Biomedical subjects

Stephen K Thompson

Publications and source records attributed to Stephen K Thompson.

5 recordsLinked to original sources

PubMed2004

Comparison of dual energy detector system performance.

Dual energy detector systems are combinations of x-ray detectors, x-ray source spectrum switching, and x-ray filter attenuation that provide two measurements of transmitted flux through the object with different effective spectra. We describe technology independent methods to measure and compare the quantum noise and sensitivity to motion artifacts of these systems. The experimental methods use relatively simple phantoms to measure the parameters in the general mathematical expressions for the noise in the subtracted image. The parameters are used to compute an x-ray energy spectrum quality factor and a subtracted image noise per unit patient dose quality factor. Patient motion causes artifacts in switched spectrum systems, particularly with the heart in chest radiography. We describe a method to measure effective interexposure time using subtracted image data of a uniformly moving object. This parameter measures the sensitivity to patient motion artifacts. We use these methods to compare three examples of systems with different dual energy detector technologies: a passive, "sandwich" detector with two computed radiography plates separated by a copper filter, an "active" detector that uses voltage switching with an electro-optical system and computed radiography plates, and a flat-panel, solid state detector with voltage switching.

Artifacts↗

PubMed2002

Evaluation of soft copy distribution of diagnostic studies before soft copy interpretation.

To meet the imaging needs of an expanding clinical campus and clinical volume, a web-based image distribution system (Stentor, San Francisco, CA) was implemented before the implementation of soft copy interpretation. This study sought to assess system utilization as a metric of system's capability to meet demand for enterprise image review. Study period included all examinations stored on the system and subsequently viewed from June 1, 2001 to August 8, 2001. Server log files were analyzed for study storage and subsequent study retrieval. A total of 24,887 studies were stored on the server and available for immediate retrieval, and, of these, 12,458 studies (50%) subsequently were reviewed. Modality-specific study review included 65% for computed radiography, 46% for digital radiography, 56% magnetic resonance, 54% for computed tomography, and 18% for ultrasound scan. Enterprise image distribution before the implementation of picture archiving communication system is a viable operational decision and can be implemented successfully before implementation of soft copy interpretation. System utilization indicates a great value in the electronic availability of image studies.

Radiology Information Systems↗

PubMed2002

Enterprise utilization of "always on-line" diagnostic study archive.

To meet demands for enterprise image distribution, an "always on-line" image storage archive architecture was implemented before soft copy interpretation. It was presumed that instant availability of historical diagnostic studies would elicit a substantial utilization. Beginning November 1, 2000 an enterprise distribution archive was activated (Stentor, SanFrancisco, CA). As of August 8, 2001, 83,052 studies were available for immediate access without the need for retrieval from long-term archive. Image storage and retrieval logs for the period from June 12, 2001 to August 8, 2001 were analyzed. A total of 41,337 retrieval requests were noted for the 83,052 studies available as August 8, 2001. Computed radiography represented 16.8% of retrieval requests; digital radiography, 16.9%; computed tomography (CT), 44.5%; magnetic resonance (MR), 19.2%; and ultrasonography, 2.6%. A total of 51.5% of study retrievals were for studies less than 72 hours old. Study requests for cases greater than 100 days old represented 9.9% of all accessions, 9.7% of CT accessions, and 15.4% of MR accessions. Utilization of the archive indicates a substantial proportion of study retrievals for studies less than 72 hours after study completion. However, significant interest in historical CT and MR examinations was shown.

Online Systems↗

PubMed2002

Implementing the DICOM Grayscale Standard Display Function for mixed hard- and soft-copy operations.

The aim of this work was to implement the DICOM Grayscale Standard Display Function (GSDF) at all stages of image presentation for computed radiography (CR) and direct digital radiography (DR) modalities. Cathode-ray tubes (CRT) were calibrated according to vendor procedures. Printer look-up-tables (LUT) were measured. Custom LUTs were created and loaded. Fuji CR gradation processing parameters were adjusted to accommodate a GSDF printer LUT. Conformance to the GSDF for hard-copy and soft-copy displays was measured with DICOM Part 14 procedures. One system was intended to completely incorporate the GSDF, although the hard-copy result was correct. The CR systems required creation of custom GSDF printer LUTs, adjustment of gradation processing parameters, and/or calibration of CRT luminance response at the quality control station. The picture archiving and communication system workstations from one vendor required third-party software for calibration. Current implementations of DICOM GSDF by vendors may be inconsistent or nonexistent. Significant effort by in-house staff must be expended to properly incorporate the GSDF.

Data Display↗

PubMed2002

Microcalcification detectability for four mammographic detectors: flat-panel, CCD, CR, and screen/film).

Amorphous silicon/cesium iodide (a-Si:H/CsI:Tl) flat-panel (FP)-based full-field digital mammography systems have recently become commercially available for clinical use. Some investigations on physical properties and imaging characteristics of these types of detectors have been conducted and reported. In this perception study, a phantom containing simulated microcalcifications (microCs) of various sizes was imaged with four detector systems: a FP system, a small field-of-view charge coupled device (CCD) system, a high resolution computed radiography (CR) system, and a conventional mammography screen/film (SF) system. The images were reviewed by mammographers as well as nonradiologist participants. Scores reflecting confidence ratings were given and recorded for each detection task. The results were used to determine the average confidence-rating scores for the four imaging systems. Receiver operating characteristics (ROC) analysis was also performed to evaluate and compare the overall detection accuracy for the four detector systems. For calcifications of 125-140 microm in size, the FP system was found to have the best performance with the highest confidence-rating scores and the greatest detection accuracy (Az = 0.9) in the ROC analysis. The SF system was ranked second while the CCD system outperformed the CR system. The p values obtained by applying a Student t-test to the results of the ROC analysis indicate that the differences between any two systems are statistically significant (p<0.005). Differences in microC detectability for the large (150-160 microm) and small (112-125 microm) size microC groups showed a wider range of p values (not all p values are smaller than 0.005, ranging from 0.6 to <0.001) compared to the p values obtained for the medium (125-140 microm) size microC group. Using the p values to assess the statistical significance, the use of the average confidence-rating scores was not as significant as the use of the ROC analysis p value for p value.

Breast Neoplasms↗