Performance of a PSPMT based detector for scintimammography

• Published in: Physics in medicine & biology 2000-03, Vol.45 (3), p.781-800
• Main Authors: Williams, Mark B, Goode, Allen R, Galbis-Reig, Victor, Majewski, Stan, Weisenberger, Andrew G, Wojcik, Randolph
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Equipment Design; Female; Gamma Cameras; Genital system. Mammary gland; Humans; Image Processing, Computer-Assisted; Investigative techniques, diagnostic techniques (general aspects); Mammography - instrumentation; Mammography - methods; Medical sciences; Phantoms, Imaging; Radiodiagnosis. Nmr imagery. Nmr spectrometry; Radionuclide Imaging - instrumentation; Scintillation Counting; Sensitivity and Specificity; Technetium; Technology, Radiologic; Tissue Distribution
• ISSN: 0031-9155; 1361-6560
• DOI: 10.1088/0031-9155/45/3/315

In breast scintigraphy, compact detectors with high intrinsic spatial resolution and small inactive peripheries can provide improvements in extrinsic spatial resolution, efficiency and contrast for small lesions relative to larger conventional cameras. We are developing a pixelated small field-of-view gamma camera for scintimammography. Extensive measurements of the imaging properties of a prototype system have been made, including spatial resolution, sensitivity, uniformity of response, geometric linearity and energy resolution. An anthropomorphic torso phantom providing a realistic breast exit gamma spectrum has been used in a qualitative study of lesion detectability. A new type of breast imaging system that combines scintimammography and digital mammography in a single upright unit has also been developed. The system provides automatic co-registration between the scintigram and the digital mammogram, obtained with the breast in a single configuration. Intrinsic spatial resolution was evaluated via calculation of the phase-dependent modulation transfer function (MTF). Measurements of extrinsic spatial resolution, sensitivity and uniformity of response were made for two types of parallel hole collimator using NEMA (National Electrical Manufacturers Association) protocols. Geometric linearity was quantified using a line input and least squares analysis of the measured line shape. Energy resolution was measured for seven different crystal types, and the effectiveness of optical grease coupling was assessed. Exit gamma spectra were obtained using a cadmium zinc telluride based spectrometer. These were used to identify appropriate radioisotope concentrations for the various regions of an anthropomorphic torso phantom, such that realistic scatter conditions could be obtained during phantom measurements. For prone scintimammography, a special imaging table was constructed that permits simultaneous imaging of both breasts, as well as craniocaudal views. A dedicated breast imaging system was also developed that permits simultaneous acquisition and superposition of planar gamma images and digital x-ray images. The intrinsic MTF is nonstationary, and is dependent on the phase relationship between the signal and the crystal array matrix. Averaged over all phases, the MTF is approximately 0.75, 0.57 and 0.40 at spatial frequencies of 1.0, 1.5 and 2.0 cycles per cm, respectively. The phase averaged line spread function (LSF) has a FWHM value of 2.6 mm. Following unif