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94 Cards in this Set
- Front
- Back
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What is the uncoupling effect?
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The image quality in CT is not directly linked to the dose, so even when an mA or kVp setting is too high, a good image results.
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What is spatial resolution?
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the ability to resolve (as separate objects) small, high contrast objects
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What is contrast resolution?
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The ability to differentiate between objects with very similar densities as their background.
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What type of phantom measures spatial resolution?
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Line pairs phantom
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What is MTF (modulation transfer function) used to measure?
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Spatial resolution
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On an MTF graph, if the curve extends to the right, what would this indicate?
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MTF is y axis, spatial frequency is x axis. This indicates a greater spatial resolution.
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What is the relationship (equation) between pixel size, DFOV, and matrix size?
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pixel size = DFOV/matrix size
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What is the sampling theorem?
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Also called the Nyquist Sampling Theorem. Because an object may not lie entirely within a pixel, the pixel dimension should be half the size of the object.
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How does pitch relate to spatial resolution?
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Increasing pitch reduces resolution
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In film screen imaging an object must have at least a __% difference in contrast from its background to be visible. In CT it is __%.
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5%, .5%
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How does slice thickness impact spatial and contrast resolution?
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May increase contrast resolution by reducing noise but decrease spatial resolution on the z axis.
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How does the signal to noise ratio impact contrast resolution?
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High SNR means more noise so reduces contrast resolution.
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What is temporal resolution?
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Refers to how rapidly data is acquired.
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What are scanning parameters?
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The factors the tech can control: mA, time, thickness, FOV, reconstruction algorithm, and kVp.
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What does a beam hardening artifact look like?
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Streaking or cupping artifact (the periphery of the image is lighter)
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What causes partial volume artifact? What is the best method to prevent this?
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When more than one tissue density is contained in one voxel. This can occur when a dense object lies to the edge of the FOV. Thinner slices reduce the partial volume artifact.
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What type of artifact is created by undersampling? What does it look like? How can this be reduced?
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Aliasing artifacts. They appear as evenly spaced lines radiating from a dense structure. Reduce by reducing pitch or slowing gantry rotation speed (increasing scan time).
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What causes the edge gradient effect and what can be done to prevent it?
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The streak artifact or shading arises from irregularly shaped objects that have a big difference in density. Ex: barium and air in the stomach. Using a lower HU contrast in place of barium and smaller slices can reduce the artifact.
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What causes ring artifact?
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Faulty detectors
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What causes a tube arc?
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Residual oil or gas molecules in the tube or just tube aging.
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What does a cone beam effect look like? What can be done to resolve it?
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Windmill appearance. Using a low pitch.
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How is a water phantom used to measure noise?
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Noise is measured by obtaining the standard deviation of the CT numbers within one ROI. The SD should not exceed 10.
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What tools do physicists use to measure radiation dose while performing safety inspections?
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Head and body CTDI phantoms and a pencil ionization chamber
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What are the three classifications of artifacts?
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Physics based (associated with the physical process associated with data acquisition), patient based, and equipment induced.
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What factors impact beam hardening?
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Filters, calibration, and correction software. May also be reduced by increasing kVp.
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What is the purpose of MinIP?
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Selects voxels of lowest HU value (ex. imaging of the bronchial tree)
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What is a banding artifact?
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Motion artifacts in cardiac CT related to heart rate irregularities.
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What causes a stair-step artifact?
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When the slice thickness exceeds the pixel dimensions.
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What are the three types of segmentation (data selected to be saved or removed)?
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Manual, fully automated, and semiautomatic
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How many bits are in a byte?
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Eight
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What is the normal BUN range?
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7-25 mg/dL
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What is the normal range for serum creatinine?
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.6 - 1.7 mg/dL
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In which CT exams would a patient's PT and PTT be relevant?
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Biopsies or drainages as they provide information about the blood coagulation ability.
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What is the typical range for PT?
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11 - 14 seconds
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What is the typical PTT range?
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25 - 35 seconds
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What is a typical platelet count?
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150,000 - 400,000 cubic millimeters
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What is the normal range and the average oral temperature?
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36 - 38 C
96.8 - 100.4 F Average: 37 C or 98.7 F |
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What is the normal range and average rectal temperature?
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36.7 - 38.7 C
97.2 - 100.8 F Average: 37.7 C or 99.1 F |
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What is the normal range and the average axillary temperature?
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35.4 - 37.4 C
95.8 - 99.4 F Average: 36.4 C or 97.7 F |
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What is the average adult pulse rate?
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60 to 100 bpm unless the patient is athletic, then it may be as low as 45 bpm
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What is the average child's pulse rate? Infant?
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95 - 110 bpm, infants 100 - 160 bpm
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What is the average respiratory rate in adults, adolescents, children, and infants?
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Adults: 14-20 per min
Adolescents: 18 - 22 Children: 22 - 28 Infants: 30 or more |
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_______ is defined as the force exerted by circulating blood on the walls of the vessels.
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Blood pressure
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_______ is the peak pressure in the arteries, which occurs near the beginning of the cardiac cycle.
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Systole
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______ is the lowest pressure (at the resting phase of the cardiac cycle).
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Diastole
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In adults, what is the normal range for systolic pressure?
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90 to 140 mm Hg
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What is the normal range for diastolic pressure in adults?
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60 - 90 mm Hg
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What is the normal systolic range in children? Diastolic?
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65 - 130 mm Hg systolic
45 - 85 mm Hg diastolic |
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Two tissues must differ by at least __ HU to be visibly different on a CT.
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10
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Proper administration of contrast provides a __ to ___ HU increase in the difference of attenuation between tissues.
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45 to 70 HU
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High osmolar contrast agents may have up to __ times the number of particles in solution per unit of liquid as blood. Low osmolar __ times.
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7 times, 2 times
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What is the osmolality of blood plasma?
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290 mOsm/kg water
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What is the osmolality of LOCM?
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600 - 850 mOsm/kg
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What is an isosmolar contrast agent?
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Visipaque
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_______ is a physical property that may be described as the thickness or friction fluid as it flows.
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Viscosity
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How does the concentration of iodine impact its viscosity?
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Greater concentration of iodine = more viscous
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Can LOCM be ionic?
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Yes!
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What is the half life of iodinated contrast media?
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Two hours
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How does reduced muscle mass impact SCr?
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Can cause a decrease in SCr
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How can the ingestion of cooked meat impact SCr?
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Can cause an increase in SCr
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How can malnutrition impact SCr?
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Can cause a decrease in SCr
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How can ketoacidosis (high amount of keytones in the blood, commonly as a result of hyperglycemia) impact SCr?
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Can cause an increase in SCr
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What is the biggest concern with injecting a patient with contrast who has multiple myeloma?
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Dehydration and thus renal function
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What is the biggest concern with patients taking metformin who also receive contrast?
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The possibility of lactic acidosis occuring
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What are concerns of giving contrast to a patient with a thyroid condition?
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Those with hyperthyroidism or Graves' disease can end up with thyroid toxicosis and in severe cases a thyroid storm may occur.
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What is a chemotoxic reaction?
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Results from the physiochemical properties of the contrast, the dose, and speed of injection. All hemodynamic (relating to blood circulation) disturbances and injuries to organs or vessels are included. CIN and pain at injection site are examples.
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What is an idiosyncratic reaction?
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Largely unpredictable, usually occuring within one hour of injection. Mild, moderate, or severe. Hives, nausea, difficulty breathing are examples.
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What does AVID stand for and how is it measured?
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Arteriovenous iodine difference. It is the difference in HU between the aorta and IVC.
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What is the bolus phase? What must the AVID be?
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Immediately following injection. Characterized by a difference of 30 or more HU AVID.
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What is the nonequilibrium phase? What is the AVID?
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The second phase. Follows the bolus phase. It is characterized by 10-30 HU AVID. It is also referred to as the venous phase and starts about 1 minute after injection begins and lasts only about 1 minute.
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What is the equilibrium phase?
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The last phase. It can begin as early as 2 minutes after the bolus phase. it is characterized by an AVID of less than 10 HU.
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How long should the delay be for scanning a brain with contrast?
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At least 4 minutes
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Put these in order for route of IV contrast following injection:
a. Renal arteries to kidneys b. Right atrium into right ventricle c. Hepatic veins to inferior vena cava d. Antecubital vein e. Splenic vein f. Femoral veins from lower extremities g. Jugular veins from head h. Subclavian vein to superior vena cava i. Femoral arteries to lower extremities j. Inferior mesenteric vein k. Carotid arteries to head l. Pulmonary arteries into pulmonary veins m. Renal veins from kidneys n. Superior mesenteric vein o. Left atrium into left ventricle and out aorta |
d, h, b, l, o, k, a, i, g, m, e, n, j, c, f
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What is the unit of xray exposure in air?
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Roentgen (R)
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The ionizing radiation used in CT is an xray with max energy from ___ to ___ and an average energy near ___.
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120-140 keV with average near 70 keV
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What is the SI unit of absorbed dose?
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the gray (Gy)
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How do rads translate to grays?
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100 rads = 1 Gy
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Recognizing the effects of xrays, another conversion factor is applied to the absorbed dose. It accounts for the different biologic effects produced from different types of ionizing radiation. What is it called?
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Quality factor
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When the quality factor has been applied to the radiation absorbed dose the new quanity is called the:
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dose equivalent
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What is the unit for dose equivalent?
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rem (Roentgen equivalent man)
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What is the SI equivalent unit of the rem?
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The sievert (Sv)
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What is the relationship between the rem and sievert?
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100 rem = 1 Sv
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There is a newer quanitity similar to the dose equivalent. It is the product of the absorbed dose and a radiation weighting factor. What is it?
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equivalent dose (H)
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The unit for the equivalent dose (H) is:
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the rem or the sievert (Sv)
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This measurement attempts to account for the effects particular to the patient's tissue that has absorbed the radiation. What is the unit?
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Effective dose or effective dose equivalent. Rem or sievert (Sv)
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This is the unit that represents quality factor being applied to rad.
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Roentgen equivalent man (rem)
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This is the term used for the dose calculated from multiple scans.
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MSAD - multiple scan average dose
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This is the dose reported to the FDA in which case the slices must be contiguous.
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CTDI - computed tomography dose index
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True or false. When there is no gap between slices, CTDI = MSAD.
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True
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This is the preferred expression of radiation dose in CT dosimetry.
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CTDI vol
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U.S. residents are exposed to average annual background radiation levels of about ____: exposure from a chest xray is about ____, and exposure from a whole body CT is about ____.
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3 mSv, .1 mSv, 10 mSv
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How is pitch calculated?
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Single slice: pitch = distance traveled in a 360 rotation/collimated width of the beam
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If the table moves 30 mm per rotation for 10 mm slices and the CT system collimates the beam for four 10 mm slices, what is the pitch?
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30 mm/(4 x 10 mm) = .75
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The dose of one abdomen CT is equivalent to how many chest xrays?
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100 - 250
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