A new method of obtaining an x-ray tomographic image of a slice is proposed. An x-ray fan beam and detector array are moved in a line across the patient, allowing single scans that are not necessarily transaxial. Projection data is formatted and scaled by micro-processor, and an encoding process is utilized in forming an intermediate record film. This record has a format which somewhat resembles that of synthetic aperture radar, but the coherent light reconstruction of the final image is more complex. All the fundamental limitations of CAT are inherent to the process, except for the slice orientation flexibility. A number of additional limitations are present, some of which are technological. Besides the slice orientation flexibility, there is the potential of achieving better resolution of high contrast objects than current CAT scanners at a much lower total dose than for conventional tomography under comparable contrast conditions.

Three-dimensional reconstruction images of anatomic structure are obtained by compu-terized x-ray tomographic scanning of a three-dimensional volume containing the organ of interest. The three-dimensional image data are displayed using numerical projection (reprojection) images. Reprojection images of reconstructed volumes are generated numerically by summing the reconstructed volume element (voxel) x-ray density values along selected parallel paths through the reconstruction. In this manner, two-dimensional reprojection images of a three-dimensional reconstruction at any desired angle of view are generated. Obscuring superposed structures can be selectively removed from the reconstruction prior to reprojection to enhance the visibility of structures of interest. Noninvasive numerical dissection is the term applied to the process whereby the voxels representing obscuring structure are ignored in the parallel path summation process such that only the desired portions of a reconstruction are reprojected at selected viewing angles. The term noninvasive numerical tissue dissolution is applied to the process whereby structures are selectively "dimmed" but not removed from the reconstruction before reprojection, achieving a "see through" or "ghosting" effect. Under these conditions, specific anatomic structures can be observed while looking "through" superposed structures which serve as references for anatomic relationships.

Preliminary results have been obtained with a non-linear filter system for projection data in computed tomography imaging. The non-linear filter system consists of a sequence of three filters: a non-linear median smoother, a linear smoother and a non-linear correction filter. The non-linear correction filter is a modified Kalman filter. Both patient data and simulated phantom data have been used in evaluating and designing the non-linear filter system. There are six parameters to be adjusted to the type of projection data considered. Additional work is required to optimize the filter system. Our preliminary results show a significant improvement in image resolution for a noise reduction comparable to what is obtained with conventional linear filtering techniques. However, this is at the cost of enhancing the streak artifacts.

The reduction of spectral artifacts in computerized tomography by X-ray tube filtration is studied. Due to quantum limited nature of the imaging system a reduction in exposure with filtration is followed by an increase of noise in the images. A combination of x-ray filtration and water table monochromatization is shown to work extremely well. A figure of merit which reflects the complex interplay of exposure, noise, contrast and spectral artifacts, is defined. The figure of merit is used in the determination of best filters to optimize some of the image quality parameters of the polychromatic CT images.

Present medical ultrasound systems are based on energy detection methods and therefore only utilize echo intensity information. Phase information is recorded by the transducer, which is a pressure sensitive device, but is not utilized in present display or measurement schemes. This investigator has developed one approach for utilizing both the phase and amplitude information available in an ultrasound waveform. The approach is based on a time-domain characterization of system dynamics in terms of an impulse response function and has been termed impediography. This paper describes preliminary in vivo results obtained with an impediographic measurement system applied to the human eye. A conventional ophthalmic B-scan unit was modified so that any single A-scan line of interest could be digitized by a fast A/D converter. The resulting signals were recorded on magnetic media and subjected to impediographic processing using an off-line computer. Although the study was limited to several types of intraocular and orbital lesions, unique and distinctive ultrasonic signatures (in terms of impedograms) could be associated with each lesion type. The study suggests that impediography can be applied to other body regions and that the method can differentiate between a wide range of pathologies.

The right angle geometry between the sound field and the interrogating light wedge suggests that Bragg imaging should be well suited for the study of reflected images. In an effort to improve the intensity and clarity of the reflected images a pulsed dye laser has been developed and tested. Image photographs of various test objects and some anatomical structures were taken and comparisons to earlier transmission mode images were made. Results suggest the possibility that the technique of reflection Bragg imaging can be developed into a viable clinical tool. Efforts have also been directed to improve the optical design for Bragg imaging systems. Those systems previously described in the literature incorporate several optical components which must have dimensions comparable to the desired image size, and, for optimal imaging, these components should also have low f-numbers and be diffraction limited. Alternate lens systems have been studied and designs realized which incorporate large and small cylindrical triplet lenses and prisms. Design specifications for two such systems will be presented.

The complete characterization of tissue is extremely important for objectively identifying abnormalities and disease states. Optical methods of microscopy have been exploited to a great degree and now the electron microscope is being used in search of diagnostic clues at higher magnification levels. It is well appreciated, however, that these methods provide only limited access to the physical properties of tissue. Furthermore, the physical nature of an abnormality may prohibit its ever being revealed with visual observation techniques. Acoustic microscopy, on the other hand, can reveal new information, the structural elastic characteristics of viable tissue. Acoustic microscopy can also provide quantitative data on these tissue characteristics. As this additional information should have great diagnostic value, a general discussion of the methods and procedures employed is presented.

"Dynamic" imaging of superficial body organs has increased the diagnostic capabilities of ultrasound. A linear array clinical system has been developed to provide dynamic, high-resolution examinations. This system provides a simultaneous wide-range gray scale B-mode image and calibrated A-mode image on the same display. Use of a TV monitor allows full gray scale representation of the 45 dB echo amplitude range after appropriate logarithmic amplification. The A-mode is presented immediately below the B-mode display and represents the echo amplitude information along the central axis. The ultrasonic probe in the instrument contains a linear array of 35 elements which makes direct contact with the skin. Electronic scanning is performed by custom-made multi-plexers in the probe at a 60 frame per second rate. Push-buttons in the hand-held probe allow for remote frame-freezing, photographic documentation or control of a videotape recorder. The 32 scan lines of the individual transducer elements are expanded to 256 lines on the video display using electronic interpolation to provide a smooth, full B-mode image without streaking, and television crispening techniques used on the ultrasonic signals sharpen the image. A microprocessor in the system aids in controlling system function and simplifies the operational controls adjusted by the physician.

Production of a diagnostic quality fluoroscopic image is predicated on the delivery of a controlled amount of x-radiation to the input phosphor of an image amplifier. Variations in patient thickness and limitations on table top dose rate make it difficult to define simple operating protocols. The work reported on here attempts to resolve this problem by presenting experimental data showing the variation of table top dose with kVp and mA for various water phantom thicknesses required to yield acceptable radiation levels at the intensifier input phosphor. Possible algorithms for resolving the conflict between dose rate and image quality are developed and discussed. The possibility of minimizing patient dose rate for a predescribed spacial resolution is suggested as a fruitful avenue for new work.

A number of methods for visualizing the cardiovascular system of dogs and humans in real time have been developed and are grouped under the heading computerized fluoroscopy. Such techniques provide images capable of high contrast sensitivity and moderate spatial resolution (~ 1 mm). A standard image intensifier - television chain used in connection with a Lpecially constructed digital video image processor (V.I.P.) is capable of producing contrast enhanced difference images at rates up to 60/second. Such difference images can isolate small concentrations of iodine which have been administered intravenously through peripheral veins. Such non-invasive techniques have been used to visualize: 1) The carotid arteries and fine structures in dogs and humans at typical rates of 2 per second, and 2) the heart chambers of both dogs and humans at typical display rates of 15-60 per second. For such studies 0.6-1.0 gms (Iodine)/kg (body mass) have provided excellent visualization of the cardiac chamber dynamics.

Heavy ion radiography is a new experimental form of medical imaging. The Lawrence Berkeley Radiation Laboratory is the only facility in the world with enough flux of heavy ions to satisfactorily visualize objects. A. model is described showing the superiority of heavy ion radiography, in regard to density resolution, compared to diagnostic x-ray energies and computerized tomography. Examples are shown. Tissue specimens are used for heavy ion radiography and the superior density resolution is demonstrated. Heavy ions are also being used for radiation therapy and early work on reconstruction is currently being done.

The making and interpretation of radiographs for 100,000 patients was studied so that time parameters could be established that might be of help to x-ray equipment designers. In producing films, it is found that the average patient stays thirty to fifty minutes in an x-ray department for 3.4 exposures. For a single exposure there are twelve steps in the production cycle taking 14.1 minutes. Some speculative tables were drawn suggesting automated equipment and computer-aided devices that might cut production time from twenty to sixty percent. Interpretation of the radiographs by the radiologist indicates that each case takes an average of five minutes. These gross case averages are deceptive. Stop-clock monitoring of all a radiologist's activities indicates that only forty-five percent of his time on the job is truly spent film reading. The remainder is given to consultation with the referring physicians, fluoroscopy, and managing the x-ray department. From this it was inferred that the average x-ray case was processed by the radiologist in two to two-and-one-half minutes, thus establishing a time frame in which any image-assisting device or computer aid must work.

Physical measurements have been made to determine image quality performance of an x-ray unit designed for conventional nonmagnification and magnation mammography using screen-film and xeroradiographic image recording systems. The unit has 2 focal spots: one for nonmagnification mammography and a microfocus spot for the magnification technique. The measurements include the geometric resolution at the extremes of focal spot-to-object distances of the breast for 1.5x magnification and for the nonmagnification technique. Unsharpness due to the image receptor and due to motion will be discussed relative to the geometric resolution. Half value layer and radiation dose measurements using both the nonmagnification and magnification techniques are presented for various kVp and filtration combinations. The effect of reciprocity law failure when screen-film systems are used for the magnification technique is also described. The tradeoff between radiation output and adequate "beam hardening" to maintain low patient exposure, an especially important consideration for this unit, is discussed. Conventional nonmagnification and magnification xeroradiegraphs are shown.

The paper is a two part discussion of: (1) indices which characterize focal spot (F.S.) performance, and (2) the usefulness of these indices for a future F.S. standard. - (1) The two primary parameters of an x-ray source are source geometry (intensity distribution) and maximum source strength (loadability). Source geometry is often summarized by a number called "size", and loadability by a kw-number. We define as an overall F.S. Performance Factor p the ratio of two "size" indices: (a) a "loadability size" we and (b) a "Resolv-ing (imaging performance) size" B (e.g. "RMS equivalent focal spot"). Both describe the given F.S. in terms of a uniform square F.S.; for (a) having same loadability, for (b) having same systems related imaging performance, as the given F.S. - (2) The present F.S. standard specifies two size parameters: geometrical F.S. extent F, and "effective" F.S. size Feq derived from resolution patterns. Both parameters are in general not a measure of either loadability (we) or imaging performance (B). It is suggested to base a future standard on a rigorous criterion. Since rigorous data are difficult to obtain at present, approximate methods for compliance verification must be allowed; e.g. by utilizing the classical methods of resolution, pinhole and slit camera in a meaningful way.

A scanning and imaging system utilizing 10 GHZ microwave beams for the detection of soft tissue tumors is proposed. Detection of such tumors is based on the fact that the micro-wave attenuation coefficient in muscle tissue is a factor of 10 greater than in fat. Thus a tomographic image computed from the transmission of a beam of microwaves scanned in a planar CT type raster through a body section should very easily identify areas of fatty tissue and muscle tissue on the order of 0.5 cm or possibly smaller. Since ionizing radiation is not used, this non-carcinogenic microwave technique is of particular interest for surveying and detecting tumors of the breast which are primarily muscle-like tissue in a fatty parenchema. The greatest risk results from the production of heat in the scanned tissue by the microwave beam, but it is shown to be negligible for the proposed scanner. An overall scanner design is discussed.

Abnormal laryngeal function during speech produced by many profoundly deaf students attending the National Technical Institute for the Deaf is indicated by acoustical and perceptual measures. To assist in objectifying the diagnosis and treatment of these vocal disorders, a physiological assessment of laryngeal activity is warranted. High speed laryngeal photography was selected as a principle tool for this assessment because of the very rapid vibratory period of the vocal cords. To illuminate the larynx for film speeds of up to 6,000 frames per second, a xenon arc light source is coupled with an optical system to project a high intensity light beam on the vocal folds. The projected beam is filtered to reduce infra-red and ultra-violet radiation. Light is projected paraxial to the camera lens to intersect on a laryngeal mirror positioned in the oropharynx of the subject. Methods of synchronizing the high speed film with additional acoustic and physiologic measures will be discussed.

Current emission computed tomographic (ECT) scanners suffer from the inability to perform dynamic studies. The investigation presented here was initiated with a specific goal in mind, that is, to design a system to image a radionuclide distribution in cross-section in a stationary arrangement capable of dynamic data acquisition. Two systems are proposed. Both systems utilize a two-dimensional cross-section type of geometry. The first consists of multiple pinhole apertures each with its own separate one-dimensional detector. The second system employs coded-aperture techniques and is a result of allowing the projections from each pinhole aperture to overlap. The initial reconstructed image with both systems is degraded by a high level of correlated background noise. This background is significantly reduced by an iterative subtraction technique which is described. Computer simulations are presented to illustrate the technique.

The performance of the gamma camera, conceived by Anger 20 years ago, has been improved continually. Recent advances in clinical imaging are mainly the result of improvements in the intrinsic resolution of gamma cameras. By collecting a larger fraction of the available scintillation light with photomultiplier tubes of advanced design, the spatial resolution of the camera is greatly improved. Low-energy, parallel-hole collimators with thinner septa and increased sensitivity are now being introduced. With a multiple pinhole collimator, the heart can be imaged simultaneously from seven directions. Spatial distortions have been minimized, but regular tuning of modern gamma cameras remains critical for maintaining good field uniformity. Finally, the newer gamma cameras show a much improved temporal resolution, allowing the collection of counts at high rates with a minimum of counting losses. Data are presented illustrating the importance of the various gamma-camera performance parameters.

Most Anger scintillation cameras are now fitted with mircoprocessors for live correction of field non-uniformities. The purpose of this work was to evaluate the corrected flood field uniformity under conditions simulating clinical usage. Uniformity was eval-uated by computing the location and percentage of cells in a 64 x 64 matrix that were within + 5% of the mean cell count. When reference floods were stored at high data input rates, corrected floods measured at low rates showed a 10% decrease in the number of cells within + 5%. From 3 to 17% more time was required to generate corrected images. The addition of as much as 10.2 cm of scatter medium during the correction process caused the number of cells to decrease by 1.5%. Change of collimator type after storage of the reference flood caused as much as a 10% decrease in the number of cells falling within +5%. Changes in analyzer window size and location also produced significant decreases in the number of cells falling within the prescribed limits.

Wall motion studies of the left ventricle are made with commercially supplied hardware and software. The patient is imaged with the scintillation camera 10 minutes after the in-jection of 20 mCi labeled red cells. The camera images are digitized and stored in com-puter memory. The computer divides the cardiac cycle into 28 segments and stores a separate image sequentially for each segment. In order to provide images of adequate statistical quality several hundred cycles are acquired and summed by the computer, each sequence of 28 images being triggered by a signal from the R wave. Three or more projections of the heart are acquired in order to demonstrate various portions of the wall tangentially. A number of case studies are displayed in real time cine on a monitor from a video recorder to demonstrate normal wall motion and various degrees of motion impairment.