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Biomedical subjects

R M Summers

Publications and source records attributed to R M Summers.

At least 19 recordsLinked to original sources
PubMed2001

Automated polyp detection at CT colonography: feasibility assessment in a human population.

PURPOSE: To test the feasibility of and improve a computer algorithm to automatically detect colonic polyps in real human computed tomographic (CT) colonographic data sets. MATERIALS AND METHODS: Twenty patients with known polyps underwent CT colonography in the supine position. CT colonographic data were processed by using a shape-based algorithm that depicts masses that protrude into the lumen. We studied nine shape criteria and three isosurface threshold settings. Results were compared with those of conventional colonoscopy performed the same day. RESULTS: There were 50 polyps (28 were > or =10 mm in size; 12, 5-9 mm; 10, <5 mm). The sensitivity with optimal settings for detecting polyps 10 mm or greater was 64% (18 of 28). Sensitivity improved to 71% (10 of 14) for polyps 10 mm or greater in well-distended colonic segments. Performance decreased for polyps less than 10 mm, poorly distended colonic segments, and other shape algorithms. There was a mean of six false-positive lesion sites per colon. These sites were reduced 39% to 3.5 per colon by sampling CT attenuation at the lesion site and discarding sites having attenuation less than a threshold. CONCLUSION: Automated detection of colonic polyps, especially clinically important large polyps, is feasible. Colonic distention is an important determinant of sensitivity. Further increases in sensitivity may be achieved by adding prone CT colonography.

Adult↗
PubMed2001

Hepatic MR angiography: a multiobserver comparison of visualization methods.

OBJECTIVE: MR angiography (MRA) is an established diagnostic method; however, controversy remains over the best technique for display. In this study, we compared five methods of depicting hepatic MRA, including a novel skeletonization approach, using receiver operator characteristic (ROC) curves, interobserver variability (kappa values), and speed of interpretation. SUBJECTS AND METHODS: Twenty-one patients scheduled for isolated liver perfusion therapy for metastatic disease underwent contrast-enhanced three-dimensional MRA to determine vascular anatomy. Vascular anatomy was validated at the time of surgery. We displayed the image data, using five techniques: maximum intensity projection, targeted maximum intensity projection, isointensity surface (isosurface), connected isointensity surface (connected isosurface), and ordered region growing skeleton (skeleton). Four observers, blinded to the surgical results, interpreted each technique in random order without patient identifiers. Areas under the ROC curves, kappa values of interobserver variability, and time to interpret each display were compared. RESULTS: Skeletonized MRA had the highest area under the ROC curve (A(z), 0.90 +/- 0.04) compared with the other techniques (p < 0.013). Kappa scores of agreement were also highest for skeletonized MRA (0.75 +/- 0.04) and had no overlap at the 95% confidence level compared with other techniques. Compared with source images, all visualization methods were faster to interpret, but the skeleton technique was more quickly (p = 0.04) interpreted than the other techniques. CONCLUSION: Skeletonized MRA with the skeleton connectivity algorithm is a semi-automated method of displaying complex arterial anatomy. Compared with other techniques, it is more accurate, more consistent among observers, and slightly faster to interpret. Skeletonization should be applicable to CT angiography and MRA.

Female↗
PubMed2000

Magnetic resonance imaging detection of occult skin and subcutaneous abnormalities in juvenile dermatomyositis. Implications for diagnosis and therapy.

OBJECTIVE: To assess the utility of magnetic resonance imaging (MRI) of skin, subcutaneous tissue, and fascia in evaluating disease activity in juvenile dermatomyositis (DM). METHODS: Short tau inversion recovery (STIR) MRI of the proximal thighs and buttocks, cutaneous assessment, and other measures of disease activity were prospectively obtained in 26 children meeting criteria for probable or definite juvenile DM. Also undergoing STIR MRI assessment were 8 subjects who were being evaluated for muscle disorders and who were not diagnosed as having juvenile DM. RESULTS: Skin, subcutaneous, or fascial edema of the thighs and buttocks were seen on STIR MRI in up to 85% of juvenile DM patients at baseline evaluation compared with no more than 38% of the comparison group without juvenile DM. In juvenile DM, STIR MRI skin and subcutaneous edema scores correlated (r(s) = 0.51, P = 0.008), as did fascial and muscle edema scores (r(s) = 0.58, P = 0.002). Skin global disease activity scores correlated with MRI skin edema scores (r(s) = 0.41, P = 0.04), and serum aldolase levels correlated with both MRI skin and subcutaneous edema scores (r = 0.44 and 0.40, P = 0.03 and 0.05 respectively). The extent and severity of STIR MRI changes in the skin, subcutaneous tissue, and fascia were not predicted by most other measures of juvenile DM disease activity. Five juvenile DM patients with thigh MRI subcutaneous edema developed clinically apparent calcinosis at the same location within 9 months. CONCLUSION: Edema or inflammation in the skin, subcutaneous tissue, and fascia, found on STIR MRI, is common in juvenile DM patients and is often undetected by standard assessments. These MRI changes can precede the development of calcinosis. STIR MRI may be a useful adjunct for assessing disease activity and guiding the treatment of juvenile DM.

Adolescent↗
PubMed2000

Gray-scale skeletonization of small vessels in magnetic resonance angiography.

Interpretation of magnetic resonance angiography (MRA) is problematic due to complexities of vascular shape and to artifacts such as the partial volume effect. We present new methods to assist in the interpretation of MRA. These include methods for detection of vessel paths and for determination of branching patterns of vascular trees. They are based on the ordered region growing (ORG) algorithm that represents the image as an acyclic graph, which can be reduced to a skeleton by specifying vessel endpoints or by a pruning process. Ambiguities in the vessel branching due to vessel overlap are effectively resolved by heuristic methods that incorporate a priori knowledge of bifurcation spacing. Vessel paths are detected at interactive speeds on a 500-MHz processor using vessel endpoints. These methods apply best to smaller vessels where the image intensity peaks at the center of the lumen which, for the abdominal MRA, includes vessels whose diameter is less than 1 cm.

Algorithms↗
PubMed2000

Automated polyp detector for CT colonography: feasibility study.

An abdominal computed tomographic scan was modified by inserting 10 simulated colonic polyps with use of methods that closely mimic the attenuation, noise, and polyp-colon wall interface of naturally occurring polyps. A shape-based polyp detector successfully located six of the 10 polyps. When settings that enhanced the edge profile of polyps were chosen, eight of 10 polyps were detected. There were no false-positive detections. Shape analysis is technically feasible and is a promising approach to automated polyp detection.

Colon↗
PubMed1999

Mucosal morbidity in patients with epidermolysis bullosa acquisita.

BACKGROUND: Epidermolysis bullosa acquisita is an acquired inflammatory and/or dermolytic subepidermal blistering disease characterized by IgG autoantibodies to type VII collagen. Four patients with documented epidermolysis bullosa acquisita were evaluated by a multidisciplinary team of care providers (4 dermatologists, an ophthalmologist, a radiologist, a voice and speech specialist, and an otolaryngologist) for 1 to 5 years to characterize mucosal involvement and its complications and response to treatment. Patients were evaluated clinically and by slitlamp examinations, endoscopies, computed tomographic scans, and videofluorographic swallowing studies. Spiral computed tomographic scans for virtual endoscopy were used for the nontraumatic evaluation of airways in 2 patients with respiratory tract compromise. OBSERVATIONS: Involvement of 5 or more mucosal sites--mouth, nose, conjunctiva, pharynx, and larynx--was documented in all patients. Complications included ankyloglossia, periodontal disease, scarring and crusting of nasal mucosa, symblepharon formation, obstruction of nasolacrimal ducts, deformation of the epiglottis, impaired phonation, dysphagia, esophageal strictures, and supraglottic stenosis requiring emergency tracheostomy. CONCLUSIONS: Epidermolysis bullosa acquisita may extensively (or predominantly) affect mucosal epithelia in a manner resembling cicatricial pemphigoid. Mucosal disease in these patients is often subclinical, can lead to serious complications, and is best managed using a multidisciplinary approach.

Adult↗
PubMed1999

13N-ammonia myocardial blood flow and uptake: relation to functional outcome of asynergic regions after revascularization.

OBJECTIVES: In this study we determined whether 13N-ammonia uptake measured late after injection provides additional insight into myocardial viability beyond its value as a myocardial blood flow tracer. BACKGROUND: Myocardial accumulation of 13N-ammonia is dependent on both regional blood flow and metabolic trapping. METHODS: Twenty-six patients with chronic coronary artery disease and left ventricular dysfunction underwent prerevascularization 13N-ammonia and 18F-deoxyglucose (FDG) positron emission tomography, and thallium single-photon emission computed tomography. Pre- and postrevascularization wall-motion abnormalities were assessed using gated cardiac magnetic resonance imaging or gated radionuclide angiography. RESULTS: Wall motion improved in 61 of 107 (57%) initially asynergic regions and remained abnormal in 46 after revascularization. Mean absolute myocardial blood flow was significantly higher in regions that improved compared to regions that did not improve after revascularization (0.63+/-0.27 vs. 0.52+/-0.25 ml/min/g, p < 0.04). Similarly, the magnitude of late 13N-ammonia uptake and FDG uptake was significantly higher in regions that improved (90+/-20% and 94+/-25%, respectively) compared to regions that did not improve after revascularization (67+/-24% and 71+/-25%, p < 0.001 for both, respectively). However, late 13N-ammonia uptake was a significantly better predictor of functional improvement after revascularization (area under the receiver operating characteristic [ROC] curve = 0.79) when compared to absolute blood flow (area under the ROC curve = 0.63, p < 0.05). In addition, there was a linear relationship between late 13N-ammonia uptake and FDG uptake (r = 0.68, p < 0.001) as well as thallium uptake (r = 0.76, p < 0.001) in all asynergic regions. CONCLUSIONS: These data suggest that beyond its value as a perfusion tracer, late 13N-ammonia uptake provides useful information regarding functional recovery after revascularization. The parallel relationship among 13N-ammonia, FDG, and thallium uptake supports the concept that uptake of 13N-ammonia as measured from the late images may provide important insight regarding cell membrane integrity and myocardial viability.

Adult↗
PubMed1998

Stress-induced reversible and mild-to-moderate irreversible thallium defects: are they equally accurate for predicting recovery of regional left ventricular function after revascularization?

BACKGROUND: In patients with coronary artery disease, stress-redistribution-reinjection thallium scintigraphy provides important information regarding myocardial ischemia and viability. Although both reversible and mild-to-moderate irreversible thallium defects retain metabolically active, viable myocardium, we hypothesized that stress-induced reversible thallium defects may better differentiate reversible from irreversible regional left ventricular dysfunction after revascularization. METHODS AND RESULTS: Twenty-four patients with chronic coronary artery disease underwent prerevascularization and postrevascularization exercise-redistribution-reinjection thallium single photon emission CT, gated MRI, and radionuclide angiography. After revascularization, mean left ventricular ejection fraction increased from 30+/-9% to 37+/-13% at rest (P<0.001). Before revascularization, abnormal contraction at rest was observed in 56 of 110 reversible and 20 of 37 mild-to-moderate irreversible thallium defects (51% and 54%, respectively). After revascularization, regional contraction improved in 44 of 56 reversible compared with 6 of 20 mild-to-moderate irreversible thallium defects (79% and 30%, respectively; P<0.001). The final thallium content (maximum tracer uptake on redistribution-reinjection images) was significantly higher in regions with reversible defects that improved than in those that did not improve after revascularization (86+/-16% versus 66+/-9%, P<0.001). In contrast, final thallium content was similar in regions with mild-to-moderate irreversible defects that improved and in those that did not improve after revascularization (69+/-9% versus 65+/-10%, P=NS). Furthermore, when asynergic regions were grouped according to the final thallium content, at 60% threshold value, functional recovery was observed in 83% of regions with reversible defects compared with 33% of regions with mild-to-moderate irreversible defects (P<0.001). CONCLUSIONS: These findings suggest that although both reversible and mild-to-moderate irreversible thallium defects after stress retain viable myocardium, the identification of reversible thallium defect on stress in an asynergic region more accurately predicts recovery of function after revascularization. Even at a similar mass of viable myocardial tissue (as reflected by the final thallium content), the presence of inducible ischemia is associated with an increased likelihood of functional recovery.

Adult↗
PubMed1998

Evaluation of the aortic root by MRI: insights from patients with homozygous familial hypercholesterolemia.

BACKGROUND: In homozygous familial hypercholesterolemia (HFH), the aortic root is prone to develop atherosclerotic plaque at an early age. However, the aortic wall and plaque have not yet been assessed in this condition by MRI. We evaluated the aortic root by use of MRI in 17 HFH patients and 12 normal control subjects in a prospective, blinded, controlled study. METHODS AND RESULTS: Morphological assessment of the aortic root was done with spin-echo and gradient-echo MRI scanning. Comparisons were made with a number of measures of disease severity, including cholesterol-year score, calcium score on electron-beam CT (EBCT), and size of Achilles tendon xanthomas. Atherosclerotic plaque, visible on fat-suppressed images but never on water-suppressed images, was present in 9 HFH patients (53%). Supravalvular aortic stenosis was present in 7 patients with HFH (41%). Maximum supravalvular aortic wall thickness was significantly greater and OD and lumen cross-sectional area (CSA) were smaller in patients than in control subjects (P=0.006, 0.0005, and 0.06, respectively). Maximum wall thickness was associated with a greater calcium score on electron-beam CT (P=0.02). Although the cumulative exposure of the aortic root to cholesterol (the cholesterol-year score) was significantly correlated with the Achilles tendon CSA and vascular calcification, this score did not correlate with the wall thickness or aortic CSA. CONCLUSIONS: This study not only demonstrates the utility of MRI for detecting and characterizing aortic root atherosclerotic plaque and supravalvular aortic stenosis in HFH patients but also suggests that the LDL receptor plays a direct or indirect role in aortic mural development and vascular growth.

Achilles Tendon↗
PubMed1998

Polypoid lesions of airways: early experience with computer-assisted detection by using virtual bronchoscopy and surface curvature.

PURPOSE: To test the application of a technique developed by the authors for the computer-assisted diagnosis of polypoid airway lesions from surface rendered virtual bronchoscopic reconstructions. MATERIALS AND METHODS: A computer algorithm was developed to detect polypoid airway lesions by means of segmentation of the bronchial surface with curvature classification. This method was tested with a bronchial phantom, five cadaveric lung specimens, and virtual bronchoscopic studies in 16 patients. RESULTS: For the patient studies, the sensitivity and specificity of the method were 47%-88% and 58%-89%, respectively, depending on the value of an adjustable parameter (the mean curvature threshold). The sensitivity increased (by 20% to 34%) when only lesions larger than 5 mm in diameter were considered. CONCLUSION: With this method, polypoid airway lesions can be detected automatically, although false-positive diagnoses present an important limitation.

Adult↗
PubMed1998

Juvenile idiopathic inflammatory myopathy: exercise-induced changes in muscle at short inversion time inversion-recovery MR imaging.

PURPOSE: To study the effect of exercise on short inversion time inversion-recovery (STIR) magnetic resonance (MR) images of thigh muscles in children with juvenile idiopathic inflammatory myopathy. MATERIALS AND METHODS: Thirty-two MR studies were performed in 19 patients with juvenile idiopathic inflammatory myopathy who performed stair-stepping exercise for up to 10 minutes (mean, 5.7 minutes). Baseline T1-weighted (n = 32) and STIR (n = 32) images and STIR images immediately (n = 32) and at 30 (n = 24) and 60 (n = 29) minutes after exercise were obtained at 0.5 T. Four radiologists graded STIR signal intensity changes, in observer performance experiments in which they were blinded to the order of image acquisition in relation to exercise. RESULTS: Changes in muscle signal intensity were observed on STIR images obtained immediately after exercise in 20 of 32 (63%) studies. The mean signal intensity score immediately after exercise (1.7 +/- 1.0 [SD]) increased compared with the mean baseline score (1.4 +/- 1.1) (P = .0005) and resolved by 30 minutes after exercise. The magnitude of exercise-induced changes correlated with the amount of work performed (r = 0.51, P = .003) but not with disease activity or baseline signal intensity when the changes were corrected for work (r < 0.17, P > .35). Radiologists demonstrated moderate to substantial agreement in the grading of signal intensity changes after exercise (kappa = 0.60-0.84). CONCLUSION: In patients with juvenile idiopathic inflammatory myopathy, stair-stepping exercise induces signal intensity changes on STIR MR studies of muscle for approximately 30 minutes after exercise, in a distribution that may mimic active muscle inflammation.

Adolescent↗
PubMed1997

Fructose transport mechanisms in humans.

BACKGROUND & AIMS: The possible mechanisms of fructose transport are diffusion, a disaccharidase-related transport system, and glucose-facilitated fructose transport. However, these mechanisms in the human small intestine have not been systematically examined. This study was designed to investigate the mechanisms of fructose transport in the human duodenojejunum. METHODS: A triple-lumen tube was fluoroscopically positioned in the duodenojejunum of 7 men. Nine carbohydrate-electrolyte solutions were perfused at the rate of 15 mL/min. Acarbose and lactulose were used to examine the disaccharidase-related transport system and glucose-facilitated fructose transport, respectively. RESULTS: Fructose absorption was greater (P < 0.05) from fructose-glucose (FruGlu) and fructose-glucose-acarbose (FruGluA) solutions than from fructose-mannitol (FruMann) and fructose-mannitol-acarbose (FruMannA) solutions, but there was no difference between FruGlu and FruGluA solutions. A sucrose solution produced greater (P < 0.05) sucrose absorption than a sucrose-acarbose solution. Lactulose absorption (0.016-0.039 mmol.h-1.cm-1) was observed from solutions containing glucose or sucrose. Water absorption was not different among sucrose, FruGlu, and glucose solutions. FruMann solution produced net water secretion. These data suggest that free fructose and glucose transport were not inhibited by acarbose and that the presence of glucose induced lactulose absorption and enhanced fructose absorption. CONCLUSIONS: Fructose is transported transcellularly by facilitated diffusion and paracellularly (based on lactulose transport) via glucose-activated solution drag. In the human small intestine, free fructose and glucose transport does not occur via the disaccharidase system.

Acarbose↗
PubMed1997

Navigational aids for real-time virtual bronchoscopy.

OBJECTIVE: Virtual bronchoscopy is a recently described technique for performing simulated bronchoscopy using data obtained from thin-section CT scans of the airways. Although the detail visible during virtual bronchoscopy can be striking, the lack of global context and physical cues can lead to disorientation for the radiologist, especially during real-time "fly-throughs." We investigated the use of seven software tools (coordinate axes, global maps, trail markers, cross-references to standard two-dimensional projections, rear-view windows, collision avoidance, and stereoscopic displays) that are navigational aids to overcome such disorientation. CONCLUSION: The navigational aids performed satisfactorily on virtual bronchoscopy studies from 21 patients. A frame rate of one to seven frames per second, depending on the complexity of the bronchial model, could be attained. Several of the aids worked best when used selectively or when updated frequently but not continuously. Navigational aids are potentially useful for guiding radiologists who do virtual bronchoscopy studies. Such aids are general tools that may be applicable to other types of virtual endoscopy.

Adult↗
PubMed1996

Fast spoiled gradient-recalled MR imaging of thoracic aortic dissection: preliminary clinical experience at 1.5 T.

The purpose of this study was to evaluate fast spoiled gradient-recalled (FSPGR) magnetic resonance (MR) imaging in the diagnosis of thoracic aortic dissection (TAD). Twenty-eight patients with suspected TAD underwent MR imaging with FSPGR and either cine or cardiac-gated spin-echo MR techniques. The average scanning time for the FSPGR images was approximately 1 min. Three readers interpreted the FSPGR images for the presence or absence of TAD. An ROC analysis was done. At a specificity of 90%, the sensitivity ranged from 52% to 90% for the three readers. Pulsatility artifacts and mural thrombus were causes of false-positive and false-negative readings. The areas under the ROC curves (Az) ranged from 0.85 to 0.97 for the three readers. There was a statistically significant difference in the Az values for two of the experienced readers (p = .02). The correct type of dissection was determined in only 65% of the true-positive diagnoses. FSPGR has a very limited role in screening and for rapid evaluation of the unstable patient. The results are reader dependent and susceptible to pulsatility artifacts. Determination of the type of dissection is limited. With a suspected thoracic aortic dissection, therefore, additional imaging sequences should be obtained to maximize accuracy.

Adolescent↗
PubMed1996

A Fourier based algorithm for tracking SPAMM tags in gated magnetic resonance cardiac images.

A method is described for automatically tracking spatial modulation of magnetization tag lines on gated cardiac images. The method differs from previously reported methods in that it uses Fourier based spatial frequency and phase information to separately track horizontal and vertical tag lines. Use of global information from the frequency spectrum of an entire set of tag lines was hypothesized to result in a robust algorithm with decreased sensitivity to noise. The method was validated in several ways: first, actual tagged cardiac images at end diastole were deformed known amounts, and the algorithm's predictions compared to the known deformations. Second, tagged, gated images of the thigh muscle (assumed to have similar signal to noise characteristics as cardiac images, but to not deform with time) were created. Again the algorithmic predictions could be compared to the known (zero magnitude) deformations and to thigh images which had been artificially deformed. Finally, actual cardiac tagged images were acquired, and comparisons made between manual, visual, determinations of tag line locations, and those predicted by the algorithm. At 0.5 T, the mean bias of the method was < 0.34 mm even at large deformations and at late (noisy) times. The standard deviation of the method, estimated from the tagged thigh images, was < 0.7 mm even at late times. The method may be expected to have even lower error at higher field strengths.

Algorithms↗