Design and performance of gamma and beta intra-operative imaging probes
A prototype small area scintillation camera capable of imaging both gammas and betas by use of inter-changeable detector front ends was characterized. In the camera's application, patients are injected with tumor seeking radiopharmaceuticals before surgery, during surgery the body of tumor is removed, and the residual tumor is located with gamma or beta imaging probes. Common elements of both types of camera include: (1) a 2-3 meter long fiber optic bundle, consisting of 19 sets of groups of three 0.9 mm diameter multiclad fibers that allow a flexible optical connection to the scintillator in addition to electrical isolation of the patient from the electronics, (2) fibers are connected to a Multi-Channel Photomultiplier (MC-PMT) which has 64 parallel channels, (3) the parallel PMT outputs feed a resistive divider network and an i-V converter/line driver network with gain adjustments, producing balanced + X, -X, + Y, and -Y outputs for analog image signals, (4) four ADCs connected to a Macintosh PC for digitizing and displaying the image. The beta camera utilized a 0.5 mm thick by 1.25 cm diam. CaF2(Eu) scintillation crystal coupled to 19 2-mm diameter multiclad optical fibers, which are in turn coupled by a longer fiber bundle to the MC-PMT The crystal is coupled to fibers through a diffusing light guide ensuring adequate distribution of scintillation light among fibers. Image signals are directly histogrammed and displayed after Anger logic computations are performed on analog signals. The gamma camera concept was tested with 3 mm thick continuous crystals and matrices of CsI(T1) as the system front end with the same fiber optic coupling as the beta camera, and data processing analogous to the beta camera. With the matrices of crystals, a configuration which used a light diffuser between the matrix and fiber optics was evaluated. The beta imaging probe produced images with 0.6 mm FWHM resolution and a flood field uniformity of ± 15%. The continuous crystal imaging probe gave intrinsic resolutions of 1.4 ± 0.2 mm FWHM at 122 keV. Flood field images, made with the diffuser between fiber optics and discrete crystals, completely resolved the 1 x 1 mm2 elements Intrinsic resolution as measured by a line spread function was 0.92 ± 0.03 mm FWHM.
Hoffman, EJ; Tornai, MP; Levin, CS; MacDonald, LR; Siegel, S
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