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Biomedical subjects

G L Wismer

Publications and source records attributed to G L Wismer.

At least 19 recordsLinked to original sources
PubMed1989

Circle of Willis variant analogous to fetal type primitive trigeminal artery.

Primitive caroticobasilar anastomoses are uncommon embryonic arterial connections between the carotid (anterior) and vertebrobasilar (posterior) circulations. With the exception of extracranial proatlantal intersegmental arteries, these embryonic arterial anastomoses are named according to the cranial nerves which they parallel. In this report, a previously undescribed variant circle of Willis with supraclinoid caroticobasilar anastomosis, functionally equivalent to a fetal type primitive trigeminal artery, is presented.

Aged↗
PubMed1988

Hematologic bone marrow disorders: quantitative chemical shift MR imaging.

Twenty-one in vivo studies of bone marrow of the lumbar spine were performed with a 0.6-T commercial MR imager and proton chemical shift imaging techniques. Six healthy volunteers served as controls. Multiple measurements in the volunteers demonstrated reproducibility within errors of 5% for fat fraction and 6% for T1 of water. Ten patients who had histologically proved leukemia or aplastic anemia were then examined. The data show that changes in fat fraction represent the underlying reason for many of the changes observed in conventional spin-echo (SE) images of these disorders. Although both conventional and chemical shift images showed differences among the pathologic groups and healthy volunteers, fat fraction determined with chemical shift imaging was the single best discriminator among them. A two-point estimate of fat fraction was also evaluated. This rapid imaging protocol performed almost as well as the complete quantitative analysis in discriminating between pathologic and healthy tissue and showed improved discrimination compared with conventional SE techniques.

Adipose Tissue↗
PubMed1986

Magnetic resonance imaging during acute myocardial infarction.

Experimental canine studies have demonstrated the potential of magnetic resonance imaging (MRI) for detecting and characterizing acute myocardial infarction (AMI) in humans. Accordingly, electrocardiographic-gated spin-echo MR images of the left ventricular short axis were obtained in 34 patients a mean of 11 +/- 6 days (range 3 to 30) after AMI. This imaging technique allowed division of the left ventricle into segments corresponding to the left ventricular segments on angiography. Patients were separated into 2 groups; the first 16 patients (group I) were examined using a variety of imaging techniques. Information derived from this experience resulted in a standard imaging protocol and development of criteria for the presence of AMI. The imaging protocol and interpretation criteria were used in the assessment of a subsequent group of 18 patients (group II). Of the 14 patients in group II with satisfactory image quality, all showed an increase in myocardial signal intensity consistent with an AMI. In addition, the anterior or inferior location of the abnormal MR segments corresponded to the electrocardiographic infarct location. MR segments showing increased signal intensity corresponded with severely hypokinetic or akinetic segments on the left ventriculogram in 8 patients having both procedures. In a group of volunteers who underwent imaging and whose images were interpreted in the same manner as those of the patients with AMI, 1 of 9 subjects had regional variation in myocardial signal intensity compatible with an AMI. In summary, AMI is readily detected, located and characterized by electrocardiographic-gated MRI. These findings suggest that MRI techniques may have a role in the evaluation of AMI in humans.

Adult↗
PubMed1986

Quantitative proton chemical-shift imaging.

Recently W. T. Dixon (Radiology 153, 189 (1984))introduced a simple method of proton chemical-shift imaging which requires only two images, a conventional (in-phase) image and an image in which fat and water protons are 180 degrees out of phase during signal acquisition, to separate the signals from fat and water protons. We have tested the application of this method to the quantitative determination of fat content and fat and water longitudinal relaxation times, and analyzed the effects of random and systematic errors. Ten phantoms were constructed with a range of fat contents (0-50% by weight) and water T1's (300-800 ms). Fat and water T1's were measured with a 0.6-T clinical imaging system in two ways: using the system as a spectrometer with all gradients off, and from least-squares fits to in-phase and out-of-phase image data made with six values of TR. The image-derived values of water T1 agreed well with spectrometer-derived values (r = 0.97) and the image derived fat fraction correlated strongly with the fat fraction by weight (r = 0.995). The effects of random and systematic errors were analyzed for a minimum data set of four images: in-phase and out-of-phase images at two values of TR. The pair of TR values which minimize the variance in water T1 were calculated, and for these pulse sequences the effects of two potential systematic errors were calculated: inhomogeneities in the main field, which will reduce the intensity in out-of-phase images compared to in-phase images even for pure water samples, and an incorrect shift of the 180 degrees pulse in the out-of-phase pulse sequence, corresponding to an inaccurate assumed chemical shift. With careful attention to such systematic effects the Dixon method is capable of producing reliable quantitative measurements.

Fats↗
PubMed1986

Ejection fraction determination by MR imaging: comparison with left ventricular angiography.

To determine the accuracy of left ventricular ejection fractions (EFs) calculated from magnetic resonance (MR) images, 22 patients who underwent coronary angiography and left ventriculography were studied within 1-3 days by MR imaging. ECG-gated spin-echo 30-msec echo-delay images were obtained in end systole and end diastole in a plane through the long axis of the left ventricle perpendicular to the septum at a level through the aortic valve and apex. The area-length method was then used to calculate the EF from left ventriculograms and MR images. Angiographic EF correlated linearly with MR determinations. The mean differences in EF calculation between two observers were 5.0 +/- 6.9 for ventriculography and 2.7 +/- 7.8 for MR imaging. MR imaging, using image planes oriented to the left ventricular axes, can allow accurate EF calculation. This has the potential to be clinically useful in noninvasive evaluation of cardiac function.

Adult↗
PubMed1986

Measurement of normal left heart dimensions using optimally oriented MR images.

In order to establish normal values for left heart dimensions by magnetic resonance imaging (MRI), electrocardiographically gated MRI was performed in 16 normal asymptomatic subjects using a whole-body 0.6-T superconducting magnet with a spin-echo pulse sequence and an echo delay (TE) of 30 msec. Images were oriented along the long and short axes of the left ventricle in planes similar to two-dimensional echocardiograms (2DE). Comparable 2DE images were obtained for validation of the MRI measurements. The following measurements of the left heart were made at end diastole and end systole in both long- and short-axis views using both techniques: left ventricular cavity diameters, interventricular septum and posterior wall thicknesses at chordal and mid-papillary-muscle levels, and anteroposterior mid-left-atrial diameter. There was good correlation between the two techniques in a total of 141 measurements (MRI = 0.94 2DE + 1.42, p less than 0.0001, r = 0.97) and in the individual measurements considered separately (p less than 0.001). There was no significant difference in the mean values. MRI measurements obtained with the image planes oriented to the intrinsic axes of the heart are similar to those obtained by 2DE. These data provide normal values for measurements of the left heart using a standardized MRI technique.

Adolescent↗
PubMed1986

Magnetic resonance imaging of thoracic aortic aneurysms: comparison with other imaging methods.

Fifteen patients with thoracic aortic aneurysms had magnetic resonance images (MRI) and at least one additional diagnostic image study: thoracic aortography, computed tomography (CT), or two-dimensional echocardiography. Twenty aneurysms were demonstrated by MRI, 19 by the other studies. One small saccular aneurysm was missed by CT. There was complete agreement between MRI and other studies regarding aneurysm morphology, and good correlation in diameter measurements of the aneurysms and at multiple additional aortic levels.

Adolescent↗
PubMed1985

Magnetic resonance imaging: present and future applications.

Magnetic resonance (MR) imaging has created considerable excitement in the medical community, largely because of its great potential to diagnose and characterize many different disease processes. However, it is becoming increasingly evident that, because MR imaging is similar to computed tomography (CT) scanning in identifying structural disorders and because it is more costly and difficult to use, this highly useful technique must be judged against CT before it can become an accepted investigative tool. At present MR imaging has demonstrated diagnostic superiority over CT in a limited number of important, mostly neurologic, disorders and is complementary to CT in the diagnosis of certain other disorders. For most of the remaining organ systems its usefulness is not clear, but the lack of ionizing radiation and MR's ability to produce images in any tomographic plane may eventually prove to be advantageous. The potential of MR imaging to display in-vivo spectra, multinuclear images and blood-flow data makes it an exciting investigative technique. At present, however, MR imaging units should be installed only in medical centres equipped with the clinical and basic research facilities that are essential to evaluate the ultimate role of this technique in the care of patients.

Abdomen↗
PubMed1985

MR imaging of the acoustic nerves and small acoustic neuromas at 0.6 T: prospective study.

To evaluate the capability of magnetic resonance (MR) in imaging normal acoustic nerves, 12 volunteers without signs or symptoms of intracranial disease were examined using a 0.6 T superconductive system. Several spin-echo (SE) pulse sequences were tested to identify the optimal sequence for demonstration of the acoustic nerve bundle. Repetition times (TRs) varied from 300 to 2000 msec and echo times (TEs) from 30 to 120 msec. A single-slice technique was used with 5 and 8 mm sections, one or two data acquisitions per projection, and axial and coronal imaging. The normal acoustic nerves were demonstrated readily by MR in axial and/or coronal sections. The distal parts of the nerves and tumors were imaged best with SE 1500/60. The medial extremities of the seventh and eighth nerves tended to be obscured in this sequence by brightening the cerebrospinal fluid signal adjacent to the brainstem, but they were demonstrated clearly with 500 or 800 msec TR and 30 msec TE. Five patients were studied who had hearing loss and evidence of retrocochlear disease. In four patients, MR imaging demonstrated five acoustic nerve tumors ranging in size from purely intracanalicular to a 12 mm cisternal component. In the fifth case, no tumor was identified by MR imaging or gas computed tomographic (CT) cisternography. Contrast-enhanced CT using a Siemens Somatom DR 3 or GE CT/T 8800 scanner failed to provide convincing evidence of tumor in any case, while gas CT cisternography was positive in all five tumors. All five acoustic neuromas were identified readily using the SE sequences that proved optimal for demonstration of normal nerves. This experience revealed that MR imaging can demonstrate the eighth nerve complex well and reliably. Single-slice (5 or 8 mm) technique is adequate, but multislice without tissue gaps (used recently) is more efficient. Small, even intracanalicular, acoustic neuromas are imaged effectively, indicating that the method is capable of superseding contrast CT cisternography, particularly with improving technology.

Atrophy↗
PubMed1985

High-resolution surface-coil imaging of lumbar disk disease.

Seventeen patients with lumbar disk disease were studied using a prototype magnetic resonance (MR) surface coil. The high signal-to-noise ratio achieved with the surface coil permitted increases in spatial resolution to 0.9 X 0.9 mm in-plane resolution with 5 mm slice thickness. The surface coil was also compatible with multiplanar, multiecho imaging techniques. The spatial resolution achieved in this study was nearly equivalent to that achieved by state-of-the-art computed tomographic (CT) scanners, and MR showed a superior range of soft-tissue contrast. One significant limitation of MR was its inability to demonstrate small calcifications. Nevertheless, MR imaging provided diagnostic information comparable to CT or myelography in a completely noninvasive manner. With further technical advances, MR is likely to become the initial procedure of choice for evaluating patients with suspected lumbar disk disease.

Humans↗
PubMed1985

Sacrococcygeal chordoma: magnetic resonance imaging and computed tomography.

Magnetic resonance imaging (MRI) was compared to computed tomography (CT) in four cases of sacrococcygeal chordoma. Both techniques yielded important anatomic information and represented important advances over early radiologic imaging methods. MRI provides superior contrast with surrounding soft tissues because of the prolonged T1 and T2 times of the tumors. This was especially important in a case of recurrent chordoma. The direct sagittal images obtained by MRI were valuable in determining the extent of lesions. Either MRI or direct CT coronal images were needed for the demonstration of tumor involving the sacral nerve roots. It was not possible to reliably distinguish between tumor adherent to bowel wall and bowel wall invasion by either technique. It is concluded that MRI is at least equal to CT for demonstration of these lesions and seems likely to become the imaging method of choice.

Adult↗
PubMed1985

Magnetic resonance imaging of the interatrial septum and atrial septal defects.

Magnetic resonance images were obtained in six patients with known or suspected interatrial septal defects (ASD) and 33 subjects without congenital heart disease. Image planes were oriented to the long and short axes of the left ventricle and septum and provided reproducible display of pertinent anatomic landmarks. Of the images in 33 control subjects, three (9%) were falsely positive showing apparent ASD. ASDs were correctly identified and localized in all six patients (five secundum, one primum). Long-axis views provided excellent display of the location and diameter of defects. All were confirmed at cardiac catheterization and four at surgery with good agreement in measurement of defect size and location. All showed signs of right-sided volume overload. Five had previous echocardiography, which showed definite or suspected ASD in four.

Adult↗
PubMed1985

Chemical shift imaging of bone marrow: preliminary experience.

A phase-contrast method of chemical shift imaging was used to evaluate bone marrow in normal volunteers and in patients with metabolic, inflammatory, traumatic, and neoplastic disorders. Five normal volunteers were examined in order to obtain preliminary data on normal patterns of signal intensity in hematopoietic and fatty marrow using both conventional magnetic resonance imaging and proton chemical shift imaging. Normally, hematopoietic marrow yields low signal intensity on phase-contrast images; pathologic conditions affecting hematopoietic marrow typically result in increased signal intensity due to either accumulated lipid or water. Because of its high fat content, yellow marrow normally yields high signal intensity on phase-contrast images, whereas abnormal conditions usually result in decreased phase-contrast signal intensity due to increased tissue water. Proton chemical shift imaging is likely to be a valuable supplement to standard magnetic resonance imaging techniques in the study of bone marrow in vivo.

Adult↗
PubMed1985

Magnetic resonance imaging of the heart using image planes oriented to cardiac axes: experience with 100 cases.

Electrocardiographically gated magnetic resonance images were acquired in 100 patients with a variety of cardiac diagnoses in planes oriented to intrinsic axes of the heart and aorta. The technique used combines patient positioning and alteration of magnetic gradient angle. Images in these planes appear to have advantages over conventional orthogonal images, both for display of cardiovascular anatomy and for evaluation of cardiac size and function.

Adolescent↗
PubMed1984

Magnetic resonance imaging of the heart: positioning and gradient angle selection for optimal imaging planes.

Electrocardiographically gated magnetic resonance images were acquired in 20 subjects using a spin-echo pulse sequence. For optimizing the display of cardiac anatomy, a technique was developed which uses patient positioning in addition to alteration of gradient angle to select image planes. High-quality images were acquired in three basic cardiac projections: (1) the long axis of the left ventricle, through the aortic valve and apex, parallel to the interventricular septum, (2) the long axis of the left ventricle, perpendicular to the septum, and (3) the short axis of the left ventricle at multiple levels including outflow, papillary muscle, and apex. Images of the aorta included axial images at multiple levels and long-axis images oriented to display the plane of the aortic arch. Images of these planes are easily achieved and, in contrast to standard images orthogonal to the chest wall, provide a reproducible and logical display of cardiac anatomy.

Adolescent↗
PubMedDate not supplied

Contrast in rapid MR imaging: T1- and T2-weighted imaging.

Partial saturation (PS) is an imaging technique that is useful in applications that require rapid image acquisitions (imaging time less than 1 min). Image contrast in PS imaging, as in other magnetic resonance methods, depends on the often conflicting effects of differences in proton density, T1, and T2. Previous analyses of pulse sequence optimization to maximize image contrast have assumed 90 degrees pulses and examined the effects of varying repetition times (TR) and echo times (TE). In this paper we present theoretical calculations and images made with a 0.6 T imager to show that the radiofrequency pulse tip angle alpha, and not the pulse sequence timing parameters, is the most important parameter for producing image contrast. For large tip angles (alpha greater than or equal to 60 degrees), contrast is primarily determined by differences in T1, but for small tip angles (alpha approximately equal to 25 degrees), contrast is primarily due to differences in T2. The T2-weighted images can be produced as quickly as T1-weighted images by using a small pulse angle and a long TE; it is not necessary to use a long TR to reduce the effects of T1 differences. Optimum pulse angles are calculated, and the potential advantages and disadvantages of T2-weighted and T1-weighted PS imaging are discussed.

Humans↗