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Biomedical subjects

F G Sommer

Publications and source records attributed to F G Sommer.

At least 37 records · Page 2Linked to original sources
PubMed1994

Spiral CT of renal artery stenosis: comparison of three-dimensional rendering techniques.

PURPOSE: To evaluate the accuracy of computed tomographic (CT) angiography in the detection of renal artery stenosis (RAS). MATERIALS AND METHODS: CT angiography was performed in 31 patients undergoing conventional renal arteriography. CT angiographic data were reconstructed with shaded surface display (SSD) and maximum-intensity projection (MIP). Stenosis was graded with a four-point scale (grades 0-3). The presence of mural calcification, poststenotic dilatation, and nephrographic abnormalities was also noted. RESULTS: CT angiography depicted all main (n = 62) and accessory (n = 11) renal arteries that were seen at conventional arteriography. MIP CT angiography was 92% sensitive and 83% specific for the detection of grade 2-3 stenoses (> or = 70% stenosis). SSD CT angiography was 59% sensitive and 82% specific for the detection of grade 2-3 stenoses. The accuracy of stenosis grading was 80% with MIP and 55% with SSD CT angiography. Poststenotic dilatation and the presence of an abnormal nephrogram were 85% and 98% specific, respectively. CONCLUSION: CT angiography shows promise in the diagnosis of RAS. The accuracy of CT angiography varies with the three-dimensional rendering technique employed.

Adult↗
PubMed1994

Renal artery blood flow: quantitation with phase-contrast MR imaging with and without breath holding.

PURPOSE: To compare the accuracy of 16-frame cine phase-contrast (PC) magnetic resonance (MR) imaging with those of two breath-hold PC techniques in the measurement of renal artery blood flow. MATERIALS AND METHODS: In vitro flow measurements were performed in a segment of harvested human artery embedded in gel. For the cine PC acquisition, respiratory motion was simulated. In eight subjects with recently obtained para-amino-hippurate-clearance renal blood flow data, renal artery flow measurements were subsequently performed with two breath-hold imaging techniques and with cine PC imaging during shallow respiration. RESULTS: Breath-hold sequences were significantly more accurate than conventional cine PC sequences both in vitro (P < .005) and in vivo (P < .05). Cine PC imaging tended to overestimate flow (in vivo mean, 24.47% +/- 9.94), reflecting artifactual enlargement of the apparent vessel size. CONCLUSION: Reliable blood flow measurements in the renal artery are possible with breath-hold PC MR imaging.

Adult↗
PubMed1994

Color Doppler sonography of focal gastrointestinal lesions: initial clinical experience.

Graded compression color Doppler sonography was used to evaluate gastrointestinal blood flow in 20 normal fasting subjects and 32 patients with focal gastrointestinal lesions. Imaging was optimized for color sensitivity using a 5 MHz linear array transducer. Criteria were established for normal mural blood flow based on findings in normal controls. Two reviewers blinded to the final diagnosis compared patterns of mural vascularity in normal and abnormal patients. Increased mural blood flow was demonstrated in all 32 patients with gastrointestinal inflammatory disorders and in seven of nine patients with neoplasms. No mural flow was demonstrated in four patients with small bowel infarction. The greatest overall degree of flow was noted in patients with Crohn's disease and cytomegalovirus colitis. Flow in tumors was variable, ranging from strikingly increased flow in a giant villoglandular polyp to absent flow in a metastasis from lung carcinoma. Our preliminary experience suggests that the presence of considerable overlap in the color Doppler patterns of mural blood flow in inflammatory and neoplastic lesions. Color Doppler sonography alone without spectral waveform analysis may not distinguish focal inflammatory from neoplastic disorders of the gastrointestinal tract reliably. However, this technique potentially may be useful in diagnosing small bowel ischemia when thickened segments of small bowel are identified with absent flow.

Adult↗
PubMed1994

Quantitative magnetic resonance flow imaging.

Time-of-flight and phase shift methods have both been used for vascular imaging with magnetic resonance. Phase methods, and phase contrast in particular, are well suited to quantitative measurements of velocity and volume flow rate. The most robust methods for measuring flow encode through-plane velocity into phase shift and compute flow by integrating the measured velocity over the vessel lumen. The accuracy of the flow data can be degraded by the effects of acceleration and eddy currents and by partial volume effects, including the effects of finite slice thickness and resolution, pulsatile waveforms, motion, and chemical shift. The reproducibility depends on the signal-to-noise of the data and the strength of the flow encoding and can be degraded by inconsistent definition of the vessel boundary. The adjustable flow sensitivity inherent in this method is a particular asset, allowing phase contrast flow measurement to operate over a dynamic range exceeding 10(5). Recently developed rapid imaging methods are helpful in applications that would be compromised by respiratory motion. With care, excellent quantitative data can be quickly obtained in vivo, and the resulting flow information is valuable for the diagnosis and management of a variety of conditions.

Humans↗
PubMed1993

Gadolinium-enhanced MRI of the abnormal prostate.

A prospective study of the use of a low osmolar gadolinium-based intravenous contrast material for MRI of the abnormal prostate was performed. Eight patients scheduled for prostatectomy, six with prostate cancer and two with benign prostatic hyperplasia (BPH), were imaged preoperatively on a 1.5 T system using a pelvic coil array and employing Gadodiamide (0.3 mmol/kg). T2-weighted fast-spin echo (FSE) imaging was also performed in the same axial planes employed for gadolinium-enhanced studies. Detailed pathologic correlation was performed for the six patients with carcinoma. While regions of BPH and cancer enhanced to a similar degree following intravenous contrast agent, BPH enhancement was more heterogeneous than cancer. No advantages in detecting prostate cancer, in differentiating cancer from BPH or normal prostatic tissue, or in assessing extra-prostatic spread of cancer were observed for the contrast-enhanced studies compared to T2-weighted FSE imaging.

Aged↗
PubMed1993

Adnexal masses: comparison of specificity of endovaginal US and pelvic MR imaging.

In a prospective study, 32 women with suspected pelvic masses at physical examination underwent both endovaginal ultrasound (US) and magnetic resonance (MR) imaging to compare their ability in diagnosis of adnexal masses. Criteria for the diagnosis of various types of adnexal masses with MR imaging and endovaginal US were prospectively defined, and the ability of either modality to allow a specific diagnosis was assessed. For each modality, measures of sensitivity, specificity, and accuracy were obtained. Results indicated higher diagnostic capability of endovaginal US for simple cysts (five of five), hemorrhagic cysts (eight of nine), endometriomas (nine of 14), and ovarian carcinomas (three of three). MR imaging demonstrated higher diagnostic capability for dermoids (three of three). MR imaging and endovaginal US showed equal diagnostic capability for pedunculated fibroids (two of two). For all masses, observers, and observations, the overall sensitivity of endovaginal US was 76% versus 49% for MR imaging, and the overall accuracy of endovaginal US was 83% versus 70% for MR imaging. The authors suggest that endovaginal US is a better modality than MR imaging for the assessment of suspected pelvic masses.

Adnexal Diseases↗
PubMed1993

Determining the volume of prostatic carcinoma: value of MR imaging with an external-array coil.

OBJECTIVE: The size of prostatic carcinomas, as determined by estimations of the tumor volume, has a direct correlation with the histologic grade and stage. Therefore, accurate information about tumor volume can play an important role in determining appropriate treatment and establishing a patient's prognosis. Accordingly, we performed a study to assess the accuracy of MR imaging with external-array coils and the fast spin-echo technique for determining tumor volume in patients with prostatic cancer. SUBJECTS AND METHODS: In a prospective study, 20 patients with biopsy-proved prostatic cancer had MR imaging before radical prostatectomy. A 1.5-T system, a prototype external-array coil, and fast spin-echo technique were used to obtain axial T2-weighted (4000/120 [TR/TE]) MR images throughout the prostate and seminal vesicles. Contiguous 5-mm sections were obtained with a 256 x 256 or 256 x 192 matrix, 24-cm field of view, four excitations, and fat suppression. The volumes of cancer obtained with MR imaging and surgical specimens were determined independently. The areas of tumor were determined from individual axial sections by summing and multiplying by the section thickness. RESULTS: Seventeen of the 20 cancers were detected on MR images. A significant correlation between the volume of the tumor as determined with MR imaging and measurements of the specimens was observed (r = .81, p < .001). Four transition zone tumors were detected as zones of rather homogeneous decreased intensity. One important source of error for volumes determined with MR images was a limitation in the histologic specificity of MR imaging for the delineation of cancer; in some cases benign changes or normal prostates were interpreted as cancer. Another limitation was the presence of changes after biopsy that concealed portions of 10 of the 17 tumors visualized. CONCLUSION: The accuracy of the MR technique used was not sufficient for reliable prediction of tumor volume. The lack of specificity of T2-weighted MR imaging for cancer detection and the presence of changes caused by biopsy were major sources of error.

Aged↗
PubMed1993

Prospects for ultrasonic spectroscopy and spectral imaging of abdominal tissues.

A system for the digitization and frequency spectral analysis of radiofrequency data for ultrasonic waveforms backscattered from abdominal tissues is described. Studies of phantoms meant to simulate abdominal tissues of differing scattering characteristics indicated that frequency spectral differences due to differences in the frequency dependence of backscattering were seen with 5 MHz probes, but not with a 3.5 MHz probe. Studies of a phantom with a simulated lesion of altered scattering characteristics indicated potential for improved lesion detection and characterization, using custom circuitry developed for variable bandwidth filtering of received ultrasonic beams. The techniques discussed have potential for improved diagnosis of diffuse and focal abdominal abnormalities over that obtained with conventional ultrasonic imaging.

Abdomen↗
PubMed1993

Follow-up sonography in suspected acalculous cholecystitis: preliminary clinical experience.

Fourteen adult patients with clinically suspected AAC and inconclusive initial sonograms underwent follow-up sonography within 24 hours. Eight patients had initial studies demonstrating a normal thickness of the gallbladder wall. Four of these patients demonstrated progressive thickening of the gallbladder wall on follow-up scans and were diagnosed as having AAC. In three of these patients AAC was proved at surgery, and the remaining patient improved clinically after percutaneous cholecystostomy. Four other patients with normal gallbladder wall thickness on both the initial and follow-up sonograms had benign clinical follow-up results without evidence of AAC. The remaining six patients had a thickened gallbladder on the initial sonogram. In one of these patients, the gallbladder wall thickening resolved on follow-up sonography. In the remaining five patients the gallbladder wall thickening did not change. Four of these patients had benign follow-up results but one patient was found to have AAC at surgery. Follow-up sonography may be helpful to confirm AAC if there is progressive edema of the gallbladder wall. A normal gallbladder wall on an initial study does not exclude early AAC. Thickening of the gallbladder wall on initial studies still remains a problem and other ancillary criteria must be used to establish the diagnosis of AAC.

Adult↗
PubMed1992

The pelvis: T2-weighted fast spin-echo MR imaging.

Fast spin-echo (SE) T2-weighted magnetic resonance (MR) imaging provides images with highly T2-weighted contrast in substantially reduced imaging times. In a prospective evaluation, fast SE T2-weighted imaging of the pelvis was compared with conventional SE T2-weighted imaging in 30 consecutive patients in whom pelvic pathologic conditions were suspected. Three reviewers independently analyzed the images for (a) overall image quality, (b) pelvic organ definition, (c) conspicuity of pelvic fluid, and (d) conspicuity of pelvic pathologic conditions. Fast SE images were rated superior to conventional SE T2-weighted images in 60% (54 of 90) of the case reviews for overall image quality, in 69% (62 of 90) for pelvic organ definition, in 63% (57 of 90) for conspicuity of pelvic fluid, and in 68% (43 of 63) for conspicuity of pelvic pathologic conditions. The fast SE examinations were typically three to four times faster than conventional SE T2-weighted examinations. No pathologic findings seen on conventional SE T2-weighted images were undetected on fast SE images. Fast SE images may replace conventional SE T2-weighted images in MR imaging of the pelvis.

Abdomen↗
PubMed1991

Gynecologic vascular abnormalities: diagnosis with Doppler US.

The authors describe the use of duplex and/or color Doppler ultrasonography of the pelvis in three women to demonstrate the presence of venous malformations. One patient with a pulsatile vaginal mass was shown to have an arteriovenous malformation of the vaginal wall. The second patient was shown to have an unsuspected venous angioma in the endometrial cavity. The third patient was shown to have adnexal varices that closely mimicked hydrosalpinx. In the latter two cases, the duplex and color flow capabilities of an endovaginal probe were especially important.

Adult↗
PubMed1991

Prostatic MR imaging performed with the three-point Dixon technique. Work in progress.

The three-point Dixon technique is an enhancement of the original Dixon method for the creation of water- and fat-proton magnetic resonance (MR) images. With the three-point Dixon technique, three measurements of phase shift at 0, pi, and -pi between the fat and water resonances are employed. Compensation for B0 inhomogeneity leads to an error-free decomposition into water- and fat-proton images; an accurate B0 map is also created. The lack of chemical shift artifact in the water- and fat-selective MR images permits the application of narrow receive bandwidth for the creation of T2-weighted images with a high signal-to-noise ratio. The technique was applied in vivo with four healthy subjects, seven patients with prostatic carcinoma, and one patient with benign prostatic hypertrophy and compared with conventional T2-weighted imaging. The three-point technique yielded images with improved definition of normal intraprostatic structures and zonal anatomy and, in some cases of prostatic carcinoma, provided better visualization of extraprostatic spread of tumor.

Adult↗
PubMed1989

Characterization of splenic structure in Hodgkin disease by using narrow-band filtration of backscattered ultrasound.

A preliminary study was performed to evaluate the effectiveness of narrow-band filtration of backscattered ultrasound for the detection of splenic involvement in patients with Hodgkin disease. Regions of interest were identified in the spleens of 14 normal volunteers and eight Hodgkin disease patients before staging laparotomy. An analysis of the narrow-band-filtered waveforms showed that the mean amplitudes of the filtered ultrasonic signals received correlated with the presence of extensive splenic involvement with Hodgkin disease (defined as more than four grossly visible nodules on cut section) (p = .0004). Conversely, mean amplitudes of unfiltered ultrasonic backscatter, employed in conventional sonographic imaging, did not correlate with splenic involvement (p = .5). Phantom studies were performed to develop a tissue model for the observed phenomena; images of the phantoms and of the involved and uninvolved spleens were made by using techniques involving narrow-band filtration of backscattered ultrasound. Our results indicate that narrow-band-filtered sonography holds promise for detecting lymphomatous involvement of the spleen, although larger studies, with equipment allowing real-time implementation of narrow-band filtering, are needed.

Acoustics↗
PubMed1988

Noise reduction in magnetic resonance imaging.

This paper describes a noise-reduction technique applicable to multiple-measurement systems. This method, known as measurement-dependent filtering (or MDF), can be used to advantage in a number of MRI applications. We present the general theory for one of these applications, material-canceled projection imaging. We discuss and show the results of MDF for material-canceled images as well as for heavily T2-weighted spin-echo images and computed T2 images. Significant improvements in SNR are demonstrated while spatial resolution is preserved.

Electricity↗
PubMed1987

The abnormal prostate: MR imaging at 1.5 T with histopathologic correlation.

Thirteen patients with biopsy-proved adenocarcinoma were prospectively examined with magnetic resonance (MR) imaging with use of a 1.5-T superconducting magnet. All patients subsequently underwent radical prostatectomy and careful, axial, histologic mapping of prostatic disease. Histologic findings were recorded on serial, axial diagrams to ensure precise pathologic correlation with the MR images. MR permitted identification of eight of 12 (67%) adenocarcinomas as hypointense foci (relative to the surrounding, higher intensity, peripheral zone); but tumor volume was under-estimated with MR imaging in five of eight cases (63%). Nodules of prostatic hyperplasia were identified correctly in only one of nine patients (11%). These findings suggest that, despite that fact that high field strength MR imaging currently does not depict all pathologic foci within the prostate, it may be of predictive value in the differential diagnosis of prostatic abnormalities when their locations are demonstrable.

Adenocarcinoma↗
PubMed1987

Frequency diversity speckle processing.

Ultrasonic waveform data from a tissue-mimicking phantom containing low contrast targets was digitized, stored and processed prior to creating and displaying ultrasonic images. Speckle reduction was performed by digital filtering of the waveform data with appropriately spaced and weighted digital filters, prior to both coherent and incoherent image averaging. The resultant images showed increased signal-to-target boundaries was noted in the processed, compared to unprocessed, images. Incoherent and coherent processing were investigated, and appeared to be equivalent.

Humans↗
PubMed1986

Removal of air from liver specimens via vacuum.

Fresh liver specimens have been ultrasonically imaged in vitro in order to evaluate specimen air content before the acquisition of ultrasonic waveform data for tissue characterization studies. It was found necessary to expose liver slices to vacuum for about 16 h in order to remove enough air to acquire waveform data from air-free regions of interest in these slices. Larger portions of liver, and whole liver, were found to retain large amounts of air even after 16 h of exposure to vacuum.

Air↗