Biomedical subjects

L P Clarke

Publications and source records attributed to L P Clarke.

8 recordsLinked to original sources

PubMed1992

Composite and classified color display in MR imaging of the female pelvis.

Because of its superior soft-tissue-imaging capabilities, MRI has proved to be an excellent modality for visualizing the contents of the female pelvis. In an effort to potentially improve gynecological MRI studies, we have applied color composite techniques to sets of spin-echo and gradient-echo gray-tone MR images obtained from various individuals. For composite generation, based on tissue region of interest calculated mean pixel intensity values, various colors were applied to spatially aligned images using a DEC MicroVAX II computer with interactive digital language (IDL) so that tissue contrast patterns could be optimized in the final image. The IDL procedures, which are similar to those used in NASA's LANDSAT image processing system, allowed the generation of single composite images displaying the combined information present in a series of spatially aligned images acquired using different pulse sequences. With our composite generation techniques, it was possible to generate seminatural-appearing color images of the female pelvis that possessed enhanced conspicuity of specific tissues and fluids. For comparison with color composites, classified images were also generated based on computer recognition and statistical separation of distinct tissue intensity patterns in an image set using the maximum likelihood processing algorithm.

Color↗

PubMed1992

Bremsstrahlung imaging using the gamma camera: factors affecting attenuation.

Quantitative imaging of bremsstrahlung from pure beta emitters is proposed as a means for in vivo management of antibody therapy. The method involves the use of high-energy collimation, an empirically selected broad photon energy window to enhance detector sensitivity, and a Wiener restoration filter to compensate for system blur. The measured and filtered data were obtained for an idealized scattering medium and isolated spherical sources. An effective linear attenuation coefficient of about 0.13 cm-1 was determined from the raw image data of 32P. A coefficient of 0.14 cm-1 was determined after the images were restored using the Wiener filter. The measured attenuation was not significantly dependent on the size of the region of interest or the size of the source. Its variation was within the experimental error of measurement (+/- 5%). The measured sensitivity (6 x 10(-6) cps/Bq) was sufficient for imaging therapy doses of 32P or 90Y.

Filtration↗

PubMed1991

Uterine junctional zone: correlation between histologic findings and MR imaging.

Uterine zonal anatomy as visualized on T2-weighted (repetition time, 2,500 msec; echo time, 80 msec) magnetic resonance (MR) images consists of a high-intensity central (endometrial) zone, a subjacent low-intensity junctional zone of myometrium, a moderately intense zone of myometrium, and a thin, low-intensity subserosal zone of myometrium. To better define the histologic correlates of these diagnostically significant zones, T2-weighted MR images of 17 in vivo and 13 extirpated human uteri were compared with histologic sections of 17 uteri stained with hematoxylin-eosin, Mallory trichrome, and immunofluorescence staining for actin. Morphometric and electron microscopic observations of uterine surgical specimens were also made. The observations indicate that both the junctional zone and the subserosal zone consist of compact smooth muscle fibers with little extracellular matrix compared with the myometrium proper. Also, the junctional zone is divided into a compact region and a transitional region. The compact region correlates well with the hypointense MR appearance of the junctional zone.

Adult↗

PubMed1978

An improved uptake probe designed for a large crystal rectilinear scanner.

Stationary probes are frequently used to estimate the uptake of radionuclides in particular organs such as the liver, spleen, heart or thyroid. Conventional probes have both a non-uniform response volume along the detector axis and a large diverging field of view. Therefore the sensitivity of these probes is strongly dependent on organ depth and the extent of the activity in the surrounding tissues. This paper describes a focused probe which can be used to give an improved response relative to organ depth and reduces the effect of the surrounding activity. Phantom measurements suggest that under suitable circumstances the probe could be used to measure absolute organ activity.

Radiometry↗

PubMed1977

Imaging of spontaneous canine tumours with ammonia and L-glutamine labeled with N-13.

Ammonia and 6-glutamine, labeled with N-13, were tested as imaging agents for a variety of spontaneous canine tumors. The imaging capabilities of these compounds were compared with each other, with other scanning agents, and with radiologic and pathologic procedures. Good agreement between positive gamma images and postmortem findings occurred in 11 of 15 cases with [13N] ammonia as the localizing agent. Eight of the nine scans using [13N] glutamine as the imaging agent showed positive correlation with postmortem findings. In cases where both ammonia and glutamine were used to image the same lesion, no qualitative differences in tumor uptake were found between the two.

Ammonia↗

PubMed1976

Imaging of tumors involving bone with 13N-glutamic acid.

Nitrogen-13 labeled L-glutamic acid was evaluated as an imaging agent for tumors involving bone. The enzymatically prepared labeled compound was administered intravenously to dogs with spontaneous tumors, and tumor uptake was determined with a gamma camera and rectilinear scanner. These tumors were well visualized with 13N-glutamic acid, and the results compared favorably with uptake studies performed on the same animals with 99mTc-diphosphonate.

Animals↗

PubMedDate not supplied

Image segmentation in digital mammography: comparison of local thresholding and region growing algorithms.

Local thresholding and region-growing algorithms are developed and applied to digitized mammograms to quantify the parenchymal densities. The algorithms are first evaluated and optimized on phantom images reflecting varying image contrast, X-ray exposure conditions, and time-related changes. The difference between the segmentation results of the two techniques is less than 6% on the phantom images and 11% on the mammograms. The agreement between the computerized procedures and a manual one is in the range of 74-98%, depending on the breast parenchymal pattern and segmentation algorithm. The results show that computerized parenchymal classification of digitized mammograms is possible and independent of exposure.

Algorithms↗

PubMedDate not supplied

Calibration methods for measuring splenic sequestration by external scanning.

Conventional methods for measuring splenic sequestration of labeled cells rely on stationary probe counting over the liver and spleen. A quantitative spleen-scanning method is proposed as a means of performing a more accurate diagnosis of the degree of splenic sequestration. Improved methods for calibrating a rectilinear scanner employing "constant resolutions" collimators, designed for the in vivo measurement, are reported, Clinical evaluation of this method was performed by scanning several patients scheduled for splenectomy. Good correlation between in vivo and in vitro measurements of splenic radioactivity for 29 patients was obtained. A least-squares fit to the data yielded a coefficient of determination r2=0.93.

Chromium Radioisotopes↗