Emission-computed tomography and its application to imaging of acute myocardial infarction in intact dogs using Tc-99m pyrophosphate.

The techniques of emission-computed tomography have been used to obtain in vivo quantitative estimates of the three-dimensional distribution of gamma-emitting radionuclides in dog hearts. Conjugate views, obtained for 60 equiangular projections around 360 degrees by rotating the object in front of a gamma camera, were used to reconstruct multiple-level emission transaxial images for various test objects, and for dogs with surgically induced acute myocardial infarcts. Corrections for attenuation were performed in the backprojection step of the convolution algorithm used for reconstruction. Quantitative estimates of the spatial extent and concentration of activity were obtained to within 10--15% rms error. Correlations were obtained between the radionuclide and histopathologic estimates of the extent and location of infarction.

Evaluation of ischemic heart disease with a prototype volume imaging computed tomographic (CT) scanner: preliminary experiments.

A prototype synchronous volumetric computed tomographic X-ray scanner was used to demonstrate, in individual experiments, the possibility of estimating percent coronary arterial stenosis, regional myocardial blood supply and regional myocardial wall dynamics. Scans were obtained during angiography in intact anesthetized dogs or in an isolated metabolically supported working left ventricular preparation. Percent arterial stenosis was quantitated using the percent change in brightness area product of successive cross-sectional images of contrast agent-filled Tygon tubing sutured to the epicardium. Myocardial blood supply was evaluated by the transmural and circumferential extent and th time rate of change of myocardial opacification during coronary angiography. The regional time rate of change of left ventricular wall thickening during the systolic phase of the cardiac cycle was demonstrated in the isolated ventricle preparation. The recently installed Dynamic Spatial Reconstructor high speed volumetric scanning system will be used to make these measurements from scan data obtained during a single angiogram in man.

The effects of motion on quantitative vessel measurements.

Optimal visualization of moving structures such as the heart and coronary arteries using digital radiographic imaging systems is a difficult problem that can involve tradeoffs between temporal, spatial, and density resolution. The motion dependence of four angiographic measures of vessel dimensions is given and demonstrated experimentally. Although the densitometric cross-sectional area is shown to be independent of motion, densitometric thickness (contrast) decreases and the apparent width (distance between edges) and densitometric width both increase with motion. Knowledge of the velocity allows the apparent width but not the densitometric width to be corrected. It is also shown that current limitations which result in tradeoffs between kVp and x-ray pulse duration seriously compromise the advantages of using small focal spots in coronary artery imaging.

Computed transaxial imaging using single gamma emitters.

Emission computed tomography (ECT) studies were performed on test objects and dogs. Conjugate views were obtained for 60 to 120 projections equispaced around 360 degrees by rotation of the subjects in front of a gamma camera. A convolution reconstruction algorithm in which gamma ray attenuation corrections are included in the backprojection step were used to reconstruct the emission images. Reconstructions of x-ray transmission data provided data for gamma ray attenuation corrections of the emission images of 99mTc-pyrophosphate uptake in dogs. Reconstructed images of test objects show spatial resolution uniformity, and attenuation corrections enable estimation of relative activity densities to within 10--15% rms errors, thus demonstrating quantitative imaging capabilities of emission CT.

Left ventricular border recognition using a dynamic search algorithm.

Initial results obtained with a simple, fully automated algorithm for detection of left ventricular boundaries are presented. The strength of this approach is the use of dynamic programming search techniques, which allow determination of local border points to be influenced by the entire global border location. The relative contributions of mask mode subtraction and the dynamic search technique are evaluated with respect to accurate border definition. These computer-determined ventricular borders are compared with hand-traced borders on subtracted and unsubtracted images. The modular dynamic search algorithm is shown to perform better than previously described algorithms, which generally require operator interaction. It is also shown that for both manual and automated techniques, ventricular borders derived from subtracted images may be significantly different from borders derived from nonsubtracted images.

A computerized data base system for medical diagnostic studies (Diastu).

A computerized database system (DIASTU) has been developed for the storage and selective retrieval of the results of medical diagnostic studies. The system is being used to analyze the disease process and the efficacy and yield of selected diagnostic studies. The system runs on a DEC PDP-11/60 computer. It consists of three FORTRAN IV programs linked to a general-purpose assembly language database handler. One program, DSENT, interactively modifies the information in the database. The second, DSLIST, prints all or portions of the database. The third program, DSTAT, interactively assembles the parameters for selective searches of the database and executes them. A query language is used that allows the use of time and size specifications and Boolean operators in nested loops.

Cryptophyte algae are robbed of their organelles by the marine ciliate Mesodinium rubrum.

Mesodinium rubrum (Lohmann 1908) Jankowski 1976 (= Myrionecta rubra) is a common photosynthetic marine planktonic ciliate which can form coastal red-tides. It may represent a 'species complex' and since Darwin's voyage on the Beagle, it has been of great cytological, physiological and evolutionary interest. It is considered to be functionally a phytoplankter because it was thought to have lost the capacity to feed and possesses a highly modified algal endosymbiont. Whether M. rubrum is the result of a permanent endosymbiosis or a transient association between a ciliate and an alga is controversial. We conducted 'feeding' experiments to determine how exposure to a cryptophyte alga affects M. rubrum. Here we show that although M. rubrum lacks a cytostome (oral cavity), it ingests cryptophytes and steals their organelles, and may not maintain a permanent endosymbiont. M. rubrum does not fall into recognized cellular or functional categories, but may be a chimaera partially supported by organelle robbery.

US extended-field-of-view imaging technology.

PURPOSE: To develop an ultrasound (US) extended-field-of-view scanning technique that combines the convenience of a real-time scanner with the spatial advantages of a static B-mode scanner and provides a panoramic image in real time without position sensors or cumbersome articulated arms. MATERIALS AND METHODS: An image-registration-based position-sensing technique was used to track probe motion and reconstruct a large composite image during real-time scanning. The probe motion (translation and rotation) was estimated by combining multiple local motion vectors. This computationally intensive process required a special programmable image processor. RESULTS: Large, resolution-preserved composite images up to 60 cm long were obtained. Measurement accuracy as determined with phantom experiments was better than 5%. The method could be applied to any probe or image format. CONCLUSION: In addition to providing a panoramic image to expand diagnostic capabilities, extended-field-of-view US provides a more easily interpretable image and is an effective cross-specialty communication tool.

Antireflection coatings for germanium IR optics: a comparison of numerical design methods.

Refinement and thin film synthesis methods were used by members of six different institutions to design antireflection coatings for germanium substrates. The solutions are based on the use of zinc sulfide and germanium layers only. Several systems were found with an average reflectance that is less than 1% in the 7.7 to 12.3 microm spectral region.