Partial Thromboplastin Time is a lab measure of blood coagulation, it used for screening pt's for invasive procedures, normal ranges vary from place to place.
2. Which of the following is the correct angle of insertion for placing a butterfly needle into a vein for intravenous administration of a contrast agent?
B. 15 degrees
15 degrees, bevel facing up.
3. A total volume of 125 mL of an iodinated contrast agent is administered intravenously via automatic injector in 50 seconds. The Flow Rate for this injection is:
a 0.75 mL/sec
b. 1.25 mL/sec
c. 1.75 mL/sec
d. 2.5 mL/sec
d. 2.5 mL/sec
125mL divided by 50 sec = 2.5mL/sec
4. The acronym CTDI is used to describe which of the following?
C. the radiation dose to the patient during a CT scan
CT dose index (CTDI) is used to quantify the radiation dose received by the patient during a CT scan. It involves the use of an ionization chamber to accurately measure radiation exposure for a given set of technical factors.
5. While one is obtaining a thorough history from a patient prior to the intravenous injection of an iodinated contrast material, which of the following topics should be included?
1. any prior allergic reaction to contrast media
2. presence of HIV or hepatitis infection
3. history of asthma
B. 1 and 3 only
6. Which of the following factors may affect a patients calculated Glomerular Filtration Rate (GFR)?
1. age
2. sex
3. race
D. 1, 2, and 3
GFR is calculated using a pt's measured serum creatinine level and takes into account the pt's age, sex, and race.
7. Which of the following intravenous contrast agent administration methods provides the greatest over-all plasma iodine concentration?
D. Bolus Technique
8. A patient in shock may exhibit which of the following symptoms?
1. tachycardia
2. rapid, shallow breathin
3. cyanosis
A. 1, 2, and 3
General signs and symptoms that a pt is going into shock include: rapid breathing, tachycardia, hypotension, weak pulse, pallor, cyanosis, and cold, clammy skin.
9. The drug SOLU-CORTEF may be classified as which of the following?
D. corticosteroid
SOLU-CORTEF is a brand name for hydrocortisone, which is a type of corticosteroid. This drug, or other corticosteroids, may be used to treat anaphylactoid reactions to iodinated contrast materials.
10. Which of the following technical factors has a direct effect on patient dose?
B. mAs
With no consideration of image quality, reductions in mA and/or scan time are direct methods of decreasing pt dose during a CT exam.
11. Which of the following is a non-ionic contrast material?
C. iohexol
Non-ionic contrast media include iopamidol (Isovue), iohexol (Omnipaque), and iopromide (Ultravist).
12. Which of the following terms is used to describe a patient who is having difficulty breathing?
B. dyspnea
13. Which of the following devices is used to measure the patient dose from a CT examination?
B. ionization chamber
Radiation causes ionization within the chamber, which is measured by an electrode. The amount of charged particles is proportional to the radiation exposure. The ionization chamber is an extremely accurate device that is used to quantify radiation exposure from a CT scan.
14. Which of the following describes the situation in which an assumption is made that an unconscious or otherwise physically unable patient consents to medical treatment?
B. implied consent
15. Complete Cardiac diastole corresponds to which portion of the cardiac cycle on an electrocardiogram (ECG)?
D. T wave
Complete cardiac diastole is the period of atrial and ventricular relaxation after heart contraction. The T wave of an ECG corresponds to cardiac diastole.
16. During CT arthrography, iodinated contrast media is injected directly into the:
D. joint space
17. Which of the following is considered one of the iso-osmolar contrast media (IOCM)?
B. iodixanol
Iodixanol (Visipaque) is an example of a non-ionic iso-osmolar contrast agent. Iohexol (Omnipaque), iopamidol (Isovue), and ioversal (Optiray) are all non-ionic low-osmolar contrast media (LOCM).
18. A common site for the IV administration of iodinated contrast media is the anterior recess of the elbow, otherwise known as:
C. antecubital space
The antecubital space contains the basilic vein medially and the cephalic vein laterally. Both veins are common injection sites for contrast.
19. The potentially serious decline in renal function following the IV administration of contrast material is called:
A. contrast-induced nephrotoxicity (CIN)
CIN is typically marked by an increase in serum creatinine concentration in comparison with a baseline measurement obtained prior to contrast administration.
20. The quantity of absorbed radiation dose based on the radiosensitivity of a particular tissue type is called:
B. effective dose
The unit of measurement for effective dose is the sievert (Sv).
21. Advantages of a saline flush immediately following the IV administration of iodinated contrast material include:
1. reduction in required contrast agent dose
2. reduction in the incidence of contrast-induced nephrotoxicity (CIN)
3. reduction of streaking artifact from dense contrast agent in the vasculature
A. 1, 2, and 3
The use of a saline flush also improves the overall contrast agent utilization efficiency of the CT exam.
22. Which of the following medications may be administered to dilate the coronary vasculature prior to a cardiac CT examination?
B. sublingual nitroglycerine
23. A normal range for diastolic blood pressure in an adult:
B. 60-90 mm Hg
Diastolic pressure is the measurement of blood pressure at its lowest point, in between contractions of the heart.
24. Which of the following is a parental route of medication administration?
A. intramuscular
Parenteral administration involves the injection of medication into the body. Common routes of parenteral medication administration include intramuscular, intravenous, intradermal, and subcutaneous.
25. Which of the following methods may be employed to reduce the radiation dose to the pediatric patient undergoing CT?
1. reduced mA
2. limit phases of acquistion
3. increase pitch
A. 1, 2, and 3
The selected mA should be adapted to each pt according to size and/or weight. Eliminating unnecessary CT scans at the discretion of the physician is an additional way to reduce pediatric dose.
26. Radiation exposure and its potentially harmful effects have a relationship that is termed_______in nature?
B. stochastic
Certain harmful effects of exposure to diagnostic x-rays, such as cancer formation and genetic mutations, are said to be random, or stochastic, in nature. A stochastic effect is one that has no threshold dose but increases in probability with increasing dose.
27. Which of the following types of isolation techniques protects against infection transmitted through fecal material?
A. enteric precautions
Gowns and gloves are common protective devices used for enteric precautions. The use of a surgical mask is not warranted.
28. Which of the following is considered one of the ionic radiopaque contrast media (RCM)?
D. iothalamate meglumine
Ionic contrast media are salts consisting of sodium and/or meglumine.
29. The radiation dose index calculations that takes into account the variations in absorption across the field of view due to beam hardening is termed:
C. CTDIw
CTDIw is calculated from measurements made with dosimeters placed at the center and periphery of a phantom and accounts for the variance in dose distribution due to the effects of beam hardening.
30. Direct contraindications to the administration of iodinated contrast material include:
1. prior life threatening reaction to iodinated contrast material
2. multiple myeloma
3. diabetes
C. 1 only
Multiple myeloma and diabetes, although not absolute contraindications to IV contrast, do require attention to the pt's hydration level to limit renal complications.
31. Which of the following units is used to express the total patient dose from a helically acquired CT examination?
C. mGy-cm (milligrays per centimeter)
The dose length product (DLP) is the total pt dose over a given scan acquisition length (z) and can be illustrated as the product of CTDIvol and scan length. The DLP is expressed in units of milligrays per centimeter (mGy-cm).
32. Components of a comprehensive CT stroke management protocol typically include:
1. pre-contrast sequence of the brain
2. CTA of the brain brain and carotids
3. CT Perfusion (CTP) of the brain
C. 1, 2, and 3
Found typically in the emergency setting, a comprehensive acute stroke CT imaging protocol begins with a pre-contrast sequence to evaluate for hemorrhage. After the IV administration of iodinated contrast, a CTA acquisition is performed through the carotid vessels and brain. CTP is then performed to evaluate potential cerebral perfusion defects secondarty to stroke.
36. Simple cysts of the kidney have average attenuation values in the range of:
B. 0 to +20 Hounsfield units
Simple cysts contain primarily water and therefor exhibit CT numbers ranging from approximately 0 (or slightly below) to +20 Hounsfield units.
37. After initiation of rapid bolus administration of an iodinated contrast agent, the arterial phase of hepatic contrast enhancement occurs at approximately:
C. 25-35 seconds
During this phase, hypervascular tumors or tumors supplied by the hepatic artery undergo maximal enhancement.
41. The Abdominal Aorta bifurcates at the level of:
C. L4
The abdominal aorta bifurcates at L4 into the left and right common iliac arteries.
42. On an ECG of the complete cardiac cycle, at which portion of the R-R interval is the heart muscle in diastole?
B. 55%-75%
The least heart motion occurs at approximately 55-75% of the R-R interval, typically corresponding to the point of mid-diastole.
43. The accumulation of gas within a degenerating intervertebral disc is called the:
B. vacuum phenomenon
Small amounts of gas may appear in the areas of degenerated intervertebral discs. The accumulation of gases such as nitrogen occurs as a by-product of the physical breakdown of the disc material.
44. During a spiral or helical CT examination, the scanner acquires data:
1. continuously as the patient travels through the gantry
2. one section at a time
3. in the form of a computer volumetric data set
D. 1 and 3 only
Spiral/helical CT exams are obtained with the scanner continuously acquiring data as the pt travels through the gantry. The data acquired are volumetric, containing all of the attenuation information for a given area of anatomy.
45. Which of the following CT studies of the head is typically performed without a contrast agent?
A. CT of the brain to r/o subdural hematoma
Because of the increase in CT number, subdural hematomas may be well visualized without the use IV contrast.
46. Which of the following phases of renal contrast enhancement best demonstrates transitional cell carcinoma (TCC) of the bladder?
A. excretory
Excretory phase acquisition after a delay of 3-15mins demonstrate the urinary tract while it is opacified with a contrast agent. Transitional cell lesions of the urothelium appear as filling defects within the bladder, ureters, and/or renal pelvis.
49. CT examinations of the abdomen in the right lateral decubitus are often performed in this position to demonstrate the relationship between the:
D. duodenum and pancreatic head
51. Which of the following sets of section width and spacing would be most suitable for a general survey CT of the neck?
A. 3mm thick every 3mm
A contiguous study with section widths ranging from 3 to 6mm is sufficient for a general survey CT study of the neck.
52. The still viable ischemic cerebral tissue that surrounds the infarct core in a patient with an acute stroke is termed the:
A. ischemic penumbra
Penumbra is the ischemic, yet still viable tissue immediately surrounding the infarct core. It can be described as the region of ischemic brain parenchyma where cerebral blood volume (CBV) is compromised but still higher than 2.5 mL per 100 g of tissue.
53. Complex fractures of the wrist are most common in which of the following carpal bones?
B. scaphoid
54. A complete CT study of the orbits should include:
C. 2.5mm x 2.5mm axial and coronal sections
Narrow sections (1-3 mm) are required in both axial and coronal planes to properly demonstrate the orbits.
55. High-Resolution computed tomography (HRCT) is most commonly used for the evaluation of the:
D. lungs
High-resolution CT is a specialized technique using narrow section widths and a high resolution algorithm for image reconstruction. It is used to maximize detail of high spatial frequency tissue, such as lungs and bony structures.
56. Which of the following technical maneuvers may be used to remove unwanted pulsation artifacts from cardiac motion during a CTA of the chest for pulmonary embolism?
D. retrospective ECG gating
Retrospective gating involves scanning throughout the entire cardiac cycle. Only data from specific user-determined portions of the ECG waveform are reconstructed into images.
57. During a general CT examination of the abdomen, an intravenous contrast agent is indicated and is administered with the aid of an automatic injector. Which of the following ranges of flow rate should be used?
B. 1.0-3.0 mL/sec
58. Diffuse fatty infiltration of the hepatic parenchyma may be referred to as:
D. steatosis
Fatty liver disease, or hepatic steatosis, is a condition in which large quantities of fats (lipids) are retained within the liver. Normal liver parenchyma has values of approx. 10 HU higher than those of the spleen, liver with steatosis has values of at least 10 HU below those of the spleen.
63. CT images of the chest should be acquired with the patient:
D. at full inspiration
Pt inspiration provides optimal chest expansion and allows for better demonstration of anatomic structures.
64. During CT scanning of the head, the gantry should be angled:
A. 15 degrees above the IOML
This angle produces axial sections of the brain while limiting beam-hardening artifacts and direct orbital exposure.
65. During the CT examination of the larynx, the patient is often instructed to phonate the letter "E" in order to properly evaluate the:
D. vocal cords
70. During the CT examination of a female pelvis for a suspected malignancy, ascites may be present in an area posterior to the uterus and ovaries known as:
A. the cul-de-sac
71. Which of the following pathologic processes may be considered an interstitial disease of the lungs?
D. bronchiectasis
Interstitial diseases of the lungs are usually diffuse pathologic processes involving the interstitium, or framework, of the lungs. Examples of interstitial diseases are bronchiectasis, emphysema, asbestosis, and sarcoidosis.
72. An enterovesical fistula is an abnormal communication between the bowel and the:
D. bladder
Enterovesical fistulas typically result from inflammatory processes of the colon such as diverticulitis.
73. Prior to a CT colonography, the patient may undergo a process of bowel cleansing termed:
A. catharsis
Catharsis describes the process of bowel cleansing that is required to improve the exam quality of CT colonography. A combination of restricted diet and bowel cleansing with polyethylene glycol (PEG) or magnesium citrate is used to achieve catharsis.
74. Positioning the patient with the knees flexed over a foam cushoin during a CT examination of the lumbar spine assists in:
1. decreasing the kyphotic curvature of the lumbar spine
2. making the patient more comfortable throughout the exam
3. decreasing the lordotic curvature of the lumbar spine
D. 2 and 3 only
75. The imaging plane that is parallel to the foot's plantar surface is called the:
A. axial plane
The axial plane is parallel to the foot's plantar surface. The oblique axial plane is parallel to the metatarsals, approx. 20-30 degrees caudal from the direct axial plane.
76. The condition of intermittent cramping pain in the legs due to poor circulation is called:
D. claudication
79. The HRCT images of the chest are most likely acquired with a section width of:
C. 1mm
81. The pituitary gland is best demonstrated during CT in which of the following imaging planes?
C. coronal
The pituitary and other structures involving the sella turcica are usually imaged in the coronal plane with CT. The coronal plane provides the best visualization of the pituitary gland with regard to its position within the sella turcica and involves less partial volume averaging of the pituitary with surrounding structures than scans obtained in the axial plane.
82. The most common site of organ injury due to blunt abdominal trauma is the:
D. spleen
Hematoma, hemorrhage, and laceration are typical signs of traumatic splenic injury.
86. The adult spinal cord ends at what vertebral level?
A. L1-L2
At this level it tapers to a point known as the conus medullaris.
87. Which of the following protocols would provide the best image quality for a 3D disarticulation study of the hips?
B. 1.5mm x 1.0mm sections, bone algorithm
3D studies are best performed with the use of narrow sections acquired with no spacing or, preferably, an overlap. A detail (bone) algorithm is used for optimal demonstration of bony structures.
88. Which of the following terms is used to describe a fibroid tumor of the uterus?
B. leiomyoma
A leiomyoma is a benign mass of smooth muscle. It commonly occurs in the uterus and is readily identified on CT exams as a bulky, nonspecific uterine enlargement.
90. The section thickness that would best demonstrate the greatest detail of the paranasal sinuses is:
A. 3mm
The section thickness of a CT scan directly affects the detail and spatial resolution of the image. Narrow section widths result in greater detail for imaging of small anatomic parts such as the sinuses.
92. Which of the following anatomic organs is located within the peritoneal cavity?
D. liver
The peritoneal cavity is formed by the membranous sac called the peritoneum. It contains the stomach, liver, gallbladder, spleen, ovaries, transverse colon, and most of the small bowel.
93. Which of the following may be included as part of a routine preparation for a general contrast-enhanced CT examination of the abdomen and pelvis?
1. instructing the patient to take nothing by mouth (NPO) for 4 hours prior to exam
2. 1200mL of oral contrast agent administered 90 minutes prior to exam
3. having the patient drink 4 liters of poly-ethylene glycol (PEG) 24 hours prior to exam
B. 1 and 2 only
Oral contrast is used for opacification of the GI tract. Pt's are typically instructed to be NPO for up to 6 hours prior to exam. PEG is used for bowel cleansing prior to colonography and may have certain applications for CT prep limited to CT colonography.
94. During a complete CT scan of the pelvis, sections should be obtained from the:
A. iliac crests to the pubic symphysis
The scan range may be extended if clinically warranted. Scan parameters (slice thickness, incrementation, etc.) can be adjusted to correlate with the pt's clinical history.
95. The recommended scan field of view (SFOV) for a CT examination of the cervical spine is:
D. 50.0 cm
Acquisition of the C-spine is performed with a large SFOV, 48-50 cm. Targeted reconstructions are made using a DFOV between 10 and 15 cm. Larger DFOV recons may be used to retrospectively display a greater anatomic area as clinical indication dictates.
100. Because of its inherent iodine concentration, the thyroid gland appears________on CT images.
C. hyperdense
This density increases even further with the use of contrast.
101. Air trapping within the trachea and bronchial tree may be optimally demonstrated with multiplanar volume reconstruction (MPVRs) of the thorax known as:
a. maximum intensity projection
(MIPs)
b. 3D volume rendering
c. shaded-surface displays (SSDs)
d. minimum intensity projections (min-IPs)
d. minimum intensity projections (min-IPs)
In the min-IP technique, displayed pixels represent the minimum attenuation value encountered along each sampled ray. This type of multiplanar volume reconstruction (MPVR) can be applied to a volume of the thorax to demonstrate air trapping within the trachea and bronchial tree.
105. Which of the following is NOT a portion of the small bowel?
A. cecum
The cecum is the proximal portion of the large bowel; it is connected to the small bowel at the ileocecal valve.
106. Which of the following is used as the IV administered radiopharmaceutical during a PET-CT fusion examination?
C. fludeoxyglucose F 18 (FDG)
107. The specialized CT examination of the bladder in which an iodinated contrast-agent is directly administered under gravity into the bladder via Foley catheter is termed:
C. CT cystography
108. Which of the following best describes the shape of the x-ray beam utilized in MDCT?
B. cone-shaped
Multidetector CT (MDCT), or Multislice CT (MSCT), utilizes a cone-shaped beam that is incident upon an expanded array of detectors. The detector array consists of multiple rows along the z-axis and requires a cone shaped beam to measure incident radiation.
109. Collimation of the CT x-ray beam occurs-
1. at the x-ray tube, regulating slice thickness
2. just beyond the patient, focusing off-axis transmitted radiation
3. before the detectors, limiting the amount of scatter radiation absorbed
D. 1 and 3 only
Collimation of the x-ray beam in CT is accomplished by both pre-patient and pre-detector collimators, or detectors. The pre-patient detectors restrict the field size, directly influencing the reconstructed section thickness. The pre-detector or post-patient detectors absorb scatter radiation before it contributes to the signal produced by the detector array.
110. CT numbers are usually provided in the form of:
D. Hounsfield units
The CT number is a relative value based on the attenuation that occurs within a voxel of tissue. The Hounsfield unit is used for this value.
111. The mathematical technique allowing the reconstruction of the motion-free images from helically acquired CT data is called:
C. interpolation
Interpolation is the mathematical process whereby data from tube rotations just above and just below a given slice position are used for image reconstruction. Interpolation allows for the reconstruction of a thin, motion-free image from a volumetric data set acquired from a moving patient.
112. The full width at half maximum (FWHM) of a CT scanner is used to describe:
D. spatial resolution
The spatial resolution of a CT scanner can be measured by studying the amount of blurring that occurs around a point within the CT image. Known as the point spread function (PSF), this image unsharpness may be graphically represented. The spatial resolution can then be quantified by measuring the graph at half its maximum value. This measurement, called the full width at half-maximum (FWHM), is used to illustrate the spatial resolution of a CT scanner.
113. A first generation CT scanner consists of an x-ray tube and two detectors that translate across the patients head while rotating in 1-degree increments for a total of:
B. 180 degrees
First generation CT scanners were based on a translate-rotate principle. The x-ray tube and detectors would translate across the pt's head and then rotate 1 degree. This process would repeat in a semicircular fashion, for 180 degrees around the pt's head.
114. Which of the following abbreviations is used to identify a computerized network that stores, retrieves, communicates, and displays digital medical images?
A. PACS
Picture Archival and Communication Systems (PACS) are computerized networks charged with the responsibility of storing, retrieving, distributing, and displaying CT and other digital medical images.
115. The CT "window" controls the _____ of the CT image as it appears to the viewer.
A. contrast and brightness
The operator may control the contrast and brightness of the CT image by adjusting the "window" setting. As a form of gray-scale mapping, the window determines the pixels assigned shades of gray on the basis of their CT numbers.
116. Voxels with equal dimensions along the x-, y- and z- axes are referred to as:
B. isotropic
The ability to acquire an isotropic data set is a distinct advantage of MDCT.
117. Which of the following artifacts is not affected by the CT technologist?
B. ring
Although the CT technologist must be able to readily identify them, ring artifacts are caused by detector malfunction and are beyond his/her control. Pt motion, partial volume averaging, and edge gradient artifacts can all be limited by the CT tech through adequate preparation and careful scan procedures.
118. When one is viewing a multiplanar reformation (MPR) image, each voxel represents:
B. the average attenuation occurring within the voxel
119. Statistical noise appears as _____ on a CT image.
A. graininess
Statistical noise is a term that may be used for quantum noise, or mottle. Caused by an insufficient number of photons being detected, this type of noise appears as graininess on the CT image.
120. An acquisition is made on a 64-slice MSCT system in which each detector element has a z-axis dimension of 0.625 mm. With a selected beam width of 40 mm and the beam pitch is set at 1.50, how much will the table move with each rotation of the gantry?
A. 60mm
40 mm x 1.5 = 60 mm
121. The component of the CT computer system responsible for the data processing of image reconstuction is the:
B. array processor
It is responsible for receiving scan data from the host computer, performing all of the major processing of the CT image, and returning the reconstructed image to the storage memory of the host computer.
122. For single-slice CT (SSCT) systems, which of the following statements regarding retrospective image reconstruction is FALSE?
D. the slice thickness and SFOV may be changed
Retro Reconstruction uses scan or "raw" data to change the matrix, DFOV, center, and/or algorithm used for a CT image. The slice thickness and SFOV are specifically used for data acquisition and cannot be altered retrospectively with a single-slice CT (SSCT) system. The advent of multislice CT (MSCT) has made retrospective adjustments in section width possible. The scan field of view (SFOV) remains an item that may not be altered retrospectively.
123. The loss of anatomic information between contiguous sections due to inconsistent patient breathing is called:
D. misregistration
Misregistration is an artifact that occurs when a pt suspends respiration at different depths during consecutive scans, resulting in the loss of anatomic information.
124. Before a CT image can be reconstructed by a computer, the transmission signal produced by the detectors must be converted into numerical information by an:
B. analog-to-digital converter (ADC)
The ADC is responsible for transforming the analog signal from the detectors into a digital form that may be used by the computer. Analog information is based on a scale, whereas digital information is in numerical form.
125. A CT image is formed in part by projecting back all of the attenuation values recorded during data acquisition onto a:
D. matrix
The back-projection method of image reconstruction involves the acquisition of attenuation values, which is then projected back onto a matrix for subsequent display.
126. Which of the following archival media is capable of storing the largest number of CT images?
B. optical disk
Magnetic optical disks vary in storage capacity, with some capable of storing several thousand 512² matrix CT images. This considerably more than magnetic tape, which had previously been the standard choice for CT image archival.
127. Areas of a CT image that contain abrupt changes in tissue density are electronically represented by which of the following?
B. high spatial frequencies
The contrast of a CT image is controlled by the spatial frequencies of the tissues within the section. Tissues of differing densities are represented electronically by different spatial frequencies. Adjacent tissues that greatly differ in density are represented by high spatial frequencies.
131. Which of the following terms is used to describe a set of rules for solving a mathematical problem?
A. algorithm
The programs used by the CT computer to reconstruct the image are often referred to as algorithms.
132. Which of the following factors does not affect the dimensions of a voxel?
D. kernel
The dimensions of a voxel are determined by multiplying the pixel dimensions by the slice thickness. The dimensions of a pixel are directly controlled by the matrix size and the field of view.
133. The size of the CT image displayed on a computer monitor can be enlarged by increasing the:
1. DFOV
2. SFOV
3. image magnification
D. 3 only
Increasing the display field of view (DFOV) for a reconstructed CT image decreases its displayed size. Electronically magnifying the image on the display system results in a larger displayed image but has no effect on pixel or voxel dimension.
134. The average photon energy of the primary beam of a CT scanner operating at a tube potential of 120 kVp is approximately?
D. 70 keV
The average photon energy of the primary beam used in CT is approx. 70 keV. The average photon energy of any radiographic primary beam is typically 30% to 40% of the applied kilovoltage. The average photon energy of the CT beam is increased through beam filtration.
135. MSCT systems typically employ which of the following detector geometries?
D. third generation
All MSCT systems utilize third-generation geometry and solid-state scintillation detectors.
136. The acquisition of a series of CT images at a single anatomic location over a set period is referred to as:
A. cine CT
Cine CT acquisition involves multiple axial scans obtained at a single anatomic level over a predetermined period. Clinical applications of cine CT acquisition include contrast bolus tracking, dynamic imaging of physiologic processes such as respiration, swallowing, and the cardiac cycle, as well as for CT perfusion studies.
137. The rate at which a quantity of x-radiation emitted from a CT tube passes through a unit area over a unit of time is called the:
B. photon flux
May also be referred to as the fluence rate.
Photon fluence=quantity of radiation.
138. An average CT number value for bone is:
B. +1000 HU
This may vary widely with the density of the particular bone in question and with the beam quality of the CT scanner.
139. A standard CT image reconstructed on a 512² matrix has a digital size of appoximately:
A. 0.5 MB
140. The term used to describe the relationship between the linear attenuation coefficient of an object and the calculated CT numbers is:
B. linearity
It is used to measure the accuracy of the CT scanner.
141. Quality control measurements to test the accuracy of the CT scanners calibration should be performed:
B. daily
CT units should be calibrated with their reference CT number for water at approx. 0. The CT number for air should be at approx. -1000.
142. The 3D CT technique that includes all of the acquired voxel information in the recontructed model with adjustments to its opacity is termed:
C. volume rendering
Volume rendering adjusts the opacity of voxels included in the 3D model according to their tissue characteristics. Unlike the thresholding concept used for shaded-surface display (SSD), or surface rendering, volume rendering does not exclude voxels, but instead alters their appearance so that the 3D model contains the entire volume dataset.
143. Where is the high-frequency generator often located in a modern CT scanner?
B. inside the gantry
The high-frequency generator used to produce the three-phase power used in modern CT scanners is located in the gantry. It may be positioned in a corner of the gantry or fixed to the rotating tube assembly.
144. The smallest unit of information used in the binary language of computers is the:
C. bit
Its name is derived from the term "binary digit" and can appear as either a number 1 or 0. A sequence of eight bits constitutes a byte.
145. The continuous gantry rotation required by helical CT acquisition is made possible by the application of:
D. slip-rings
Eliminating the need for cables, slip-ring technology allows for continuous gantry rotation by utilizing a system of contact brushes that supply electricity to power the system, enabling the passage of transmission data to the computer system.
146. The process of applying a mathematical filter to remove blurring from the reconstructed CT image is termed:
D. convolution
The process known as convolution is applied to reduce image unsharpness. An algorithm, or convolution kernel, acts as a mathematical filter, modifying the ray sum data and removing the unwanted blurring effect of the back-projection.
147. Which of the following acquisitions may be characterized as contiguous?
B. 3.75mm sections reconstructed every 3.75mm
Contiguous images are those acquired with equal section thickness and interval. For example, 3.75 mm sections reconstructed every 3.75 mm completely cover a given volume of tissue with no unmeasured tissue.
148. Pixels representing tissues with average attenuation coefficients greater than that of water have which of the following types of values?
B. positive
149. For a single-slice CT (SSCT) system, which of the following statements regarding pre-patient collimation is true?
1. an increase if pre-patient collimation increased patient dose
2. pre-patient collimation is used to focus radiation through the section of interest
3. pre-patient collimation directly controls slice thickness
C. 3 only
Pre-patient collimation influences the slice thickness by reducing the size of the primary beam. This is accomplished with the use of lead shutters that absorb the outer margins of the primary beam. Increases in pre-patient collimation diminish patient radiation dose by reducing the number of x-ray photons that reach the patient.
150. Digital CT images are networked and archived in accordance with a standardized computer protocol identified by which of the following abbreviations?
D. DICOM
The Digital Imaging and Communications in Medicine (DICOM) standard confirms the process of recording, storing, printing, and transmitting medical image data.
151. The contrast resolution of a CT scanner is NOT related to which of the following?
A. focal spot size
The contrast resolution of a CT scanner depends on several factors, including section width, algorithm selection, detector sensitivity, and noise. The focal spot size is a geometric factor that influences the spatial resolution of a CT scanner.
154. The average photon energy of the CT x-ray beam can be increased by:
B. increasing filtration
Increases in filtration cause a greater amount of low-energy x-ray photons to be absorbed thus increasing the average photon energy of the beam. Higher mAs values increase the intensity of the beam but do not affect average photon energy.
155. Which of the following is a solid-state device used to record the light flashes given off by a scintillation crystal?
D. photodiode
Scintillation crystals are used in cooperation with photodiodes in a scintillation-type CT detector. The photodiode is a solid-state device that absorbs the light flashes given off by the crystal. The photodiode then emits an electrical signal in response to this light.
156. Automatic tube current modulation (ATCM) software is used in current MDCT systems to control:
D. patient radiation dose
Automatic tube current modulation (ATCM) programs adjust the mA throughout an acquisition to reduce pt radiation 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.
157. The type of MSCT detector array that contains multiple rows of detector elements, each of the same lengths, is called a(n):
B. uniform matrix array
A uniform matrix array consists of multiple detectors in the longitudinal direction, each with the same dimensions.
158. A CT image is displayed in a window with a level of 0 and a width of 500. Which of the following statements is correct?
A. pixels with values between -250 HU and + 250 HU will be assigned shades of gray
The width of a window determines the range of pixel values that will be assigned shades of gray around a given level. In this example, all pixels within the range of -250 to +250 HU will be assigned shades of gray. Pixels below -250 HU will appear black, and pixels above +250 HU will appear white.
159. Reformatted CT image planes that lie perpendicular to the original plane of acquisition may be decribed as:
C. orthogonal
Orthogonal planes are at right angles to each other. Orthogonal reformations are perpendicular to the original plane of data acquisition.
160. Segmenting the data acquisition process into separate components of smaller rotation angles may improve which of the following components of CT image quality?
B. temporal resolution
The controlling factors of the temporal resolution of a CT system are the gantry rotation speed and reconstruction method. Temporal resolution can be improved by segmenting the data acquisition process into separate components of smaller rotation angles. Single-segment or half-scan acquisitions reconstruct data obtained from half of the rotation time. For example, this type of segmentation would yield a 250-msec temporal resolution from a 0.5-sec gantry rotation time.
161. Which of the following image artifacts is unique to multislice CT systems?
D. cone beam artifact
Cone beam artifacts are unique to the cone beam geometry of MDCT systems and typically manifest much like partial volume artifacts.
162. Which of the following is considered an analytic form of image reconstruction?
1. iterative technique
2. Fourier reconstruction
3. filtered back projection
A. 2 and 3 only
The analytic methods of CT image reconstruction include the filtered back-projection and the Fourier transform method. These techniques are called analytic because they utilize precise formulas for image reconstruction.
163. A 16-slice MSCT system utilizes an adaptive array of 24 detectors, each ranging in size from 0.625 to 1.25 mm. What is the maximum number of sections the system can acquire with each rotation of the gantry?
C. 16
The number of data channels controls the number of sections the scanner can simultaneously acquire with each gantry rotation. A 16-slice system possesses 16 data channels and is capable of acquiring 16 images per gantry rotation. The configuration of the detector array with regard to the size of the individual detector elements controls the possible section widths for each reconstructed CT image.
164. The measurements of transmitted radiation made by an individual detector is called a(n):
D. ray sum
The measurement of transmitted radiation made by an individual detector is called a ray sum. It equals the total attenuation occurring along a straight-line path from tube to detector.
165. The information included during the 3D reconstruction of a CT scan is controlled by the:
A. threshold setting
The threshold setting is used to include and exclude information during the 3D reconstruction of a CT scan. For example, a high threshold (+150 HU) may be set to produce a 3D model of a bony structure. This threshold eliminates any density value below +150 HU from the data set. The reconstructed 3D model would include only bone tissue or any other substance with a Hounsfield value above +150.
