Amber Flashcards
(104 cards)
1
Q
To best image a possible Schwannoma found within the Schwann cells of th eighth cranial nerves, CT examinations should include which of the following
Thalamus Thymus Internal auditory canal Mastoid air cells
A
Internal auditory canal
An acoustic neuroma (schwannoma) is formed from Schwann cells of the eighth cranial nerve (vestibulocochlear nerve). This type of cranial mass is best imaged with CT examinations of the internal auditory canals.
2
Q
A CT examination of the liver shows an abnormal finding of reduced density, which of the following is most likely the cause?
Fatty infiltrate Hyperdense cyst Contrast-enhancing tumor None of the above
A
Fatty infiltrates greatly reduce the density of the liver.
3
Q
To best demonstrate a three-dimensional disarticulation study of the hip which of the following scan parameters should be used?
- Overlapping sections
- Small scan field of view (SFOV)
- 1 to 2 mm slice width
A
1 and 3
4
Q
An acoustic neuroma would be found in which of the following cranial nerves?
A
8th
An acoustic neuroma (schwannoma) is formed from Schwann cells of the eighth cranial nerve (vestibulocochlear nerve).
5
Q
CT images acquired in a plane which divides the body into dorsal and ventral sections are considered ____________ images.
A
CORONAL The coronal(y-axis) extends from the anterior to posterior through the patient when the patient is in anatomic position.
6
Q
A bolus injection of iodinated contrast media is administered to a patient scheduled for a CT examination of the liver, a delay of ________ should be applied.
A
To allow the portal vein to become completely opacified a delay of 45 seconds is necessary.
7
Q
To best demonstrate a tumor of the liver the CT scan should be performed during which of the following phases of contrast enhancement?
Non-equilibrium phase Equilibrium phase Dynamic phase Bolus phase
A
NON EQUILIBRIUM PHASE
Bolus phase, dynamic phase and equilibrium phase will not provide the best contrast enhancement needed for liver tumor evaluation.
8
Q
Which of the following lab test results may have an impact on the decision to administer IV contrast media?
- PT
- BUN
- Creatinine
A
All
9
Q
When performing a multi-slice CT study, the slice thickness may be ___________ to cover the region of interest, in order to minimize the dose to the patient.
Decreased slightly Increased Decreased greatly A change in slice thickness will not affect patient dose
A
INCREASE
Due to radiation penumbra, a multiple slice study results in a greater patient dose than the same number of individual slices. By covering a specific region of interest with fewer slices (increase in slice thickness) the resulting radiation overlap from adjacent slices is reduced, reducing the dose to the patient.
10
Q
The blood pressure of a patient measures 120/68 mm Hg. The number 120 represents:
A
The top # is The pressure within the arterial vessels as the heart contracts.
The top number represents the systolic pressure. This is the measurement of the pressure exerted on the arterial walls during a contraction of the heart.
11
Q
The scan range for a CT evaluation of a lumbar disk space should include…
A
To ensure complete coverage of a lumbar disk scanning from the pedicle of the vertebra above to the pedicle of the vertebra below the disk should be included.
12
Q
When scanning CT studies requiring multiplanar reformats which of the following technical parameters will improve the quality of the CT images?
CT slice thickness greater than 5mm Noncontiguous scans Contiguous scans with wide slice thickness Overlapping scans with narrow slice thickness
A
Overlapping scans with narrow slice thickness
13
Q
Of the following types of image noise which does the CT technologist have the ability to most easily reduce?
Artifactual noise Quantum noise Electronic noise Detector noise
A
Quantum noise also called statistical noise of a CT image is reduced by increasing mAs and/or increasing the pixel and voxel dimension. This increases the number of x-ray photons abosorbed by the detectors for each voxel to tissue
14
Q
The matrix size of a reconstructed image will be __________ when the DFOV is 25 cm and the pixel area is 0.25 mm 2 .
A
To calculate the matrix size the DFOV is divided by the pixel dimension. A pixel whose area is 0.25 millimeter squared has a linear dimension of 0.5 mm. The DFOV of 250 mm is divided by the pixel dimension of 0.5 mm, resulting in an approximate matrix size of 512 x 512 pixels.
15
Q
I = Ioe-ux is a formula for determining the linear attenuation coefficient. What does the variable x represent?
A
This formula is the Lambert-Beer Law and x is equal to absorber thickness.
16
Q
Atteunated values in a CT image are projected onto a _____.
Reformat Matrix Pixel Voxel
A
MATRIX
The back-projection method of image reconstruction uses the attenuated values projecting them back onto a matrix for display.
17
Q
When speaking of the binary number system, the byte represents a series of __________________ bits of information.
A
Bytes and bits are part of the binary language used by computers to process information. A byte is a series of 8 bits.
18
Q
The estimation of an unknown value from values on either side of it is a mathematical technique termed…
Interpolation Convolution Filtering Summation
A
Interpolation is a reconstruction process of spiral/helical CT. Interpolation uses a mathematical technique to estimate the unknown value from information on either side.
19
Q
The decline in intensity of the x-ray beam as it passes through and interacts with matter is…
A
Attenuation
20
Q
To be accurate a modern CT scanner should be capable of a spatial resolution of up to…
10 lp/mm 20 lp/mm 10 lp/cm 20 lp/cm
A
20 lp/cm
The resolution of a modern CT scanner is approximately 20 line pairs (lp)/cm. The resolution can vary greatly depending on scan factors making it much less than traditional radiography.
21
Q
The term used to describe the part of the CT scanner used to house the x-ray tube and data acquisition system is…
A
Gantry
22
Q
An increase in pitch during a spiral CT examination will adversely affect spatial resolution along which of the following?
x axis y axis z axis axial plane
A
Z AXIS
An increase in pitch results in less information being acquired for each section of reconstruction. This increase in pitch reduces spatial resolution which is represented by the z axis.
23
Q
During a CT examination which of the following is the primary interaction between the x-ray photon and matter?
A
Compton scatter
24
Q
CTDI in computed tomography is an acronym used to describe…
A
The radiation dose to the patient during a CT scan.
The ct dose index uses an ionization chamber to accurately measure radiation exposure to a patient for a given set of technical factors.
25
The greatest factor affecting contrast resolution of a CT scanner is...
Beam hardening
Patient motion
Noise
Hardware malfunction
Noise
26
In the year 1917, the Austrian mathematician named ___________________ proved it was possible to reconstruct a three-dimensional object from an infinite set of all of its projections.
Radon
Radon an Austrian mathematician proved he could build an image of an object using a large set of its projections. This early research is the foundation research for the reconstruction principles used in CT today.
27
The process used to produce electrons from the cathode of a CT x-ray tube is known as...
Thermionic emission
The term "boiling off" is often used when describing the heating of the cathode and the subsequent release of electrons. This is thermionic emission.
28
What does the CT technologist have control of in regards to the x-rays used in a CT exam?
KVP And mAs can be controlled by the tech
The energy level and the quantity of x-rays can be selected
29
Which of the following statements is correct concerning a CT image displayed in a window with a level of 0 and a width of 500?
1) Pixels with values between -250 and +250 Hounsfield units are assigned shades of gray.
2) Pixels with values between 0 and 500 Hounsfield units appear white.
3) Pixels with values greater than +500 Hounsfiel units are black.
4) Pixels with negative values appear white.
Pixels with values between -250 and +250 Hounsfield units are assigned shades of gray.
30
```
In a CT image of uniform homogenous material, the fluctuation of CT numers is referred to as...
Noise
Linearity
Artifact
Partial volume effect
```
NOISE
By scanning a homogenous object(water phantom) the noise of a CT scanner can be measured. Fluctuations in CT number between pixels in an image indicate noise in a CT image.
31
A CT technologist has just completed a CT abdomen/pelvis exam, upon review it is necessary to reconstruct a portion of the data acquisition process to reduce patient motion artifacts, this is called...
Filtered images
Dynamic images
Segmented images
Subtraction images
Segmented images
The process of segmentation is capable with most modern CT scanners. CT images are constructed from transmission data acquired during a 360 degree rotation. With segmentation an image can be constructed using a portion of this data, eliminating the motion artifact from the image.
32
The region of interest measurement is taken in an area of the liver, the figure provides an average density of +1.9 Hounsfield units. The linear attenuation coefficeint of this measurement would be approximately...
The +1.9 Hounsfield unit measurement is very close to the CT number of water - 0. Water has an average attenuation coefficient value of 0.206.
33
The reconstruction by the computer of a CT image received from the transmission signal produced by the detectors must be converted into numeric information by a(n)...
ADC(analog-to-digital converter)
34
The appearance of statistical noise on a CT image resembles...
Graininess
Increased brightness
Concentric circles
Decreased contrast
Graininess
Also called quantum noise, statistical noise is caused by an insufficient number of photons being detected, appearing as a graininess on the CT image.
35
Of the following which is not commonly used as CT scintillation detector material?
Silver halide
Ceramic rare earth
Bismuth germinate
Cadmium tungstate
Silver halide is not used as a detector material in CT.
36
The differences in the generations of CT scanners is based on the configuration of the...
Tube and detectors
Patient and gantry
Anode and cathode
Tube and collimators
Tube and detectors
CT generation classification is based on the relationship of the tube and detectors and the position of each during data acquisition.
37
The high-frequency generator used in a modern CT scanner is found located where?
within the gantry
38
The dimensions of a voxel are calculated as the product of which of the following?
DFOV X matrix size
DFOV X pixel size
Matrix size X pixel size
Pixel size X slice width
The dimensions of the voxel are calculated by multiplying the pixel dimension by the slice width. The pixel is a two-dimensional representation of the voxel. The slice width it equal to the length of the voxel.
39
The ability of a CT scanner to differentiate objects with minimal differences in attenuation coefficients is termed...
Linearity
Modulation
Spatial resolution
Contrast resolution
Contrast resolution
Contrast resolution also referred to as low-contrast resolution or the sensitivity of the CT scanner is the ability of the CT scanner to differentiate objects with similar densities.
40
The scan geometrics of a third-generation CT scanner has which of the following relationships?
Translate - axial
Translate - rotate
Rotate - rotate
Rotate - stationary
Rotate - rotate
During scanning with a third-generation CT scanner both the tube and detector array rotate around the patient.
41
A(n) ______________ is capable of causing an edge gradient artifact.
Tube arcing
Detector malfunction
Dense bone
Involuntary patient motion
Dense bone
42
For a displayed image of the abdomen the display window width would be...
80
500
1300
3800
500
The width of a window should allow visualization of all tissues within the area. A CT image of the abdomen will provide excellent visualization of the soft-tissue structures displayed in a window width range of 350 - 600 Hounsfield units.
43
Which of the following tube - detector geometric relationships produces ring artifacts on the CT image?
Translate - rotate
Rotate - nutate
Rotate - stationary
Rotate - rotate
Rotate - rotate
44
When speaking of prepatient collimation which of the following statement(s) is true?
1. An increase in prepatient collimation decreases patient does.
2. Prepatient collimation directly controls slice thickness
3. Prepatient collimation is used to focus radiation through the section of interest
All of three are accomplished. Patient dose is decreased by the use of lead shutters to absorb the outer margins of the primary beam. Collimating to the area of interest focuses radiation on the region of interest. Slice thickness is reduced as collimation increases by reducing the size of the primary beam.
45
A CT examination using parameters of: large focal spot size, 10-mm slices, 512 X512 mm matrix was completed, which of the following would increase spatial resolution?
1. Use 5 mm slices
2. Change to small focal spot size
3. Reconstruct images in a 320 X 320 mm matrix
1 and 2
To improve spatial resolution use small focal spots, small slices and large matrixes.
46
The Nobel Prize in Physics in 1901 was awarded to which of the following men?
Godfrey Newbold Hounsfield
Geoffrey Newton
Wilhelm Conrad Rontgen
Allan MacLoed Cormack
Wilhelm Conrad Rontgen was honored for his outstanding contributions in the field of x-ray production with the Nobel Prize for Physics in 1901.
47
The following statements concerning retrospective image reconstruction are true, EXCEPT...
* Retrospective image reconstruction may be used to adjust the center of the displayed image.
* Retrospective image reconstruction must be done using scan (raw) data.
* The slice thickness and SFOV may be changed.
* The algorithm , matrix size, and DFOV may all be changed.
*The slice thickness and SFOV may be changed.
Slice thickness and scan-field-of-view (SFOV) are used for data acquisition and cannot be changed once the scan is completed.
48
To decrease the noise of a CT image which of the following would be used?
Decrease the effective dose
Decrease the slice thickness
Increase the matrix size
Decrease the matrix size
A decrease in matrix size increases the number of x-ray photons passing through each pixel increasing the signal-to-noise ratio subsequently decreasing noise in the CT image.
49
Calulate the DFOV for an image with a 320 2 matrix and a pixel dimention of .75 x .75 mm.
24cm
The formula for DFOV is pixel dimension x the matrix size. 320 x .75 mm = 240mm or 24 cm DFOV.
50
Of the following, which describes the physical phenomena termed "beam hardening"?
* The increase in average photon energy of a homogeneous x-ray beam.
* The decrease in average photon energy of a heterogeneous x-ray beam.
* The increase in average photon energy of an attenuated heterogenous x-ray beam.
* None of the above
The x-ray beam used in CT is comprised of numerous different energy level x-ray photons. The beam hardens as it passes through the patient and the lower energy photons are absorbed, increasing the average photon energy.
51
The _________________ of the CT scanner determines the ability of the scanner to image small high-density objects.
Contrast resolution
Sensitivity
Spatial resolution
More than one is correct
Spatial resolution is the controlling factor of the CT scanner to image small structures accurately.
52
Partial volume averaging is most likely to be caused with which of the following slice widths?
1 mm slice width
3 mm slice width
5 mm slice width
10 mm slice width
10 mm slice width
53
The appearance of statistical noise on a CT image resembles ____________.
graininess
54
What is a voxel described as?
A volume element
55
The signal-to-noise ratio of a CT image increases with which of the following?
Increased filtration
Decrease in pixel size
Increased aperture size
Decreased milliamper-seconds (mAs)
Decreased milliamper-seconds (mAs)
56
The _________ artifact is NOT affected by the CT technologist.
Ring artifacts are caused by detector malfunction and are not within the control of the CT technologist. Careful preparation and careful scan procedures by the CT technologist can reduce the occurance of patient motion, partial volume averaging, and edge gradient artifacts.
57
To increase the average photon energy of the CT x-ray beam which of the following must be increased?
Increasing filtration
Increasing mAs
Increasing collimation
To increase the average photon energy the low-energy x-ray photons must be filtered(absorbed), thereby increasing the average photon energy of the beam.
Increasing mAs will increase the intensity of the beam but does not affect the average photon energy. Collimation removes both low-energy and high energy photons from the area of collimation.
58
What type of mathematical manipulations are required to reconstruct a CT image?
1. Algorithm
2. Mathematical filter function
3. Kernal
The three terms algorithm, kernel and mathematical filter function can all be used interchangeably to describe the mathematical process used to complete the calculations needed for CT image reconstruction.
59
CT numbers are usually recorded in the form of...
Hounsfield units
60
When speaking of the analytic form of image reconstruction which of the following is correct?
1. Fourier reconstruction
2. Iterative technique
3. Filtered back - projection
1 and 3
Analytic techniques use precise formulas for image reconstruction, these include Fourier transform and filtered back-projection.
61
Inconsistent patient breathing can cause a loss of anatomic information between contiguous slices called:
Misregistration
62
The type of image reconstruction used in the first-generation prototype CT scanner was _____________.
Convolution method
Fourier transform
Back-projection
Iterative technique
The first generation CT scanner designed by Dr. Godfrey Hounsfield used an iterative form of image reconstruction.
63
The term "full width at half-maximum" of a CT scanner is used to describe which of the following?
Contrast resolution
Spatial resolution
Image noise
Calibration accuracy
Spatial resolution
The point spread function is a process used to measure spatial resolution of a CT scanner. Spatial resolution is measured by studying the amount of blurring occurring around a point within the CT image. This image unsharpness is represented on a graph. The spatial resolution is then expressed numerically by measuring the graph at half its maximum value. This measurement is known as the full width at half-maximum.
64
The incoming primary x-ray beam that interacts with a single detector is known as a...
View
Ray
Profile
Sample
The ray is describe as the portion of the x-ray beam that falls on a single detector.
65
CT number values for pixels with average attenuation coefficients less than water will be...
A negative Hounsfield unit
Extremely large Hounsfield unit
Positive Hounsfield unit
None of the above
A negative Hounsfield unit
66
Upon completion of a CT of the abdomen, an area within the liver is measured with the ROI (region of interest) the area has an average density of + 1.7 Hounsfield units. This material is most likely...
Blood
Fat
Tumor
Water
WATER
| The CT number for water is near or at zero. This area is most likely a watery liquid representative of a hepatic cyst
67
Abrupt changes in tissue density found between adjacent areas of a CT image are represented electronically by...
High spatial frequency
Positive CT numbers
Negative CT numbers
Low spatial frequency
High spatial frequency
68
The low-contrast resolution of a CT scanner is extremely poor, causes may include:
1. Increase in tube output
2. Increase in electronic noise
3. Decrease in patient dose
2 and 3
69
The CT scanner uses which of the following components to calculate the mathematical portion of CT image reconstruction?
Array processor
Digital-to-analog converter
Analog-to-digital converter
Data acquisition system (DAS)
The array processor is capable of performing massive calculations required in the CT image reconstruction process.
70
What is the average CT value for blood?
The average Hounsfield unit for blood is +40.
71
To decrease partial volume averaging and increase resolution on the CT image which of the following should be employed?
Matrix size increased
Matrix size decrease
Slice thickness increased
Slice thickness decreased
Slice thickness decreased
72
Which of the following is the Hounsfield value of a pixel directly related to?
Window width and window level
Field of view
Linear attenuation coefficient of water
CTDI(CT dose index)
Linear attenuation coefficient of water
73
When using the CT "window" controls, the technologist is manipulating __________________ of the CT image.
```
Detail and density
Contrast and spatial resolution
Attenuation coefficient and the Hounsfield unit
Brightness and contrast
More than one is correct
```
Brightness and contrast
74
Collimation of the CT x-ray beam is used to accomplish several outcomes, which of the following is NOT true in respect to collimation?
To limit the detection of scatter radiation the use of collimation is employed.
Increases in collimation result in the intensity of the primary beam increasing.
Collimation of the beam occurs along in z-axis, controlling slice thickness
Collimation of the beam occurs both prepatient and postpatient.
Increases in collimation result in the intensity of the primary beam increasing.
Collimation is contstructed of lead shutters that close down upon the beam limiting its projected area. These shutters absorb portions of the primary beam reducing the intensity.
75
During the three-dimensional reconstruction of a CT scan the information included is controlled by the...
Window width and window level
Algorithm
Threshold setting
Gray scale map
Threshold setting
76
Which of the following characteristics does the first-generation CT scanners possess?
A rotate-rotate geometry
A pencil-thin x-ray beam
Silver halide detectors
Nutating detector array
A pencil-thin x-ray beam
77
The difference in an analog signal and a digital signal is...
Analog is based on a scale, digital is in numeric form.
Analog is in numeric form, digital is based on a scale.
Analog and digital are both in numeric form.
Analog and digital are both based on a scale.
Analog is based on a scale, digital is in numeric form.
78
The appearance of metal in a CT localizer image will result in streaks emanating from the metal object.
True
False
FALSE
In helical/spiral and conventional CT images metal objects will result in streaking. The localizer image is not generated from multiple projections and a complex reconstruction process and therefore metal is represented as a simple 2D projection.
79
Of the following which does NOT affect the total dimensions of the voxel?
DFOV (Display field of view)
Matrix size
Kernal
Slice thickness
KERNAL
To determine the dimensions of a voxel multiply the pixel dimension by the slice thickness. Pixel dimension is direclty controlled by the matrix size and the field of view.
80
Of the following terms, which are used to describe the ability of a CT scanner to differentiate between objects with similar linear attenuation coefficients?
1. Sensitivity
2. Contrast resolution
3. Spatial resolution
Sensitivity
And
Contrast resolution
Contrast resolution or sensitivity, is the CT scanners ability to image objects with similar densities accurately.
81
Fourth generation scanners uniquely use:
Scintillation crystals
Sodium crystals
central rays
multiple detectors
Scintillation crystals
82
To best demonstrate the bony details of a shoulder joint a ___________________ algorithm should be used.
High spatial frequency
83
Most cupping artifacts occur in CT images of the____________.
Brain
84
The tube-detector configuration of fourth-generation CT scanners is...
Rotate-stationary
85
Specialized CT images reconstructed from a CT angiography formed from the greatest density reading encountered from each ray is called a(n)...
Surface-rendered image
Three-dimensional model
Volume-rendered image
MIP image
MIP image
86
In regards to the radiographic film used to archive CT images, which of the following statements is correct?
1. Double-emulsion film is used
2. It is sensitive only to ultraviolet light
3. May be used with both a multiformat or laser camera
3 only
The radiographic film used in CT image archiving is a single-emulsion film, compatable with both multiformat and laser cameras. A laser beam is used to expose the film in a laser camera and light is used for film exposure with the multiformat camera.
87
The relationship between the calculated CT number and the linear attenuation coefficient is described by the term...
Linearity is the relationship between the CT number and the actual linear attenuation coefficient of a given object and is used to measure the accuracy of a CT scanneer.
88
The beam in modern CT units forms a fan-shaped x-ray beam, the disadvantage of the fan-shaped beam when compared to "pencil-thin" beam is/are...
The fan-shaped x-ray beam increases the total volume of tissue irradiated causing an increase in scatter radiation produced. This increases patient dose compared to the pencil pen of the older CT scanners.
89
What is volume scanning
Volume scanning refers to a technique of scanning a volume of tissue by moving the patient continuously through the gantry of the scanner while the x-ray tube and detectors rotate continuously.
90
The reference detectors in a third-generation CT scanner are positioned at the peripheral portions of the detector array to...
Be exposed to homogeneous radiation
Be exposed to unattenuated radiation
Monochromatic radiation
Remnant radiation
Be exposed to unattenuated radiation
Reference detectors measure the incident radiation intensity. This information is calculated by the computer to compute the linear attenuation coefficient. An incorrectly placed patient within the gantry may block the reference detectors causing out-of-field artifacts.
91
Modern CT scanners employ which of the following reconstruction methods?
Filtered back-projection
Back-projection
Iterative method
Fourier transform
Filtered back-projection
The filtered back-projection also called convolution method of image reconstruction is used in modern CT scanners.
92
Of the following which will reduce the scatter radiation before it reaches the detectors?
a) Predetector collimation
b) Postpatient collimation
c) Prepatient collimation
d) Both a and b
A and b
Postpatient collimation and predetector collimation are synonymous terms used to describe collimation designed to remove scatter radiation before it reaches the detectors.
93
Of the following mathematical techniques which is used exclusively for image reconstruction with spiral CT scanners?
Convolution
Back-projection
Interpolation
Iterative techniques
Interpolation
94
The technologist notices a possible herniated disk at the level of L3-L4 on a CT examination of the lumbar spine. To best demonstrate the posterior compression of the disk material onto the spinal cord, the reformats should be in which plane?
The sagittal plane divides the body into left and right halves best demonstrating the relationship of the disk material as it protrudes posteriorly onto the spinal cord.
95
Listed below are several contrast media. Which may be used during a CT examination of the gastrointestinal tract?
1. Diatrizoate meglumine (Gastrografin)
2. Effervescent agents
3. Iopamidol (Isovue)
1 2 and 3
All three are correct. The use of intravenous contrast agents such as gastrografin and Isovue are necessary to properly visualize the blood vessels and are helpful in the differentiation of mass vascularity. Effervescent agents aid in proper gastric distension.
96
Which of the following technical factors should be used during dynamic CT scanning?
1. Patient continuously moving through the gantry during data acquisition.
2. Rapid scanning with minimal interscan delays.
3. Intravenous bolus administration of iodinated contrast media.
2 and 3
Dynamic scanning is a technique used during imaging of the chest and abdomen. After the bolus injection of contrast media the scanning follows rapidly through the area of interest. Interscan delays are kept to the minimum amount allowed by the tube cooling requirements of the scanner.
97
A female patient is scheduled for a double-contrast CT study of the bladder, an intravenous injection of iodinated contrast and _________________ is indicated to accurately visualize the bladder.
To properly evaluate the bladder it is necessary to administer intravenous iodinated contrast media and to insert a Foley catheter into the bladder and administer 100-300 mL of air and 100 mL of diluted (approximately 30%) diatrizoate meglumine.
98
A CT exam is done with a slice thickness of 10mm, and a 2mm gap is between the slices, the pitch is 1:2 and the total scan time is 5 seconds. What is the table increment for this exam?
12mm
The table increment is determined by adding the slice thickness with the gap between the slices. 10mm + 2mm = 12mm table increment. The other information given is just that other information to distract you.
99
A given CT exam yields a CTDI of 4.5 rads, with a slice thickness of 10mm, and a 2mm gap between slices, the MSAD for this exam is ________ rads.
3.75 rads
The MSAD is equal to the CTDI X the ratio of the slice thickness to the table increment. With a 2mm gap and a 10mm slice the table increment will be 12mm. The MSAD = (4.5 rads) X (10mm/12mm)
100
modified so that it is appropriate for children by decreasing which of the following?
1. kVp
2. mAs
3. Pitch
The standard protocols should be adjusted for small adults and children. The most effective way to modify the protocol is to adjust the kVp and mAs.
101
A patient is brought to the CT department with a creatinine level of 3.1 mg/dl, this indicates:
1. The patient's kidneys are not removing waste products from the urine
2. The patient is not a good candidate to receive IV contrast material
3. The creatinine value is below the normal range
2 only
Creatinine is a test of renal function. The normal range for creatinine is 0.6 to 1.7 mg/dl. The patient's kidneys clear the contrast media from the blood not the urine. A creatinine value greater than 3 mg/dl is considered high and the patient is at risk to enter renal failure if IV contrast medi is administered.
102
Platelets are small cell fragments responsible for the clotting of blood. The normal range for an adult is between _________________.
Platelets are the portion of blood that is responsible for clotting at the site of a puncture. Normal platelet levels range between 150,000 and 400,000 platelets/mm 3 of blood.
103
A CT scan of the pelvis resulted in a dose at the entrance to the patient's skin of 6 rads, the dose at the center of the patient will be _____ mGy, if it is two-thirds less than the skin dose.
20mGy
The skin dose of 6 rads - 4 rads = 2 rads( 1 Gy = 100 rads)
104
Which of the following changes will NOT decrease the patient dose?
Decrease the scan time while all other parameters remain the same
A decrease in slice thickness while covering the same area of interest
An increase in pitch
A decrease in scan time will reduce the mA reducing the mAs which reduces patient dose. An increase in pitch reduces dose to the patient because the anatomy is covered in fewer rotations. Reformatting eliminates the need to rescan and is an excellent way to minimize dose. A decrease in slice thickness while scanning the same anatomical area means more slices are necessary to cover the region of interest and more dose to the patient.
