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Biomedical subjects

K R Hoffmann

Publications and source records attributed to K R Hoffmann.

27 records · Page 2Linked to original sources
PubMed1993

An "intelligent" workstation for computer-aided diagnosis.

Computer-aided diagnosis (CAD) involves a computerized analysis of radiographs that is used as a "second opinion" by the radiologist. The approach presented incorporates computer vision and artificial intelligence techniques and includes schemes for the analysis of lung nodules, interstitial infiltrates, and cardiomegaly seen on chest radiographs; masses and clustered microcalcifications on mammograms; and stenoses and blood flow on angiograms. The demonstration of various CAD schemes in chest radiography and mammography on a six-monitor workstation simulates one possible clinical implementation of CAD in radiology. Whether soft- or hard-copy display media are used, the radiologist can refer to the CAD results and still use the original radiograph for the final diagnosis. Although initial impressions of this simulated "intelligent" workstation are encouraging, CAD is still in a preliminary stage of development. Various methods for effectively and efficiently integrating CAD into a clinical radiology department are being investigated.

Angiography↗
PubMed1992

Computer-aided diagnosis: development of automated schemes for quantitative analysis of radiographic images.

Preliminary results obtained with computer-aided diagnosis (CAD) from various radiographic examinations are very encouraging. However, CAD is still at an early stage of its development. It will be necessary to increase further the understanding of image features of normal and abnormal patterns, to establish databases, and to devise specific approaches for particular types of pathology. Although the existing schemes are designed to be applied to digital radiographs, similar techniques can be applied in the future to cross-sectional images such as CT, MRI, and ultrasound. We believe that CAD will become clinically practical in the near future.

Angiography↗
PubMed1991

Determination of instantaneous and average blood flow rates from digital angiograms of vessel phantoms using distance-density curves.

We have developed a new method for quantitation of blood flow rates based on determination of the spatial shift of the distribution of contrast material in opacified vessels in digital angiograms that are acquired while the contrast material proceeds through the vessel. The distance that the contrast material travels during the time between image acquisitions is determined by comparison of density-vs.-distance curves, which represent the distribution of contrast material along the length of the vessel in the respective images. The flow rate between image acquisitions is calculated by multiplication of the distance traveled by the frame rate and the vessel cross-sectional area. Therefore, for high-frame-rate acquisitions, "instantaneous" flow rates can be determined. In these vessel-phantom studies, the root-mean-square (RMS) difference between instantaneous flow rates measured with our technique and those measured with an electromagnetic method was 2.9 ml/sec; the RMS difference for average flow rates was 0.8 ml/sec.

Absorptiometry, Photon↗
PubMed1990

Automated tracking and computer reproduction of vessels in DSA images.

We are developing an automated vessel-tracking method based on the double-square-box region-of-search technique, for efficient tracking of the connected vascular tree in a digital subtraction angiography (DSA) image. Tracking points and branch vessels are located by searching of the perimeter of boxes, which are centered on previously determined tracking points. The most accurate results (90% true-positive rate with six false-positives per image) are obtained by tracking using the double-square-box method. In relatively straight regions of vessels, a large box is employed for efficient tracking; in curved regions of vessels, a small box is employed to ensure accurate tracking. When tracking is completed, accurate vessel information, ie, the vessel position, size, and contrast determined at each tracking point, is available for further quantitative analysis. Computer reproductions of tracked vessel trees appear to correspond well to those in DSA images.

Angiography, Digital Subtraction↗
PubMed1987

Basic imaging properties of a large image intensifier-TV digital chest radiographic system.

The basic imaging properties of a large (57 cm) image intensifier (I.I.)-TV digital imaging system were examined to determine the effects of various physical parameters on the quality of the digital chest images obtained, and also to explore the clinical usefulness of the system. The characteristic curve of the digital system, which relates the output pixel value to the input relative x-ray intensity, was measured with an aluminum stepwedge. MTFs were determined using slit images, and the veiling-glare fraction was measured with a lead-disk technique. Noise Wiener spectra were obtained from uniformly exposed images. The current limitations of the large II-TV digital chest system are its low spatial resolution, and the presence of large amounts of veiling glare and structure mottle. Advantages of this system over other digital chest imaging systems include the high speed of image data acquisition and the capability of "real-time" dynamic imaging of the chest at a radiation dose comparable to that in conventional radiography of the chest.

Humans↗
PubMedDate not supplied

Automatic bone segmentation technique for CT angiographic studies.

PURPOSE: The purpose of this work was to develop and evaluate an automatic bone segmentation technique for CT angiographic studies. METHOD: An automatic bone segmentation scheme was developed and applied to 40 CT examinations. The results of the segmentation were evaluated subjectively by two radiologists. RESULTS: The bone segmentation was, on average, rated between excellent and good. Automatic segmentation required approximately 25 s/case. CONCLUSION: With this high quality technique, bone can be segmented easily and accurately and subsequently can be removed from CT data sets for further 3D visualization and analysis of various organs.

Angiography↗
PubMedDate not supplied

Development of a high quality film duplication system using a laser digitizer: comparison with computed radiography.

A high quality film-duplication system was developed in order to improve the image quality of duplicated radiographs and to recover improperly exposed films. The system consists of a laser film digitizer, a laser film printer, a workstation, and a magneto-optical disk. Radiographs are digitized by the laser digitizer, processed by the computer for image enhancement, and then printed on a film by the laser printer. A nonlinear density-correction technique is employed in recovering improperly exposed radiographs using the H&D curve of the screen-film system. Using the new duplication system in our department, the average recovery rate was over 80% for chest and abdominal films rejected due to over- or underexposed. The basic imaging properties of the duplication system were compared with those of a Computed Radiography (CR) system and a conventional screen-film system. For low spatial frequencies, the MTF of the CR system is superior to that of the digital duplication system; however, for high spatial frequencies, the MTF of the duplication system is superior. The noise in the duplication system is about half of that in the CR system.

Biophysical Phenomena↗