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Biomedical subjects

K D Hopper

Publications and source records attributed to K D Hopper.

At least 19 recordsLinked to original sources
PubMed2001

Optimization of shaded surface display for CT angiography.

RATIONALE AND OBJECTIVES: The authors performed this study to determine the optimum threshold for performing computed tomographic (CT) angiography with shaded surface display (SSD). MATERIALS AND METHODS: A dedicated phantom was developed with an 8-mm luminal diameter. Each of 19 vessels had stenoses ranging from 0% to 93.8%. Five blinded, experienced reviewers separately measured each vessel by using SSD with display thresholds of 50, 100, 150, and 200 HU. RESULTS: For vessel diameters of 2 mm and larger, the best threshold value was 100 HU. This yielded measurements within 2% of the actual diameter and produced no false occlusions. For vessels 1 mm in diameter, the best threshold remained 100 HU, but this threshold was significantly less accurate than the standard (P = .0001) and produced two false occlusions in 15 vessels. For vessels 0.5 mm in diameter, the best threshold was 50 HU, although this still produced measurements significantly less accurate than the gold standard (P = .036) and one false occlusion in 15 vessels. CONCLUSION: CT angiography with SSD and an optimized threshold value is a useful technique in vessels 1 mm and larger.

Angiography↗
PubMed2001

Transbronchial biopsy with virtual CT bronchoscopy and nodal highlighting.

Transbronchial biopsy to sample lymph nodes and tumors that are not visible at endoscopy has a poor (<50%) success rate. These nodes can be highlighted easily at virtual computed tomographic (CT) bronchoscopy to provide a guide. This study was performed to evaluate if the addition of this information to the bronchoscopist improved the success rate of transbronchial biopsy of subcarinal and aortopulmonary lymph nodes. The addition of virtual CT bronchoscopy with lymph node highlighting significantly (P < .5) increased biopsy success rates for pretracheal, hilar, and high pretracheal adenopathy.

Adult↗
PubMed2001

Quantitative and qualitative evaluation of volume of low osmolality contrast medium needed for routine helical abdominal CT.

OBJECTIVE: The purpose of our study was to determine the minimum optimal dose of IV contrast medium for helical CT that can preserve image quality while reducing cost. SUBJECTS AND METHODS: Four hundred sixty-three patients from six centers were enrolled in a prospective trial in which patients were randomized into one of four weight-based dose categories of iopromide, 300 mg I/mL: 1.25, 1.50, 1.75, and 2.0 mL/kg. Six of 463 patients were excluded from analysis. A radiologist at each center who was unaware of the volume of contrast medium administered determined whether the scans were acceptable. The responses were analyzed by dose, in aggregate, and by weight. Enhancement values (in Hounsfield units) in regions of interest in the liver, pancreas, aorta, and kidneys were obtained at a single time during the scan. The participating radiologist was unaware of these values. Finally, three additional nonparticipating site observers assessed the images for acceptability, diagnostic quality, and overall level of confidence. A cost model comparing incurred charges in using 150 or 100 mL, or 1.5 mL/kg, of low osmolality contrast medium was developed from experience in an additional 303 patients. RESULTS: We found no clinically significant difference in acceptability of scans at doses greater than 1.5 mL/kg. However, significant variability occurred among the centers. The use of 1.5 mL/kg led to a savings of $9927.16 for 303 patients when compared with the use of 150 mL at list price. The cost is the same for 1.5 mL/kg or use of 100 mL of contrast medium. CONCLUSION: A weight-based dose at 1.5 mL/kg of low osmolality contrast medium can provide acceptable scans in most patients, with a significant cost savings.

Body Weight↗
PubMed2001

CT angiography: in vitro comparison of five reconstruction methods.

OBJECTIVE: Five image reconstruction techniques have been used with CT angiography: axial (cross-sectional), maximum intensity projection (MIP), curved multiplanar reconstruction (MPR), shaded-surface display, and volume rendering. This study used a phantom to compare the accuracy of these techniques for measuring stenosis. SUBJECTS AND METHODS: A 19-vessel phantom containing various grades of concentric stenoses (0-100%) and three lengths (5, 7.5, and 10 mm) of stenoses was used for this study. Scans were obtained with a slice thickness of 2.0 mm, slice interval of 1.0 mm, pitch of 1.0, 120 kVp, 200 mA, and with the vessels oriented parallel to the z-axis and opacified with nonionic contrast material. CT angiography images were produced using five optimized techniques: axial, MIP, MPR, shaded-surface display, and volume rendering; and measurements were made with an electronic cursor in the normal lumen and mid stenosis by five separate investigators who were unaware of vessel and stenosis diameters. Each of the techniques was first optimized according to the radiology literature and our own preliminary testing. RESULTS: For vessels greater than 4 mm in diameter, axial, MIP, MPR, shaded-surface display, and volume-rendering CT angiography techniques all had a measurement error of less than 2.5%. However, axial, MIP, MPR, and shaded-surface display techniques were less accurate in estimating smaller (<or=4 mm) diameters. Volume rendering tended to be more accurate in the measurement of vessels with a 2.0- to 4.0-mm diameter and was statistically more accurate for diameters of 0.5-1.0 mm (p < 0.001). CONCLUSION: All five CT angiography display techniques (axial, MIP, MPR, shaded-surface display, and volume rendering) accurately display vessels and stenoses greater than 4 mm in diameter. However, volume rendering tends to be more accurate for stenoses of 2-4 mm and was statistically better in the measurement of diameters of 0.5-1.0 mm (p < 0.001). Volume rendering is an accurate method for evaluating all grades of stenoses.

Angiography↗
PubMed2000

Mucosal detail at CT virtual reality: surface versus volume rendering.

PURPOSE: To evaluate computed tomographic virtual reality with volumetric versus surface rendering. MATERIALS AND METHODS: Virtual reality images were reconstructed for 27 normal or pathologic colonic, gastric, or bronchial structures in four ways: the transition zone (a) reconstructed separately from the wall by using volume rendering; (b) with attenuation equal to air; (c) with attenuation equal to wall (soft tissue); (d) with attenuation halfway between air and wall. The four reconstructed images were randomized. Four experienced imagers blinded to the reconstruction graded them from best to worst with predetermined criteria. RESULTS: All readers rated images with the transition zone as a separate structure as overwhelmingly superior (P <.001): Nineteen cases had complete concurrence among all readers. The best of the surface-rendering reconstructions had the transition zone attenuation equal to the wall attenuation (P <.001). The third best reconstruction had the transition zone attenuation equal to the air attenuation, and the worst had the transition zone attenuation halfway between the air and wall attenuation. CONCLUSION: Virtual reality is best with volume rendering, with the transition zone (mucosa) between the wall and air reconstructed as a separate structure.

Animals↗
PubMed2000

Body CT and oncologic imaging.

The most commonly used imaging modality in patients with cancer is computed tomography (CT). Whether to evaluate primary tumor or metastases to the neck, chest, abdomen, or pelvis, oncologic body CT has become invaluable to medical, gynecologic, and radiation oncologists. CT is the principal tool used to stage tumor, assess response, and guide radiation therapy. This review provides a discussion of how we optimize oncologic CT to best meet the needs of the patient with cancer.

Follow-Up Studies↗
PubMed2000

CT angiographic measurement of the carotid artery: optimizing visualization by manipulating window and level settings and contrast material attenuation.

PURPOSE: To evaluate a broad range of window and level settings for various contrast material attenuation coefficients and degrees of vascular stenosis to obtain the most accurate computed tomographic (CT) angiographic measurements. MATERIALS AND METHODS: A total of 25, 480 measurements were made transversely (perpendicular to the lumen) and by means of maximum intensity projection (MIP) in a phantom with stenoses of 0%-100%, contrast material with attenuation coefficients of 150-350 HU, and 14 window and 13 level settings. Edge definition was also evaluated. RESULTS: There was an inherent relationship between the contrast material attenuation coefficient and the optimal window and level settings in the measurement of stenoses at both transverse and MIP CT angiography. This relationship between the contrast material attenuation coefficient D: and the optimal settings for window W: and level L: was represented by the following simple equations: W:/D: = [-2 x (L:/D:)] + 1.3, where -0.2 < L:/D: < 0.5, and W:/D: = [3.3 x (L:/D:)] - 1.3, where 0.5 < L:/D: < 1.0. With a vascular contrast material attenuation coefficient of 250-350 HU, the best transverse and MIP display settings for the window and level were 96 and 150 HU, respectively. CONCLUSION: The use of optimized window and level settings at CT angiography reduces measurement variability.

Carotid Arteries↗
PubMed1999

A comparison of wavelet and Joint Photographic Experts Group lossy compression methods applied to medical images.

This presentation focuses on the quantitative comparison of three lossy compression methods applied to a variety of 12-bit medical images. One Joint Photographic Exports Group (JPEG) and two wavelet algorithms were used on a population of 60 images. The medical images were obtained in Digital Imaging and Communications in Medicine (DICOM) file format and ranged in matrix size from 256 x 256 (magnetic resonance [MR]) to 2,560 x 2,048 (computed radiography [CR], digital radiography [DR], etc). The algorithms were applied to each image at multiple levels of compression such that comparable compressed file sizes were obtained at each level. Each compressed image was then decompressed and quantitative analysis was performed to compare each compressed-then-decompressed image with its corresponding original image. The statistical measures computed were sum of absolute differences, sum of squared differences, and peak signal-to-noise ratio (PSNR). Our results verify other research studies which show that wavelet compression yields better compression quality at constant compressed file sizes compared with JPEG. The DICOM standard does not yet include wavelet as a recognized lossy compression standard. For implementers and users to adopt wavelet technology as part of their image management and communication installations, there has to be significant differences in quality and compressibility compared with JPEG to justify expensive software licenses and the introduction of proprietary elements in the standard. Our study shows that different wavelet implementations vary in their capacity to differentiate themselves from the old, established lossy JPEG.

Algorithms↗
PubMed1999

CT bronchoscopy.

CT bronchoscopy with volumetric rendering can play a significant role in patients with mediastinal/hilar tumor and lymphadenopathy. By localizing (tagging) tumor foci on the axial images, volumetric rendering allows the tumors to be seen through normal-appearing mucosa. Such images can guide the bronchoscopist in finding the ideal site to biopsy and allow the bronchoscopist to become more aggressive in the biopsy of more difficulty positioned lesions. In addition, delineation of normal extraluminal vessels and other vital anatomical structures potentially decreases biopsy complications. Although further research is needed to prove the value of CT bronchoscopy, preliminary work performed to date by the author and others indicates great promise.

Bronchoscopy↗
PubMed1999

Detection of Björk-Shiley convexo-concave heart valve outlet strut single leg separations: consensus image acquisition and interpretation using two different cineradiographic imaging technologies.

BACKGROUND: Conventional cineradiology has been used clinically to detect partially broken outlet struts (single leg separations, SLSs) in normally functioning Björk-Shiley convexo-concave (C/C) heart valves. The value of radiographic screening has, however, been debated in the medical literature. This study uses the same radiographic technique in sheep implanted with known-status C/C valves in combination with a newly developed geometric image magnification radiography system. This study was designed to test whether sensitivity and specificity of radiographic screening of C/C valves in detecting SLSs could be improved through the combination of readers and imaging modalities. METHODS: Twenty-one sheep with mitral C/C valves were studied on both systems. Five were used for extensive scanning training. When operators were expert on both systems, 16 blinded study valves (4 intact and 12 with outlet strut SLSs) were scanned twice on both systems, first on a modified conventional and then a prototype geometric image magnification (Feinfocus(TM)) cineradiographic system by two expert physicians working together. RESULTS: Among the 32 scanned valves, the two combined expert physicians were required to evaluate 40 intact legs and 24 with an SLS. For all SLS valves, the conventional and Feinfocus systems separately detected 50 (12/24) and 54% (13/24), respectively. When the two systems were combined, the final consensus score was correct in 67% (16/24) of all SLS valves. CONCLUSIONS: Combined modality, paired expert physicians detected 67% of all SLSs. The Feinfocus system might be best reserved for those patients in whom the Siemens screening study demonstrates in minimally suspicious (grade 2) or suspicious (grade 3) appearance of a C/C valve outlet strut leg.

Animals↗
PubMed1998

In vivo accuracy of two radiographic systems in the detection of Björk-Shiley convexo-concave heart valve outlet strut single leg separations.

OBJECTIVE: Modified cineradiographic systems have been used clinically to detect partially broken outlet struts in normally functioning Björk-Shiley convexo-concave heart valves. Almost all such valves were explanted, presuming that full failure would likely follow. Inasmuch as the clinical setting only rarely permits examination of normally rated valves, the accuracy of radiographic detection cannot be clinically defined. This study uses the clinical radiographic technique in sheep implanted with known-status convexo-concave valves, comparing its accuracy and that of a newly developed, geometric image magnification radiography system. METHODS: Twenty-one sheep with mitral convexo-concave valves were studied on both systems. Five were used for extensive training. When operators were expert with both systems, images of four intact valves and 12 valves with outlet strut single leg separations, along with a seventeenth single leg separation valve used for calibration, were integrated into 112 image sets organized into a balanced incomplete block design for evaluation by eight trained, blinded reviewers. RESULTS: Cineradiography sensitivity was 24% versus 31% for direct image magnification. The odds ratio for detection of single leg separation by direct image magnification versus cineradiography was 2.0 (95% confidence interval, 0.76 to 5.9; p = 0.13). Cineradiography specificity was 93% versus 90% for direct image magnification. Sensitivity and specificity varied markedly by reviewer, with sensitivity ranging from 8% to 55% and specificity from 51% to 100% for the combined technologies. CONCLUSIONS: The data support the need for more intensive training for convexo-concave valve imaging and further investigation of unconventional radiographic technologies. Clinical cineradiography of convexo-concave valves may detect as little as 25% of valves having a single leg separation, underestimating the prevalence of single leg separations and thereby implying more rapid progression to full fracture than is actually the case.

Animals↗
PubMed1998

The readability of currently used surgical/procedure consent forms in the United States.

BACKGROUND: Informed consent forms are universally used by hospitals throughout the United States before surgery or invasive procedures. This survey was undertaken to determine the content of these forms and their ability to be understood by individuals with differing reading comprehension levels. METHODS: Ten percent of all U.S. hospitals were requested to forward a copy of their current surgical/procedural informed consent form. The forms received were digitized and computer assessed for readability. In addition, each form was evaluated for a variety of items with respect to content. RESULTS: Of the 2194 requests mailed, 681 responses were received including 616 with surgical/procedural consent forms. The mean grade level required to understand these consent forms was 12.6 (+/- 3.1). There was no variability in readability scores on the basis of hospital bed size. Of the 616 consent forms reviewed, 29, 146, 347, and 461 forms could be understood by individuals reading at a grade level of less than 8 and at least 8, 10, and 12 years of education, respectively. Although most required the name of the patient, physician, and procedure, the majority did not describe or provide a full-in blank for the specific benefits, risks, and alternatives to the procedure. CONCLUSIONS: The majority of surgical/procedural informed consent forms currently used by U.S. hospitals are complex and are not easily understood by the average patient. In addition, the majority of reviewed consent forms do not list specific benefits or potential complications of the planned surgery/procedure.

Hospitals↗
PubMed1998

CT bronchoscopy: optimization of imaging parameters.

The authors evaluated the relative importance of the following scanning parameters at computed tomographic bronchoscopy in an anesthetized adult sheep's thorax: section thickness (2, 4, 8 mm), pitch (1.0, 1.5, 2.0), milliampere setting (100, 175, 250 mA), and overlap of reconstructed sections (0%, 25%, 50%, 75%). Five blinded readers ranked the images twice in comparison with photographs of the mounted specimen. Differences in image quality were significant (P < .001) with section thickness of 2 mm and a pitch of 1.0. The milliampere setting had only a minor effect on image quality, and a 50% overlap of reconstructed sections was best.

Animals↗
PubMed1998

Measuring carotid artery stenosis using CT angiography: the dilemma of artifactual lumen eccentricity.

OBJECTIVE: This study assesses artifactual luminal distortion, or eccentricity, that affects measurement of stenosis on CT angiography performed with a variety of helical protocols. MATERIALS AND METHODS: A 32-vessel carotid artery phantom was built with five known grades of stenoses (25%, 50%, 75%, 88%, and 94%) and three lengths of stenosis (1, 3, and 5 mm). This phantom was scanned with conventional and 1.0-, 1.5-, and 2.0-pitch helical CT with slice thicknesses of 2, 4, and 8 mm, and three vessel orientations: parallel, 45 degrees oblique, and perpendicular to the z-axis. Oblique multiplanar reconstruction was performed with the latter two vessel orientations to produce images similar to the parallel to z-axis orientation. The cross-sectional images were then used to measure the maximum and minimum (longest and shortest) luminal diameters in and out of each stenosis at a computer workstation by a single investigator who was unaware of the scanning technique. Percentage of stenosis was assessed by three methods: cross-sectional area in and out of the stenosis, maximum diameter out of stenosis and minimum in stenosis (North American Symptomatic Carotid Endarterectomy Trial method), and minimum diameter in and out of the stenosis. Comparisons were made with the gold standard using the equation (measured percentage of stenosis-actual percentage of stenosis) based on known luminal diameters of the phantom. Luminal eccentricity was assessed for each of the vessels and scanning parameters as a ratio of minimum to maximum diameters. RESULTS: All three methods of measuring stenoses were strongly affected by luminal eccentricity. The North American Symptomatic Carotid Endarterectomy Trial method overestimated percentage of stenosis an average of 1.64%. The most accurate results were obtained when using the minimum diameter in and out of the stenoses (-0.45% from the gold standard). Eccentricity was significantly greater in stenoses than in normal lumen (p < .0001) and when the vessels were oriented perpendicular to the z-axis (p = .0003). A progressive increase in eccentricity was seen in the 4- and 8-mm slice thicknesses and the 3- and 5-mm-long stenoses (p < .001; p < .001). CONCLUSION: Artifactual luminal eccentricity has significant implications for measuring percentage of stenosis revealed by CT angiography. Eccentricity increases in longer stenoses, thicker slices, and vessels oriented perpendicular to the z-axis. With CT angiography, measurement of minimum diameters in and out of a stenosis provides the most accurate assessment of percentage of stenosis.

Artifacts↗
PubMed1997

Radiographic detection of single-leg fracture in Björk-Shiley Convexo-Concave prosthetic valves: a phantom model study.

Cineradiography can identify patients with single-leg fractured Björk-Shiley Convexo-Concave valves, although little is known about the sensitivity and specificity of this technique. We evaluated three normal and six (0 microm gap) single-leg fractured Björk-Shiley valves that were placed in a working phantom model. Valves were randomly imaged a total of 33 times and duplicated into a 120-valve series with a 1:9 ratio of abnormal/normal valves. Six reviewers independently graded each valve and demonstrated markedly different rates of identifying the fractured valves. Average sensitivity at the grade that clinically results in valve explanation was 47%. Among the normal valves, a correct identification was made 96% (range 91% to 99%) of the time. Present radiographic technology may have significant difficulty in identifying true single-leg fracture in Björk-Shiley valves with limb separations that are common among clinically explanted valves.

Angiocardiography↗
PubMed1997

The clinical usefulness of routine stacked multiplanar reconstruction in helical abdominal computed tomography.

RATIONALE AND OBJECTIVES: The authors evaluate the usefulness of stacked multiplanar reconstructions in routine, thick-section abdominal computed tomography. MATERIALS AND METHODS: Twenty-five routine, thick-section contrast abdominal CTs performed with equivalent technique were reformatted by multiplanar reconstructions in sagittal and coronal planes sequentially from side-to-side and front-to-back. The image sets were submitted, first axial images only followed by axial plus multiplanar reconstructions (MPRs), to 5 separate physician readers including 2 radiologists and 3 nonradiologists. These readers graded the visualization of a variety of normal and up to 5 pathologic lesions per patient on a scale of 1 to 5 (5 = best). RESULTS: The addition of sagittal and coronal multiplanar reconstructions significantly improved the visualization of all normal anatomic structures (mean axial only, 3.8; mean axial plus MPR, 4.1; P < 0.0001). In addition, most pathologic lesions were statistically better visualized with the addition of multiplanar reconstructions (mean axial images only, 3.9; mean axial plus MPR, 4.1; P < 0.0001). All five readers found improved visualization in nearly every category with the addition of the multiplanar reconstructions. However, in only 7% of cases, did a reviewer find new diagnostic information with the addition of MPR images. CONCLUSIONS: Stacked multiplanar reconstructions of routine, thick-section abdominal CT has clinical value in both the display of normal anatomic and pathologic lesions. Further studies, however, are required to confirm these findings before it is commonly used.

Humans↗
PubMed1997

Comparison of 1.0-, 1.5-, and 2.0-pitch abdominal helical computed tomography in evaluation of normal structures and pathologic lesions.

RATIONALE AND OBJECTIVES: The authors performed a comprehensive prospective clinical trial comparing 1.0-, 1.5-, and 2.0-pitch abdominal helical computed tomography (CT) in the evaluation of normal and pathologic structures/lesions. METHODS: Seventy-five consecutive patients were randomized by computer into one of three equal groups: helical CT pitch 1.0, 1.5, and 2.0. The imaging parameters and contrast enhancement of all 75 patients were kept constant. The 75 studies were masked, placed into a randomized order, and evaluated by five separate experienced radiologists who rated visualization of 25 normal structures and up to five pathologic findings per patient using a scale of 1 (not seen) to 5 (very well seen/very sharp margins). RESULTS: There were no statistical differences in 1.0- and 1.5-pitch abdominal CT scans when assessing the display of normal and pathologic lesions. In addition, helical pitch 1.0 and 1.5 studies were equivalent for both normal and pathologic structures/lesions, whereas equivalency was not demonstrated for helical pitch 2.0 studies. Overall study assessment questions again found equivalency between helical 1.0- and 1.5-pitch studies. CONCLUSIONS: Abdominal CT performed with pitches of 1.0 and 1.5 are equivalent. Because of its advantages, we advocate the routine use of an extended pitch (1.5) in routine abdominal CT. Further studies are required to evaluate the usefulness of the helical 2.0-pitch technique.

Contrast Media↗