The positron emission mammography/tomography breast imaging and biopsy system (PEM/PET): design, construction and phantom-based measurements.

Tomographic breast imaging techniques can potentially improve detection and diagnosis of cancer in women with radiodense and/or fibrocystic breasts. We have developed a high-resolution positron emission mammography/tomography imaging and biopsy device (called PEM/PET) to detect and guide the biopsy of suspicious breast lesions. PET images are acquired to detect suspicious focal uptake of the radiotracer and guide biopsy of the area. Limited-angle PEM images could then be used to verify the biopsy needle position prior to tissue sampling. The PEM/PET scanner consists of two sets of rotating planar detector heads. Each detector consists of a 4 x 3 array of Hamamatsu H8500 flat panel position sensitive photomultipliers (PSPMTs) coupled to a 96 x 72 array of 2 x 2 x 15 mm(3) LYSO detector elements (pitch = 2.1 mm). Image reconstruction is performed with a three-dimensional, ordered set expectation maximization (OSEM) algorithm parallelized to run on a multi-processor computer system. The reconstructed field of view (FOV) is 15 x 15 x 15 cm(3). Initial phantom-based testing of the device is focusing upon its PET imaging capabilities. Specifically, spatial resolution and detection sensitivity were assessed. The results from these measurements yielded a spatial resolution at the center of the FOV of 2.01 +/- 0.09 mm (radial), 2.04 +/- 0.08 mm (tangential) and 1.84 +/- 0.07 mm (axial). At a radius of 7 cm from the center of the scanner, the results were 2.11 +/- 0.08 mm (radial), 2.16 +/- 0.07 mm (tangential) and 1.87 +/- 0.08 mm (axial). Maximum system detection sensitivity of the scanner is 488.9 kcps microCi(-1) ml(-1) (6.88%). These promising findings indicate that PEM/PET may be an effective system for the detection and diagnosis of breast cancer.

Endoprobe: a system for radionuclide-guided endoscopy.

Methods to guide the surgical treatment of cancer utilizing handheld beta-sensitive probes in conjunction with tumor-avid radiopharmaceuticals [such as 18F-fluorodeoxyglucose (FDG)] have previously been developed. These technologies could also potentially be used to assist in minimally invasive techniques for the diagnosis of cancer. The goal of this project is to develop and test a system for performing radionuclide-guided endoscopies. This system (called Endoprobe) has four major subsystems: beta detector, position tracker, endoscope, and user interface. The beta detection unit utilizes two miniaturized solid state detectors to preferentially detect beta particles. The position tracking system allows real-time monitoring of the unit's location. The beta detector and position tracking system's receiver are mounted on the tip of an endoscope. Information from the beta detector and tracking system, in addition to the video signal from the endoscope, are combined and presented to the user via a computer interface. The system was tested in a simulated search for radiotracer-avid areas of esophageal cancer. The search for esophageal cancer was chosen because this type of cancer is often diagnosed with endoscopic procedures and has been reported to have good affinity for FDG. Accumulations of FDG in the normal organs of the abdomen were simulated by an anthropomorphic torso phantom filled with the appropriate amounts of radioactivity. A 1.5- mm-thick gelatin film containing FDG was used to simulate radiotracer uptake in the lining of normal esophagus. Esophageal lesions (both benign and malignant) were simulated by thin disks of gelatin (diameters=3.5-12 mm) containing appropriate concentrations of FDG embedded in the gelatin film simulating normal esophagus. Endoprobe facilitated visual identification and examination of the simulated lesions. The position tracking system permitted the location of the Endoprobe tip to be monitored and plotted in real time on a previously acquired positron emission tomography-computed tomography (PET-CT) image of the phantom. The detection system successfully acquired estimates of the beta flux emitted from areas chosen by the user. Indeed, Endoprobe was able to assist in distinguishing simulated FDG-avid areas as small as 3.5 mm in diameter from normal esophagus (p value <0.025). In addition to FDG, Endoprobe can be used with other positron or electron-emitting radionuclides such as IC or 131I. The next phase of this project will focus on modification of the prototype to make it more suitable for clinical use.