CT review, Mosby
The correct order for the stages of infection is:
incubation, prodromal, active, convalesence
Which of the following oral contrast agents offers the best visualization of the enhancing GI wall on post-IV contrast CT examination?
water Water as a negative oral contrast agent improves visualization of the enhancing enteral wall when an IV contrast agent is administered. Other agents, such as VoLumen and milk, may also be effective as agents capable of distending the bowel while allowing for wall visualization.
Which of the following oral contrast agents offers the best visualization of the enhancing GI wall on post-IV contrast CT examination? -low-osmolar water-soluble iodinated solution -high-osmolar water-soluble iodinated solution -water -barium sulfate suspension
water water as a negative oral contrast agent improves visualization of the enhancing enteral wall when an IV contrast agent is administered. Other agents, such as VoLumen and milk, may also be effective as agents capable of distending the bowel while allowing for wall visualization
A CT system measures the average linear attenuation coefficient of a voxel of tissue to be 0.189. 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:
+44 HU The CT number of a pixel may be calculated by subtracting the linear attenuation coefficient of water from the linear attenuation coefficient of the tissue within the voxel. This number is divided by the linear attenuation coefficient of water. The quotient is multiplied by a contrast factor of 1000 to yield the value of the pixel in Hounsfield Units
A CT scanner capable of producing an image that is a perfect reproduction of the actual anatomic section is said to have an MTF of:
1 The MTF of a CT scanner measures the ability of the system to faithfully reproduce the area of anatomy. It can be thought of as a comparison of the actual anatomy with the image produced. If the two are exactly alike, the MTF of the scanner is 1. If the image produced contains no useful information, the MTF is 0. The MTF of most CT scanners falls somewhere in between.
Prior to and after contact with each patient, a proper hand-washing technique requires that the technologist use warm soap and water with a circular rubbing motion for at least:
30 seconds Proper hand-washing technique requires a minimum of 30 seconds. The technologist should use warm soap and water with a firm circular motion.
Which of the following components of CT image quality is/are being evaluated? 1. linearity 2. section width 3. spatial resolution
1 and 2 only A linearity phantom contains four inserts of various materials surrounded by water. Known ranges of CT values are compared with those obtained by CT acquiation to ensure system accuracy and linearity. This American College of Radiology (ACR) phantom also contains two ramps consisting of series of wires spaced 0.5 mm apart along the phantoms Z-axis. The accuracy of the selected section width is evaluated by counting the number of wires visible in cross-section.
Which of the following statements accurately describes the effects of administering an iodinated IV contrast agent during imaging procedures of the brain? 1. The contrast agent increases the attenuation values for normal grey mater. 2. The contrast agent improves the differentiation of subtle hemorrhage 3. The contrast agent enhances neoplasms that have disrupted the blood-brain barrier.
1 and 3 only During CT imaging for suspected intracranial bleeding, contrast administration is initially contraindicated because the associated enhancement may mask subtle signs of hemorrhage.
Which of the following technicial adjustments would decrease the quantum noise of a CT image? 1. Increase mAs 2. Decrease section width 3. Increase section width
1 and 3 only The quantum noise of a CT image can be reduced by an increase in the number of x-ray photons reaching the detectors. This reduction may be accomplished by increasing mAs or section width (decreasing collimation).
High-resolution computed tomography (HRCT) of the chest incorporates which of the following protocols? 10 mm sections, standard algorithm 10 mm sections, bone algorithm 3 mm sections, standard algorithm 1 mm sections, bone algorithm
1 mm sections, bone algorithm HRCT of the chest is used to examine diffuse pulmonary disease. This technique offers excellent visualization of the lungs, airways, and pulmonary hilum. HRCT involves the use of narrow sections (1-3 mm) and a high resolution algorithm.
The normal range of Cerebral blood volume (CBV) contained within 100 g of brain tissue is:
4-5 mL/100 g The normal range of CBV in brain is 4-5 mL/100 g
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/100g/min
An acquisition is made on a 4-slice MSCT system with a detector array of 16 1.25 mm detector elements along the z-axis. With a selected beam width of 20 mm, what beam pitch would result in the table moving 35.00 mm for each rotation of the gantry?
1.75 The beam pitch for a given acquisition is equal to the table feed per rotation divided by the total collimation. The total collimation for this acquisition is equal to the total number of sections (detectors) multiplied by the detector dimension, or 16 multiplied by the detector dimension, or 16 multiplied by 1.25 mm. The beam pitch may be therefore calculated by dividing 35.00/20 or 35.00/1.75
Each 1.0% in contrast between adjacent objects amounts to a difference in pixel value of approximately:
10 HU 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
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 a average osmolality between 1000-2400 mOsm/kg.
Which of the following section widths would cause the greatest amount of partial volume averaging? 1mm 3mm 5mm 10mm
10mm large section widths result in long voxel lengths with possibly several tissues types accounted got within the voxel. When a CT number is assigned to the representative pixel, the density of all of the tissues types is averaged, yeilding one attenuation coefficient. Narrown section widths tend to decrease the partial volume effect.
The normal range of glomerular filtration rate (GFR) for women is:
60 +/- 10 mL/min/m2 Normal range of GFR is 60+/- 10 WOMEN normal range of GFR is 70 +/- 14 MEN
The human eye is capable of differentiating approximately ________ shades of gray.
60-80 the human eye is capable of differentiating only about 60-80 individual shades of gray. The 256 shades utilized in CT are therefore sufficient to represent the total range of pixel values possible in a 12-bit system
A normal range for systolic blood pressure in an adult is:
95-140 mm Hg The normal range for systolic blood pressure in adults is 95-140 mm Hg. Systolic pressure is the measurements of blood pressure at its peak during contraction of the heart.
The normal range for systolic blood pressure in an adult is:
95-140 mm Hg the normal range for systolic blood pressure in adults is 95-145 mm Hg. Systolic pressure is the measurement of blood pressure at its peak during contraction of the heart.
The average range for normal prothrombin (PT) time is approximately:
12-15 seconds Normal prothrombin (PT) times are lab-specific and range between approximately 11 and 15 seconds. This test is used to evaluate the coagulation ability of a patient scheduled to undergo an invasive CT procedure.
The normal platelet count range for an adult is:
140,000-440,000/mL of blood
After initiation of rapid bolus administration of an iodinated contrast agent, the early arterial phase of hepatic contrast enhancement occurs at approximately:
15-20 seconds Occurring at 15-20 seconds after the initiation of contrast administration, the early arterial phase of contrast enhancement is the optimal phase for angiographic applications of liver CT. During this phase, the hepatic arterial supply is well opacified with little or no parenchymal enhancement.
What is the maximum allowable blood glucose measurement for patients scheduled to undergo PET-CT examination?
150 mg/dL The patients blood glucose may be measured prior to the injection of F-19-fluorodexoxyglucose (FDG). It should be below 150 mg/dL to prevent FDG uptake inhibition by glucose circulating in the bloodstream
The plasma half-life of intavenously administered iodinated contrast material is approximately:
2 hours After approximately 2 hours, the percentage of iodinated contrast material in blood plasma is reduced to half of the administration volume.
The water-soluble 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 soluble 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-soluble contrast media include Gastrografin and Hypaque.
For general contrast enhanced MDCT of the chest, sufficient opacification of vascular structures can be typically obtained with injection rates of:
2.5-4.0 mL/sec Administration of 50-150 mL of iodinated contrast agent at a rate between 2.5 and 4.0 mL/sec provides adequate opacification of the mediastinum and other vascular structures for most CT examinations of the chest.
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 or test bolus technique is recommended to ensure appropriate scan timing.
The following formula is used to calculate the linear attenuation coefficient: -ux I=I e 0 The symbol ''x'' identifies
Absorber thickness The Lambert-Beer law, is used to calculate the attenuation coefficient of a volume of material. The symbol ''x'' represents the thickness of the absorber attenuating the radiation.
The interaction between x-ray and matter that is responsible for the production of the scatter radiation absorbed by the patient and detectors is:
Compton effect In the Compton interaction, 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 formation of the CT image.
Which of the following corresponds to the period of the cardiac cycle known as ventricular systole? -relaxation of the left and right atria -contraction of the left and right atria -relaxation of the left and right ventricles -contraction of the left and right ventricles
Contraction of the left and right ventricles ventricular systole describes the period of the cardiac cycle when the left and right ventricles are contracting.
The term _________ describes the ability of a CT scanner to differentiate objects with minimal differences in attenuation coefficients.
Contrast resolution The contrast resolution of a CT scanner refers to the systems ability to differentiate objects with similar densities. This ability is also commonly referred to as the low-contrast resolution or the sensitivity of the CT scanner.
Which of the following steps could be taken to reduce the artifact? reduce section thickness angle gantry around fillings decrease kVp
Angle gantry around fillings the only effective method of reducing streak artifact due to metal is to remove the metal object(s) from the scanning field. In this case, the dental fillings cannot be removed, but the gantry could be angled to avoid their interference.
____________ is a term that refers to an excessive amount of nitrogenous materials in the blood and is a symptom of renal failure.
Azotemia Azotemia describes the condition of excessive nitrogenous materials in the blood. This condition is also commonly called uremia. Azotemia is a symptom of renal insufficiency and may occur during chronic renal failure.
Infection may occur indirectly through contact with contaminated objects known as:
Fomites Fomites are objects that have been contaminated by an infectious organism or microbe. The spread of the infection may occur when someone comes in contact with the fomite. This is an indirect means of infection transmission.
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 a water-filled phantom. Beam hardening occurs as low-energy x-ray 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.
The computer technique used to reduce the size and storage requirements of digital CT image data is called:
Compression Image compression is a complex computer technique that reduces the size of digital CT image data. COmpression of CT images reduces the storage requirements and increases the speed at which CT images may be transmitted across computer systems.
The type of compensating filter used at the X-ray tube of a CT scanner is called a:
Bow-tie filter The bow-tie filter used at the X-ray tube of a CT scanner absorbs a larger amount of radiation at the periphery of the patient where the part thickness is reduced. The center of the patient is placed at the center of the filter, where the largest amount of radiation is allowed to pass through. The use of this type of filter attempts to compensate for the differences in thickness of the often oval shaped patient.
Which of the following may be used for the archival storage of CT images? CD-ROM VHS Tape Magnetic optical disk
CD-ROM and Magnetic optical disk CD-ROM and MOD are two media commonly employed for CT image archival.
An IV contrast enhanced specialized CT evaluation of the small bowel after the oral administration of a low-density (0/1%) barium sulfate solution is termed:
CT enterography CT enterography dose not involve contrast agent administration through a nasogastric tube and is therefore less invasive than CT enteroclysis
Evaluation of the venous vascular structures of the brain is known as:
CT venography CT venography (CTV) of the brain is a variation of the CTA technique whereby the timing of data acquisition is optimized for the period of peak venous opacification.
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.
The period of peak enhancement of the renal cortex following rapid bolus injection of an iodinated contrast agent is termed the:
Corticomedullary phase This phase is a late arterial phase beginning 30-40 seconds after the initiation of contrast agent administration. Optimal enhancement of the renal cortex and renal veins occurs during his period.
A test phantom containing water scanned and if I region of interest measurements are performed. The subsequent density measurements are compared and demonstrate maximum deviation of less than 2 HU. This quality assurance test was performed to valuate the scanner's
Cross-field uniformity The test described is used to evaluate the cross-field uniformity of a CT scanner. The ROI measurements are arranged with one at the center of the image and the others rotated about the periphery. Each of the five ROI measurements taken from the water phantom should yield relatively the same CT number value.
The term _____ describes the ability of a CT scanner to differentiate objects with minimal differences in attenuation coefficients.
contrast resolution The contrast resolution of a CT scanner refers to the system's ability to differentiate objects with similar densities. This ability is also commonly referred to as the low-contrast resolution or the sensitivity of the CT scanner.
IN which of the following cranial nerves would an acoustic neuroma be found?
Eighth An acoustic neuroma (schwannomma) arises from Schwann cells of the eighth cranial nerve, or vestibulocochlear nerve. This type of cranial mass may be imaged with CT examinations of the internal auditory canals.
Ct scanning of the liver for tumor evaluation should NOT be performed during which of te following phases of contrast enhancement?
Equilibrium phase Contrast enhancement is at its lowest 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.
*Which of the following is not a category of isolation technique? enteric precautions gram-negative isolation contact isolation strict isolation
Gram-negative isolation the categories of isolation technique are: drainage-secretion precautions; enteric precautions; acid-fast bacillus isolation; respiratory isolation; contact isolation; and strict isolation.
Which of the following laboratory values is used to measure the coagulation ability of a patient prior to an invasive CT study? (multiple answer) PTT hematocrit PT
PTT and PT the coagulation capabilities of a patient may be evaluated with the measurement of prothrombin time (PT) and partial thromboplastin (PTT). Each of these laboratory values attempts to detect defocoemcies 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.
Parenteral contrast administration refers to which of thew following? oral administration rectal administration IV administration nasogastric administration
IV administration the injection of a medication or contrast agent directly into the bloodstream is a type of parenteral administratiion. Other parenteral routes include intramuscular, subcutaneous, intradermal and intrathecal.
The abdominal aorta divides into the left and right common iliac arteries at approximately the level of:
L4 the abdominal aorta divides into the right and left common iliac arteries at approximately the level of L4
Severe reactions to intravenous iodinated contrast material occur in approximately ________ of all patients.
Less than 1% severe reactions to intravenous iodinated contrast media occur in less than 1% of all patients. Examples of severe reactions are shock, myocardial infarction, and death.
The quantity of radiation dose received by the patient from a series of CT scans is referred to as the:
MSAD The multiple-scan average dose (MSAD) is used to quantify the amount of exposure a patient receives from a series of CT scans. It is calculated from the computed tomography dose index (CTDI) through a series of equations. The quantity of radiation per scan is measured with an ionization chamber.
The addition of ______ makes an autoclave more efficient at sterilization than an oven.
Moisture An autoclave is a mechanical device used for sterilization. It involves the use of heat and steam under pressure to eliminate microbes. An oven uses only high heat and is not as efficient as an autoclave.
Which of the following formulas may be used to calculate the dimensions of a pixel?
Pixel size = DFOV/matrix size Dimensions of a pixel may be calculated by dividing the DFOV by the matrix size. Keep in mind that the pixel is a square with four equal sides and the dimension of one side is usually given in mm. The area of the pixel is calculated by squaring the dimension, and the units are then adjusted to square millimeters mm^2
In 1917, Austrian mathematician ________ proved that it was possible to reconstruct a three-dimensional object from the infinite set of all of its projections.
Radon J. Radon, an Austrian mathematician, was responsible for some of the earliest scientific research for the reconstruction principles used in computed tomography. In 1917 he proved that it was possible to build an image of an object through the use of an extremely large set of its projections.
Which of the following is NOT a component of the blood supply to the brain commonly referred to as the circle of Willis? right middle cerebral artery left posterior communicating artery anterior communicating artery left posterior cerebral artery
Right middle cerebral artery The circle of Willis is composed of the anterior cerebral, anterior communicating, internal carotid, posterior cerebral, and posterior communicating arteries. The basilar artery and middle cerebral arteries are important vessels supplying blood to the brain, but they do not form a part of the circle of Willis.
Ct images that have been reconstructed from a portion of the data acquisition process in the hopes of reducing patient motion artifacts are called:
Segmented images CT images are usually constructed from transmission data acquired during a 360-degrees rotation of the x-ray tube. A CT image can also be constructed from a portion of the data acquisition phase. For example, if a patient moves during the last third of a 2-second scan, an image can be constructed from the first 240 degrees of tube rotation, yielding an image free of motion. This process, refereed to as segmentation, is a software capability of many modern CT scanners.
A portion of a herniated intervertebral disc that has migrated from its normal position is called a(n)
Sequestered disc Sequestered disc or free fragment is used when a portion of the disc nucleus completely breaks free and migrates from its normal position.
___________________ is the term used to describe the ability of a PACS to tansmit data from the imaging facility to an off-site location
Teleradiology refers to the ability of a PACS to transmit image data across a local area network (LAN) or wide area network (WAN) from the imaging facility to an off-site location.
The type of compensating filter used at the x-ray tube of a CT scanner is called a:
bow-tie filter The bow-tie filter used at the x-ray tube of a CT scanner absorbs a larger amount of radiation at the periphery of the patient, where the part thickness is reduced. The center of the patient, where the patient is placed at the center of the filter, where the largest amount of radiation is allowed to pass through. The use of this type of filter attempts to compensate for the differences in thickness of the often oval-shaped patient
The portion of the male reproductive system responsible for storage of the majority of mature sperm is the:
Vas Deferens the majority of mature sperm is stored in the vas deferens. Sperm is produced in the sminiferous tubules and passes through the epididymis, where a small amount may be stored.
The primary advantage of prospective ECG gating for cardiac CT over retrospective ECG gating is:
a reduction in patient radiation dose The main benefit is prospective ECG gating is the potential for up to 70% reduction in patient radiation dose. Prospective ECG gating requires a steady heartbeat to limit motion artifact, and the evaluation of cardiac function is not possible because data is acquired only during diastole.
A patient demonstrates diffuse urticaria shortly after intravenous administration of iodinated contrast media. Correct treatment would include:
administration of an antihistamine drug Administration of an anthihistamine drug is the usual treatment for the development of urticaria (hives) following the injection of iodinated contrast media.
During HRCT of the lungs, image acquisition upon full expiration may be performed to improve demonstration of:
air trapping COPD Suspension of breathing at the end of forced expiration (static expiratory HRCT) may be utilized to demonstrate air trapping in patients with suspected small airway disease, such as chronic obstructive pulmonary disease (COPD), and emphysema.
The detectors of a PET system absorb and measure what type of radiation?
annihilation photons Annihilation photons are emitted from the radionuclide F-18-fluorodeoxyglucose (FDG) that has been taken up by the tumor cells. PET detectors absorb the emitted photons, measuring the activity of a given area of potential malignancy.
Which of the following phase of contrast enhancement optimally demonstrates the relationship between pancreatic neoplasm and the surrounding vasculature?
arterial phase During arterial phase acquistion through the pancreas, there is maximum opacification of the surrounding vasculature, including the aorta and superior mesenteric artery. An important goal of pancreatic CT is so evaluate the involvement of surrounding vessels by pancreatic neoplasm.
Which of the following technical adjustments would result in a decrease in patient dose? (multiple answer) -decrease mAs -increased detector pitch -decrease kVp
decreased mAs increased detector pitch decreased kVp The relationship between mAs and dose is directly proportional. Any reduction in mAs results in a reduction in dose when all other factors remain equal. Increasing detector pitch raises the rate at which the patient moves through the gantry during data acquisition; when all other factors remain constant, increases in detector pitch reduce patient dose. A decrease in kVp also results in lower patient dose primarily through the reduction in overall beam energy at lower tube potentials. This may seem counter intuitive to those who recall the use of high-kVp techniques in radiography as a means of lowering required mAs and the associated patient dose. When we reduce kVp to reduce patient dose in CT, the assumption is again made that all other technical factors remained unchanged.
Which of the following technical adjustments may be employed to improve the temporal resolution of an MDCT system? decreased scan time decreased section width decreased DFOV
decreased scan time temporal resolution quantifies the CT system's ability to freese motion and to provide an image free blurring. The controlling factors of the temporal resolution of a CT system are the gantry rotation speed and reconstruction method.
Which of the following technical factors exhibit an effect upon longitudinal spatial resolution? (multiple answer) detector collimation detecotr pitch interpolation algorithm
detector collimation detector pitch interpolation algorithm the factors that affect longitudinal spatial resolution and the SSP include the type of spiral interpolation algorithm inherent to the system and the selected detector pitch. Thin-section image reconstruction reduces or completely eliminates broadening of the SSP and also improves longitudinal spatial resolution.
A straight line apperaing vertically on the scanogram (pilot) of a 4th generation CT scanner is an artifact most likely caused by:
detector malfunction A straight line artifact on a scanogram (pilot) image is most likely caused by a malfuntioning detector in both 3rd and 4th generation scanners. As the patient travels through the gantry, the faulty detector does not record any information, leading to the blank line that appears on the image.
Which of the following technical factors exhibits an effect upon longitudinal spatial resolution? (multiple answer) detector pitch interpolation algorithm display field of view (DFOV)
detector pitch interpolation algorithm the factors that affect longitudinal spatial resolution and the SSP include the type of spiral interpolation algorithm inherent to the system and the selected detector pitch
Which of the following symptoms indicate(s) a vagal reaction to an iodinated intravenous contrast agent? (multiple answer) -bradycardia -systolic pressure below 80 mm Hg -diastolic pressure above 90 mm Hg
diastolic pressure above 90 mm Hg a vagal reaction to iodinated intravenous contrast must be recognized early so that proper initial treatment is provided. A combination of bradycardia (heart rate below 50/min) and hypotension (systolic pressure below 80 mm HG) indicates a vagal reaction.
The presence of outpocketings in the wall of the colon is referred to as:
diverticulosis Diverticulosis is the presence of small pouch like openings in the wall of the colon. Diverticulitits is used when the diverticula become inflamed.
In which of the following cranial nerves would an acoustic neuroma be found?
eighth An acoustic neuroma 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 quantity of blood pumped out of a ventricle every heartbeat is termed the:
ejection fraction Ejection fraction describes the percentage of blood pumped out of a cardiac ventricle during each contraction. It is a measure of cardiac function and can be accurately determined during a cardiac CT examination. With system software, the ejection fraction can be calculated from a comparison between the volume of blood within a ventricle at the end of filling (end-diastolic volume) and the volume at end of contraction (end-systolic volume).
Infection may occur indirectly through contract with contaminated objects known as:
fomites fomites are objects that have been contaminated by infectious organism or microbe. The spread of the infection may occur when someone comes in contact with the fomite. This is an indirect means of infection transmission.
The type of MSCT detector array that contains midline narrow elements flanked by wider detectors is called a(n):
hybrid array A hybrid array consists of two detector sizes. The narrow detectors are positioned midline, flanked by the wider detectors. For example, the central rows of a 16-channel MDCT system are 0.625 mm with the remaining peripheral rows at 1.25 mm.
Following the intravenous administration of iodinated contrast media, a hepatic hemangioma may become ___________ and may no longer appear on the CT image.
isodense the diagnosis of hemangioma is confirmed on CT by evaluation of its pattern of enhancement. Hemangiomas enhance from the periphery inward, until they become isodense with the surrounding hepatic tissue. Once isodense, the hemangioma attenuates the beam in the same way as the hepatic tissue. The CT numbers of the hemangioma and hepatic tissue become equal and the structures may become impossible to differentiate.
Which of the following types of image reconstruction was used in the first prototype CT scanner? convolution method iterative technique Fourier transform back-projection
iterative technique the first-generation prototype CT scanner designed by Dr. Godfrey Hounsfield used an iterative form of image reconstruction.
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 artery (LCX)
The ability of an object to attenuate the x-ray beam is assigned a value known as the:
linear attenuation coefficient The ability of an object to attenuate the x-ray beam is assigned a value termed the linear attenuation coefficient (u)
An Agatston score of 5 on an MDCT cardiac examination for coronary artery calcification is rated as:
minimal
Multiplanar reformation (MPR) images along the long axis of the optic nerve would be best described by which of the following anatomic planes? sagittal coronal oblique sagittal oblique coronal
oblique sagittal the optic nerve runs along a lateral-to-medial path from the orbit anteriorly and to the optic chiasma posteriorly. Oblique saggital MPR images will demonstrate the optic nerve in a profile parallel to its long axis.
Which of the following technical parameters would greatly improve the quality of CT studies requiring multiplanar reformation (MPR) images? noncontiguous scans wide section thicknesses contiguous scans with wide section thickness overlapping scans with narrow sections
overlapping scans with narrow sections the quality of multiplanar reformats can be greatly improved with the use of narrow, overlapping scans.
The oral administration of barium and iodinated contrast media prior to CT colonography serves the primary purpose of:
polyp tagging Dual-agent tagging involves the oral administration of both barium and water-soluble iodinated contrast. The barium tags residual stool and coats the surface of polyps. The iodine contrast tags residual fluid. Tagged fluid and fecal matter exhibit high CT density and appear ''white'' on the CTC image. Tagging allows for differentiation of polyp from fecal matter and improves the visualization of polyps that may be surrounded by residual fluid.
The component of the DAS responsible for strengthening the signal emitted from a detector is termed the:
preamplifier the weak electronic signal emitted from the detectors in response to the measurement of transmitted radiation must be strengthened before it is utilized for image reconstruction. The preamplifier is the component of the data acquisition system (DAS) responsible for amplifying the detector signal.
Where should the tourniquet be positioned during preparation of a patient for intravenous contrast administration? directly over injection site proximal to the injection site distal to the injection site below the injection site
proximal to the injection site Prior to the IV injection of contrast media, a tourniquet is placed proximal to the injection site. The tourniquet helps distend the vein, making needle insertion easier.
Which of the following contrast agents may be used for the purpose of colon insufflation during a CT colonography examination? (multiple answer) room air CO normal (0.9%) saline
room air CO Colon insufflation involves the introduction of room air or carbon dioxide into the colon for the purpose of bowel wall distention
Which of the following technologic advances has led to the development of spiral/helical CT scanning? (multiple answer) slip-ring technology electron beam technology high-efficiency x-ray tubes
slip-ring technology high-efficiency x-ray tubes Spiral/helical CT scanners are a recent development in computed tomography technology. The advents of slip-ring technology and improvements in x-ray tube design have made this innovation possible. Slip-rings have taken the place of the cumbersome cables previously used to transmit the CT signal and supply power to the tube and detectors. This development enables the tube and detectors to rotate continuously around the patient, acquiring data in the form of a helix. The longer exposure times of up to 60 seconds require extremely efficient x-ray tubes with enormous heat capacities.
Which of the following components of CT image quality may be controlled by the technologist? (multiple answer) -spatial resolution -contrast resolution -noise
spatial resolution contrast resolution noise Each component of CT image quality may be affected- either positively or negatively- by the CT technologist. Spatial resolution is affected by geometric factors such as focal spot size and slice thickness, Contrast resolution may be altered by slice thickness, algorithm selection, and noise. The noise level of an image is dependent upon several factors, including patient dose and pixel dimension. Each of these factors must be considered by the CT technologist in an effort to provide high quality CT studies.
Radiation protection of the CT patient should involve which of the following principles? (multiple answer) strict clinical indication protocal optimization shielding
strict clinical indication protocol optimization shielding Specific clinical indications ensure that CT is performed only when alternative nonionizing radiation examinations have been deemed inconclusive or inappropriate. An optimized protocol is one that acquires CT images with acceptable levels of noise at the lowest possible dose. Lead shielding should be utilized during CT whenever clinically possible.
The term beam hardening is used to describe which of the following physical phenomena?
the increase in average photon energy of a heterogenous x-ray beam beam hardening occurs as the x-ray beam traverses the patient. The x-ray beam used in CT is composed of x-ray photons with numerous different energies. The heterogenous beam undergoes an increase in average photon energy as it passes through the patient and the lower-energy photons are absorbed.
The rights of the patient include which of the following? (multiple answer) -the patient has the right to considerate and respectful care -the patient has the right to receive a copy of the diagnostic procedure performed -the patient has the right to refuse medical treatment
the patient has the right to considerate and respectful care the patient has the right to receive a copy of the diagnostic procedure performed the patient has the right to refuse medical treatment The American Hospital Association drafted A Patient's Bill of RIghts in 1973. Included among the 12 ''rights'' are the patient's right to considerate and respectful care and the right to refuse treatment. Release of the patient's diagnostic examination results is not an inherent right and is at the discretion of the physician(s) involved.
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, a 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.
Which of the following terms describes a condition in which cerebral ischemia is caused by systemic hypertension? vasovagal reaction myocardial infarction transient ischemic attack hydrocephalus
vasovagal reaction the term vasovagal pertains to systemic hypertension often leading to cerebral ischemia.