A stationary hemispherical SPECT imager for three-dimensional brain imaging.

A completely stationary, hemispherical-coded aperture SPECT imaging system was designed to produce three-dimensional images of the brain. The system consisted of a hemispherical multiple-pinhole coded aperture and 20 small (100 x 100 mm crystal area) digital gamma cameras. Reconstructions and measured performance specifications from two laboratory versions of the imager are presented. The reconstructed field of view of these systems was an ellipsoidal region with semi-diameters of 100 x 100 x 50 mm. The reconstructed spatial resolution for a point source in air at the center of this field was found to be 4.8 mm FWHM and the corresponding system sensitivity was 36 cps/microCi. An analysis using an ideal-observer model indicated that the multiplexed projection data suffered a 21% degradation relative to similar, but nonmultiplexed SPECT data. Therefore, by this measure, the effective sensitivity of the brain imager was 79% of the measured value.

A full-field modular gamma camera.

A modular gamma ray camera is described that gives useful image information over its entire crystal face. The lack of dead area on the periphery of the camera is made possible by a unique application of digital electronics and optimal position estimation using maximum likelihood (ML) estimates. The ML estimates are calculated directly from photomultiplier tube responses and stored in a lookup table, so the restriction of calculating the position estimates in separate circuitry is removed. Each module is designed to be optically and electronically independent, so that many modules can be combined in a large system. Results from a prototypical module, which has an active crystal area of 10 cm X 10 cm, are presented.

Sentinel node staging of early breast cancer using lymphoscintigraphy and the intraoperative gamma-detecting probe.

Sentinel node staging for breast cancer is increasingly used in place of axillary lymph node dissection but is not yet universally accepted. The problems of non-standardized methodologies and lack of consensus on the optimum techniques to identify sentinel nodes are being addressed. Complementary use of radionuclide imaging before surgery, intraoperative probe detection, and blue dye have yielded the best reported sensitivities for finding a sentinel node (94%). The importance of imaging is summarized as identifying sentinel node(s), distinguishing sentinel from secondary nodes, guiding surgical incision planning, and facilitating lower doses. The learning curve phenomenon, which applies to the surgeon and the nuclear medicine physician, has been recognized; measures to minimize it are being implemented. Radiation exposure to operating room and pathology personnel is very low; estimates of exposure to the surgeon's hands are 0.2% of the annual whole body dose received by every human being from natural background and cosmic sources.

A miniature gamma camera.

We have described a mobile miniature-gamma-camera system for use in electrical trauma units and have presented images and imaging characteristics of a prototype system. The system has as its principal component a miniature gamma camera based on a PSPMT. The camera is 92 mm x 92 mm x 190 mm in size, weighs 5 kg, has a 48 mm x 48 mm field of view, and has an intrinsic resolution of approximately 3 mm FWHM and 6 mm FWTM. It is expected that devices of this type will be useful as imaging tools in electrical trauma units and laboratories where imaging studies regarding uptake mechanisms of radiopharmaceuticals for assessing tissue viability are carried out.

Sentinel node staging of early breast cancer using lymphoscintigraphy and the intraoperative gamma detecting probe.

Lymphoscintigraphy combined with intraoperative gamma-probe detection of sentinel lymph nodes in patients with inoperable early primary breast cancers is effective for staging the disease. The clinical alternative is axillary lymph node dissection, which is a far more invasive procedure and is accompanied by significant morbidity. Accuracy of staging is enhanced by immunohistochemical staining of micrometastases, which pathologists can easily perform for one to three sentinel lymph nodes, but not for 20 to 30 nodes, using axillary dissection procedure. Optimum methodology is presented for performing sentinel lymph node imaging and is important for accurate identification of sentinel node(s).

The 1995 Lindberg Award. Nonthermally mediated muscle injury and necrosis in electrical trauma.

Joule heating has long been considered the principal component of tissue damage in electrical injury. Recent studies suggest electroporation, a nonthermally mediated mechanism of cell membrane damage, is also a factor. We investigated whether electroporation-mediated muscle necrosis can occur in vivo without significant Joule heating. Pulsed electric fields approximately 150 V/cm were produced in the hind limbs of anesthetized rats. In shocked limbs core muscle temperature rose less than 1.8 degrees C, yet significant damage occurred as determined by technetium-99m pyrophosphate uptake, elevated serum creatine phosphokinase, and prominent hypercontraction band degeneration of myofibers on histopathologic examination. This study is significant because it directly addresses whether nonthermal mechanisms of cell damage can cause tissue necrosis. These results indicate that electroporation effects can mediate skeletal muscle necrosis without visible thermal changes. Thus the phenomenon of "progressive recognition" may be characteristically largely explained by the occurrence of nonthermally mediated tissue damage.

Intraoperative probes.

OBJECTIVE: Design features of intraoperative probes are presented. A brief discussion of the sentinel node concept and relevant radiopharmaceuticals is given. The importance of the injection technique and the necessity of imaging in radiotracer techniques for sentinel node detection are explained. Probe calibration, procedural precautions, intraoperative techniques, and radiation dosimetry relevant to the successful use of intraoperative probes are discussed. Intraoperative use of gamma probes requires a team effort involving surgery and nuclear medicine personnel and requires that team members understand the fundamentals of probe use. After reading this paper, the nuclear medicine technologist will be able to: (a) describe present day and future potential use of intraoperative probes; (b) define the sentinel lymph node (SLN) concept; (c) state the radiopharmaceuticals and injection techniques used for SLN evaluation; (d) name several SLN detection procedures; and (e) discuss the design features and care of currently available probes.