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Biomedical subjects

T Sund

Publications and source records attributed to T Sund.

At least 19 recordsLinked to original sources
PubMed2006

Detection of simulated microcalcifications in fixed mammary tissue: An ROC study of the effect of local versus global histogram equalization.

PURPOSE: To investigate whether sliding window adaptive histogram equalization (SWAHE) of digital mammograms improves the detection of simulated calcifications, as compared to images normalized by global histogram equalization (GHE). MATERIAL AND METHODS: Direct digital mammograms were obtained from mammary tissue phantoms superimposed with different frames. Each frame was divided into forty squares by a wire mesh, and contained granular calcifications randomly positioned in about 50% of the squares. Three radiologists read the mammograms on a display monitor. They classified their confidence in the presence of microcalcifications in each square on a scale of 1 to 5. Images processed with GHE were first read and used as a reference. In a later session, the same images processed with SWAHE were read. RESULTS: The results were compared using ROC methodology. When the total areas AZ were compared, the results were completely equivocal. When comparing the high-specificity partial ROC area AZ,0.2 below false-positive fraction (FPF) 0.20, two of the three observers performed best with the images processed with SWAHE. The difference was not statistically significant. CONCLUSION: When the reader's confidence threshold in malignancy is set at a high level, increasing the contrast of mammograms with SWAHE may enhance the visibility of microcalcifications without adversely affecting the false-positive rate. When the reader's confidence threshold is set at a low level, the effect of SWAHE is an increase of false positives. Further investigation is needed to confirm the validity of the conclusions.

Breast Diseases↗
PubMed2006

Sliding window adaptive histogram equalization of intraoral radiographs: effect on image quality.

OBJECTIVES: To investigate whether contrast enhancement by non-interactive, sliding window adaptive histogram equalization (SWAHE) can enhance the image quality of intraoral radiographs in the dental clinic. METHODS: Three dentists read 22 periapical and 12 bitewing storage phosphor (SP) radiographs. For the periapical readings they graded the quality of the examination with regard to visually locating the root apex. For the bitewing readings they registered all occurrences of approximal caries on a confidence scale. Each reading was first done on an unprocessed radiograph ("single-view"), and then re-done with the image processed with SWAHE displayed beside the unprocessed version ("twin-view"). The processing parameters for SWAHE were the same for all the images. RESULTS: For the periapical examinations, twin-view was judged to raise the image quality for 52% of those cases where the single-view quality was below the maximum. For the bitewing radiographs, there was a change of caries classification (both positive and negative) with twin-view in 19% of the cases, but with only a 3% net increase in the total number of caries registrations. For both examinations interobserver variance was unaffected. CONCLUSIONS: Non-interactive SWAHE applied to dental SP radiographs produces a supplemental contrast enhanced image which in twin-view reading improves the image quality of periapical examinations. SWAHE also affects caries diagnosis of bitewing images, and further study using a gold standard is warranted.

Algorithms↗
PubMed1997

Receiver operating characteristic study of image preprocessing for teleradiology and digital workstations.

The purpose of this study was to evaluate whether digitized analog images displayed on a digital workstation can be improved by using a preprocessing algorithm, and if so, whether the quality of the resulting images can reach that of the original films. The material contained 120 difficult cases (about 50% with selected pathology). Four radiologists each evaluated half of the randomly ordered cases with the digital workstation and half of the cases with the original radiographs. The data were compared with a previous similar study, where the workstation had no option for preprocessed images. Preprocessed digital images were clearly superior to digital images without preprocessing, although for those of the highest diagnostic difficulty they were inferior to the original films. The preprocessing algorithm has improved the diagnostic quality of the digital workstation. There is room yet for improvement compared to plain films, although the current setup may be sufficient in some settings.

Bone and Bones↗
PubMed1997

ROC-study of a teleradiology workstation versus film readings.

PURPOSE: We have used receiver operating characteristic (ROC) analysis to compare screen assessment of digitized radiographic films transmitted by a teleradiology system, with evaluation of the original radiographs on film. MATERIAL AND METHODS: The material contained 120 cases (about 50% with selected pathology) that were difficult to diagnose. Four radiologists each evaluated half of the cases on film, and half on computer screen. The screen display was 1024 x 836 pixels with 8 bits/pixel. RESULTS: We found the accuracy and sensitivity of the teleradiology system to be clearly inferior to film evaluation. CONCLUSION: Improvement is needed both in the teleradiology system, and in the training of radiologists to work on the electronic workstation.

Baltimore↗
PubMed1997

Four years with teleradiology: a technical description.

Since September 1992, Troms Military Hospital (Norway) has been connected to the larger University Hospital of Tromsø by a teleradiology link transmitting about 6000 examinations annually. In the spring of 1995, the system was upgraded with a digital X-ray unit, thereby almost eliminating the scanning of analog radiographs. This article describes the technical development of the link. The discussion suggests ways of improving the teleradiology link, particularly in terms of integrating the radiology information system (RIS) and picture archiving and communication system (PACS).

Computer Communication Networks↗
PubMed1992

Nordic teleradiology development.

In the Nordic countries there are several reasons why teleradiology has been an interesting topic of research during the last years. The distances in rural areas are long, and radiology expert service is not available in every health centre which is able to provide X-rays. Also, the telecommunication network is on a very advanced level in the Nordic countries. The staff is well educated and they are used to operating with computers. This all means that the infrastructure to develop and use systems like teleradiology exists. This paper describes two separate systems developed in Norway and Finland. Their development has been in many respects the same. The common hardware and software features, as well as the differences and the clinical experiences, are discussed in this paper.

Computer Systems↗
PubMed1983

Right ventricular mechanics: a comparison of models.

Using data from an isolated supported cat right ventricle preparation, we investigated the following models or methods for characterising the mechanical function of the ventricle: (1) a pressure generator in series with an internal impedance; (2) a variable elastance in series with an internal, pressure dependent flow resistance; (3) pulse response analyses, theoretically based on the pressure response to a small volume step of short duration; and (4) geometric mapping of the variables pressure and volume as functions of time. We tested the reproductive and predictive strengths of the four models, and found that all methods could reproduce 50% of the observed pressure curves with an RMS error less than 0.2 kPa, and in most cases also gave a close prediction of pressure curves which were not used to establish the respective model parameters. We see this as one reason for the fact that no single ventricular model has yet been universally accepted.

Animals↗
PubMed1982

Does normal pulmonary impedance constitute the optimum load for the right ventricle?

Right ventricular performance of isolated supported cat hearts was experimentally characterized by a relationship among ventricular pressure (P), volume (V), and time after onset of systole. This characterization was combined with a hypothetical load network consisting of lumped central and peripheral lung vascular resistances (Rc and Rp), inertance (L), and compliance (C). We calculated ventricular and load pressure, flow, external ventricular work (Wext), static ventricular P-V energy (Wstat), and pump efficiency Q = Wext/Wstat over a broad range of load conditions. Magnitudes of load network variables resulting in a maximum value of Q would define the load impedance matching the ventricle. A practical optimum magnitude of lumped vascular compliance was obtained at C = 150 x 10(-6) g-1 . cm4, above which no substantial change in Q took place. We obtained maximum Q at approximately 4 ml stroke volume (heart rate = 2 Hz) and at characteristic impedance between 0.75 and 1.1 x 10(3)g . cm-1 . s-1. As these values are quite close to those encountered in the intact animal, we conclude that the right ventricular and the pulmonary arterial tree appear to constitute a matched pump-load system.

Animals↗
PubMed1980

Performance of the right ventricle: a pressure plane analysis.

A load invariant presentation of the heart's ventricular performance has been investigated. Flow from the right ventricle of isolated cat hearts was passed through a controlled, variable load. Ventricular pressure and flow were recorded and ventricular volume computed by flow integration. The three-dimensional trajectories of ventricular pressure, ventricular volume and time after onset of contraction all closely followed a single three-dimensional surface, which was denoted as the PVt surface. The PVt surface depends on the inotropic condition of the heart, but is load invariant. It is therefore a measure of the intrinsic ventricular performance. Given the arterial load on the ventricle, it can be applied for predictions of pressure and flow profiles, as well as any parameter related to them.

Animals↗
PubMed1979

Flow and power output of right ventricle facing load with variable input impedance.

The output from the right ventricle (RV) was studied at different load impedances. Isolated cat hearts were perfused with Tyrode solution with erythrocytes. Coronary perfusion pressure and RV end-diastolic pressure were kept constant. The RV pumped into an artificial hydraulic load with independently variable resistance (R) and compliance (C). Mean RV flow (RVO) decreased after R increase or C reduction. For each heart, RVO and mean RV pressure were linearly related. The slope of the regression line is interpreted as an "apparent source resistance" (Rs). Rs was on average 3.4 X 10(3) (dyn.s.cm-5). The static hydraulic power output was maximum at a certain load R (Rm). Rm was C dependent at an average high C of 5 X 10(-5) dyn-1.cm5, Rm was 9.4 X 10(3) dyn.s.cm-5 on average and shifted to 5.4 X 10(3) at low C (avg 0.8 X 10(-5). Theoretical considerations show that Rm/Rs will be equal to total heart period divided by ejection period in the extreme case C leads to infinity, and Rm/Rs leads to 1 when C leads to 0. Experimentally, Rm/Rs was 2.4 (avg) for high C, and approached 1 for low C, which fits the theoretical predictions. The results indicate that high C facilitates the matching between the right heart and the vascular resistance in the lung.

Animals↗