NMTCB(RS) flashcards
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- Tc-99m physical half-life
- Tc-99m decays with a 6.02-hour physical half-life and emits a 140.5 keV gamma photon, which is well suited to gamma camera imaging.
- Mo-99 breakthrough limit
- Generator eluate must contain no more than 0.15 kBq of Mo-99 per MBq of Tc-99m (0.15 µCi/mCi); exceeding this limit prevents patient administration.
- Effective half-life formula
- Effective half-life combines physical and biological decay: 1/Teff = 1/Tphysical + 1/Tbiological. It determines how long activity remains in the patient.
- Tc-99m MAA particle size
- Tc-99m macroaggregated albumin particles range from 10 to 90 micrometers and lodge in pulmonary capillaries; typical doses contain 200,000 to 500,000 particles.
- High-probability PE pattern
- A high-probability ventilation/perfusion scan shows two or more large segmental perfusion defects with normal ventilation (mismatched defects), suggesting pulmonary embolism.
- Meckel scan radiopharmaceutical
- Tc-99m pertechnetate is used for Meckel diverticulum imaging because it is taken up by ectopic gastric mucosa; pentagastrin or H2 blockers can improve sensitivity.
- Acute cholecystitis HIDA finding
- On a hepatobiliary (HIDA) scan, nonvisualization of the gallbladder with normal hepatic uptake and biliary transit by 60 minutes is positive for acute cholecystitis.
- GI bleed radiopharmaceuticals
- Tc-99m sulfur colloid clears rapidly via the liver and detects about 0.1 mL/min bleeding; Tc-99m labeled RBCs allow longer imaging for intermittent bleeding.
- Normal 24-hour thyroid uptake
- Normal 24-hour thyroid uptake of I-123 is approximately 10 to 30 percent. Graves disease shows elevated uptake, while subacute thyroiditis shows low uptake.
- Occupational dose limit
- The occupational effective dose limit for radiation workers is 50 mSv (5 rem) per year; the public limit is 1 mSv per year.
- Bone scan timing and dose
- Adult Tc-99m MDP bone scans use about 740 to 925 MBq (20 to 25 mCi) intravenously, with imaging delayed 2 to 4 hours after injection.
- Sentinel node injection site
- For breast lymphoscintigraphy, Tc-99m sulfur colloid is injected peritumorally or periareolarly; imaging and a gamma probe identify the first draining node.
- Radioactive decay equation
- Activity remaining after time t is A = A0 × e^(−0.693t/T½), where T½ is the physical half-life of the radionuclide.
- Collimator selection rule
- Use a low-energy collimator for photons below about 150 keV, medium-energy for 150 to 300 keV, and high-energy above 300 keV to limit septal penetration.
- Photopeak energy window
- A typical gamma camera energy window is ±10 percent around the photopeak; for Tc-99m at 140.5 keV this is roughly 126 to 154 keV.
- Hounsfield unit formula
- CT number in Hounsfield units equals 1000 × (µtissue − µwater)/µwater, so water is 0, air about −1000, and dense bone about +1000.
- Window width versus level
- Window width controls displayed contrast; a narrow width increases contrast. Window level sets the center gray value of the displayed range.
- Pitch definition
- Pitch equals table travel per gantry rotation divided by total collimated beam width. Pitch above 1 reduces dose and scan time.
- CTDIvol meaning
- CTDIvol estimates radiation dose per unit volume in milligray for a given scan protocol and is displayed on the scanner dose report.
- Dose-length product formula
- DLP equals CTDIvol multiplied by scan length in centimeters, expressed in mGy·cm; multiplying DLP by a body region factor estimates effective dose.
- Bone window settings
- Bone windows use a wide width near 2000 HU and a high level near 400 to 500 HU to display high-attenuation osseous structures without clipping.
- Tube current modulation
- Automatic exposure control varies tube current with patient attenuation along the scan, lowering dose while maintaining a target image noise level.
- Iterative reconstruction effect
- Iterative reconstruction reduces image noise compared with filtered back projection, permitting lower dose, but can change image texture and low-contrast detectability.
- Beam hardening artifact
- Beam hardening produces dark streaks or cupping because lower-energy photons are preferentially absorbed; higher kVp and metal artifact reduction help reduce it.
- Photon starvation artifact
- Photon starvation occurs when very few photons reach detectors through high-attenuation regions such as shoulders, producing prominent streak artifacts across the image.
- Multidetector row advantage
- Multiple detector rows allow thinner acquisition slices and faster table speed, improving z-axis resolution and enabling high-quality multiplanar reconstructions.
- Bolus tracking purpose
- Bolus tracking monitors contrast arrival in a target vessel and triggers the scan at a preset threshold, optimizing arterial or venous phase timing.
- Iodinated contrast risk factors
- Reduced renal function (low eGFR), prior contrast reaction, and dehydration increase risk with iodinated contrast; renal function should be checked before elective contrast CT.
- CT effective dose estimate
- Effective dose in CT is estimated by multiplying DLP by a region-specific conversion factor, typically about 0.015 mSv/mGy·cm for the body.
- Reconstruction slice thickness
- Reconstructed slice thickness can be thinner than the acquired detector width; overlapping thin reconstructions improve multiplanar and three-dimensional image quality.
- CT number of water
- Water is assigned 0 HU by definition, providing the reference point for the Hounsfield scale used to characterize tissue attenuation.