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Biomedical subjects

L Axel

Publications and source records attributed to L Axel.

At least 37 records · Page 2Linked to original sources
PubMed1988

Tumor recurrence versus fibrosis in the female pelvis: differentiation with MR imaging at 1.5 T.

Twenty-two women with previous malignancies of the pelvis were examined with magnetic resonance (MR) imaging. In 21 of 22 patients, the MR imaging findings were confirmed with laparotomy on transvaginal biopsy. Twelve of the 22 patients had recurrent tumors; ten had a localized fibrotic mass, and two were found to have coexistent local fibrotic masses and distant recurrence. In 11 of the 12 patients with recurrence, MR imaging demonstrated the recurrent tumor as an area of increased signal intensity on long repetition time, long echo time spin-echo pulse sequences. Signal intensity of localized fibrosis varied with the time since initial treatment. Separate signal intensity measurements for T1- and T2-weighted images were obtained in regions of interest in recurrent tumors, early fibrosis (1-6 months after first treatment), and late fibrosis (more than 12 months). Ratios of signal intensity of muscle to that of fat were calculated, and a statistical analysis (Student t test) was performed. On heavily T2-weighted pulse sequences, the differences in signal intensity between late fibrosis and recurrent tumors were statistically significant (P less than .001). MR imaging is useful in identifying recurrent pelvic neoplasm and distinguishing it from posttreatment fibrosis.

Adult↗
PubMed1987

Adnexal masses: MR imaging observations at 1.5 T, with US and CT correlation.

To assess the role of 1.5-T magnetic resonance (MR) imaging in evaluation of the adnexa, 43 consecutive examinations that revealed 61 adnexal masses were retrospectively reviewed. T1- and T2-weighted images in coronal, axial, and/or sagittal planes were included. Available ultrasound (US) (n = 30) and/or computed tomographic (CT) (n = 9) scans were then correlated with the MR images. On T2-weighted images at least part of all adnexal masses was of higher signal intensity than surrounding muscle and adipose tissue, and therefore the adnexal masses were best seen with these sequences. T1-weighted imaging improved tissue characterization by revealing signal characteristics of fat in teratomas and characteristics of blood in endometriomas or hemorrhagic cysts, pelvic inflammatory disease, ovarian carcinomas, serous cystadenomas, and teratomas. MR imaging provided additional information or increased diagnostic confidence in 25 of 30 patients who underwent US or CT. MR imaging is a promising problem-solving modality after US in the study of adnexal abnormalities.

Adenoma↗
PubMed1987

Abnormal parathyroid glands: high-resolution MR imaging.

High-resolution magnetic resonance (MR) images of the neck were obtained in 23 patients with hyperparathyroidism. Surgical confirmation was available in all cases. MR imaging allowed accurate localization of 14 of 17 parathyroid adenomas, two of two parathyroid carcinomas, and five of eight hyperplastic glands, the latter from three patients. MR depicted nine of 11 (82%) abnormal glands that were 0.5-1.0 cm in size and 12 of 14 (85.7%) glands larger than 1 cm in diameter. In all but one case, abnormal glands had signal intensity greater than or equal to that of fat on spin-echo images with long repetition time and echo time. Parathyroid adenomas, carcinomas, and hyperplasia could not be distinguished from each other. The overall sensitivity and specificity of MR imaging in the detection of parathyroid abnormalities was 77.8% and 95.4% respectively, resulting in an accuracy of 90.2%. This compares favorably with other imaging modalities.

Adenoma↗
PubMed1987

Prostatic disorders: MR imaging at 1.5 T.

Pelvic magnetic resonance (MR) images obtained at 1.5 T of 31 men with known genitourinary disease were reviewed retrospectively. In most, peripheral and central prostatic zones could be seen on axial images obtained with long repetition times/echo times (TRs/TEs). The prostate had no specific signal intensity that enabled differentiation between benign and malignant changes. Each patient with known extracapsular prostatic carcinoma had a peripheral zone defect--1 cm or greater in diameter with ill-defined borders and relatively lower signal intensity than that of the remainder of the peripheral zone--that correlated with the site of clinical-pathologic involvement. Correlation of a peripheral zone defect on long TR/TE images as a sign for extracapsular spread of prostatic cancer was 100% sensitive, yet 54% specific, with excellent interobserver agreement. Stage A2 and B1 prostatic carcinoma was not detected. Benign prostatic hyperplasia was seen as centrally located proliferation and nodularity, usually with discrete margins and a wide spectrum of low- to high-signal-intensity features. MR imaging may have a role in differentiating between intracapsular and extracapsular prostatic carcinoma.

Adult↗
PubMed1987

Normal prostate and adjacent structures: MR imaging at 1.5 T.

Pelvic magnetic resonance images obtained at 1.5 T of 29 male patients with no known genitourinary tract disease were retrospectively reviewed. Normal anatomic features of the prostate and its adjacent structures were studied with spin echo techniques with short and long repetition times/echo times (TR/TE). Long TR/TE (T2-weighted) images routinely showed differentiation of peripheral and central prostatic zones, as well as a separate periprostatic venous plexus. Guidelines were developed to optimize imaging of the relationship of the prostate to adjacent structures.

Adult↗
PubMed1987

Thyroid imaging with high-field-strength surface-coil MR.

Magnetic resonance (MR) imaging of the thyroid was performed with a 1.5-T system and local receiver coil in 19 "healthy" subjects and 34 patients with various focal and diffuse thyroid disorders. The normal gland was typically homogeneous with increased intensity relative to that of muscle on images obtained with long repetition times (TRs) and long echo times (TEs). Adjacent structures in the neck and upper mediastinum were well displayed. Thyroid nodules as small as 4-5 mm were identified. Follicular adenomas appeared as well-circumscribed nodules of heterogeneous intensity, increasing significantly in signal with long TRs/TEs. Colloid cysts and hemorrhagic cysts had homogeneous high signal with both short and long TRs/TEs. Two of three carcinomas were seen as poorly marginated lesions with associated cervical lymphadenopathy clearly depicted as increased intensity with long TRs/TEs. A follicular adenoma containing microscopic papillary carcinoma appeared similar to other benign adenomatoid nodules. A functioning nodule was isointense with normal gland at all pulse sequences. Characteristic patterns of diffuse abnormality were observed in cases of multinodular goiter, Hashimoto thyroiditis, and Graves disease, although additional cases are required to determine specificity. High-field-strength surface-coil MR imaging appears to be a sensitive method for identifying gross morphology of focal, multinodular, and diffuse disorders of the thyroid and involvement of surrounding structures in the neck.

Adult↗
PubMed1987

Orbital lesions: proton spectroscopic phase-dependent contrast MR imaging.

Thirteen orbital lesions in 12 patients were evaluated with both conventional spin-echo magnetic resonance (MR) imaging and phase-dependent proton spectroscopic imaging. This technique, which makes use of small differences in the resonant frequencies of water and fat protons, provides excellent high-resolution images with simultaneous chemical shift information. In this method, there is 180 degrees opposition of phase between fat protons and water protons at the time of the gradient echo, resulting in signal cancellation in voxels containing equal signals from fat and water. In this preliminary series, advantages of spectroscopic images in orbital lesions included better lesion delineation, with superior anatomic definition of orbital apex involvement; more specific characterization of high-intensity hemorrhage with a single pulse sequence; elimination of potential confusion from chemical shift misregistration artifact; further clarification of possible intravascular flow abnormalities; and improved apparent intralesional contrast.

Female↗
PubMed1986

A computer simulation of nuclear magnetic resonance imaging.

A modular, user-friendly computer simulation of NMR imaging was created for the DEC VAX computer. This simulation is novel in that complex imaging phenomena, such as chemical shifts and flow, may be easily studied. Other features include spin warp and backprojection imaging, movie generation, and simulation of image contrast, composite pulse sequences, motion artifacts, aliasing, selective excitation, field inhomogeneity, noise and signal averaging. The simulation incorporates fast Fourier transform and graphics modules for processing and display of one- and two-dimensional images. Examples which illustrate features of the program are shown. The simulation is a useful tool for both the sophisticated and the beginning user of NMR imaging. It serves as a drawing board for studying MRI phenomena and a teaching program for demonstrating basic techniques.

Adipose Tissue↗
PubMed1986

Magnetic resonance imaging of avascular necrosis of the femoral head.

This study investigates the role of magnetic resonance imaging (MR) in identifying avascular necrosis (AVN) of the femoral head and in monitoring its therapy. The detection of AVN, particularly in its early stages, is imperative to give therapeutic intervention the best opportunity for successful management. The results of magnetic resonance imaging are compared with those of the standard diagnostic modalities in evaluation of patients with the lesion. Examinations were performed at 0.12T with a repetition time (TR) of 143 ms and times to echo (TE's) of 10 or 20 ms. This study represents a retrospective review of 90 hips which were examined in 45 consecutive patients. Of these, 52 hips were biopsied as part of treatment. MR was shown to be sensitive in the detection of AVN. Comparison of MR with radionuclide imaging showed comparable sensitivity and specificity. MR was also noted to be sensitive in the detection of early AVN. Preliminary results suggest that MR can monitor treatment of the affected hip, and may even be able to predict patient response to therapy. Although further work is necessary to determine the role of MR in the evaluation of the patient presenting with hip pain, MR is a sensitive method in detecting AVN and in monitoring its course in patients suspected of having the disease.

Adult↗
PubMed1986

A time-of-flight method of measuring flow velocity by magnetic resonance imaging.

A new time-of-flight method for direct imaging of flow velocities by magnetic resonance is presented. The technique uses selective exciting and refocusing RF pulses to selectively affect planes oriented in orthogonal directions in space, with the region of excitation perpendicular to the flow and the refocusing region parallel to and including the flow. The positions of the sources of the resulting spin echoes are imaged, showing a displacement equal to the product of the velocity and the echo time. These images clearly show the profile of the velocity distribution, both in laminar and nonlaminar flows.

Blood Flow Velocity↗
PubMed1986

Agarose as a tissue equivalent phantom material for NMR imaging.

Phantoms for evaluation of nuclear magnetic resonance (NMR) imaging systems were made from water-based agarose gels, according to a standard procedure herein described. Copper sulfate (CuSO4) was included in the gels to further affect their proton relaxation characteristics. The proton relaxation rates of each batch of gel are dependent on the concentrations of agarose and copper ions in it, with T1 depending more on copper than on agarose, and T2 depending more strongly on agarose than on copper. The wide range of T1 and T2 which can be covered, and the stability and physical characteristics of the agarose gel material make it well-suited for phantom use.

Copper↗
PubMed1986

Polycystic ovaries: MR imaging.

To determine the characteristic appearance of polycystic ovaries on magnetic resonance (MR) images, seven women with polycystic ovarian disease (PCOD) underwent MR examination of the pelvis. These MR images were compared with sonograms. Histologic material was available in two patients. Six of the seven women had characteristic, small peripheral cysts, best seen on T2-weighted MR images; these cysts were seen sonographically in only one case. The centers of nine of 14 ovaries were of low intensity with all MR pulse sequences; this low intensity corresponded with low echogenicity in six cases. Histologically, these areas correlated with hypertrophic cellular stroma. Coexisting central teratomas were seen in three ovaries. The ability of MR to display the findings of PCOD better than ultrasound and its ability to demonstrate coexisting pathologic conditions are valuable in imaging the female pelvis.

Adult↗