John McKisson

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.

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.

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.

Molecular Imaging of Conscious, Unrestrained Mice with AwakeSPECT

We have developed a SPECT imaging system, AwakeSPECT, to enable molecular brain imaging of untrained mice that are conscious, unanesthetized, and unrestrained. We accomplished this with head tracking and motion correction techniques. Methods: The capability of the system for motion-corrected imaging was demonstrated with a 99mTc-pertechnetate phantom, 99mTc-methylene diphosphonate bone imaging, and measurement of the binding potential of the dopamine transporter radioligand 123I-ioflupane in mouse brain in the awake and anesthetized (isoflurane) states. Stress induced by imaging in the awake state was assessed through measurement of plasma corticosterone levels. Results: AwakeSPECT provided high-resolution bone images reminiscent of those obtained from CT. The binding potential of 123I-ioflupane in the awake state was on the order of 50% of that obtained with the animal under anesthesia, consistent with previous studies in nonhuman primates. Levels of stress induced were on the order of those seen in other behavioral tasks and imaging studies of awake animals. Conclusion: These results demonstrate the feasibility of SPECT molecular brain imaging of mice in the conscious, unrestrained state and demonstrate the effects of isoflurane anesthesia on radiotracer uptake.

Positron emission tomography detector development for plant biology

There are opportunities for the development of new tools to advance plant biology research through the use of radionuclides. Thomas Jefferson National Accelerator Facility, Duke University, West Virginia University and the University of Maryland are collaborating on the development of radionuclide imaging technologies to facilitate plant biology research. Biological research into optimizing plant productivity under various environmental constraints, biofuel and carbon sequestration research are areas that could potentially benefit from new imaging technologies. Using 11CO2 tracers, the investigators at Triangle University Nuclear Laboratory / Duke University Phytotron are currently researching the dynamical responses of plants to environmental changes forecasted from increasing greenhouse trace gases involved in global change. The biological research primary focus is to investigate the impact of elevated atmospheric CO2 and nutrients limitation on carbon and nitrogen dynamics in plants. We report here on preliminary results of 11CO2 plant imaging experiments involving barley plants using Jefferson Lab dual planar positron emission tomography detectors to image 11CO2 in live barley plants. New detector designs will be developed based on the preliminary studies reported here and further planned.

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.

Intrinsic feature pose measurement for awake animal SPECT imaging

New developments have been made in optical motion tracking for awake animal imaging that measures 3D position and orientation (pose) for a single photon emission computed tomography (SPECT) imaging system. Ongoing SPECT imaging research has been directed towards head motion measurement for brain studies in awake, unrestrained mice. In contrast to previous results using external markers, this work extracts and tracks intrinsic features from multiple camera images and computes relative pose from the tracked features over time. Motion tracking thus far has been limited to measuring extrinsic features such as retro-reflective markers applied to the mouses head. While this approach has been proven to be accurate, the additional animal handling required to attach the markers is undesirable. A significant improvement in the procedure is achieved by measuring the pose of the head without extrinsic markers using only the external surface appearance. This approach is currently being developed with initial results presented here. The intrinsic features measurement extracts discrete, sparse natural features from 2D images such as eyes, nose, mouth and other visible structures. Stereo correspondence between features for a camera pair is determined for calculation of 3D positions. These features are also tracked over time to provide continuity for surface model fitting. Experimental results from live images are presented.

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.

Feasibility study of using detection of direct positrons in plant imaging research

While nuclear methods find application in plant biology there are very limited amount of instrumentation that is geared to the unique challenges that plant biology presents. Mostly researchers are utilizing devices created for clinical and preclinical imaging. The majority of the biologically significant elements involved in plant formation have positron emitting isotopes, making positron emission tomography a naturally fitting imaging modality. One particular caveat in using PET instrumentation in plant imaging is extremely small thickness of the leaf as an annihilation medium for emitted positrons. For positron energies around 1MeV (as in case of C-11), about 1 mm of water equivalent material is required for positron conversion, so most of the positrons would not annihilate inside the leaf, therefore limiting both sensitivity and spatial resolution of the imaging system. In this work we made an attempt of determining whether direct imaging of positrons could be beneficial in plant biology studies. We compared performance of direct positron detector with a planar PET system. Detection efficiency ratio of ~ 650 in favor of direct positron detection system was measured. Direct comparison of spatial resolutions yielded comparable numbers for a setup, when a phantom was placed directly onto the entrance window of the positron detector. We also determined quick deterioration of spatial resolution as a function of source to detector distance. The last observation makes it necessary to maintain close proximity of the object to the detector, but this condition can be met in plant biology study.

Molecular breast imaging with directly opposing compact gamma cameras

The goal of this study was to evaluate the efficacy of operating a two-head gamma camera system in a configuration in which the two cameras are positioned on opposite sides of the compressed breast, aligned precisely with each other and with precisely anti-parallel viewing directions. The main objective of the present study was to determine if the combination of the two resulting images might allow for better sensitivity for small lesions in all regions of the breast. Two pairs of gamma cameras were evaluated; one composed of commercially available gamma cameras and the other composed of two research-based gamma cameras. For each pair, an acrylic box phantom, with two spherical lesions suspended inside, was used to evaluate contrast and SNR as a function of lesion position, first for images from the two cameras separately and then for images obtained from pixel- by-pixel multiplication or summation of the individual images. A capillary phantom was used to quantify the spatial resolution as a function of lesion depth for the cameras individually as well as for the resulting multiplied images. Lastly, gelatin phantoms were imaged, each containing a single cube-shaped lesion of ~8 mm side length positioned at varying depths within the phantom. Relative to the single camera images or the summed images, the lesion contrast and SNR of the multiplication image were superior, irrespective of lesion depth, and were much more constant with changing lesion depth. Except when the lesion was less than a centimeter from one of the cameras, the SNR of the multiplied image exceeded that of a single camera image obtained using twice the acquisition time. These findings suggest that improved lesion detectability is possible by imaging simultaneously from both sides of the breast, especially if the location of the lesion within the breast is not known a priori.