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PubMed1990

Knowledge-based analysis and understanding of medical images.

Knowledge-based image analysis and interpretation of radiological images is of significant interest for several reasons including a means to identify and label each part of the image for further automated diagnostic analysis. Also, there is a need to develop a knowledge-based biomedical image analysis system which can analyze and interpret the anatomical images (such as those obtained from X-ray computed tomography (CT) scanning) in order to help analysis of functional images (such as those obtained from positron emission tomography (PET) scanning) of the organ of the same patient. This paper deals with the design and implementation of a knowledge-based system to analyze and interpret CT anatomical images of the human chest. In the approach presented here, the emphasis has been on the development of a strong low-level analysis system with the capability of analyzing in both bottom-up and top-down modes; and on the use of hierarchical relational, spatial, and structural knowledge of human anatomy in the process of high-level analysis and recognition.

Artificial Intelligence↗
PubMed1992

An introduction to model-based imaging.

The purpose of this paper is to clarify the distinction between the recognition of form, i.e. pattern recognition, and the interpretation of visual scenes, i.e. image understanding. Pattern recognition is part of image understanding, but the latter also includes cognitive tasks such as learning and inference. The key to developing image-understanding systems is to concentrate on the representation and use of models. This paper is a brief outline of the components of a model-based image-understanding system. First, the notions of iconic, categorical and symbolic knowledge are described. Although they appear to be disparate, the common notion is that the image understanding is based on recognizing concepts and not recognizing form. Next, the notion of a concept is defined, followed by representation techniques and control strategies for using concepts. Last, an example is given of an image-understanding system that learns to recognize concepts such as radiographic projections of teeth in panoramic radiographs.

Expert Systems↗
PubMedDate not supplied

Combining evidence from multiple imaging modalities: a feature-analysis method.

This study was designed to develop methods to improve radiologists' ability to detect and diagnose breast cancer. We evaluated the ability of a feature-analysis method to help radiologists merge judgements constructively from two rather disparate breast imaging tests. To accomplish these goals, we developed a list of perceptual features and quantitated the importance of each in the diagnosis of patients having both diaphanography (Test 1) and mammography (Test 2). Then, two decision aids were developed: One was a checklist of the critical diagnostic visual features from both tests that also assisted readers in rating these features numerically. The second was a computer-based classifier that assisted readers in merging the assessments of the two tests into one overall diagnostic probability. The value of these aids was assessed by comparing radiologists' accuracy in reading a set of proven cases in their standard fashion with their accuracy when reading in an enhanced mode, utilizing the checklist and computer classifier. When Test 1 was read adjunctively with Test 2, use of the decision aids led to a significant improvement in accuracy (p = .013) over the unenhanced, combined readings. For Test 1 alone, the aids led to a significant improvement over its low level of unenhanced reading (p = .046). For Test 2 alone, the enhancements provided little gain in accuracy over an already high level of performance on the full case set (p = .081), although significant gains were realized on the most difficult ones. We conclude that methods to aid standardization and merging of feature-based judgements can improve radiologists performance on complex diagnostic tasks.

Breast Neoplasms↗
PubMed1992

Image preprocessing for a picture archiving and communication system.

OBJECTIVES AND RATIONALE: In a picture archiving and communication system (PACS), images are acquired from multiple modalities and displayed on an electronic workstation. Each modality has different image characteristics. This variability must be addressed before the image is displayed. METHODS: The authors developed methods to automatically process magnetic resonance (MR), computed tomographic (CT), and computed radiography (CR) images before display and subjectively evaluated their effectiveness. RESULTS: Unwanted background successfully was automatically removed from 89.5% of 615 CR images. Of 803 chest, abdomen, and hand images 93% were automatically rotated to the correct orientation. CONCLUSIONS: Automated preprocessing of PACS images can be performed successfully, improving speed and convenience for the radiologist interpreting images at an electronic workstation.

Image Processing, Computer-Assisted↗
PubMed1990

Feasibility of digital teleradiology for imaging evaluation of patients with acute right upper quadrant abdominal pain.

To assess the utility of a commercially available digital teleradiology system in evaluating patients with acute pain in the right upper quadrant, hard-copy images from 100 examinations (50 hepatobiliary scintigrams and 50 sonograms of the right upper quadrant) were digitized, transmitted via standard telephone lines, and viewed remotely on a video monitor. Video and hard-copy interpretations were then compared for degree of concordance. For the scintigraphic studies, hard-copy and video images were equal in demonstrating gallbladder and bile duct activity. Video images failed to depict the presence of bowel activity in one case. Gallstones were depicted equally well on hard-copy and video sonographic images. The video interpreters overestimated the presence of abnormal hepatic parenchyma and overlooked one case of right hydronephrosis. The video interpretations of the scintigrams and sonograms showed an overall error rate of 4%, comparable to the rate obtained when radiographs are interpreted remotely with digital teleradiology systems.

Abdominal Pain↗
PubMed1992

Bending and fracture of the femoral component in cemented total hip replacement.

A computer method was used to make 41 measurements on the geometry of insertion of the femoral component in 200 Charnley total hip replacements. Surgery had been performed at least 12 years before, giving results which were classified as: success (90); fracture (56); or loose (54), according to rigid selection criteria. Fracture was associated with heavier patients in which there was poor proximal fixation of the femoral component but adequate distal fixation. Stems with a medial disposition proximally were more common in the fracture group than in the successful or loose groups. Sequential measurements of bending and subsequent fracture were made on the follow-up radiographs of 24 of the 200 cases (6 fracture and 18 successful). These measurements allowed bending to be detected at an earlier stage than by simple inspection of the radiographs.

Aged↗
PubMed1991

Computed tomography of asbestos-related pulmonary parenchymal and pleural diseases.

Computed tomography has acquired an increasingly central role in the evaluation of asbestos-exposed individuals. The advantages of increased contrast resolution and axial image display have extended our ability to interrogate areas of the pulmonary parenchyma and pleura that are inadequately seen on chest radiographs. The additional information to be gained from CT evaluation must be balanced by the additional expense and time required, particularly in view of the large numbers of asbestos-exposed individuals who will undergo screening over the coming decades. Ideally, imaging strategies that include CT should emphasize those problematic situations in which additional information will serve a differential or diagnostic function, alter the management or habits of the individuals, modify the working environment, or improve our understanding of asbestos-induced diseases. The chest radiograph is the mainstay in the imaging evaluation of asbestos-exposed individuals, providing an inexpensive and rapid appraisal of the presence of both focal and diffuse abnormalities of the pleura and lung parenchyma. Conventional (whole-thorax) CT may be an important adjunct in the following situations: (1) to clarify the presence of pleural thickening, particularly in distinguishing pleural disease from normal extrapleural soft tissues; (2) to stage and determine tumor extent in malignant pleural mesothelioma; (3) to identify optimal sites for biopsy of suspicious pleural changes; and (4) to detect and characterize lung cancers or other focal masses that may be obscured by extensive pleural or parenchymal fibrosis. Limited HRCT studies are roughly competitive in time and cost with four-view radiographic examinations. There is growing evidence that HRCT can detect interstitial disease in advance of conventional clinical or radiographic studies. However, the application of limited HRCT for large-scale screening is controversial. This issue will be resolved as we gain greater understanding of the specificity of HRCT and establish guidelines for standardizing the technique and image interpretation. At present, limited HRCT scans can supplement the evaluation of subjects in whom there is equivocal parenchymal or pleural disease on radiographs or unexplained abnormalities on pulmonary function tests. In individuals with significant pleural disease, HRCT can effectively define the presence and extent of interstitial fibrosis. In individuals with combined cigarette smoking-asbestos exposure in whom symptoms or functional abnormalities are present, HRCT may play a central role in distinguishing emphysematous lung destruction from the peripheral interstitial changes of asbestosis.

Asbestosis↗
PubMed1991

Digital chest radiography.

It is apparent that digital radiography holds considerable promise. Although there are some immediate advantages to be gained from using digital technology at present, such as more consistent image quality in portable radiography, most of the benefits have not been fully realized. To do so requires a completely integrated digital radiology department using high-resolution video displays throughout the hospital connected to a large digital image archiving system. This concept, referred to as picture archiving and communication systems (PACS), represents the logical culmination of the extensive research that is continuing in this area. Because of the great expense involved, it is likely that the transition from conventional to digital radiography will be evolutionary in most medical centers, with establishment of local PACS networks initially, such as between the intensive care units and the radiology department. At a more basic level, limited digital radiography systems can function in isolation and address specific needs successfully. Although the science of computer-aided diagnosis is at an early stage, it seems likely that the sensitivity and specificity of these programs will continue to improve. Their eventual utility will depend on their accuracy and ease of use. The ultimate goal would be a relatively "transparent" multifaceted program that would screen all radiographs prior to interpretation to provide the radiologist or clinician with diagnostic suggestions and quantitative data. Given the present rate of progress in this area, such a concept is not unrealistic. However, even the most ardent enthusiasts do not envision totally independent computer-based interpretation of radiographic images for some time. Although digital image processing has not greatly improved diagnostic accuracy merely by enhancing the appearance of the radiographs, there are other potential diagnostic advantages in using digital images, such as rapid retrieval of previous examinations and the ability to correlate chest radiographs with CT or MRI studies rapidly on a video display. Direct image correlation with registration and superimposition has been achieved in the case of positron-emission tomography and MRI studies of the brain. For chest radiograph examinations, superimposition and subtraction of earlier radiographs to enhance the detection of interval change is being studied. The question of when digital chest radiography will replace conventional imaging is controversial. In a recent multiauthored review of this subject, it was estimated that digital chest radiography will replace conventional film radiography in at least 50% of large teaching hospitals by the turn of the century.(ABSTRACT TRUNCATED AT 400 WORDS)

Diagnosis, Computer-Assisted↗
PubMedDate not supplied

Retrospective fusion of radiographic and MR data for localization of subdural electrodes.

Prior to epilepsy surgery, subdural electrodes are often implanted and monitored for a few days to identify the focus of abnormal electrical activity. During the implantation and subsequent brain resection, there may be uncertainty about the exact location of the electrodes with respect to features of brain anatomy such as specific gyral convolutions or lesions. In experiments with a phantom and patients, implanted electrodes were imaged with multiplanar skull radiographs (or CT scans). After retrospective registration with preimplantation MR data, the electrodes were mapped from these studies onto an MR-derived three-dimensional brain model. The resulting multimodality displays showed the relationship of the electrodes to brain anatomy. In one patient the position of each electrode with respect to a metabolic lesion was also displayed by mapping preimplantation PET data onto the same brain model. This new display of electrode positions may strengthen the interpretation of subdural electrical recordings and thereby reduce uncertainty in planning the resection of epileptic tissue.

Adult↗
PubMed1991

Comparison of a PACS workstation with conventional film for interpretation of neonatal examinations: a paired comparison study.

The diagnostic value of neonatal examinations using picture archiving and communication systems (PACS) was compared with that of conventional radiographs. A total of 202 consecutive chest or abdominal radiographs from the newborn intensive care unit were digitized for display on a commercially available PACS console. Experimental design was a paired comparison study. Plain films and PACS images were reviewed alternately in unbiased fashion. After the examination was evaluated using the second modality, any change in diagnosis or confidence in diagnosis was noted. Overall evaluation showed slight preference for the PACS modality. Change of diagnosis or in confidence of diagnosis was more than twice as likely to occur with evaluation of PACS (35%) after hardcopy than with evaluation of conventional radiographs (14%) after PACS. Of the variety of image processing features available on PACS, only window and leveling were judged to be of significant value. These results indicate that PACS and conventional radiographs of the neonatal chest and abdomen are of similar diagnostic value.

Humans↗
PubMedDate not supplied

Image processing in digital chest radiography: effect on diagnostic efficacy.

The usefulness of digital image processing of chest radiographs was evaluated in a clinical study. In 54 patients, chest radiographs in the posteroanterior projection were obtained by both 14 inch digital image intensifier equipment and the conventional screen-film technique. The digital radiographs (512 x 512 image format) viewed on a 625 line monitor were processed in three different ways: (1) standard display; (2) digital edge enhancement for the standard display; and (3) inverse intensity display. The radiographs were interpreted independently by three radiologists. The diagnoses were confirmed by CT, follow-up radiographs and clinical records. Chest abnormalities of the films analyzed included 21 primary lung tumors, 44 pulmonary nodules, 16 cases with mediastinal disease and 17 cases with pneumonia/atelectasis. Interstitial lung disease, pleural plaques, and pulmonary emphysema were found in 30, 18 and 19 cases, respectively. The sensitivity of conventional radiography when averaged overall findings was better than that of the digital techniques (P less than 0.001). The differences in diagnostic accuracy measured by sensitivity and specificity between the three digital display modes were small. Standard image display showed better sensitivity for pulmonary nodules (0.74 vs 0.66; P less than 0.05) but poorer specificity for pulmonary emphysema (0.85 vs. 0.93; P less than 0.05) compared with inverse intensity display. We conclude that when using 512 x 512 image format, the routine use of digital edge enhancement and tone reversal at digital chest radiographs is not warranted.

Adolescent↗
PubMed1990

Developments towards the slice-wise three-dimensional reconstruction of the distribution of the contrast perfusion in the myocardial muscle from biplane angiographic views.

In theory, radiographic myocardial perfusion imaging allows a quantitative assessment of the functional significance of a coronary stenosis. However, in the conventional two-dimensional projection images there does not exist a one-two-one relationship between a selected myocardial region of interest (ROI) and one particular coronary segment perfusing that area due to over-projection of myocardial regions in front of and behind the selected ROI perfused by other arterial segments, which may result in measurements which are difficult to interpret or even unreliable. To overcome these problems, we have developed two algorithms to determine the spatial distribution of perfusion levels in slices of the heart, selected approximately perpendicular to the left ventricular long axis, from two orthogonal angiographic views: the Segmental Reconstruction Technique (SRT) and the Network Programming Reconstruction Technique (NPRT). Both techniques require a priori geometric information about the myocardium, which can be obtained from the epicardial coronary tree (epicardial boundaries) and the left ventricular lumen (endocardial boundaries). Using the SRT approach, pie-shaped segments are defined for each slice within the myocardial geometric constraints such that superimposition of these segments when projected in orthogonal biplane views is minimal. The reconstruction process uses a model with identical myocardial geometry and definition of segments. Each segment of the model is assigned a relative perfusion level with unit one if no other a priori information is available. In this case, the model contains geometric information only. In case a priori information about expected segmental perfusion levels is available, a level between zero and one is assigned to each segment. The a priori information on the myocardial perfusion levels can be extracted from either anatomic information about the location and severity of existing coronary arterial obstructions, or from a slice adjacent to the one under reconstruction. Using the NPRT approach perfusion levels are computed for each volume picture element of a slice within the reconstructed myocardial geometry, thus resulting in a much higher spatial resolution than the SRT approach. A priori information of perfusion levels must be included in this approach, again based upon anatomical information, or upon the slice adjacent to the one under reconstruction. The very first slice of a myocardial study will be reconstructed by the SRT approach. Extensive computer simulations for the SRT have proved that the mean difference between the actual and reconstructed segmental perfusion levels, on a scale from 0 to 1, is smaller than 0.45 (SEE = 0.0033, REE = 1.80) for various coronary artery disease states without the use of a priori information on expected perfusion levels. This error becomes smaller than 0.36 (SEE = 0.0026, REE = 1.42), if a priori information in the reconstruction technique is included. Similar computer simulations for the NPRT have proved that these mean differences in geometric segments equal to those defined for the SRT, are smaller than 2.94 (SEE = 0.0308, REE = 0.77) on a scale from 0 to 16, without the use of a priori information on expected perfusion levels, and smaller than 1.72 (SEE = 0.0304, REE = 1.10) on the same scale when a priori information is included. Therefore, it may be concluded that slice-wise three-dimensional reconstruction of perfusion levels is feasible from biplane computer-simulated data, and that a similarity exists for mean perfusion levels in corresponding regions in the simulated and reconstructed slices, for various states of single coronary artery disease.

Algorithms↗
PubMed1990

Teleradiology image transmission system: diagnostic accuracy at three matrix sizes for various types of images.

The interpretability of transmitted digitized radiographic images is an important factor in the operation and use of teleradiology systems. Matrix size may influence diagnostic accuracy of the interpretation. Commercially available equipment has certain built-in image enhancement controls that may increase the interpretability of the image received. Evaluation of the effect of varying the matrix size and other factors on diagnostic accuracy are described.

Computer Communication Networks↗
PubMedDate not supplied

A review on biomedical image processing and future trends.

The last two decades have witnessed a revolutionary development in the field of biomedical and diagnostic imaging. Imaging procedures and modalities which were only in the experimental research phase in the early part of the last two decades, have now become universally accepted clinical procedures. They include computerized tomography (CT), magnetic resonance imaging, ultrasound imaging, nuclear medicine imaging, computerized hematological cell analysis, etc. In the past, the conventional and relatively simple image processing techniques such as image enhancement, gray-level mapping, spectral analysis, region extraction, etc. have been modified for biomedical images and successfully applied for processing and analysis. The role of image enhancement, gray-level mapping, and image reconstruction from projections algorithms in CT and other radiological imaging modalities is well evident. Recently, many advances in biomedical image processing, analysis, and understanding algorithms have shown a great potential for enhancing and interpreting useful diagnostic information from these images more accurately. This paper presents a review on the current state-of-the-art techniques in biomedical image processing and comments on future trends.

Algorithms↗
PubMed1991

Carpal orientation from computed reference axes.

Carpal instability is usually diagnosed by abnormal two-plane radiographic angles. These angles are often unreliable. A method that eliminates interpretation of overlapping shadows and uses all of the carpal geometry should improve clinical diagnoses. The digital data from computed tomography scans can be manipulated to describe the carpal orientation in the normal wrist. The digital data from the computed tomography scans of twenty-two normal wrists were used to compute distances with and without directions between the volumetric centroids of the carpal bones. An expansion technique also extracted from the computed tomography data an orthogonal set of vectors, the principal axes. The first principal axis describes the longest dimension of each bone. The average angle produced by the first principal axes of the scaphoid and lunate was 23.6 degrees, scaphoid and capitate was 73.2 degrees, and the capitate and the lunate was 93.5 degrees. These computations represent new carpal axes and intercarpal angles that are not related to the commonly measured two-plane radiographic angles. They should prove helpful in the study of kinematics and pathomechanics in the wrist joint.

Carpal Bones↗
PubMed1991

Computer-aided interpretation and quantification of angular periodontal bone defects on dental radiographs.

Capabilities of human observers to detect and describe small bone defects objectively are limited. Digital image processing can provide a useful contribution to the diagnostic process. This paper describes the evaluation of a computer-aided procedure for the interpretation and quantification of angular periodontal bone defects on dental radiographs. The computer-aided procedure was able to rank series of artificial periodontal bone lesions as accurate as experienced clinicians. Comparison of data from clinical inspection of lesions during surgery and quantitative results of the digitized procedure shows that the latter produced reliable information on the lesions size. Reproducibility is satisfactory. It was concluded that computer-aided detection and description of periodontal bone defects decreases the interobserver variability in general and the time-dependent variability in repeated assessments of a single observer.

Alveolar Bone Loss↗
PubMed1992

Subperiosteal resorption: effect of full-frame image compression of hand radiographs on diagnostic accuracy.

Image compression is essential to handle a large volume of digital images, including computed tomographic, magnetic resonance, computed radiographic, and digitized images in a digital radiology operation. Developed during the past few years, full-frame bit allocation performed with the cosine transform technique has been proved to be an excellent irreversible image compression method. This article describes the effect, on the accuracy of diagnosis of subperiosteal resorption, of using the hardware compression module to produce hand radiographs. Receiver operating characteristic analysis of the interpretation of 71 radiographs by five observers demonstrated that there is no statistically significant difference in diagnostic accuracy between the original radiographs and compressed and reconstructed images obtained with a compression ratio as high as 20:1.

Bone Resorption↗