A. occurs with digital technology and refers to the fact that the relationship between dose and image quality is less direct than in film-screen radiopgraphy
Which of the following is a high-attenuation structure?
B. petrous bone
The process of using raw data to create a new image after the initial image has been generated is typically referred to as:
B. retrospective reconstruction
In a CT system, what is the function of the generator?
A. it produces high voltage and transmits it to the x-ray tube
A detectors dynamic range is the:
B. ratio of the maximum signal measured to the minimum signal the detector can measure
The part of the CT system referred to as the DAS is responsible for:
C. sampling each of the detector cells many times per second
Increasing the kilovoltage results in an increase in the:
A. speed of the electrons as they travel from filament to anode
The configuration of the x-ray tube to the detectors determines a scanners:
Which are parts of the systems primary memory?
C. ROM, RAM
What is an example of a computer output device?
What two factors control the slice thickness of an MDCT scanner?
A. collimation of the x-ray beam and width of the detectors in the z-axis
What part of the CT system is responsible for converting the digitized data into shades of gray?
A. display processor
A hardware component of a CT system that resembles small shutters with an opening that adjusts, dependent on the operators selection of slice thickness, is a:
D. source collimator
The fraction of a beam of x-rays that is absorbed or scattered per unit thickness of the absorber is referred to as the:
A. attenuation coefficient
In the production of x-rays, approximately what percentage of the kinetic energy of the projectile electrons is converted to thermal energy?
The area of the anode where the electrons strike and the x-ray beam is produced is the:
B. focal spot
MDCT systems that contain parallel rows of equal size detectors are called:
D. uniform arrays
Which of the following could be retrospectively reconstructed for MDCT data that requires four 2.5mm slices with each gantry rotation?
A. slices can be combined to produce two 5 mm slices
Computer memory that is imprinted at the factory and is used to store frequently used instructions such as those required for starting the CT system is called:
D. read-only memory (ROM)
Interpolation, as it is used in CT, is:
C. a mathematical method to estimate a missing value by taking an average of known values at neighboring points
Image data can be used for:
B. creating multiplanar reformation
Why is it necessary to apply a filter function to an attenuation profile to create a CT image?
D. to minimize streaks
What type of filter accentuates the difference between neighboring pixels to enhance spatial resolution?
B. a bone algorithm
The window width of a specific CT image is set at 120 and the level is set at 50. How is a structure with a measurement of -40 HU displayed?
B. it is black
A narrow window width is best for:
C. displaying the white and gray matter of the brain
How is a cursor measurement different than obtaining a region of interested measurement?
B. a cursor measurement is the HU measurement for a single pixel, whereas an ROI is the average HU for all pixels within the ROI
Using a standard 512 matrix for all studies, which contains the largest pixels?
D. a scan of the abdomen; DFOV= 44, slice thickness= 5mm
Why is it more common pracice to manipulate the mAs, rather than the kVp, for a CT exam:
D. scanners offer more mA options and the effect of mAs on image qualit is more predictable
What scan parameter determines how the raw date are filtered in the reconstruction process?
A. reconstruction algorithm
Which of the following is an imaging challenge that depends on spatial resolution?
D. tiny, contrast filled arteries that are just 1mm apart
In-plane resolution refers to the resolution:
B. in the xy direction
Which of the following parameters will produce near isotropic voxels?
C. DFOV= 35, slice thickness= 0.625mm
Temporal Resolution refers to:
A. how rapdily the data is acquired by the CT system
What two factors define the quantity of the x-rays energy?
B. mA and scan time
Which of the following can be described as possessing high inherent contrast?
In the computing world, _____ is used to describe an arrangement in which two or more components perform the same task- if one element fails the duplication keeps the system functioning while the failed component is repaired.
Which is an example of an offline archiving device?
B. compact disks
Spatial Resolution can be calculated from the analysis of the spread of information within the system using the modulation transfer function. What is a simpler and more direct way to measure spatial resolution?
A. using a line / pairs phantom
Which aspect of the CT quality control program must be performed by a medical physicist?
B. dosimetric data
The process in CT by which different tissue attenuations are averaged to produce one less accurate pixel reading is called?
A. the partial volume effect
The primary method of reducing beam-hardening artifacts is:
A. filtering the x-ray beam
Effective slice thickness blooming is:
B. a disadvantage often associated with the interpolation of helical data
If measurements taken around the perimeter if a water phantom are different from those taken at the center of the phantom, than there is a problem with the systems:
C. cross-field uniformity
Estimate the radiation dose for one CT exam versus the dose from one chest radiograph
C. one CT exam is equal to or greater than 100 -250 chest radiographs
Which image artifact can result from an improperly centered patient?
A. out-of-field artifact
Which type of artifact is only present on images produced from MDCT systems?
What causes ring artifacts?
B. imperfect detector elements either faulty or simply out of calibration
The presence of noise on an image degrades its quality, particularly in:
D. low-contrast resolution
An image of the abdomen is greatly degraded by quantum mottle. The scan parameters used are as follows: DFOV= 38 cm, slice thickness= 5mm, mA= 240, tube rotation= 0.5 seconds, kVp= 120. What action will have the best chance of reducing or eliminating the quantum mottle for subsequent scans?
D. increase the mA to 300 and increase tube rotation time to 0.8 seconds
A circular ROI is defined and placed on the image, and the resultant measurement is 3 HU. The standard deviation is 0. It can be surmissed that:
C. all of the pixels within the region have identical values
The display function that creates a bar graph to show how frequently a range of CT numbers occurs within a specified ROI is called a:
Comparing the spatial resolution of CT to other modalities:
A. CT is inferior to general radiography
Changing the slice incrementation is also referred to as:
A. z-axis reconstruction or chaning the reconstruction interval
Which of the following is NOT an advantage of using helical CT for the diagnosis of PE?
D. quality images are produced even if the patient is uncoopertive
High density contrast agents, such as barium sulfate, are referred to as:
C. positive agents
What is the pitch in the following scenario: 64 detector channels used, 0.625mm slice thickness, table movement 55mm per rotation?
rotation/slice thickness then divided by # of detectors
55/.625= 88 88/64=1.375
When do scan protocols incorporate the use of gapped slices?
C. when a survey of an area is needed
Pitch is a parameter that is commonly used in helical CT to describe:
C. table speed
Compare 100mL of Ultravist (iopromide) 300 with 100mL of Ultravist (iopromide) 370.
C. Ultravist 370 has a higher viscosity
In which of the following situations would an LOCM be beneficial when delivered orally?
C. when oral contrast is needed for neonatal CT exam
The difference among the bolus phase, the non-equilibrium phase, and the equilibrium phase of contrast enhancement is primarily determined by the:
D. injection rate and scan delay
For routine CT if the chest, abdomen, or pelvis, the range of suggested IV contrast flow rate is:
C. 2.0-4.0 mL/s
Which of the following might be an appropriate protocol for a CT study that is performed for suspected acoustic neuroma?
D. 1mm contiguous slices, reconstructed using both standard and bone algorithm, with IV contrast, filmes in two separate window settings
Fresh blood in the brain, as in the case of a recent onset subdural hematoma, will measure approximately:
B. 70 HU
Patients with metastasis to the brain are at greater risk for _____ after the administration of an IV contrast agent.
Prospective ECG gatting methods for imaging the heart use a signal, usually derived from the ____ of the patients ECG, to trigger image acquisition.
A. R wave
When imaging the heart, particularly when the structures of interest are small, such as the coronary arteries a regular heart rate of less than _____ is important.
D. 70 bpm
Airway imaging is routinely performed:
A. at both inspiration and expiration
In addition to imaging the pulmonary arterial system for patients with suspected PE, CT venography is sometimes performed to assess for venous thrombosis within the pelvis and lower extremities. How is this accomplished?
D. a second series is obtained in a delayed venous phase (approx 180 seconds after IV contrast injected) from the iliac crest through the knees
The use of a saline flush after the injection of the iodinated contrast is recommended for CTA pulmonary studies. Why?
B. to reduce or eliminate bean-hardening artifacts from dense contrast media within the superior vena cava that may obscure small emboli in adjacent vessels
The formation, development, or existence of a clot within the vascular system is referred to as a(an)?
A CT study done for the screening, detecting, or exclusion of pulmonary nodules or infiltrates are typically done:
B. without IV contrast administration
A patient is being seen in the ER for acute respiratory distress. PEs are suspected and a CT is ordered. A review of the patients history reveals that he is allergic to shellfish. What action should be taken?
A. a CT exam using a PE protocol is done
A bolus injection of 125mL, of an iodinated contrast media with a concentration of 320mg of iodine/mL, is administered to a 150-pound patient, but becase of an unexpected equipment malfunction scan data could not be acquired. The decision must be made as to whether the patient should be moved to a functioning scanner within the department and the contrast injection repeated. What information will be particularly important for the radiologist making the decision?
D. evidence of renal impairment or dehydration
On an UNENHANCED abdominal CT, what is the range of CT attenuation values of a normal liver?
A. 38 to 70 HU
In general, the pancreas is located between the areas of the:
B. twelfth thoracic and the second lumbar vertebrae
To scan in the nephrographic phase of contrast enhancement, scans should be acquired approximately ____ after a bolus contrast injection.
A. 80 - 130 seconds
The use of flow control mechanical pressure injectors are recommended for CT studies of the chest, abdomen and pelvis because:
B. contrast media dose and timing can be easily regulated and reproduced in subsequent studies
In scanning the abdomen, what can be done if the patient is unable to take fluids by mouth?
D. a NG tube may be inserted for the administration of an oral contrast agent
It is important that all scans be completed before the equilibrium phase of contrast enhancement in studies of the:
Scanning to the adrenal glands in a CT study of the thorax is sometimes performed because:
D. lung cancer may metatasize to the adrenal glands
As a general rule, this is set at a point that has roughly the same value as the average attenuation number of the tissue of interest. What is it?
A. window level
The trachea bifurcates at the level of:
An automatic trait that can help to differentiate an adenoma from a malignant adrenal mass on CT scans is its:
B. intracellular lipid content
A set of ROIs, one placed within the liver and one placed with the spleen, is often used to document:
C. fatty infiltration of the iver
For a CT of the foot the patient is positioned supine, legs flat on the table, toes pointing straight up. There is no gantry tilt. Images acquired are in the direct _____ plane.
In a preliminary scout view of a patient, the abdomen is determined to be 360mm in length. In this four-slice CT system, the gantry makes a 360 degree rotation each second. The protocol at the institution calls for a 5mm slice thickness. To cover the entire abdominal area in a single helical scans, which set of parameters could be selected?
C. 15 second total acquisition time, 1.2 pitch
What technique is often used to differentiate the margins of the pancreas from the duodenum?
C. acquire scans while the patient is a right decubitus position
What is the superior portion of the sternum?
Which of the following factors should be adjusted when slice thickness is decreased from 10 to 3 mm?
A. increase mAs
In scanning the brain, using which of the following reference lines reduces the radiation exposure to the lens of the eye?