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CT Rad/Safety
CT Radiation & Safety
| Question | Answer |
|---|---|
| Photoelectric Interaction | Ionization. The photon strikes a K-shell electron & is completely absorbed --> electron getting ejected. Produces radiographic contrast as a result of the differential absorption of the incoming x-ray photons in the body's tissues. Charac.Radiation |
| Compton Interaction/Scatter | Ionization. Partial transfer of energy from photon--> outer shell electron, removing it from orbit. Produces recoil e- & incident xray photon scatters. Most common inter. in body. & primary occ dose. |
| Neurogenic Shock | Failure of arterial resistance -->causes blood to pool in peripheral vessels due to an injury in the nervous system (head/spinal trauma). |
| Hypovolemic Shock | Follows loss of large amount of blood/plasma. |
| Septic Shock | Occurs when toxins produced during massive infection that increases capillary permeability -->cause a dramatic decrease in blood pressure |
| Cardiogenic Shock | Results from cardiac failure or other interference w/heart function. |
| Gray (Gy) | A unit of absorbed dose in tissue. # radiation present in the beam that is absorbed by the pt. |
| Sievert (Sv) | A unit of effective/equivalent dose. Includes ionizing effects of xray/gamma/beta rays & particle radiation. Uses conversion factors that compare the type of radiation to biological effects. |
| Attenuation | Absorption and scatter (loss of intensity) of the xray beam as it passes thru the pt. The IR receives a greater # of high-energy photons b/c the lower energy ones are absorbed by the pt. |
| Bremsstrahlung Production | When an incident e- changes direction, attracted to the +nucleus, it slows down. The result is a reductions of energy, producing a Bremm photon. Most x-rays are produced this way (90%). Responsible for heterogeneous nature of the xray beam. |
| Photoelectric Absorption/Characteristic Production | An incident e- knocks an inner e- out of orbit (becomes a photo e-). When space filled in by an outer e-, the diff. in changing energy levels = charac photon. Cascade effect. Mostly absorbed and generally only high atomic #s. |
| Stochastic Effects | (i.e. probabilistic) Randomly occurring effects of radiation; the probability of such effects is proportional to the dose (increased dose = increased probability, not severity, of effects). |
| Deterministic Effects | Effects of radiation that become more severe at high levels of radiation exposure and do not occur below a certain threshold (cartaracts). Linear-nonthreshold dose curve response. |
| Overbeaming | Extension of the primary beam in a MSCT system that ensure all detectors in the array exposed to x-rays of equal intensity. Helps overcome the penumbra that occurs at the edge of detectors. |
| Overranging | The process of applying radiation dose Before & After the acquisition volume, to ensure sufficient data collection for the interpolation algorithms of the helical CT reconstruction |
| Lossless Compression | Data compressed WITHOUT any loss of data. Can be reversible. |
| Lossy Compression | Data is compressed WITH loss of data, but takes up less room and works faster. |
| Quality Control (QC) | Tests performance of a CT scanner to ensure that its performing well & meeting standards. Ensures images produced by scanner are optimal quality, while utilizing acceptable doses. Implementation of corrective actions to improve issues of CT system. |
| Quality Assurance (QA) | The measurement of a scanner's performance thru quality testing procedures & eval of the test results |
| Photon Flux | The rate that photons that pass through an area, in a set of time. Increases = decreases noise. Directly proportional to pt. dose. |
| Effective Dose | An equivalent whole-body dose from partial body exposure. Will take into account the type of radiation & the radiosensitivity of different tissues. Measured in (Sv or mSv) |
| CTDIw | ONLY AXIAL NOT HELICAL. Weighs the exposure & creates a more accurate dose approximation b/c of density variation (periphery & center). |
| CTDIvol | HELICAL. measures the radiation dose in the X, Y, Z axis. DOESN'T take Scan Range or Pt. Size into consideration. Estimation w/in a certain slice. |
| CTDI | Measure of a dose received in a SINGLE SLICE. Determined with H2O phantoms. Can only be calculated if acquisition is contiguous & DOESN'T contain gaps/overlapping slices. |
| Absorbed Dose | Amount of energy absorbed per unit of mass material (Gy or mGy) |
| Exposure | Measurement of radiation in air. Roentgens (R) |
| Dose Report | Will include kV, mAS, SFOV, pitch, detector collimation, scan length. Measured by CTDI & DLP |
| CTDI 100 | Done with 100mm long pencil radiation chamber |
| DLP | Total exposure for an exam - including scan length. DOESN'T take Pt. Size into consideration. |
| Factors Increasing Dose | Increase spatial resolution, smaller slice thickness, smaller pixel size, Noise is lessened as a result of increasing dose. |
| Calculating Pitch | Distance table travels per rotation ÷ (Slice thickness X number of slices per rotation) Example: 4-slice MDCT, uses a 1.25 mm slice thickness & a table feed of 6mm. = 1.2 Pitch. So 6÷ (4 X 1.25) =1.2 |
| Calculating Pixel Size | DFOV in mm ÷ Matrix. Example: DFOV is 35 cm and a 512 matrix is used = 0.68mm. Convert 35cm = 350mm then 350 ÷ 512 = 0.68mm |
| Calculating mAs | mA X sec. Example: 160 mA and 2 second exposure = 320 mAs. So 160 X 2 = 320 mAs. If you increase mA, seconds become shorter |
| Calculating Max collimation with a certain type CT system | Detectors' collimation in mm = (Max beam width or collimation in mm) ÷ number of detector rows. So in a 64-slice MDCT with a maximum of 40 mm collimation = .625mm maximum collimation allowed. Or 64 X .625mm = 40 max collimation |
| ADC | Converts the data into digital values, which determine the grayscale resolution |
Created by:
Crimsondrop7
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