V. Popov

Optimization of dedicated scintimammography procedure using detector prototypes and compressible phantoms

Jefferson Lab., Hampton University, and University of Virginia are collaborating on optimization of dedicated scintimammography mini gamma cameras. Several prototype imagers with a FOV of 4/spl times/4 and 8/spl times/6 were tested for an application in a dual modality mode as an adjunct technique to digital mammography imagers, or as stand-alone instruments in a dedicated breast SPECT mode. The goal of this study was to obtain experimental data allowing for selection of the best imaging geometry to detect small lesions labeled with Tc-99m. The design of the small scintimammography gamma camera prototypes used in these studies, with an active FOV from 10 cm/spl times/10 cm and 15 cm/spl times/20 cm, is based on an array of Hamamatsu R7600-00-C8 position sensitive photomultiplier tubes (PSPMTs). Optically coupled to the PSPMT array via specially designed efficient multi-element light guide is a matrix of NaI(Tl) scintillator pixels (made by Bicron Corporation) with each element 3 mm/spl times/3 mm/spl times/6 mm in size and separated by 0.4 mm thick septa. Several designs of this basic structure were used in prototypes used to detect small lesions inserted in gelatin breast phantoms under compression and in a non-compressed SPECT mode. Anthropomorphic torso phantoms were also employed to simulate realistic scatter radiation fields. Two data acquisition systems were used to collect and analyze the data: one based on a Macintosh G3 workstation with FERA ADCs and one based on a PC computer running Windows NT/KmaxNT software which makes use of two sixteen channel ADC PCl cards. The present results show that the preferred imaging geometry is planar imaging with two opposing detector heads and breast under compression, however, further study of the dedicated breast SPECT is warranted.

Optimization of breast imaging procedure with dedicated compact gamma cameras

Results are presented on studies conducted with various prototypes of a dedicated small field-of-view (SFOV) gamma camera for use in radiopharmaceutical studies of the breast. Since the experience in the clinical use of such instruments is limited, these experiments were conducted to test various clinical imaging implementations. Both planar and tomographic techniques were utilized to image various compressed and noncompressed breast phantoms. Lesion contrast was used to quantify the lesion visibility of each case. The results of this study indicate that lesion contrast is optimized with planar imaging of the compressed breast and that contrast is also dependent on lesion-to-detector distance. Based on these observations, planar imaging conducted with a system comprised of two opposed detectors providing compression to the breast would be optimal. The opposed views would ensure the minimization of lesion-to-detector distance, especially for lesions whose location is not known a-priori.

A combined scintimammography/stereotactic core biopsy digital X-ray system

Jefferson Lab, Hampton University and the Riverside Regional Medical Center are collaborating in a clinical study employing a dual modality imaging system utilizing scintimammography and digital radiography. The purpose of the study is to obtain clinical data on the reliability of scintimammography in predicting the malignancy of suspected breast lesions with the ultimate goal to reduce the number of false positives associated with conventional X-ray mammography. The scintimammography gamma camera is a custom built mini gamma camera with an active area of 5.3 cm/spl times/5.3 cm based on a 2/spl times/2 array of Hamamatsu R7600-C8 position sensitive photomultiplier tubes. The spatial resolution of the gamma camera at the collimator surface is <4 mm FWHM and the sensitivity is 4000 cps/mCi. Preliminary results are that of the six cases that indicated a lesion with high uptake of the MiraLuma (/sup 99m/Tc-sestamibi) five were positive for cancer. Out of a total of 25 patients in the study, all cases negative for MiraLuma uptake were confirmed negative via the biopsy pathology. The scintimammography results indicate that the lesions become visible with the mini gamma camera within 3 minutes post injection of MiraLuma.

Time-of-flight resolution of scintillating counters with Burle 85001 microchannel plate photomultipliers in comparison with Hamamatsu R2083

The CLAS detector will require improvements in its particle identification system to take advantage of the higher energies provided by the Jefferson Laboratory accelerator upgrade to 12 GeV. To this end, we have studied the timing characteristics of the micro-channel plate photo-multiplier 85001 from Burle, which can be operated in a high magnetic field environment. For reference and comparison, measurements were also made using the standard PMT R2083 from Hamamatsu using two timing methods. The cosmic ray method, which utilizes three identical scintillating counters 2cmx3cmx50cm with PMs at the ends, yields 59.1(0.7)ps. The location method of particles from radiative source with known coordiantes has been used to compare timing resolutions of R2083 and Burle-85001.This ``coordinate method requires only one counter instrumented with two PMs and it yields 59.5(0.7)ps. For the micro-channel plate photomultiplier from Burle with an external amplification of 10 to the signals, the coordinate method yields 130(4)ps. This method also makes it possible to estimate the number of primary photo-electrons.

Application of a small field of view gamma camera based on a 5" PSPMT and crystal scintillator array for high resolution small animal cardiac imaging

We have built a small field-of-view gamma camera based on a 5 diameter Hamamatsu R3292 position sensitive photomultiplier tubes (PSPMT) and Nal(Tl) crystal for high resolution small animal imaging. The instrument was specifically developed for high performance cardiac imaging in rats and mice. Results of measurements in both mouse and rat models will be presented. Dynamic ECG-gated and static planar pinhole pet-fusion images of rat hearts were acquired allowing semi-quantitative and functional interpretation. Additionally, molecular imaging of neutrophil infiltration in a mouse model of myocardial post-ischemic inflammation vi-as performed. We demonstrate the utility of this high resolution instrument for molecular and functional cardiac imaging in small animal models a( heart rates of 250-600 bpm. The superior performance of this new camera will allow the noninvasive monitoring of radiolabeled molecular probes for assessing physiologic processes in the heart as well as other organ systems of small animals.

Improved lesion visibility in a dedicated dual head scintimammography system - phantom results

Phantom test results are presented simulating a dedicated dual head compact gamma imaging system for scintimammography. These studies were completed with various detector prototypes constructed from pixellated scintillators coupled to various arrays of position sensitive photomultiplier tubes. A 15cm /spl times/ 20cm dual-head prototype system is currently under development that will provide sufficient imaging area for breast imaging studies. The results indicate that the use of two detector heads placed on opposing sides of breast under mild compression substantially improves the lesion contrast regardless of lesion depth in the tissue (especially for small, centrally located lesions). In addition, there is significantly improved lesion signal by using a geometric mean technique, Square Root (Image 1* Image2), to combine the images from the opposing views. In count poor cases, a smoothing kernel was applied prior to image multiplication to reduce high spatial frequency noise.

PROPOSAL FOR A PHOTON DETECTOR WITH PICOSECOND TIME RESOLUTION

A picosecond photon detector and a new timing concept are proposed here. Factors limiting time resolution of the technique are briefly discussed. Some R&D work is also reported.