Quizlet ARRT PREP 1 Flashcards
How do you reduce beam hardening?
- Increase dose.
- Reduce collimation - reduce slice thickness.
- Increase window width.
At what level does the abdominal aorta bifurcate?
L4.
What is the typical scan delay after injection of contrast media for studies of the liver?
30-45 seconds.
What window setting provides the best tissue differentiation within the liver?
WW = 140
WL = 60
What window settings that provide the best bone window for the pelvis?
WW = 2000
WL = 350
What mAs is typically used in routine CT exams of the abdomen?
200-300 mAs.
What is the result of the bifurcation of the abdominal aorta?
The right & left iliac arteries.
What is the anode target angle?
12 degrees.
At what level do the common carotids bifurcate into the internal & external carotid arteries?
C3-C4.
The floor of the orbit is formed by the _____ bones.
Maxillary & zygomatic.
The lateral walls of the orbit is formed by the _____ bones.
Zygomatic & sphenoid.
The medial wall of the orbit is formed by the _____ bones.
Ethmoid & lacrimal bones.
How do you calculate effective mAs?
MAs/pitch.
Define window level
Level: a chosen midpoint in the grayscale.
Define window width
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.
The wider the window the _____ grayscale values; the _____ the contrast.
More; Lower.
Factors that affect spatial resolution
- focal spot.
- Detector width (aperture).
- Reconstruction algorithm - bone>soft tissue.
- Slice thickness.
- Pixel/FOV/Matrix.
- Pitch - decrease pitch means no gaps.
- Nyquist limitations.
Factors that affect contrast resolution
- 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).
Give window levels for brain, lung, abdomen, bone.
Brain: W80, L40.
Lung: W1500, L-400.
Abdomen: W400, L50
Bone: W1600, L500
What is beam hardening?
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.
What are two types of beam hardening artifacts?
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.
How do you compensate for beam hardening artifacts?
- Filtration
- Calibration.
- Correct software.
- Avoidance (tilting gantry or positioning pt).
Ring Artifacts
Calibration error or detective detector cause consistently erroneous reading at each angular position, resulting in a circular artifact.
Is the focal spot large or small?
Large 0.6-1.2 — so as not to overheat the anode from such a high mA.
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.
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.
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.
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.
Voxel equation
Pixel area x section thickness.
What is interpolation?
Mathematical method for taking SPIRAL data & viewing it as AXIAL images.
Bone Windows
2000-4000 WW
200-400 WL.
Lung windows
1400-1600 WW
(-) 400-600 WL.
Modular Transfer Function
Graphical representation of SPATIAL RESOLUTION measured in lap/cm, tells you how small you can scan without blurring.
Decrease partial volume averaging?
Reduce slice thickness.
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.
Lung Window
2000 WW and - 200 WL.
(-) is air.
The Hounsfield unit that is -1000 most likely represents which of the following?
Air.
Relative to CT topography, slice thickness is best represented by which of the following axis?
Z axis.
What unit is the basis for exposure based on ionization in air?
mR or C/kg.
What radiation unit considers the biological effectiveness of radiation exposure?
mrem or mSv.
“Fan” beam technology first historically came on the scene with which acquisition geometries?
Second.
“Rotate-rotate_ applies to which of the following geometries?
Third.
In CT what imaging plane is the pituitary best visualized?
Coronal.
The third ventricle of the brain communicates with the fourth ventricle through the:
Cerebral aqueduct.
_____ refers to an excessive amount of nitrogenous material in the blood & is a symptom of renal failure.
Azotemia.
Which paranasal sinus is usually the last to fully develop?
Frontal.
What is the average annual radiation dose?
2 rem.
10 rem converted to Sieverts is what?
0.1 Sv.
Convert 10 mSv to Sv.
0.01 sV.
Annual limit for adult occupational effective dose?
0.05 Sv.
Annual limit of occupational lens dose
0.15 Sv.
Annual limit of shallow dose equivalent to skin/extremities
0.5 Sv.
Occupational exposure to embryo/fetus during pregnancy
0.5 mSv.
Total effective dose equivalent to public - also average background radiation
1 mSv.
Mild reactions to iodinated IV contrast media include
Nausea, vomiting, mild urticaria, and a warmed flushed sensation.
Moderate reactions to IV contrast?
Dyspnea, hives (urticaria), wheezing, change in pulse, facial edema, vasovagal response, hypo-hyper tension.
Severe reactions to IV contrast
Severe broncospam, anaphylaxis, drowsiness, headache, fever/chills, shock, pulmonary edema.
Osmalarity
Concentration of a solution in terms of number of dissolved particles per unit of water.
Non-ionic IV contrast media such as Omnipaque should have an average osmolarity of:
750 mOsm/kg water.
What drugs are administered for moderate reaction to injection of iodinated contrast medium?
Antihistamines and Epinephrine.
Prothrombin
Measures the amount of time necessary for a persons blood to coagulate. 10 and 14 seconds.
Why use an autoclave?
The use of an autoclave for sterilization involves heat & steam under pressure to eliminate microbes.
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.
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.
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
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.
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
Non-ionic contrast media include :
Iopamidol (isovue) Iohexol (omnipaque) and iopromide (ultravist).
Normal pulse rate for an adult?
60-100 bpm.
Normal average adult respirations per minute?
12-20.
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.
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
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.
Average pulse rate for an infant:
100-180 bpm.
General signs of shock include:
- Rapid breathing
- Tachycardia
- Hypotension
- Weak pulse
- Pallor
- Cyanosis
- Cold, clammy skin.
What is the average range for activated partial thromboplastin time?
28-34 seconds.
The average radiation dose to the pituitary gland during a CT head is:
2 rads.
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.
What is medical asepsis?
The reduction in number of infectious agents but not the complete elimination of all organisms.
Complete cardiac diastole correspond to which portion of the cardiac cycle on a ECG?
T-wave.