Quizlet ARRT PREP 1 Flashcards
(200 cards)
1
Q
How do you reduce beam hardening?
A
- Increase dose.
- Reduce collimation - reduce slice thickness.
- Increase window width.
2
Q
At what level does the abdominal aorta bifurcate?
A
L4.
3
Q
What is the typical scan delay after injection of contrast media for studies of the liver?
A
30-45 seconds.
4
Q
What window setting provides the best tissue differentiation within the liver?
A
WW = 140
WL = 60
5
Q
What window settings that provide the best bone window for the pelvis?
A
WW = 2000
WL = 350
6
Q
What mAs is typically used in routine CT exams of the abdomen?
A
200-300 mAs.
7
Q
What is the result of the bifurcation of the abdominal aorta?
A
The right & left iliac arteries.
8
Q
What is the anode target angle?
A
12 degrees.
9
Q
At what level do the common carotids bifurcate into the internal & external carotid arteries?
A
C3-C4.
10
Q
The floor of the orbit is formed by the _____ bones.
A
Maxillary & zygomatic.
11
Q
The lateral walls of the orbit is formed by the _____ bones.
A
Zygomatic & sphenoid.
12
Q
The medial wall of the orbit is formed by the _____ bones.
A
Ethmoid & lacrimal bones.
13
Q
How do you calculate effective mAs?
A
MAs/pitch.
14
Q
Define window level
A
Level: a chosen midpoint in the grayscale.
15
Q
Define window width
A
Width: number of grayscale values above & below the level.
Width is DIVIDED in half & distributed above and below the level.
Anything above the window is white; anything below the window is black.
16
Q
The wider the window the _____ grayscale values; the _____ the contrast.
A
More; Lower.
17
Q
Factors that affect spatial resolution
A
- focal spot.
- Detector width (aperture).
- Reconstruction algorithm - bone>soft tissue.
- Slice thickness.
- Pixel/FOV/Matrix.
- Pitch - decrease pitch means no gaps.
- Nyquist limitations.
18
Q
Factors that affect contrast resolution
A
- energy of X-rays - increase kVp = decrease contrast.
- # of X-rays - increase mA = decrease mottle.
- Slice thickness - thicker is better.
- Reconstruction method (iterative > filtered).
- Reconstruction algorithm (soft tissue>bone).
19
Q
Give window levels for brain, lung, abdomen, bone.
A
Brain: W80, L40.
Lung: W1500, L-400.
Abdomen: W400, L50
Bone: W1600, L500
20
Q
What is beam hardening?
A
As the X-ray beam passes through an object, lower energy photons are removed (like filtration) leaving a “harder beam” of hitting energy photons. This causes two artifacts.
21
Q
What are two types of beam hardening artifacts?
A
Cupping the center of a round object is darker than the periphery due to hardening of the beam 360 degrees around the object. Happens in the head.
Streak: these are dark brands that occur in b/t two dense objects - nearly all the photons are removed in a line b/t the two objects.
22
Q
How do you compensate for beam hardening artifacts?
A
- Filtration
- Calibration.
- Correct software.
- Avoidance (tilting gantry or positioning pt).
23
Q
Ring Artifacts
A
Calibration error or detective detector cause consistently erroneous reading at each angular position, resulting in a circular artifact.
24
Q
Is the focal spot large or small?
A
Large 0.6-1.2 — so as not to overheat the anode from such a high mA.
25
Which of the following will result in increased voxel size?
A. Decreased reconstruction.
B. Increased slice thickness.
C. Increased matrix.
D. None of the above.
B. Increased slice thickness.
26
If a tissue with a CT number of +300 appears white on the image, which of the following are the WW and WL selected?
A. WL0; WW500.
B. WL300; WW500.
C. WL100; WW1000.
D. None of the above.
A. WL0; WW500.
27
What is the e volume of a voxel is a slice thickness of 3mm, a 512x512 matrix & a reconstruction field of view of 25.6cm are used?
A. 0.75 mm^3.
B. 1.5 mm^3.
C. 6.0 mm^3.
D. None of the above.
A. 0.75 mm^3.
Solve: FOV/matrix size (that’s 0.5), then square that by 0.25, multiply that by slice thickness and you get 0.75.
28
Which of the following parameters is responsible for partial volume averaging?
A. Matrix size.
B. kVp.
C. Slice thickness.
D. Patient dose.
C. Slice thickness.
29
Voxel equation
Pixel area x section thickness.
30
What is interpolation?
Mathematical method for taking SPIRAL data & viewing it as AXIAL images.
31
Bone Windows
2000-4000 WW
200-400 WL.
32
Lung windows
1400-1600 WW
(-) 400-600 WL.
33
Modular Transfer Function
Graphical representation of SPATIAL RESOLUTION measured in lap/cm, tells you how small you can scan without blurring.
34
Decrease partial volume averaging?
Reduce slice thickness.
35
Which portion of the pancreas is the most common site for tumors? And where located?
The head of the pancreas. It is located approximately at T12.
36
Lung Window
2000 WW and - 200 WL.
(-) is air.
37
The Hounsfield unit that is -1000 most likely represents which of the following?
Air.
38
Relative to CT topography, slice thickness is best represented by which of the following axis?
Z axis.
39
What unit is the basis for exposure based on ionization in air?
mR or C/kg.
40
What radiation unit considers the biological effectiveness of radiation exposure?
mrem or mSv.
41
“Fan” beam technology first historically came on the scene with which acquisition geometries?
Second.
42
“Rotate-rotate_ applies to which of the following geometries?
Third.
43
In CT what imaging plane is the pituitary best visualized?
Coronal.
44
The third ventricle of the brain communicates with the fourth ventricle through the:
Cerebral aqueduct.
45
_____ refers to an excessive amount of nitrogenous material in the blood & is a symptom of renal failure.
Azotemia.
46
Which paranasal sinus is usually the last to fully develop?
Frontal.
47
What is the average annual radiation dose?
2 rem.
48
10 rem converted to Sieverts is what?
0.1 Sv.
49
Convert 10 mSv to Sv.
0.01 sV.
50
Annual limit for adult occupational effective dose?
0.05 Sv.
51
Annual limit of occupational lens dose
0.15 Sv.
52
Annual limit of shallow dose equivalent to skin/extremities
0.5 Sv.
53
Occupational exposure to embryo/fetus during pregnancy
0.5 mSv.
54
Total effective dose equivalent to public - also average background radiation
1 mSv.
55
Mild reactions to iodinated IV contrast media include
Nausea, vomiting, mild urticaria, and a warmed flushed sensation.
56
Moderate reactions to IV contrast?
Dyspnea, hives (urticaria), wheezing, change in pulse, facial edema, vasovagal response, hypo-hyper tension.
57
Severe reactions to IV contrast
Severe broncospam, anaphylaxis, drowsiness, headache, fever/chills, shock, pulmonary edema.
58
Osmalarity
Concentration of a solution in terms of number of dissolved particles per unit of water.
59
Non-ionic IV contrast media such as Omnipaque should have an average osmolarity of:
750 mOsm/kg water.
60
What drugs are administered for moderate reaction to injection of iodinated contrast medium?
Antihistamines and Epinephrine.
61
Prothrombin
Measures the amount of time necessary for a persons blood to coagulate. 10 and 14 seconds.
62
Why use an autoclave?
The use of an autoclave for sterilization involves heat & steam under pressure to eliminate microbes.
63
1 rem = 1 rad
When measuring the radiation dose from x-rays, rads and rems are equivalent. The units of Sv and rem are used to measure any kind of ionizing radiation where 1 Sv =100rem. The units of rad and Gy are used to measure specifically x-ray radiation where 1 Gy = 100 rads.
64
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 pt.
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.
65
A given CT exam yields a CTDI of 4.5 rads, with a slice thickness of 10 mm and a 2 mm gap between slices, the MSAD for this exam is _____ 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)
--3.75 rads
66
Calculate the DFOV for an image with a 320 2 matrix and a pixel dimension of .75mm x .75mm.
A. 36 cm.
B. 12 cm.
C. 24 cm.
D. 48 cm.
Answer C.
The formula for DFOV is pixel dimension x the matrix size
320 x .75mm = 240mm or 24 cm DFOV.
67
True or false: the units rad and rem are equivalent when measuring radiation dose used in CT X-ray radiation.
Answer: TRUE.
*When measuring the radiation dose only from x-rays, rads and rems are equivalent. The units Sv and rem measure any kind of ionizeing radiation (1 Sv = 100 rem). The units rad and Gy measure specifically x-ray radiation
(1 Gy = 100 rads
68
Non-ionic contrast media include :
Iopamidol (isovue) Iohexol (omnipaque) and iopromide (ultravist).
69
Normal pulse rate for an adult?
60-100 bpm.
70
Normal average adult respirations per minute?
12-20.
71
Which of the following iodinated contrast media may NOT be used for intrathecal injection?
Iohexol(Omnipaque), metrizamide(Amipaque) and iopamidol(Isovue) are all non-ionic contrast agents that may be used for intrathecal injection. Meglumine is not considered safe for an intrathecal injection.
72
A patient arrives with a central venous line in place. Which type of central venous line may be used for a CT examination requiring the administration of iodinated contrast media with an automatic injector?
none.. indwelling catheters or central venous lines cannot withstand the pressure produced by an automatic injector
73
The total quantity of radiation dose received by the pt from a CT scan series is termed:
MSAD(multiple-scan average dose) quantifies the amount of exposure to a patient from a series of CT scans. MSAD is calculated using a series of equations based on the CTDI(CT dose index). The radiation quantity per scan is measured using an ionization chamber.
74
Average pulse rate for an infant:
100-180 bpm.
75
General signs of shock include:
- Rapid breathing
- Tachycardia
- Hypotension
- Weak pulse
- Pallor
- Cyanosis
- Cold, clammy skin.
76
What is the average range for activated partial thromboplastin time?
28-34 seconds.
77
The average radiation dose to the pituitary gland during a CT head is:
2 rads.
78
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?
*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.
79
What is medical asepsis?
The reduction in number of infectious agents but not the complete elimination of all organisms.
80
Complete cardiac diastole correspond to which portion of the cardiac cycle on a ECG?
T-wave.
81
Gas accumulating within a degenerating intervertebral disk is termed:
Vacuum effect.
82
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.
83
During CT examination of the larynx, the pt is often instructed to pronate the letter “E” in order to properly evaluate the:
Vocal chords.
84
The exaggeration of displayed calcification within the coronary arteries during a cardiac MDCT study is referred to as:
Blooming - refers to the potential overestimation of vessel calcification due to partial volume artifact.
85
What describes a condition in which cerebral ischemia is caused by systematic hypertension?
Vasovagal reaction.
86
Patients whose posterior descending artery branches from the right coronary artery, and whose left posterior ventricular braches arise from the left circumflex artery are said to be
Codominant
7% of the population is said to be codominant... which means the PDA is supplied by the RCA.. and the left posterior ventricular braches arise from the LCX
87
Which of the following window settings would optimally display CT colonography images?
Level = -400 Width = 1600
CT colonography images are best displayed in wide “lung-type” window setting.
88
A CT scanner with a limiting resolution of 15 lp/cm can resolve an object as small as:
0.3 mm.
The minimum object size that a CT scanner can resolve may be calculated by taking the reciprocal value of the scanner's limiting resolution. The reciprocal of 15 lp/cm is 1/15 lp/cm. This is equivalent to 10/15 lp/mm, which equals 0.6 mm/lp. Because a line pair is equivalent to a line and the space adjacent to it, this value may be divided in half to provide the minimum object that this scanner can resolve..0.3
89
The total length of a CT scan may be calculated by multiplying the scan time by what?
Multiply the scan time by the aperature size.
Ex: If the scan time is 15 seconds and the aperture size(slice thickness) is 1.0cm(10mm) the length of the scan will be 150mm.
90
An abnormal density of the liver is found to be a fatty infiltrate. The CT number for this area would most likely be in the range of:
-100 Hounsfield units.
91
What is the HU of a pulmonary nodule?
+200 HU.
92
The radiologist has requested a CT examination to identify the thymus gland in a young pre-puberty patient. The thymus gland is located
Anteriosuperior portion of the mediastinum.
93
To best image a possible Schwannoma found within the Schwann cells of the eighth cranial nerves, CT examinations should include which of the following
Internal auditory canal.
94
CT examination of the liver for hepatic tumor evaluation should NOT be performed during which of the following phases of contrast enchancement?
Equilibrium phase.
95
The correct orientation or viewing CT images on the monitor is which of the following?
Cross sectional anatomy is viewed from the perspective of looking up from the patient's feet to the head and the image oriented with the left side of the patient on the right side of the viewer.
96
Some CT scanners allow the CT technologist to outline an anatomic area on a series of cross-sectional images and then define the outlined area on the localizer(scout) image. This is called
Correlation
97
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
45 second delay will allow the portal vein to become completely opacified.
98
An acoustic neuroma would be found in which of the following cranial nerves?
8th cranial nerve.
99
When performing a dynamic CT study of the chest the inter scan delay used would be:
4 seconds (shortest possible).
100
CT images acquired in a plane which divides the body into dorsal and ventral sections are considered _____ images.
Coronal.
101
A CT examination of the liver shows an abnormal finding of reduced density, which of the following is most likely the cause?
A fatty infiltrate - they greatly reduce the density of the liver.
102
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-- Bolus phase, dynamic phase and equilibrium phase will not provide the best contrast enhancement needed for liver tumor evaluation.
103
A contrast enhanced CT examination of the chest is completed, when viewing the image it appears small, making evaluation of the anatomy difficult. To improve image quality which of the following technical changes may be made?
Decreased DOV.
The image was obviously reconstructed in a display field of view larger than necessary. The image appears small because of this error. The DFOV chosen for an image should be slightly larger than the diameter of the area of interest.
104
_________ a specialized technique which uses a narrow section widths and a low-resolution algorithm for image reconstruction.
High resolution CT.
105
What is used to combat bradycardia during a vagal reaction to contrast?
Atropine.
106
CT images containing areas of abrupt changes in tissue density are electronically represented by:
High Spatial frequencies
The spatial frequencies of the tissues within a section control the contrast of a CT image. Adjacent tissues with large differences in density are represented by high spatial frequency signals
107
The definition of conversion efficiency is:
The percentage of X-rays colliding with the detector atoms which result in a measurable electrical signal.
108
Focal spot size is determined when choosing what?
Slice thickness.
109
The CT number for blood is approximately:
+45 HU.
110
The dimensions of a voxel may be calculated as the product of which of the following:
Pixel size and section width.
The pixel is a two-dimensional representation of a voxel. The section width is equal to the length of the voel. To calculate the dimensions of a voxel, the pixel dimension must be multiplied by the section width
111
Which of the following formulas may be used to calculate the dimensions of a pixel?
Pixel size = DFOV/matrix size.
112
A CT image reconstructed using a 512^2 matrix and a display field of view of 17 cm. What is the linear dimension of each pixel?
0.3 mm
The dimension of a pixel may be calculated by dividing the field of view by the matrix size. The DFOV of 17 cm must first be converted into 170 mm. This is then divided by 512 mm, for a pixel dimension of 0.33 mm. Keep in mind that the pixel is a two-dimensional item, square in shape, and the measurement of 0.33 mm corresponds to only one side
113
The portion of the nephron responsible for filtration of unwanted materials from the blood plasma is called the:
Glomerulus.
114
The ability of an MDCT system to freeze heart motion during a cardiac CT is described by its:
The temporal resolution of an MDCT system describes its ability to freeze the motion of the heart as well as the arterial motion velocity within the coronary vasculature
115
In multislice CT (MSCT), the beam pitch is equal to the table feed per rotation divided by the:
Total collimation.
The beam pitch, which is unique to multislice CT, is equal to the table feed per rotation divided by the total collimation. The total collimation is equal to the combined thickness of all of the sections that are simultaneously acquired with each gantry rotation
116
Phantom measurement of the uniformity of a CT system is performed primarily to assess the negative effects of:
Beam hardening.
117
Which of the following components of the CT system is the most common cause of ring artifacts on the reconstructed CT image?
Ring artifacts are typically cause by faulty detectors. An error in a detecor results in back-projection of an incorrect ring of density on the reconstructed CT image.
118
Ring artifacts are typically cause by faulty detectors. An error in a detecor results in back-projection of an incorrect ring of density on the reconstructed CT image.
diastolic (relaxation) phase
The heart optimally imaged with the least artifact from motion during its period of relaxation, otherwise known as the diastolic phase of the cardiac cycle.
119
Each iliac artery bifurcates into the internal and external iliac arteries at about the level of
L5-S1.
120
The volume of a voxel may be calculated by multiplying the pixel dimension (mm2) by the _____________?
section width
As a geometric cuboid, the volume of a voxel may be calculated as the product of the pixel area dimension (mm2) and the section width (mm). The pixel dimension (d) must be first calculated by dividing the display field of view (DFOV) by the matrix size. The area of the pixel may then be found by squaring the value of d (mm). The unit of measurement for voxel of volume is mm3
121
Which of the following is the primary interaction between x-ray photons and tissue during computed tomography?
Compton effect.
122
The technique that provides the detail of the outer portions of the 3D model while maintaining the typical CT detail of the lungs inside is called
Surface rendering
Computer programs are capable of constructing 3D models of anatomy with several different types of rendering techniques. A surface-rendered 3D model provides excellent surface anatomy while maintaining the normal cross-sectional anatomy apperance of the volume inside the model.
123
During CT perfusion studies, the quanity of blood (in mL) contained within 100g of brain tissue is termed the
Cerebral blood volume (CBV).
124
Which of the following is/are included in the signs & symptoms of hypovolemic shock?
(1) hypertension.
(2) oliguria.
(3) pallor.
2 and 3 only.
125
During a CT examination of the abdomen including intravenous administration of an iodinated contrast agent, which of the following abnormal findings could appear hyperdense in comparison with surrounding material?
Gallstones.
126
Which of the following units is used to quantify absorbed dose?
Grays (Gy).
127
Coronal imaging through the paranasal sinus is typically performed with the plane of imaging.
Perpendicular to the hard palate.
128
Which of the following manipulations involves the use of image data?
Window width and level changes.
129
Cupping artifacts most commonly occur where?
The brain.
130
In patients who are left dominant, the posterior descending artery branches from the:
Left circumflex artery
8% of population is considered left dominant
131
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.
The CT number of a pixel may be calculated by subtracting the linear attenuation coefficient of water from the linear attenuation coefficient of tissue within the voxel. The 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.
132
Which of the following phases of IV contrast agent administration provides the best gastric and intestinal wall enhancement
Portal Venous.
133
An Agaston Score of 250 on an MDCT cardiac examination for Coronary Artery calcification is rated as
Moderate
The Agaston system quantifies coronary artery calcium as minimal (1-10), mild (11- 100), moderate (101-400), and extensive (>400)
134
During a Coronary Artery CTA, single-segment reconstruction of a 400-msec rotation scan results in a temperal resolution of
200 msec
During single-segment, or half-scan reconstruction, data from only half a gantry rotation is used, resulting in a temperal resolution equal to one-half the gantry rotation time
135
The primary indication for a non-contrast cardiac MDCT examination is
Coronary artery calcium quantification.
The primary indication for non-contrast cardiac MDCT is coronary artery calcium (CAC) quantification for the assessment of atherosclerotic disease
136
The branches of the left coronary artery include the:
Left anterior descending artery & left circumflex artery.
137
The approximate inherent filtration of the CT x-ray amounts to an aluminum equivalent of
The tube housing, cooling oil, and so on, consitite the inherent filtration, which amounts to approximately 3.0 mm of aluminum equivalent filtration.
138
Quantitive computed tomography (QCT) is a specialized technique used most often for the diagnosis of
Osteoporosis.
Quantitive computed tomography (QCT) is used to measure the mineral content of bone. Density measurements of the patient's bone are compared with density measurements of reference phantom. The bone mineral density (BMD) values are compared with normal values to assess osteoporosis
139
What indicates a vagal reaction to iodinated IV contrast media?
A combination of brachycardia (heart rate below 50 BPM) and hypotension (systolic pressure below 80 mm hg)
140
What is the Lambert-Beer law used to calculate
attenuation coefficient of a volume of material
141
The soft center of each intervertebral disk is the
nucleus pulposus
142
Which of the following would most likely require intravenous contrast injection for accurate differentiation during a CT of the abdomen?
A. Renal stone.
B. Diverticulitis.
C. Renal Cysts.
D. Angiomyolipoma.
Renal Cysts
All others can be diagnosed without IV contrast.
143
What are the categories of isolation technique?
drainage-secretion precautions, enteric precautions, acid-fast bacillus isolation, respiratory isolation, contact isolation, and strict isolation
144
What are reference detectors used for?
Reference detectors are used to measure the incident radiation intensity. This information is used by the computer during the calculation of the linear attenuation coefficient. If the patient is placed incorrectly in the gantry, the reference detectors may be partially blocked, causing an out of field artifact
145
What are the components of the uterine wall?
outter layer- perimetrium
middle layer- myometrium
inner layer- endometrium
146
What is Automatic tube current modulation?
ATCM is a form of automatic exposure control (AEC) for CT systems. This type of software automatically decreases applied dose on the basis of size, density, and overall attenuation of part being examined
147
In patients who are right dominant, the posterior descending artery branches from the..?
Right coronary artery (RCA) 85% of people are right dominant.
148
Multiplanar reformation images alone the long axis of the optic nerve would best be described in which anatomic plane?
The optic nerves runs at a lateral to medial path from the orbit anterioraly and to the optic chiasm posteriorly.. Oblique sagittal MPR images would display the optic nerve in a profile parallel to its long axis
149
The technique that allows the user to select the range of pixel values used in a 3D CT reformation is called?
Thresholding.
150
What type of hemorrhagic stroke is a bad headache a symptom?
Arteriovenous malformation hemorrhagic stroke - direct flow into the veins causes increased pressure that can cause vessel rupture.
151
what is a "watershed" infarction and what type of stroke is it?
infarction within the Circle of Willis
it is a Hypotensive hemorrhagic stroke
152
What connect the 3rd and 4th ventricle?
Foremen of magendie.
153
The Pulmonary veins are the only veins in the body that carry oxygenated blood.. the bring oxygenated blood from the lungs to the
Left atrium
154
The Pulmonary arteries are the only arteries in the body that carry deoxygenated blood; they carry deoxygenated blood from the right ventricle to the
Lungs.
155
The period peak of hepatic parenchymal enhancement following rapid bolus injection of iodinated contras
Portal venous phase.. happens around 60-70 seconds after initiation of rapid bolus contrast administration
156
What is Azimuth setting?
The angle of the tube and detectors in relationships the patient positioned during scout acquisition. (abnomen pelvis scout image is at 0 degrees for azimuth setting)
157
The period of peak enhancement of the renal cortex following rapid bolus injection of an iodinated contrast agent is termed
corticomedullary phase ---30-40 seconds post initiation of contrast
158
What is the correct difference between ionic and non ionic contrast media?
non ionic contrast media has a lower osmolality than ionic contrast ..also lower incidence of adverse reaction
159
When one is choosing a window to display a CT image, the width define the
range of pixel values that are assigned to a shade of gray
160
The ability of a fluid to flow:
Viscosity - a high viscosity is thick and moves slow.
161
What is the typical range for pixel values in a modern CT system
-1024 to 3072 pixels ...this range equals the 4096 different possibilities of pixel values
162
What is a fomite?
Fomites are objects that have been contaminated by objects an infectious organism of microbe. The spread of the infection may occur when someone comes in contact with the fomite. This is an indirect means of infection transmission
163
Is the interface between dense bone and soft tissue is a common site for the edge gradient effect to occur?
Yes, areas of sharp change in density between dense bone and soft tissue results in the edge gradient effect, being represented by high spatial frequency. The computer has difficulty interpreting this type of abrupt change in information, resulting in streaking.
164
As the section(slice) width is increased the collimation is
decreased and vice versa
165
describe what mA controls and what kV controls
kV controls the voltage potential between the tube cathode and the anode. This controls the energy level of the electron beam which in turn controls the energy level of the resulting x-ray photons. mA or tube current controls the filament current which controls the temperature of the cathode filament from which the electron beam is emitted.
166
What do reference detectors represent?
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
167
Is ghosting a result of partial volume averaging?
Yes, partial volume averaging results in both decreased edge definition and inaccurate CT numbers. Ghosting of tissue boundaries may occur when the patient moves during the scan.
168
What is the only thing that will decrease beam hardening?
Only an increase kVp, which will reduce the number of low energy photons in the beam
169
Laser location device should be performed
annually
170
What happens as slice thickness is decreased
partial volume artifacts and edge gradient artifacts decrease
171
A(n) _____ artifact is a streak artifact which arises from a high spatial frequency interface between tissues with a great difference in density.
Edge gradient.
172
Faulty detector will result in what kind of artifact?
A straight line artifact.
173
An increase in the window width will DECREASE the appearance of noise in a CT image
The appearance of noise in the CT image can be reduced by increasing mAs and increasing the slice thickness. Both of these cause an increase in the number of photons that penetrate the slice. The more photons the less noticeable noise will appear. The perception of noise is also decreased by using a wide window width.
174
A CT scanner with a limiting resolution of 15 lp/cm can resolve an object as small as
The minimum object size that a CT scanner can resolve may be calculated by taking the reciprocal value of the scanner's limiting resolution. The reciprocal of 15 lp/cm is 1/15 lp/cm. This is equivalent to 10/15 lp/cm, which equals 0.6 mm/lp. Because a line pair (lp) is equivalent to a line and space adjacent to it, this value may be divided in half to provide the minimum object that this scanner can resolve: 0.3
175
By CT criteria, a solitary pulmonary nodule may be defined as a focal area of increased density in the lung that is smaller than
Solitary pulmonary nodules are typically ovid focal areas of increased density that are less than 3 cm in diameter. Any lesion larger than 3 cm is reffered to as a focal mass, with an increase propensity for malignancy.
176
Evaluation of the venous vascular structures of the brain is known as
CT Venography (CTV) of the brain is a cariation of the CTA technique whereby the timing of data acquisition is optimized for the period of peak venous opacification
177
What is sampling frequency?
The sampling frequency, or views per rotaion (VPM), controls the volume of transmission data acquired for each gantry rotation. Very small objects exhibit high spatial frequencies that only systems with high sampling rates will be capable of resolving.
178
After initiation of rapid bolus administration of an iodinated contrast agent, the excretory phase of renal contrast enhancement occurs at approximately
3-5 minutes..
The excretory phase is a delayed-imaging phase that begins approximately 3 minutes after the initiation of contrast agent administration. During this phase, contrast material has been excreted into the real calyces, opacifying the renal pelvis and the remainder of the urinary collecting system (ureters, bladder). The excretory phase best demonstrates the filling defects and potential lesions involving the urothelium, such as those from transitional cell carcinoma (TCC)
179
The Propensity of a contrast agent to cause fluid to move from the extravascular space to the intravascular space is called
Osmolality.
An important characteristic of iodinated radiopaque contrast media, osmolality describes the propensity of the agent to cause fluid from outside the blood vessel (extravascular space) to move into the bloodstream (intravascular space)
180
For Ct exams of the pelvis.. which types of contrast should be used?
IV contrast - low dense barium sulfate.
During CT examination of the pelvis, both intravenous and oral contrast agents are commonly administered. An intravenous contrast agent is important in differentiating pelvis blood vessels for lymph nodes. An oral contrast agent serves to opacify the small and large colon and greatly improves their visualization. Oil-based contrast media are not commonly used for CT procedures.
181
The water-soluble oral contrast agents used for CT scans of the abdomen and pelvis should contain approximately__________ iodine
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 flavoring agent to the solution or used a flavored contrast for ease of consumption. Common water-soluble contrast media include gastrografin and hypaque.
182
The vertebral level at which the adult spinal cord ends is:
The adult spinal cord ends between L1 and L2.
183
An enema containing positive contrast material administered into the large bowel is needed prior to the CT examination of the pelvis. Of the following, which is a sufficient dose to opacify the rectosigmoid area of the colon?
To opacify the rectosigmoid region, a dose of 150-250 mL is sufficient. To opacify the complete large bowel a dose of 300 - 500 mL is needed.
184
Prothrombin time measures what and normal limits?
Prothrombin measures the amount of time necessary for a person's blood to coagulate.
10 to 14 seconds are within normal range.
185
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.
The skin dose of 6 rads - 4 rads = 2 rads( 1 Gy = 100 rads)
186
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.
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)
187
What is the average range for activated partial thromboplastin time?
The partial thromboplastin time is a measure of blood-clotting ability. The range is given in an average due to the variations in individual laboratory practices. The acceptable range is between 28-34 seconds.
188
The job of the array processor is
reconstruction of the projected attenuation raw data into CT images
189
To provide the largest image for the viewer on a 14 X 17 inch film, which of the following CT film formats should be used?
The arrangement of CT images on a sheet of x-ray film will determine the size of the image for viewing. A 4:1 format stores four large images on one single 14 X 17 sheet. The more images on one sheet the smaller the image for viewing.
190
The major disadvantage of the early back-projection method of image reconstruction is the appearance of the
The star artifact resulted from the back-projection method of image reconstruction used in older CT scanners. The artifact is removed by the use of a convolution filter found in the filtered back-projection method used today.
191
When describing tube interscan delay time, which of the following are true?
1. The time required for the tube to rotate 360 degrees around the patient.
2. The time between the end of one scan and the start of the next scan, allowing the tube to cool.
3. The time necessary for the production of photons to begin after applying the voltage to the tube.
1 only.
192
True or False: Star-like artifacts on structrues at the edges of the CT images may be the result of a cone beam artifact
True
193
Where is the begining and endpoint of a CT routine chest?
Lung Cancer ussually metastisizes to the adrenal glands. Soft tissue windows should be through the adrenal glands and lung windows can be only from above apices to the bottom of the lungs.
194
The cause of the cupping artifact is?
The low energy photons are attenuated when they pass through the body resulting in the central tissues appearing darker in signal intensity than the peripheral tissues. This phenomenon is sometimes called cupping due to beam hardening on the image resulting in the contour of a cup appearance.
195
Lung window?
1400-1600 WW
-400-(-)600
196
Water soluble based oral contrast (gastroview) should not be used when?
esophogeal perforation is suspected- This type of contrast should be used with this diagnosis barium should not be used
197
As slice thickness is decreased what else decreases?
A decrease in both partial volume artifacts and edge gradient artifacts.
198
True/False: The edge gradiant effect is reduced by using a CT scanner with a small detector aperture and thin slices
True - Smaller apertures and thinner slices improve the severity of edge gradiant effect. Greater data sampling rates would improve the edge gradiant effect also.
199
Which of the following diabetic medications should be discontinued for 48 hrs after the injection of IV contrast?
Metformin is the generic of glucophage and damage could be done to kidneys after the injection of IV iodinated contrast. There are many combinations of drugs that have this medicine in them, they include avandamet (avandia-metformin) metaglip (metformin-glipizide)
200
What will most likely remove a ring artifact?
The ring artifact is one of the more common equipment artifacts found in CT. This is a result of a faulty or miscalibrated detector element.
