Rodney C. Williams

Positron emission mammography: initial clinical results.

Background: Evaluation of high-risk mammograms represents an enormous clinical challenge. Functional breast imaging coupled with mammography (positron emission mammography [PEM]) could improve imaging of such lesions. A prospective study was performed using PEM in women scheduled for stereotactic breast biopsy.Methods: Patients were recruited from the surgical clinic. Patients were injected with 10 mCi of 2-[18F] fluorodeoxyglucose. One hour later, patients were positioned on the stereotactic biopsy table, imaged with a PEM scanner, and a stereotactic biopsy was performed. Imaging was reviewed and compared with pathologic results.Results: There were 18 lesions in 16 patients. PEM images were analyzed by drawing a region of interest at the biopsy site and comparing the count density in the region of interest with the background. A lesion-to-background ratio >2.5 appeared to be a robust indicator of malignancy and yielded a sensitivity of 86%, specificity of 91%, and overall diagnostic accuracy of 89%. No adverse events were associated with the PEM imaging.Conclusions: The data show that PEM is safe, feasible, and has an encouraging accuracy rate in this initial experience. Lesion-to-background ratios >2.5 were found to be a useful threshold value for identifying positive (malignant) results. This study supports the further development of PEM.

Quantitative Assessment of Diagnostic Radiation Doses in Adult Blunt Trauma Patients

STUDY OBJECTIVE Many emergency departments and trauma centers utilize extensive radiologic studies during the assessment of trauma patients. A point of concern arises about the possible biological effects of these cumulative radiation doses. The objective of this study is to determine the amount of ionizing radiation received by adult blunt trauma patients at a Level I trauma center during the first 24 hours of their care. METHODS This nonconcurrent case series reviewed the first 100 consecutive adult blunt trauma patients who presented to a Level I trauma center in 2006. All patients met hospital standards for the less acute major triage criteria. Individual radiation dose reports calculated by the computed tomography (CT) scanner were used to determine the radiation doses from each CT procedure. Standardized tables were used to determine radiation dose for plain radiographs. The median effective dose of radiation (millisieverts) was calculated for the first 24 hours of hospitalization. RESULTS A total of 100 eligible patients presented between January 1, 2006, and March 20, 2006. Eighty-six patients had complete radiologic records available. The median age was 32 years, with an intraquartile range of 23 to 46 years; the median Injury Severity Score was 14, with an intraquartile range of 9 to 29; and the median number of CT scans was 3, with an intraquartile range of 3 to 4. The median effective total dose of ionized radiation was 40.2 mSv, with an intraquartile range of 30.5 to 47.2 mSv. A dose of 40.2 mSv is the equivalent of approximately 1,005 chest radiographs. CONCLUSION Trauma patients meeting the less acute major triage criteria are exposed to clinically important radiation doses from diagnostic radiographic imaging during the first 24 hours of their care.

Xenon-133 inhalation method for regional cerebral blood flow measurements: normal values and test-retest results.

The purpose of this investigation is to determine the normalvalues for regional cerebral blood flow (rCBF) as determined by thexenon inhalation method of Obrist. Normal values for all rCBF parameters were measured in 15 healthy individuals. Our data are compared with the normal data obtained by other investigators. In addition, test-retest rCBF measurements were performed to determine the reproducibility of the method. Our results show that the method is highly reproducible when carried out in serial studies over a short period oftime.

Evaluation of the quantitative capability of a high-resolution positron emission tomography scanner for small animal imaging.

Objective: The quantitative capability of a positron emission tomog-raphy scanner for small animal imaging was evaluated in this study. Methods: The microPET P4 (Concorde Microsystems, Knoxville, TN) scanners capability for dynamic imaging and corrections for radioactive decay, dead time, and attenuation were evaluated. Rat brain and heart studies with and without attenuation correction were compared. A calibration approach to convert the data to nanocuries per milliliter was implemented. Calibration factors were determined using calibration phantoms of 2 sizes with and without attenuation correction. Quantitation was validated using the MiniPhantom (Data Spectrum, Chapel Hill, NC) with hot features (5:1 ratio) of different sizes (4, 6.4, 8, 13, and 16 mm). Results: The microPET P4 scanners ability to acquire dynamic studies and to correct for decay, dead time, and attenuation was demonstrated. The microPET P4 scanner provided accurate quantitation to within 6% for features larger than 10 mm. Sixty percent of object contrast was retained for features as small as 4 mm. Conclusions: The microPET P4 scanner can provide accurate quantitation.

The noninvasive measurement of regional cerebral circulation

Abstract A brief introduction to the history and development of the noninvasive regional cerebral blood flow technique is presented. The procedures and apparatus are described in a nontechnical manner to provide a resource background for the other papers in this issue.

Applications of a PET device with 1.5 mm FWHM intrinsic spatial resolution to breast cancer imaging

Operation of a high resolution compact clinical PET Scanner (PEM Flex/spl trade/) device as a breast scanner is described. The device features high spatial resolution (1.5 mm FWHM intrinsic resolution) as a result of small crystals and compact position-sensitive photomultipliers. The compactness of the system allows it to reside within a stereotactic X-ray mammography unit, or as a separate standalone system capable of breast compression. The gamma rays are detected for a volumetric reconstruction by two heads, each of which contains 2,028 2 mm by 2 mm by 10 mm lutetium-containing crystals. The heads travel within X-ray transparent compression paddles. A window is provided in one of the paddles for direct correlation with ultrasound transducers and for interventional access. To enable real-time interventions, images are reconstructed and displayed while the detectors are still acquiring data. The maximum-likelihood reconstruction provides quantitative images with threefold improved contrast as compared to simple back-projections.

Hydrogen‐deuterium isotope effect in the decay of radical pairs in x‐ray irradiated hydroxyurea

The rate constants for the transformation of radical pairs to single radicals in x‐ray irradiated hydroxyurea have been determined from the decay of ESR spectra at temperatures from 253–268°K. The ratio of decay rates for a protonated to a deuterated sample changes from approximately 13 in the initial stage to 5 in the later stage. The decay curves are explained by assuming that the decay is associated with a diffusion of H (D) vacancies from one radical of a pair to a neighboring molecule, dissociating the radical pair. The decay rates in the initial stage of decay for a protonated sample, k11(H), and for a deuterated sample, k11(D), may be presented as k11(H) = 1 × 107 exp[(−0.50 eV)/k T], k11(D) = 6 × 1011 exp[(−0.82 eV)/k T].

A Simple Computer‐Spectrophotometer Interface

A modification is described which enables one to interface a Cary 14 spectrophotometer or similar instrument to a computer.

Investigation of the quantitative capabilities of a positron emission mammography system

A method for performing a quantitative calibration on a PEM system has been found. Following dead-time characterization and correction, the quantitative calibration factor was measured as a function of object thickness. The calibration allows generation of quantitative PEM imagesets over the clinical range of activity concentration. Methods: Three (8.5/spl times/9.0/spl times/3.5) cm tissue culture flasks were filled from a common source with F-I8 FDG. A series often 10-minute scans, using 1-3 flasks, was acquired over an 8-hour span. A system dead-time model was derived from the three lowest activity scans for each flask configuration. ROI analysis was performed on images reconstructed with BP and ML-EM to determine uniformity and the quantitative calibration factors. No corrections for attenuation or scatter were applied. Results: The model for dead-time was found for each flask configuration and parameterized by a linear fit of the model parameters, allowing generation of dead-time correction based on object thickness and true plus scatter coincidence count rate. A second-order polynomial fit to the ROI analysis results allowed characterization of the quantitative calibration factors as a function of object thickness. Conclusions: A dead-time model and quantitative calibration method has been found for the PEM system used in this study. Quantitative calibration factors have been derived from parameters available as part of standard data acquisition.

Implementing PET-guided biopsy: integrating functional imaging data with digital x-ray mammography cameras

Purpose: Phantom trials using the PET data for localization of hot spots have demonstrated positional accuracies in the millimeter range. We wanted to perform biopsy based on information from both anatomic and functional imaging modalities, however we had a communication challenge. Despite the digital nature of DSM stereotactic X-ray mammography devices, and the large number of such devices in Radiology Departments (approximately 1600 in the US alone), we are not aware of any methods of connecting stereo units to other computers in the Radiology department. Methods: We implemented a local network between an external IBM PC (running Linux) and the Lorad Stereotactic Digital Spot Mammography PC (running DOS). The application used IP protocol on the parallel port, and could be run in the background on the LORAD PC without disrupting important clinical activities such as image acquisition or archiving. With this software application, users of the external PC could pull x-ray images on demand form the Load DSM computer. Results: X-ray images took about a minute to ship to the external PC for analysis or forwarding to other computers on the Universitys network. Using image fusion techniques we were able to designate locations of functional imaging features as the additional targets on the anatomic x-rays. These pseudo-features could then potentially be used to guide biopsy using the stereotactic gun stage on the Lorad camera. New Work to be Presented: A method of transferring and processing stereotactic x-ray mammography images to a functional PET workstation for implementing image-guided biopsy.