1. As related to the cardiac cycle, the term ____ refers to the relaxation of heart muscle.
A. diastole
It is the period of the cardiac cycle that occurs between successive contractions of the heart muscle, which are known as systole.
2. Which of the following may be considered one of the high-osmolar contrast media (HOCM)?
1. iothalamate meglumine
2. diatrizoate sodium
3. iohexol
C. 1 and 2 only
High-osmolar contrast media (HOCM) are ionic agents that dissociate into charged particles (ions) in solution. Ionic contrast media are salts consisting of sodium and/or meglumine. Iothalamate meglumine and diatrizoate sodium are commonly known by the brand names Conray and HYPAQUE, respectively.
3. Which of the following technical changes would serve to decrease patient radiation dose during a CT examination?
C. decrease of tube rotation from 360 to 180 degrees
Many CT scanners allow the tech to reduce the total rotation of the tube, thus reducing the scan time and pt dose. This type of partial scan, referred to as a "half-scan" or segmenting, is most often used to improve the temporal resolution of the acquisition.
4. Which of the following medications may be administered to a patient who is having a severe anaphylactoid reaction to iodinated contrast material?
1. epinephrine
2. atropine
3. diphenhydramine
B. 1 and 3 only
Epinephrine (Adrenalin) is an adrenergic drug used as a bronchodilator. Diphenhydramine (Benadryl) may be used to block the physiologic effects of the body's release of histamine, thus reducing the allergic effect of the contrast material. Atropine should be used only to combat bradycardia during a vagal reaction to contrast material.
5. In an effort to reduce patient radiation dose, the technical factors of the applied CT protocol should be optimized on the basis of:
B. size or weight
6. The escape of contrast material from a needle or blood vessel into the subcutaneous tissues is called:
C. extravasation
Also known as infiltration
7. Thorough explanation of the CT procedure and proper communication with the patient are vital in ensuring that:
1. breathing instructions are properly followed
2. motion artifact does not occur
3. patient anxiety is kept at a minimum
A. 1, 2, and 3
Good communication between the tech and the pt is an extremely important factor in the production of quality CT exams. Pt's can be made to feel more comfortable, and when given detailed instructions, their greater cooperation can improve the CT results.
8. Which of the following is considered in the calculation of the MSAD for an axial (step-and-shoot) CT examination?
B. bed index
MSAD (multiple scan average dose) accounts for the effects of image spacing, or bed index, on pt radiation dose during axial scanning. MSAD increases when slice thickness is greater than image spacing and decreases when slice thickness is less than the bed index.
9. Risk factors for contrast-induced nephrotoxicity (CIN) include:
1. pheochromocytoma
2. allergy to shellfish
3. dehydration
D. 3 only
Risk factors contrast-induced nephrotoxicity (CIN) include pre-existing renal function compromise, dehydration, diabetes, myeloma, advanced age, and cardio-vascular disease.
10. During CT examinations, the patient's body should be shielded above and below because of:
B. the rotational nature of the x-ray beam
11. Normal range for oxygen (O2) saturation is:
C. 95%-100%
Saturation levels below 95% may indicate respiratory insufficiency.
12. Which of the following laboratory measurements can be used to evaluate the renal function of a patient?
1. BUN
2. PTT
3. creatinine
B. 1 and 3 only
The laboratory measurements BUN (blood urea nitrogen) and serum creatinine (a component of urine) can be used to indicate the status of a pt's renal function.
13. Which of the following would be best suited for intravenous injection of contrast material with a power injector?
B. angiocatheter
Angiocatheters and higher-gauge needles are preferred for administration of contrast using a power injector. The stability of an angiocatheter maintains proper placement within the vein while withstanding the high pressure applied by the power injector.
14. Prior to the intravenous injection of iodinated contrast material, patients should be questioned regarding their:
1. renal function
2. allergic history
3. cardiac history
D. 1, 2, and 3
15. A(n) ____ infection is one that a patient acquires during a stay in a health care institution.
A. nosocomial
Nosocomial infections may be commonly referred to as health care-associated infections. They occur within the first 48 hours of a pt's stay in a health care facility.
16. CTDIw is a weighted index that approximates radiation dose on the basis of the variations that occur across the field of view because of:
1. beam hardening
2. detector configuration
3. pitch
B. 1 only
As the beam traverses the pt, beam hardening alters the penetrability of the beam and affects the absorption across the field of view. The CTDIw is calculated by summing 2/3 of the exposure recorded at the periphery of the field with 1/3 of the centrally recorded radiation dose. This weighting yields a more accurate dose approximation.
17. Which of the following sets of values would be considered normal levels for creatinine and BUN, respectively?
A. 1.2 mg/dL; 14 mg/dL
The normal range for creatinine level is 0.5 to 1.5 mg/dL. The normal range for BUN is 7 to 25 mg/dL.
18. Which of the following sizes of butterfly needles allows for the most rapid administration of iodinated intravenous contrast media?
B. 19 gauge
19. The embryo or fetus is most sensitive to ionizing radiation during which portion of gestation?
D. first trimester
20. The choice between ionic and non-ionic contrast media should be based on:
1. the allergic history of the patient
2. the cost of the contrast material
3. the age and physical condition of the patient
B. 1 and 3 only
Pt's may be assigned to a higher-risk group for an adverse reaction to iodinated contrast material on the basis of several factors, including previous allergic history and physical condition. Pt's considered to be at high risk for adverse reactions should be administered non-ionic contrast material. Iso-osmolar contrast material is an alternative choice that may also reduce the risk of adverse reactions.
21. Which of the following is an example of a mild reaction to iodinated intravenous contrast media?
D. vomiting
Examples of mild adverse reactions to iodinated contrast material are nausea, vomiting, mild urticaria (hives), and a warm, flushed sensation. Dyspnea is a moderate reaction, whereas pulmonary edema and shock are severe reactions to contrast.
22. During which of the following CT procedures is the patient required to give informed consent?
C. abdomen scan after IV contrast agent administration
The pt is required to provide informed consent prior to the start of any invasive procedure. The administration of intravascular contrast material is invasive in nature and requires the informed consent of the pt.
23. The International Normalized Ratio (INR) is calculated to standardize which of the following laboratory values?
B. prothrombin time (PT)
Because of the inherent differences in manufactured batches of tissue factor, the International Normalized Ratio (INR) is calculated to standardize PT results. The INR compares a pt's PT with a control sample for more accurate results.
24. Which of the following infection control techniques is required at the site of an intravenous injection of iodinated contrast media?
C. surgical asepsis
Insertion of any intravenous line requires the use of sterile techniques to prevent microorganisms from entering the bloodstream.
25. In order to uniformly expose the entire detector array in an MDCT system, the primary beam must be expanded beyond the physical extent of the array in a process known as:
A. overbeaming
All detectors of the MDCT array must be exposed to x-rays of equal intensity. The beam must be expandeed even further to avoid exposing the detectors to undesirable "penumbra." This process is referred to as overbeaming.
26. Which of the following is a common site for the intravenous injection of iodinated contrast media?
1. cephalic vein
2. antecubital vein
3. basilic vein
C. 1, 2, and 3
Another common site are the accessory cephalic veins.
27. An intrathecal injection prior to a CT examination of the lumbar spine places iodinated contrast material directly into the:
A. subarachnoid space
Intrathecal injections of iodinated contrast are used in CT evaluation of the L-spine. This type of injection introduces contrast directly into the subarachnoid space, which is located between the arachnoid and pia mater. The subarachnoid space contains the cerebrospinal fluid.
28. Automatic tube current modulation (ATCM) is employed by an MDCT system for the purpose of:
B. reducing patient radiation dose
ATCM is a form of automatic exposure control for a CT system. It manages pt radiation dose on the basis of the size, density, and overall attenuation of the part being examined.
29. The range of serum iodine concentration for adequate tissue opacification during contrast-enhanced CT examinations is:
C. 2-8 mg/mL
The serum iodine concentration is a measure of the amount of iodine within the bloodstream. The specific dose depends on the pt's age, weight, and renal function, as well as on the clinical indication for the CT procedure. The specific criteria of intravenous contrast administration must always be directed by a physician.
30. Components of the aseptic technique utilized for the IV administration of contrast agents include:
1. thorough hand washing between patients
2. wearing of disposable gloves
3. establishment of a sterile field around the site
A. 1 and 2 only
Additional components of the aseptic technique include cleaning the site of venipuncture in a circular motion with alcohol swab before injection, and applying pressure with an alcohol swab to the site after the removal of the needle or catheter. It is sterile technique that involves establishing a sterile field around the area of an invasive procedure.
31. The amount of x-ray energy absorbed in a quantity of air is termed:
D. kerma
Kerma may be used to describe absorbed dose. Air kerma is the amount of radiation absorbed in a quantity of air.
37. Abnormalities of the middle and inner ear may be best demonstrated with CT utilizing ___ sections.
A. 1 to 2mm
Thin sections are required to properly assess abnormalities of the minute structures of the inner ear. The thinnest sections possible provide maximum detail.
38. The Lisfranc joint is the articulation between the:
B. tarsals and metatarsals
The Lisfranc Joint is the articulation between the tarsals and metatarsals; it can be the site of complex fractures and dislocations of the foot.
39. The volume and density of calcium measured in the coronary arteries on MDCT examination are quantified with use of a value called the:
B. Agatston score
The Agatston scoring system quantifies the volume and density of calcium within the coronary arteries.
40. Which of the following is/are (a) component(s) of the adnexal area of the uterus?
1. ovaries
2. fallopian tubes
3. vagina
B. 1 and 2 only
Adnexa is used to describe an appendage of an organ. The ovaries and fallopian tubes constitute the uterine adnexal region.
41. A CT angiogram of the neck is performed primarily for the evaluation of the:
D. carotid arteries
42. Which of the following contrast media may be utilized during the CT evaluation of the gastrointestinal tract?
1. diatrizoate meglumine (Gastrografin)
2. effervescent agents
3. iopamidol (Isovue)
D. 1, 2, and 3
Opacification of the stomach and bowel loops is imperative during general CT examinations of the abdomen and pelvis. Effervescent agents may be used to ensure proper gastric distention. Intravenous contrast agents are used to opacify blood vessels and are helpful in anatomic differentiation and evaluation of mass vascularity.
43. The liver has a dual blood supply and receives 75% of its blood from the:
B. portal vein
The liver has a dual blood supply, receiving 75% of its supply from the portal vein and the remaining 25% from the hepatic artery.
48. Which of the following pelvic bones combine(s) to form the acetabulum?
1. ilium
2. ischium
3. pubis
C. 1, 2, and 3
The acetabulum is a cup-shaped cavity that holds the head of the femur, forming the hip joint. It is composed of portions of the ilium, ischium, and pubis.
53. At what percentage of overlap should CT sections be reconstructed to improve the quality of multiplanar reformation (MPR) images?
A. 50%
It is widely recommended that volumetrically acquired CT sections be reconstructed with the use of at least a 50% overlap to improve the quality of 3D and MPR images.
54. A primary responsibility of computed tomography in combined PET-CT is to:
1. provide precise anatomic location of tumor activity
2. reduce patient radiation dose
3. improve radiopharmaceutical uptake
D. 1 only
Positron emission tomography (PET) provides a map of normal and abnormal tissue function. It offers excellent sensitivity for malignancy but suffers from an inability to accurately localize tumor activity. Fusion of PET with CT provides such precise anatomic localization.
55. The degenerative pathologic process involving the forward slipping of an upper vertebral body over a lower vertebral body is called:
A. spondylolisthesis
Spondylolisthesis refers to the forward "slipping" of an upper vertebral body over the lower as a result of degenerative changes of the facet joints.
60. Accurate demonstration of ____ would most likely require the intravenous injection of an iodinated contrast agent during a CT study of the chest.
B. mediastinal lymphadenopathy
Contrast enhancement greatly improves demonstration of lymphadenopathy within the chest in comparison with other mediastinal structures.
61. Which of the following paransal sinuses is usually the last to fully develop?
B. frontal
The frontal sinuses are absent at birth and do not usually fully develop until after puberty. The ethmoidal, maxillary, and sphenoidal sinuses begin to develop during gestation.
62. A focused, thin-section axial CT acquisition through just the region of the vocal cords should extend:
C. from just above the hyoid bone inferiorly through the cricoid cartilage
Thin-section (0.5-2.0 mm) helical acquisition specific to the larynx should extend from just above the hyoid bone inferiorly through the cricoid cartilage.
63. The most common indication for CT-guided percutaneous biopsy is the:
D. confirmation of a malignancy
The most common indication for CT-guided percutaneous biopsy is to confirm the malignancy of a mass.
64. Axial CT images of the knee may be acquired in four separate series with gantry angulations of 0, 30, 45, and 60 degrees in order to demonstrate the:
B. patellofemoral joint
This technique allows for visualization of the relationship between the patella and the femur as the knee is increasingly flexed. The patellofemoral congruence, or the position of the patella within the patellar surface of the femur, may be measured at each point of flexion. Any medial or lateral displacement of the patella may indicate an abnormality of the patellofemoral joint.
68. Which of the following contrast agent administration techniques should be used for a general CT survey of the abdoment?
1. 400-600mL oral contrast agent 45-90 minutes prior to the exam
2. 250mL oral contrast agent immediately before the exam
3. 700-900mL contrast agent administered as an enema immediately before the exam
D. 1 and 2 only
The administration of an oral contrast agent is subject to specific department protocol considerations. Generally, 400-600 mL of oral contrast administered 45-90 minutes prior to the exam should opacify the small bowel. An additional dose of contrast agent (250 mL) immediately before the exam should ensure gastric opacification. Administration of contrast agents via enema is indicated for evaluation of the distal large bowel.
69. During CT perfusion studies, the quantity of blood (in mL) that moves through 100g of tissue each minute is termed the:
B. cerebral blood flow (CBF)
Cerebral blood flow (CBF) describes the quantity of blood (in mL) that moves through 100 g of brain tissue each minute. Normal CBF range in gray matter is 50 to 60 mL/100 g/min.
71. An adequate volume of intravenous contrast agent for the SSCT examination of the neck would be:
A. 125mL
A total contrast agent volume between 100-150 mL is sufficient for imaging of the neck. The precise volume and administration technique vary from one institution to another.
74. The enhancement washout technique for CT characterization of adrenal masses includes:
1. thin-section pre-contrast acquisition through the adrenals
2. arterial phase post-contrast acquisition through the adrenals
3. 10-15 minute delayed post-contrast acquisition through the adrenals
C. 1 and 3 only
Differentiation between a metastatic lesion and a benign adenoma of the adrenal can be accomplished by calculating the percentage of enhancement washout after a 10-15 minute delay. Pre-contrast, portal venous phase, and delayed acquisitions are obtained. On delayed post-contrast imaging, metastatic lesions of the adrenal gland remain enhanced longer than adrenal adenomas.
75. Bowel obstruction due to loss of normal contractile motion in an area of intestine is termed:
C. ileus
Ileus is used to describe an area of intesting that has lost normal contractile motion, resulting in obstruction.
80. CTA of the renal arteries should be performed using a section width of:
C. 1.25mm or less
The renal arteries are small structures that are optimally visualized with MDCT section widths of 1.25 or less.
81. The third ventricle of the brain communicates with the fourth ventricle through the:
A. cerebral aqueduct
The third and fourth ventricles communicate through the cerebral aqueduct, which is commonly referred to as the aqueduct of Sylvius.
82. Complete CT examinations of the chest for investigation of bronchogenic carcinoma should include sections from the:
B. top of apices through the liver
Complete CT exams of the chest for bronchogenic carcinoma consists of an acquisition from the apices through the liver. The adrenal gland and liver are common sites for metastic disease in pt's with primary lung neoplasm. Scanning may be done in a caudocranial direction to ensure maximum contrast enhancement of the liver and adrenals when indicated.
83. The mediastinum includes which of the following anatomic structures?
1. superior vena cava
2. stomach
3. ascending aorta
A. 1 and 3 only
The mediastinum is a potential space located between the two lungs. It contains the heart, great blood vessels, thymus, and portions of the trachea and esophagus.
84. The proper scan field of view (SFOV) for a CT of the abdomen of a patient who measures 42cm is:
A. large (48cm)
The SFOV chosen must be larger than the width of the pt in order to eliminate out-of-field artifacts. Some CT scanners may have limited choices for SFOV values. Other common terminology includes full- or half-field, and body-cal and head-cal.
85. The kidneys are located in the retroperitoneum and are bound by a band of fibrous connective tissue called:
D. Gerota's Fascia
The kidney's are located in a portion of the retroperitoneum known as Gerota's space. They are held in place by fibrous connective tissue commonly referred to as Gerota's fascia.
86. After initiation of rapid bolus administration of an iodinated contrast agent, the portal venous phase of hepatic contrast enhancement occurs at approximately:
A. 60-70 seconds
The portal (or hepatic) venous phase is the period of peak hepatic parenchymal enhancement, when contrast redistributes from the blood into the extravascular spaces. It occurs at approx. 60-70 seconds after the initiation of rapid bolus contrast administration.
91. The prone position may be used for a post myelogram CT examination of the lumbar spine in an effort to:
D. reduce metrizamide pooling
The prone position during a post-myelogram CT study of the lumbar spine reduces pooling or layering of the intrathecal contrast material.
92. The bolus duration of any IV contrast agent administration can be calculated as the product of injection flow rate and:
D. contrast agent volume
Bolus duration, or the time required to inject a specific volume of contrast agent, may be calculated as the product of injection flow rate and total contrast volume.
93. During the use of CT fluoroscopy for guided interventional procedures, which of the following technical considerations may be used to reduce occupational radiation exposure?
1. increased kVp
2. lead shielding
3. use of a needle holder
C. 2 and 3 only
Low values for kVp and mA and short CT fluoroscopy time all reduce occupational radiation exposure. Greater distance from the source, as with the use of a needle holder to keep the operator's hands out of the CT fluoroscopy field, also greatly diminish exposure. Additional methods of exposure reduction are lead shielding, leaded pt drapes, and the utilization of a last-image-hold function to cut down on continuous CT fluoroscopy.
98. After initiation of rapid bolus administration of iodinated contrast material, the pancreatic phase of contrast enhancement occurs at approximately:
D. 35-45 seconds
The pancreatic phase of contrast enhancement is a delayed arterial phase occurring approx 35-45 seconds after the start of contrast agent administration, assuming an adequate volume injected at a rate of 3 mL/sec or greater.
99. Following the IV administration of iodinated contrast media, a tumor that exhibits a greater density than the surrounding parenchyma is characterized as:
A. hypervascular
Upon IV contrast enhancement, a tumor may be described as hypovascular if it is lower in density than the surrounding organ parenchyma or hypervascular if it is higher in density.
100. The retroperitoneum contains which of the following anatomic structures?
B. kidneys
The retroperitoneum is the space located between the peritoneum and the posterior abdominal wall. It contains the duodenum, pancreas, adrenal glands, kidneys, ureters, and bladder.
101. Which of the following is NOT a component of the "triple rule-out" MDCT protocol for patients complaining of chest pain?
C. prone HRCT of the lungs
The "triple rule-out" MDCT procedure is a comprehensive evaluation of the chest for cardiac and noncardiac pain. The single acquisition consists of a coronary CTA for coronary artery disease, a CTA of the aorta for aneurysm, and CTA of the pulmonary arteries for embolism.
102. During contrast-enhanced CT examinations of the chest, streaking artifact may obscure portions of the superior mediastinum because of dense concentrations of iodine in the:
B. superior vena cava
There is often significant artifact within the mediastinum from high concentrations of iodine in the superior vena cava. This artifact may be alleviated by administrating a bolus of a contrast agent with reduced iodine concentration, which is achieved by diluting a full-strength contrast agent with saline.
107. The average density of a mass within the kidney measures -75 Hounsfield units (HU). The mass is most likely a:
B. lipoma
The density of the mass in question indicates that it consists of fatty tissue. A lipoma is a benign mass consisting of fat cells. An angiomyolipoma, a common benign mass found in the kidney, consists of muscle cells, blood vessels, and fat. The average CT value range for fat is -50 to -100 Hounsfield units.
108. The component of the CT scanner responsible for the mathematical calculations of the image reconstruction process is the:
D. array processor
The array processor is a specialized component of the CT computer system. It is capable of performing the massive calculations required for CT image reconstruction.
109. Filament sizes for modern CT x-ray tubes range between:
D. 0.5 and 1.2mm
Modern CT system x-ray tubes utilize dual-filament systems with focal spot sizes ranging between 0.5 and 1.2 mm in diameter.
110. Which of the following is used to archive a hard copy of a CT image?
D. laser film
Storage on film is considered to be a hard copy. The digital storage of CT images on PACS, CD-ROM, MOD, and so on, is referred to as soft copy.
111. Which of the following would serve to increase spatial resolution of a CT exam using a large focal spot size, 5mm sections, and a 512x512 matrix?
1. change to small focal spot size
2. acquire 2.5mm sections
3. reconstruct images in a 320x320 matrix
B. 1 and 2 only
The spatial resolution of a CT exam can be improved with the use of small focal spots, narrow section width, and large matrices.
112. A CT image is formed in part by projecting back all of the attenuation values recorded during data acquisition onto a:
C. matrix
The back-projection method of image reconstruction involves the acquisition of attenuation values, which are then projected back onto a matrix for subsequent display.
113. The mathematical process that allows MDCT images to be reconstructed at any point along the acquired volume is commonly referred to as:
A. z-filtering
Multiple-detector row CT systems utilize the process called z-filtering during image reconstruction. Z-filtering allows for thin sections to be reconstructed at any point along the acquired z-axis volume. This interpolation technique utilizes multiple complimentary rays beyond those immediately above and below the particular slice plane.
114. Fourth-generation CT scanners use a ____ tube-detector configuration.
A. rotate-stationary
4th gen CT scanners operate with a rotating x-ray tube and a stationary ring of detectors. Some 4th gen scanners also use a rotating x-ray tube with a rotating detector ring.
115. Which of the following is considered an equipment-induced CT image artifact?
B. aliasing artifact
Aliasing is a type of streak artifact caused when an insufficient number of views (data samples) is obtained during data acquisition. It is typically due to a technical failure of the CT system.
116. The measurement of CT system performance through quality testing procedures and evaluation of the test results is referred to as:
C. quality assurance
Quality assurance refers to the measurement of the scanner's performance through quality testing procedures and evaluation of the test results. Quality control refers to the implementation of corrective actions to improve any identified performance inadequacies of the CT system found through quality assurance procedures.
117. During CT x-ray exposure, the product of the selected mA setting and the scan time is called the:
D. constant mAs
The mA setting in coordination with the scan time (seconds) gives the constant mAs for a CT acquisition.
118. Which of the following mathematical reconstruction methods is used by most modern CT scanners?
D. filtered back-projection
The filtered back-projection, or convolution, method of image reconstruction is used by most modern CT scanners.
119. What matrix size was used to reconstruct an image with the display characteristics DFOV 25cm and pixel area 0.25mm²?
B. 512 x 512 pixels
The matrix size used to reconstruct an image can be calculated by dividing the display field of view (DFOV) by the pixel dimension. A pixel whose area is 0.25 mm2 has a linear dimension of 0.5 mm. Dividing the DFOV of 250 mm by the pixel dimension 0.5 mm gives a matrix size of approximately 512 x 512 pixels. square root of 0.25=0.5. Convert units of DFOV.
120. When one is viewing a minimum intensity projection (min-IP) image, each pixel represents:
C. the minimum attenuation occurring within the voxel
Min-IP images display the minimum pixel value along each ray to the viewer. As the viewer faces a min-IP image, each pixel represents the minimum attenuation that occurs in the associated voxel. Min-IP reformations are used primarily during the evaluation of the bilary tree, colon, lungs, and trachea.
121. Which of the following statements regarding predetector collimation of the CT x-ray beam is true?
A. Pre-detector collimation removes scatter radiation before it reaches the detectors.
The purpose of pre-detector or post-patient collimation are to remove scatter radiation and to shape the portion of the beam that is incident on each detector.
122. Which of the following equations shows the Lambert-Beer law, which describes the relationship between matter and attenuation?
B. I= Ioe⋀-μx
This important exponential equation illustrates the mathematical relationship between the primary beam, the object thickness (density), and the radiation measured by each detector in the calculation of the linear attenuation coefficient (μ)
125. Which of the following would be considered the best method to reduce respiratory motion on the CT image?
B. good patient-technologist communication
Thorough communication between the tech and the pt is vital in ensuring superior exam quality. If the pt has been informed of the exam process, his/her anxiety may be reduced and cooperation improved. During all CT procedures, the pt must be instructed to hold still in an effort to reduce motion artifact on the CT images.
126. Which of the following types of gas is commonly used for gas ionization CT detectors?
C. Xenon
Because of its high atomic number and relative stability, xenon gas is commonly used in gas ionization CT detectors.
127. Power output for a modern MDCT x-ray tube has an approximate range of:
C. 60-100 kilowatts (kW)
The power output of modern MDCT systems is vendor-specific, within a typical range of 60-100 kilowatts (kW)
128. The mathematical manipulations required during the reconstruction of a CT image are accomplished using a(n):
1. algorithm
2. kernel
3. mathematical filter function
C. 1, 2, and 3
The terms algorithm, kernel, and mathematical filter function may all be used interchangeably in describing the mathematical process used for the complex calculations required during CT image reconstruction.
129. When an operator reduces the scan field of view for a particular body part, which of the following technical changes occurs?
C. A smaller number of detectors are activated
The SFOV size is determined by the number of detectors activated along the in-plane (x-, y-) axes during data acquisition.
130. An average CT number value for blood is:
A. +45 HU
An average range of CT numbers for blood is +42 to +58. The CT number of any material is based on many factors, including the beam quality of a particular scanner.
131. The electronic combination of signals from adjacent detectors to form a CT image is called:
A. binning
Binning refers to the electronic combination of signal from adjacent detectors to form a reconstructed slice that is thicker than the individual detector width. For example, transmission data from four adjacent 1.25 mm detectors is combined to produce a CT section 5.0 mm thick.
132. Which of the following technical adjustments may be employed to improve the temporal resolution of an MDCT system?
1. decrease in section width
2. image segmentation
3. physiologic gating
B. 2 and 3 only
Technical adjustments to improve the temporal resolution of the CT system may help reduce involuntary motion artifacts. Reductions in scan time (gantry rotation), image segmentation, and physiologic gating can be used to reduce the effects of involuntary motion.
133. The streaking artifact that occurs in the area of the posterior fossa during a CT examination of the brain may be referred to as:
A. the Hounsfield bar
The dense bony areas of the posterior fossa of the skull are especially prone to beam-hardening artifacts. Hounsfield bar is commonly used to describe this particular artifact.
134. The relative accuracy between calculated CT numbers and their respective linear attenuation coefficients is referred to as:
D. linearity
The relative accuracy between calculated CT numbers and their respective linear attenuation coefficients is termed linearity. Calibration and routine vendor maintenance procedures work to establish and maintain CT system linearity.
135. To maintain security and patient privacy when medical images are transmitted across a network, the images may be coded in a form decipherable only by software at the destination location. This process is referred to as:
B. encryption
Digital encryption is used to encode data that is transferred across a network into a form decipherable only by software at the destination location.
136. Which of the following 3D imaging techniques is utilized to provide "fly-through" images during CT colonography?
A. perspective volume rendering
Perspective volume rendering provides one a viewpoint of being within the lumen of the object, similar to an endoscopic view. Also referred to as immersive rendering, this type of 3D reconstruction is commonly used during CT colonography and CT bronchography.
137. Which of the following sets of technical factors would yield an isotropic data set when an MDCT image is reconstructed using a 512² matrix?
A. 0.625mm sections, 32cm DFOV
Thin-section reconstruction using the smallest display field of view (DFOV) possible results in the smallest pixel and voxel dimensions. Voxels with equal dimensions along the x-, y- and z-axes are described as isotropic.
138. Which of the following is NOT commonly used as a CT scintillation detector material?
B. silver halide
CT does not employ silver halide crystal as a detector material.
139. The mathematical technique that involves the estimation of an unknown value from values on either side of it is known as:
A. interpolation
Interpolation is a mathematical technique used in the reconstruction process of the spiral CT image. It involves the estimation of an unknown value from information above and below it.
140. During which of the following CT examinations is a misregistration artifact most likely to occur?
A. abdomen
Misregistration is the loss of anatomic information that occurs when a pt suspends respiration at different depths during consecutive scans. It occurs only during CT exams in which suspended respiration of the pt is necessary. The ability of MDCT systems to volumetrically acquire entire anatomic areas in a single, short breath-hold has greatly reduced the occurance of misregistration artifact.
141. In a single-slice CT (SSCT) system, which of the following technical parameters may be adjusted retrospectively?
1. section width
2. section increment
3. reconstruction algorithm
B. 2 and 3 only
Single-slice helical geometry allows for volumetric data acquisition. The reconstruction of CT sections at any point along the scanned volume is possible. The section width must be the same, however, and is controlled by the collimation (slice thickness) chosen prior to data acquisition. The advancement of multislice CT (MSCT) allows for retrospective reconstruction of sections at varying thickness.
142. Bow-tie filters are employed in a CT x-ray system to reduce:
C. patient radiation dose
Bow-tie filters, which are thicker at the ends than in the middle, help shape the beam to reduce pt radiation exposure. Because most body parts are circular or cylindrical, less radiation is necessary at the periphery than in the center. Bow-tie filters reduce beam intensity toward the outer margins, resulting in a reduction in pt radiation dose.
143. Which of the following technical factors is/are involved in the determination of section width for MDCT images?
1. scan field of view (SFOV)
2. beam collimation
3. detector configuration
C. 2 and 3 only
The thickness of the reconstructed section is controlled primarily by the detector configuration in an MDCT system. Beam collimation also exerts an indirect effect on section width by controlling the portion of the detector array exposed to transmitted radiation.
144. The fluctuation of CT numbers in an image of uniform, homogeneous material may occur because of:
A. noise
Noise appears on the CT image as an inaccuracy in CT number. The noise of a CT scanner may be measured by scanning a homogeneous object such as a water phantom. Fluctuations in CT number from pixel to pixel indicate the presence of noise.
145. A region of interest (ROI) measurement placed over a portion of a CT image provides which of the following?
C. average CT number (HU)
The region of interest (ROI) measurement provides a quantitative analysis of the Hounsfield values of a specific anatomic area. System software calculates the average CT number in HUs within the defined ROI. The average ROI measurement provides information regarding tissue characteristics that may be helpful for clinical diagnosis.
146. An MDCT image is reconstructed using a 512² matrix and a DFOV of 38cm. If the detector collimation is set to a section width of 1.25mm, what is the volume of each voxel?
B. 0.69mm³
The linear dimension of the pixel must first be calculated by dividing the DFOV, in mm, by the matrix (380 mm/512= 0.74 mm). This linear pixel dimension is squared to yield the pixel area in mm² (0.74 x 0.74= 0.55 mm²). The volume of the voxel may be calculated by multiplying the pixel area by the section width (0.55 mm² x 1.25 mm= 0.69mm³).
150. First-generation CT scanners used a method of data acquisition based on a ____ principle.
B. translate-rotate
The 1st gen CT scanner acquired data through a process based on the principle of tube translation and rotation around the pt's head.
151. The maximum beam collimation for an MDCT system with a detector array of 64 detectors, each 0.625mm wide is:
A. 40.00mm
64 x 0.625=40
At a maximum, the MSCT cone beam may be collimated to a dimension equal to the entire multirow detector array.
152. Compared with conventional radiography, computed tomography produces diagnostic images with better:
D. low-contrast resolution
Computed Tomography has better low-contrast resolution over conventional radiography. The CT system is extremely sensitive to small changes in tissue density and also removes the problem of superimposition, both leading to greater contrast resolution.
153. Writable CD and DVD media are optical disks that may be described as:
B. WORM
Write-once, Read-many (WORM) describes certain CT and DVD media capable of storing data only once. The stored images can be read multiple times, but once recorded on, the media may not be reused.
154. A CT system measures the average linear attenuation coefficient of a voxel of tissue to be 0.008. The linear attenuation coefficient of water for this scanner equals 0.181. The CT number assigned to the pixel representing this voxel of tissue equals:
C. -956 HU
0.008 - 0.181 = -0.173
-0.173/0.181 = -0.956
-0.956 x 1000 = -956
tissue - water= X/water= Y x 1000
155. During data acquisition, a CT system may continuously adjust the mA relative to the measured image noise for a method of dose reduction referred to as:
C. automatic tube current modulation
Automatic tube current modulation (ATCM) programs adjust the mA throughout an acquisition to reduce pt dose to a minimum. ATCM automatically alters the applied mA on the basis of a predetermined noise index that is acceptable for appropriate image quality.
156. Which of the following statements comparing the efficiency of scintillation and gas ionization detectors is correct?
C. The scintillation detector has a higher capture efficiency
Because of its solid nature, the scintillation detector interacts with a higher percentage of incident x-ray photons, giving it a better capture efficiency.
157. The data acquisition system (DAS) of a CT scanner is responsible for:
1. measuring transmitted intensity
2. conversion of the transmission data into a digital signal
3. sending the digital information to the computer for processing
D. 1, 2, and 3
The DAS of a CT scanner consists of the detector array, the analog-to-digital converter, and a transmission device used to send the converted digital information to the computer for image reconstruction.
158. Which of the following is used to remove image blurring during the back-projection method of CT image reconstruction?
1. z-filtering
2. convolution kernel
3. Feldkamp-Davis-Dress (FDK) algorithm
A. 2 only
During CT image reconstruction using the back-projection method, the data are manipulated with a convolution kernel or algorithm to remove image unsharpness (blurring). This method is called the filtered back-projection.
159. During CT x-ray production, the electromagnetic steering of the electron beam from the cathode to two alternating targets is referred to as:
C. flying focal spot
The oversampling technology known as flying focal spot involves the electromagnetic steering of the electron beam emitted from the cathode. The beam of electrons is directed toward two separate locations on the rotating anode, resulting in two sources of x-radiation. As the tube rotates around the pt, the number of data samples is essentially doubled because of the electronic switching between the two focal spots, improving the system's temporal and spatial resolution.
163. Areas of a CT image that contain minimal changes in tissue density are electronically represented by:
A. low spatial frequency
The contrast of a CT image is controlled by the spatial frequencies of the tissue(s) within the section. Tissues of differing densities are represented electronically by different spatial frequencies. Adjacent tissues with similar densities or areas of tissue with minimal differences in density are represented by low spatial frequencies.
164. A CT image is displayed in a window with a level of +200 and a width of 1000. Which of the following statements is correct?
D. Pixels with values between -300 HU and +700 HU will be assigned shades of gray.
The width of a window determines the range of pixel values that will be assigned a shade of gray around a given level. In this example, all pixels within the range of -300 to +700 HU will be assigned shades of gray. Pixels below -300 HU will appear black, and pixels above +700 HU will appear white. This calculation is performed by dividing the width in half (1000/2= 500) and subtracting and adding this value to the level (+200 HU +500= +700 HU, +200 HU -500= -300 HU).
165. In the binary number system, a byte is a series of ____ bits of information.
D. eight
A byte is a series of eight bits. Bits and bytes are part of the binary language used by computers to process information.
