James Proffitt

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.

Implementation of a High-Rate USB Data Acquisition System for PET and SPECT Imaging

We made substantial progress with a flexible high-rate USB data acquisition system developed for gamma-ray imaging detectors. Hardware consists of 16-channel data acquisition modules installed on USB carrier boards. One, two, and four-module units were developed. USB data rate was increased to over 30 MB/s and a 16-channel configuration achieved a trigger rate of over 700 kHz. Several high-resolution single-gamma detectors and two high-rate PET detectors were instrumented. The detectors use various configurations of Hamamatsu H8500, H9500, and Burle 85002-800 PSPMTs. System channels were expanded by synchronizing additional acquisition units. A Java client-server system was developed to link acquisition computers over Gigabit Ethernet. A Kmax tool was developed to process and display images during acquisition. C and Java utilities were developed to assist development and diagnostics.

A java distributed acquisition system for PET and SPECT imaging

The Detector and Imaging Group at Jefferson Lab is developing various compact gamma cameras for clinical and preclinical systems. Both PET and SPECT systems are under development. To facilitate that development we have designed a highly flexible Java data acquisition tool that helps to minimize software induced dead-time while maintaining the highest possible data rates from our in house built ADCs. This tool interfaces with FPGA based multi-channel ADCs which our group has developed. Using this tool we are able to process data from a number of different detector types such as the SPECT Awake Animal Imaging system at Johns Hopkins University; as well as our PET systems at West Virginia University (WVU), the University of Florida (UF), and the National Technical University of Athens. Because of the inherent flexibility of our processing software, we are also able adjust detector readout parameters during operation to provide the best possible data presentation and calibration parameters. We are using the readout capability of this software with Kmax to provide a user friendly display of detector outputs such as raw images and individual channel spectra. To accommodate the high rate nature of PET detector systems we designed this software to be scalable across an Ethernet network as well as for multi-CPU computer systems, and it also has the capability to synchronize many ADCs connected to multiple computers. We have incorporated this distributed design into the six computer PEM (Positron Emission Mammography)/PET system at WVU, and the three computer cardiac PET detector at UF.

Evaluation of imaging modules based on SensL array SB-8 for nuclear medicine applications

Recent advances in the development of silicon photomultipliers (SiPM) offer new opportunities for medical imaging applications. Specifically, novel imaging devices for positron emission (PET) and single photo-emission computed tomography (SPECT) are becoming feasible. In this investigation, we tested a monolithic array of new generation SiPMs, an SB-8 array from SensL. 8×8 array of 6-mm square SiPMs was studied with two different multiplexing readouts, 4- and 16-channels. SB-8 detector was coupled to various scintillation arrays and resulting prototypes were evaluated. Testing demonstrated that the new device is capable of resolving 1 mm LYSO and 1.5 mm NaI crystals with 16-channel readout and 1.57 mm LYSO and 3 mm NaI crystals with 4-channel readout. Energy resolution of approximately 15% at 511 keV and 19% at 122 keV were obtained with LYSO and NaI crystals, respectively. A timing resolution of 1.52 ns was measured with 1.57 mm LYSO array and the 16-channel readout. It is concluded that new B-series SiPMs from SensL are suitable for use in high spatial resolution nuclear medicine particle detectors.

Awake animal SPECT: Overview and initial results

A SPECT / X-ray CT system configured at Johns Hopkins University to image the biodistribution of radiopharmaceuticals in unrestrained, un-anesthetized mice has been constructed and tested on awake mice. The system was built by Thomas Jefferson National Accelerator Facility and Oak Ridge National Laboratory. SPECT imaging is accomplished using two gamma cameras, 10 cm × 20 cm in size based on a 2 × 4 array of Hamamatsu H8500 flat panel position sensitive photomultiplier tubes. A real-time optical tracking system utilizing three infrared cameras provides time stamped pose data of an awake mouse head during a SPECT scan. The six degrees of freedom (three translational and three rotational) pose data are used for motion correction during 3-D tomographic list-mode iterative image reconstruction. SPECT reconstruction of awake, unrestrained mice with motion compensation for head movement has been accomplished.

Development of a “resistive” readout for SiPM arrays

We are developing the charge division (“resistive”) readout for several arrangements of Silicon Photomultiplier (SiPM) arrays, based on devices from Hamamatsu and SensL. The challenge with the SiPM arrays, as opposed to position sensitive photomultipliers (PSPMTs), is that the noise level is known to be high, and signal to noise ratio (S/N) is lower than in PMTs. In addition, the S/N decreases quickly with the increasing size of the module and with increasing temperatures. Key parameters to optimize are: size and coverage of the SiPM arrays, operational temperature (potential necessity of introducing system cooling), and bias voltage. All these parameters have impact on the S/N, and in consequence on the spatial resolution and the energy resolution of the detector modules. Our somewhat arbitrary but practical goal is to achieve operation similar to the one offered by H8500/H9500 flat panel PSPMTs when using LYSO scintillation arrays in applications to small PET imaging modules. Ultimately we would like to use the reduced channel number readout in the depth-of interaction (DOI) modules. Our first application is to construct ∼5cm×5cm compact PET modules for the HelmetPET brain imager prototype under construction at WVU.

HelmetPET: A silicon photomultiplier based wearable brain imager

We are developing the HelmetPET, a wearable human PET brain imager which has the potential application of evaluating brain function utilizing PET based radiopharmaceuticals in standing, balancing or moving patients. The HelmetPET is composed of two rings of radiation detectors together providing a cylindrical reconstructed volume with an axial length of 5 cm. Each ring is composed of twenty 2.5 cm2 silicon photomultiplier (SiPM) based detector modules. Each detector module is composed of a 5×5 array of twenty-five Hamamatsu S10362-33-050P Multi Pixel Photon Counters (MPPCs). The 3 mm2 MPPCs are arranged on a 5mm step. Coupled to each of the MPPC modules is a LYSO scintillator crystal array coupled to the MPPC array using to two different LYSO pixel arrays: 1.0×1.0×10 mm3 and 1.5×1.5×10 mm3. The current phase of the project is to equip the forty 2.5 cm2 detector modules with resistive readout and assemble them in a helmet type head support and suspend from a flexible mechanical mount.

Analysis of Image Combination Methods for Conjugate Breast Scintigraphy

The main objective of the present study was to determine if combining the two images from a conjugate counting system might improve the contrast and signal-to-noise ratio (SNR) of small lesions in all regions of the breast compared to images from a single camera. Several methods for combining the opposing pixels of the two camera images were compared: multiplication, geometric mean, and summation. The image quality metrics measured were spatial resolution, lesion contrast and lesion SNR. These quantities were evaluated both theoretically and experimentally. A capillary phantom was used to measure the spatial resolution as a function of lesion depth and to assess the translation and angular offsets between the two cameras. An acrylic box phantom, with spherical lesions suspended inside, was used to evaluate contrast and SNR as a function of lesion position. Both theoretically and experimentally the spatial resolution in the product images was superior to that in the single images, geometric mean or summation images. Relative to the single camera images, the geometric mean or the summed images, the lesion contrast and SNR of the product images were superior, irrespective of lesion depth, and were more constant with changing lesion depth compared to the single camera images. These findings suggest that improved lesion detectability is possible by imaging simultaneously from both sides of the breast, and forming a combined image using pixel-by-pixel multiplication. This may be especially important if the location of the lesion within the breast is not known a priori.

Tomographic Dual Modality Breast Scanner

We are developing a breast scanner that obtains co-registered dual modality tomographic images of the breast using x-ray imaging (digital breast tomosynthesis) and gamma emission imaging (limited angle breast SPECT). The project is a collaborative effort among the Jefferson Lab (Newport News, VA), Dexela Ltd., (Sudbury MA), and the University of Virginia (UVa) (Charlottesville, VA). The scanner is currently undergoing pilot clinical evaluation at UVas Breast Care Center. Here we report on the design of the scanner, choice of acquisition parameters, and present some early phantom and human breast images.

Development of a mini gamma camera for prostate imaging

We have tested a concept of a mini gamma camera based on monolithic arrays of MPPCs from Hamamatsu. CsI(Tl), and Cs(Na) arrays and a thin scintillation GSO plate were tested with 122 keV gammas from 57Co sources. The planned application requires placement of this mini-camera in an endorectal probe and thus needs to be very compact and possess high spatial resolution. The high sensitivity and high granularity collimator and gamma shield made out composite material (tungsten powder with epoxy) completes the detector package. We are developing the dual modality (hybrid) imaging prostate probe combining in one compact device a high resolution and high efficiency single gamma imager with an Ultrasound (US) sensor. The US component will typically provide not only the usual structural 3D information, as the standard TransRectal Ultrasound (TRUS) probe, but also the tissue differentiating information through proper US signal analysis, such as elastography. The mini gamma probe will provide the direct metabolic information related to the biological state of the prostate and specifically about the presence of any cancerous structures exhibiting increased metabolic activity, when used with the single gamma labeled dedicated imaging agents for prostate cancer. In addition to cancer diagnosis, the dual-modality Gamma/US prostate probe can be used in biopsy and in surgical guidance.