NM Physics - Practical Session PDF

Converting mCi to MBq. urpe - Asia 1 millicurie [mCi] = 37 megabecquerel [MBq] why he can't desopt in 21 wear whole. scan 2 Characteristics and quality assurance of gamma images 3 Uniformity of detector response L ▪ A conventional gamma camera should give a uniform response to a uniform field. ▪ A f...

Converting mCi to MBq. urpe - Asia 1 millicurie [mCi] = 37 megabecquerel [MBq] why he can't desopt in 21 wear whole. scan 2 Characteristics and quality assurance of gamma images 3 Uniformity of detector response L ▪ A conventional gamma camera should give a uniform response to a uniform field. ▪ A flood field or sheet phantom is used to check this. ▪ It consists of a flat sealed plate, larger than the FOV and usually filled with cobalt-57 (57Co). ▪ 57Co has a similar gamma emission to but is longer-lived than 99mTc. ▪ This should give a uniform image with the collimator in place: a defective photomultiplier will be seen as an area of reduced counts in the image. ▪ A cracked in the crystal will show as a linear defect. 4 Uniformity of detector response L ▪ Non-uniformity caused by the usual slight differences in the performance on individual photomultipliers is analysed by counts in each pixel, and image data acquisition can be compensated automatically from this analysis. ▪ However, regular checks are needed to monitor any deterioration in the photomultipliers. ▪ Background radiation checks are useful to identify contamination of the gamma camera or its collimator, or even the presence of a local unshielded source. 5 Uniformity of detector response ▪ A high reading obtained whatever the camera orientation indicates contamination on the crystal or the camera head; subsequent high readings, obtained once the collimator is in place, indicate collimator contamination. for & A → Flood field images showing (a) defective photomultiplier tube and (b) damaged crystal 6