J. R. Perry

An evaluation of the effectiveness of adaptive histogram equalization for contrast enhancement

Adaptive histogram equalization (AHE) and intensity windowing have been compared using psychophysical observer studies. Experienced radiologists were shown clinical CT (computerized tomographic) images of the chest. Into some of the images, appropriate artificial lesions were introduced; the physicians were then shown the images processed with both AHE and intensity windowing. They were asked to assess the probability that a given image contained the artificial lesion, and their accuracy was measured. The results of these experiments show that for this particular diagnostic task, there was no significant difference in the ability of the two methods to depict luminance contrast; thus, further evaluation of AHE using controlled clinical trials is indicated.

Computer Simulated Cardiac SPECT Data for use in Evaluating Reconstruction Algorithms

The purpose of this work was to develop a technique for simulating SPECT projection data which realistically model a cardiac T1-201 study. The data are intended for use in evaluating image reconstruction and processing algorithms using ROC analysis. The significant physical effects of T1-201 patient acquisitions have been incorporated into the simulation, including patient anatomy, attenuation, scatter, detector response, and statistical noise fluctuations. The simulation technique involves first generating a 3D source distribution which models the radioisotope uptake of a clinical T1-201 study. A patient CT image provides an anatomical model for generating the distribution. Next, projections are calculated as ray-sums in a way which incorporates photon attenuation and detector response. Detailed attenuation information is provided by the CT image. The effects of scatter are then incorporated by filtering the projection data at each angle with an estimate of the scatter response function specific for that angle. Finally, Poisson noise is added to the projections. The results have shown that the simulation technique generates data closely modeling clinical T1-201 data.

Applications of Iterative Reconstruction Methods in SPECT

We have applied iterative reconstruction methods to compensate for the major image degrading effects of photon attenuation and geometric response in SPECT imaging. The compensation methods implement, in the projection and backprojection operations of the iterative reconstruction algorithms, an accurate model of photon attenuation in the patient’s body and the geometric response of the collimated-detector system. To evaluate the corrective iterative reconstruction methods, data from a computer-generated phantom which simulated T1-201 distribution in the thoracic region was used. Also, the techniques were assessed using data from a cardiac SPECT study with T1-201. Our studies indicate that compensations for attenuation and detector response in SPECT are possible using iterative reconstruction techniques. The compensations are especially important when the attenuation coefficient distribution in the body region, such as the thorax, is non-uniform. The attenuation compensation scheme using the iterative maximum likelihood-EM (ML-EM) algorithm can provide reconstructed images with low noise amplification, and accurate quantitative information without distortions and artifacts. Also, compensation for detector response gives additional improvement in spatial resolution.

Evaluation of total workstation CT interpretation quality: a single-screen pilot study

An interpretation report, generated with an electronic viewbox, is affected by two factors: image quality, which encompasses what can be seen on the display, and computer human interaction (CHI), which accounts for the cognitive load effect of locating, moving, and manipulating images with the workstation controls. While a number of subject experiments have considered image quality, only recently has the affect of CHI on total interpretation quality been measured. This paper presents the results of a pilot study conducted to evaluate the total interpretation quality of the FilmPlane2.2 radiology workstation for patient folders containing single forty-slice CT studies. First, radiologists interpreted cases and dictated reports using FilmPlane2.2. Requisition forms were provided. Film interpretation was provided by the original clinical report and interpretation forms generated from a previous experiment. Second, an evaluator developed a list of findings for each case based on those listed in all the reports for each case and then evaluated each report for its response on each finding. Third, the reports were compared to determine how well they agreed with one another. Interpretation speed and observation data was also gathered.

Functional Requirements For Interfacing PACS To RIS

This paper will discuss the functional requirements for interfacing Picture Archiving and Communications Systems (PACS) to todays radiology information systems (RIS). It is clear from the operational modeling study done at UNC, that a fully functional PACS will require the use of RIS data. For example, patient ID, scheduling, and information tracking are usually part of a RIS and must be available to the PACS. Similarly, the image tracking and index capabilities of the PACS will be used by the RIS. As part of our modeling data flow analysis research program, we have identified a number of these interactions. The interface points will be identified and discussed with emphasis on the operational impact of such an interface and efficiencies likely to be provided.

Comparison of coronary angiography and early oral dipyridamole thallium-201 scintigraphy in patients receiving thrombolytic therapy for acute myocardial infarction

We evaluated 50 consecutive patients who received thrombolytic therapy for acute myocardial infarction using thallium-201 single photon emission computed tomography in combination with oral dipyridamole (300 mg) to assess the frequency of residual myocardial ischemia. Thallium studies were performed early after myocardial infarction at a mean of 4.6 days (range 3 to 11) in 50 patients. The time from the onset of chest pain to the administration of thrombolytic therapy was 2.6 hours (range 0.5 to 5.5). Q wave myocardial infarction was evident in 46 patients; four patients had a non-Q wave infarction (anterior infarction in 31 patients and inferior infarction in 19 patients). The serum mean peak creatinine kinase was 1503 IU/L (range 127 to 6500). Coronary angiography was performed in all patients at a mean of 3.1 days (range 2 to 10) and revealed the infarct-related vessel to be patent in 36 patients (72%). The ejection fraction was 48% (range 26% to 67%). After dipyridamole administration, 13 patients (26%) developed angina that was easily reversed with the administration of intravenous aminophylline. Systolic blood pressure decreased from 122 to 115 mm Hg (p less than 0.05) and the heart rate increased from 76 to 85 beats/min (p less than 0.05). None of the patients had significant hypotension, arrhythmias, or evidence of infarct extension. Perfusion abnormalities were present on the initial thallium images in 48 patients. Redistribution suggestive of ischemia was present in 36 patients (72%). Ischemia confined to the vascular distribution of the infarct vessel was evident in 22 patients. Seven patients had ischemia in the infarct zone as well as in a remote myocardial segment. Thus 29 patients (58%) had ischemia in the distribution of the infarct vessel. Ischemia in the infarct zone was evident in 19 of 36 patients (53%) with open infarct vessels and in 10 of 14 patients (71%) with occluded infarct vessels. In conclusion, thallium-201 single photon emission computed tomography using oral dipyridamole was safely performed in patients with recent myocardial infarctions who receive thrombolytic therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

A Multiscreen Multiple Image Display Console

We have developed a prototype display console with which we can investigate issues related to the display of medical images. Our system is not a clinical tool, but rather a research tool that allows us to study how radiologists carry out the image reading procedure. For this study we used chest CT scans which are made up of 22 to 34 scan slices. We were able to simultaneously display up to 32 scan slices at two different intensity windows, i.e. 64 images on one screen. We used two more screens as working screens where the radiologist could display four or sixteen images per screen. Our goal was to determine how the radiologists use the mutlti-image, multiple screen format. The results of our study showed that the radiologists use different strategies in viewing images, and that a display system must allow for those variations. The display of a complete image set, even though the images were shown at much less than full-sampling, was very useful as an overview of the patient study. Simultaneous display of images at different intensity windows was also very useful. The slow times (20 secs) for access to images was a drawback of our system.

Digital Image Display Console Design Issues

Electronic image display has been envisioned as a means of alleviating some of the problems that expanding radiology departments have with film management, integration of multiple imaging modalities and as a means of improving the physicians diagnostic abilities through after acquisition image contrast enhancement. In an effort to provide an electronic image display suitable for general use, several educational institutions and industry have been in the process of developing computerbased image systems called picture archival and communication systems (PACS). Functional integration of the PACS components (network, archive, database management and display) presents problems which require the development of departmental modeling, a common communication protocol, image storage devices with enormous capacities, management software and display consoles. The latter has been the object of our focus.