Robert Pagnanelli BSRT(R)(N), CNMT, NCT, FASNC Chief Technologist, Nuclear Imaging Duke University Medical Center Thursday September 8, 2011
Quality Control Quality control should be performed because: Detector damage High Voltage drift Electronic component degradation Quality control is necessary to assure accurate results
Equipment Requiring QC Gamma Camera Survey Meter Dose Calibrator Other lab equipment
Quality Control Procedures- Planar camera Energy Peaking daily Uniformity test daily Linearity and resolution weekly Sensitivity test weekly
Energy Peaking Verifying that the pulse height analyzer s energy window over the photopeak energy Best performed 5 UFOVs from the uncollimated camera with a point source Can use a sheet source with collimated camera Most commonly performed with a collimator Often automated must check!
Uniformity Test Best performed 5 UFOVs from the uncollimated camera Most commonly performed with a Co-57 sheet source on a collimated camera Also checks the collimator MUCH faster Suggestion Perform extrinsically daily Perform intrinsically weekly
Uniformity Test Extrinsic (with collimator) Co-57 radioactive sheet source is placed on top of each detector with the collimator still in place. An image is then taken on each detector for 3-5 million counts. 256x256 matrix A visual assessment (qualitative) of the image is to be made as well as a quantitative assessment.
Co-57 Sheet Source Dimensions 17 x 11 cm - 25 x 18 cm 5 20 mci $3000.
Uniformity Test Integral uniformity Global parameter measuring uniformity over an extended area 100% x (max-min)/(max+min) Differential uniformity Regional parameter that measures uniformity over a small area Performed using all 5x1-pixel area in both the X and Y direction 100% x Largest deviation (max-min)/(max+min)
Performance parameters for detectors- ASNC guidelines PARAMETER STANDARD PREFERRED Integral Uniformity Differential Uniformity <5 <3 <5 <3
Uniformity Test
Uniformity Test Non-Uniformity caused by Malfunctioning PMT Off-peak/Wrong peak Cracked crystal
Uniformity Test ABOVE PEAK BELOW PEAK
Resolution and Linearity Performed to Document spatial resolution and its change over time Evaluate ability to image straight lines Image a flood source through a spatial resolution test phantom (using uniformity flood paramaters) If a 4-quadrant phantom is used, it should be rotated 90 degrees so that every 5 th time the pattern repeats. Evaluation How straight are the lines What are the smallest bars discerned
Resolution and Linearity
Sensitivity Test Documents the system sensitivity as well as the change of sensitivity over time. Cts/pixel/millicurie To measure change in sensitivity: record the time taken to acquire a preset number of counts using a set dose.
INSTRUMENTATION ARTIFACTS NON-UNIFORMITY Ring Artifact Uniform Flood Non-Uniform Flood FBP
Quality Control Procedures- SPECT camera COR weekly or monthly Uniformity correction manufacturer recommendation Plexiglas phantom quarterly or annually
COR Checks for alignment error between the electronic matrix of the detector and the mechanical COR. Always check after camera servicing and software upgrades. Doughnut artifact (360º) or tuning fork artifact (180º) in the transverse images
COR COR is a measure of the alignment of opposite views of camera head position Misalignment (Offset camera and center of acquisition matrix) results in donut or tuning fork artifact
COR A 1 mci point source of Tc99m is placed on camera table SPECT data is acquired over a 360 (or 180) degree orbit 60 projections per head 5-10 sec/frame
COR
Plexiglass SPECT Phantoms
Plexiglass SPECT Phantoms To determine 3D contrast, resolution, uniformity 1. Collimator - LEHR (or LEUHR if used routinely with Tc-99m, whichever is higher resolution) 2. Tc-99m Activity - Between 10-20 mci 3. Count Rate needs to be below 50 kcps 4. Matrix size = 128x128 5. Rotation = 360 degrees 6. Total Views = 120. (Implies 60 steps for dual head, 3-degrees per step) 7. Dual Headed Camera study acquired with camera head in opposed position (180) 8. Acquire for approximately 32 million total counts 9. Radius of Rotation = as close to 20 cm as possible. 10. Orbit = Circular
Plexiglass SPECT Phantoms
High Count Extrinsic Flood-Field Uniformity Correction In SPECT it is assumed that efficiency of photon detection is uniform across the collimated detector Camera systems store flood-field correction maps to correct variations before reconstruction 30 to 100 million ct images for each collimator 256x256 matrix
Image Artifact
Survey Meter Used daily to detect radioactive contamination in laboratory Aka Geiger counter, Geiger-Mueller counter, GM counter
GM Counter Battery Check Daily Ensures that the meter has adequate electrical power. The meter located in the readout scale will be located within the battery region if the power is adequate.
GM Counter Source check Daily Ensure that the meter responds to a radiation source.
GM Counter Calibration Annually Ensures that the meter responds accurately to radiation.
Dose Calibrator Used to measure the activity of the radiopharmaceutical
Dose Calibrator Standard testing Background Voltage Accuracy Constancy Linearity Geometry
Dose Calibrator Background Performed daily Background activity is checked at each setting that will be utilized Contamination Unshielded source in lab
Dose Calibrator Voltage Performed daily Ensures that the operating voltage is within manufacturers recommended range
Dose Calibrator Accuracy Performed Annually Two sealed radiation sources greater than 50 µci and one with an energy between 100 to 500 kev are assayed Isotopes used: Co-57 (122 kev, 271 days) Cs-137 (662 kev, 30 years) Ns-22 Co-60, Ge-68, or Ba-133.
Dose Calibrator The sources must be traceable to The National Institute of Standards and Technology (NIST) Compared to decay corrected calibrated activity Results must be within 5%
Dose Calibrator Geometry Performed at installation, recalibration, etc. Fine print (plug-in) Assess accuracy of the dose calibrators ability to measure consistent activity with different volumes A given amount of radioactivity is assayed in a container and the activity is recorded. Saline is incrementally added to include range typically used in lab Measurements must be within 5%.
Dose Calibrator Constancy Performed daily Designed to show that a long half-life source yields reproducible readings Compared to previous days reading Within 5% of decay corrected accuracy readings Check each setting (isotope) button Activity used should be greater than 50 µci of Co-57 or Cs-137 (or another gamma emitting sealed source)
Dose Calibrator Constancy SETTING MON TUES WED THURS FRI Cs-137 123 124 122 125 124 Tc-99m 243 244 246 244 244 Tl-201 163 164 162 165 164 I-123 194 194 196 195 195
Dose Calibrator Linearity Performed quarterly Assess ability to read both high and low activity Measured values must be within 5% of calculated values Two methods for linearity Decay method Sleeve method
Dose Calibrator Decay method Measure an initial high activity of a short halflife source. Various measurement are taken as it decays. Readings are compared to calculated decay. Elapsed Time (hr) Expected Reading (mci) Measured Reading (mci) 0 300 300 1 267 272 2 238 241 3 212 210 6 150 148 12 75 72.5 24 18.75 19.1 48 1.17 1.19 72 0.073 0.074 78 0.036 0.037
Dose Calibrator Sleeve method Decay is simulated by using lead sleeves of various thickness.
Dose Calibrator Subpart C--General Technical Requirements 35.60 Possession, use, and calibration of instruments used to measure the activity of unsealed byproduct material (a) For direct measurements performed in accordance with 35.63, a licensee shall possess and use instrumentation to measure the activity of unsealed byproduct material before it is administered to each patient or human research subject. (b) A licensee shall calibrate the instrumentation required in paragraph (a) of this section in accordance with nationally recognized standards or the manufacturer's instructions. (c) A licensee shall retain a record of each instrument calibration required by this section in accordance with 35.2060.
Other Lab Equipment Glucometer Daily calibration Accuracy Defibrillator Battery Test Voltage Test
Be Alert All Day! Raw patient data should be carefully reviewed on each patient. All problems do not happen at night Cameras Survey meters Dose calibrator
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