from outside the blood vessel (extravascular space) to move into the bloodstream (intravascular space).
The maximum dose of intravenous iodinated contrast for a child should not exceed:3 mg/kg body weight
3 mg/kg body weight
Maximum dose if IV contrast agent should not exceed 3 mg per kg of body weight during pediatric CT exams. It's been reportated to cause acute osmolar poisoning in children.
After initiation of rapid bolus administration of an iodinated contrast agent, the corticomedullary phase of renal contrast enhancement occurs at approximately:
30-40 seconds
Corticomedullary phase is a late arterial phase. Optimal enhancement of the renal cortex and renal veins occurs during this period.
Which of the follow technical factor(s) play(s) a role in the production of an isotropic dataset?
1) section width
2) scan field of view (SFOV)
3) display field of view (DFOV)
1 & 3
Isotropic resolution is approached by choosing the thinnest detector collimation available to produce the thinnest slices available and by reconstructing the acquired data with the smallest DFOV allowed according to the part of interest. Minimizing these two factors results in voxels approaching equal lengths in all directions.
The muscular contraction responsible for transporting material through the digestive tract is called:
Peristalsis
The rhythmic contraction of smooth muscle that transports material through the GI tract. Also commonly found in the bile duct and ureters.
Phantom measurement of the uniformity of a CT system is performed primarily to assess the negative effects of:
beam hardening
The uniformity of a CT system describes its ability to maintain relatively consistent CT values across the entire image of an object of equal density, such as water-filled phantom. Beam hardening occurs as low-energy xray photons are absorbed when the beam passes through the patient. The average photon energy of the beam increases along the path and may result in a loss of system uniformity.