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Biomedical subjects

G M Bydder

Publications and source records attributed to G M Bydder.

At least 163 records · Page 9Linked to original sources
PubMed1979

The temperature dependence of computed tomography attenuation values.

Attention is drawn to the variation in the computed tomography (CT) attenuation value of water with temperature. A difference of 5 to 6 Hounsfield units (1,000 scale) between typical room and body temperatures can be predicted as a consequence of the change in the density of water and was confirmed experimentally. This difference may be of significance in the calibration of CT machines, in the determination of "absolute" CT attenuation values for body tissues and fluids, and in comparing tissue attenuation values obtained in vivo and in vitro.

Animals↗
PubMedDate not supplied

The benefits of increasing spatial resolution as a means of reducing artifacts due to field inhomogeneities.

All users of NMR equipment are familiar with the desirability of achieving as high a quality of field as possible. On the other hand, it is easy to forget that the field quality of relevance in both imaging and spectroscopy is that over individual voxels, and not the whole volume. This note demonstrates in practice how performance in poor fields is improved substantially by reducing voxel size (or increasing spatial resolution), offering a potential alternative to additional shimming under appropriate circumstances. It argues that the best criterion for assessing magnet quality in spatially localized systems is the maximum field error gradient in the volume of usable field, rather than the maximum deviation in the field.

Humans↗
PubMedDate not supplied

Gadolinium-DTPA as a contrast agent in MR imaging--theoretical projections and practical observations.

The theoretical basis for the use of paramagnetic agents to enhance proton relaxation is described. Factors of importance in the design of contrast agents are considered. Measurements of changes in T1 and T2 in vitro due to Gd3+-diethylenetriamine pentaacetic acid (DTPA) are used to predict changes in the intensity of transverse magnetisation seen with different sequences in magnetic resonance imaging. The use of Gd3+-DTPA in clinical cases is illustrated.

Brain Neoplasms↗
PubMedDate not supplied

Use of spherical receiver coils in MR imaging of the brain.

Spherical receiver coils suitable for magnetic resonance (MR) imaging of the brain are described. Spherical geometry permits high field uniformity with close proximity of the coil to the patient's head giving a good filling factor. Patient acceptability has been good in more than 800 examinations of the brain. Spherical receiver coils of appropriate size can provide a simple and worthwhile improvement over conventional saddle designs for low field MR imaging.

Adolescent↗
PubMedDate not supplied

MR imaging of meningiomas including studies with and without gadolinium-DTPA.

The magnetic resonance (MR) appearances in 12 successive cases of histologically verified meningioma are described. In six of these cases intravenous gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) (0.1 mmol/kg) was administered. Each of the eight tumours for which T1 was measured displayed an increase in T1 above that of white matter although the T2 was in the normal range for brain in two of four cases. Inversion recovery was the most useful sequence for demonstration of the tumour prior to administration of intravenous Gd-DTPA and also displayed the highest level of contrast enhancement after Gd-DTPA. The overall findings compared well with contrast enhanced X-ray CT.

Adult↗
PubMedDate not supplied

MR imaging of the liver in primary hepatocellular carcinoma.

In 10 patients with hepatoma, magnetic resonance (MR) and CT of the liver were subjectively compared and correlated with surgical or autopsy findings. In five cases MR defined the extent of the tumor better. Magnetic resonance was particularly useful in differentiating the tumor from otherwise abnormal areas of the liver, mostly focal cirrhosis. Magnetic resonance has the advantage of demonstrating major vessels in relation to the hepatoma without injection of any contrast agent. Calcifications well visualized on CT are not seen on MR. The lack of dynamic bolus CT in the majority of our cases as well as our inability to examine the entire liver with all three MR pulse sequences because of time restraint are significant limitations of this retrospective study.

Adolescent↗
PubMedDate not supplied

Use of closely coupled receiver coils in MR imaging: practical aspects.

The use of closely coupled receiver coils in magnetic resonance (MR) imaging of the brain and body is described. Design considerations are outlined, aspects of the choice of materials are discussed, and clinical applications are illustrated. Closely coupled receiver coils can provide a useful improvement in MR image quality.

Abscess↗
PubMedDate not supplied

Clinical use of the partial saturation and saturation recovery sequences in MR imaging.

The partial saturation (PS) (90 degree-data collection) and saturation recovery (SR) [(90 degree-dephase)n-90 degree-data collection] sequences are described. The early data collection of the PS sequence is of value in demonstrating tissues with a short T2 such as articular cartilage and the annulus fibrosus. The PS sequence also highlights flow and this may provide specific information in vascular lesions. Appropriate choice of echo time enables chemical shift effects to be seen in normal tissues such as breast and bone marrow as well as a variety of diseases such as bone marrow infiltration, pancreatitis, and fatty infiltration of the liver in which there is mixed lipid and water. The SR sequence can be used to control flow effects as well as to calculate values of T1. Although PS and SR sequences display less T1 and T2 dependent contrast than conventional highly T1 and T2 dependent inversion recovery and spin echo sequences, they may still be of clinical value when the mechanism of contrast formation is change in proton density, chemical shift effects, flow effects, or detection of short T2 tissue components.

Abdomen↗
PubMedDate not supplied

MR imaging of central nervous system tumors that do not display increase in T1 or T2.

A retrospective review of brain tumors examined with magnetic resonance imaging has shown that 12% of tumors or their components do not display evidence of an increase in T1 or T2 when examined with highly T1 dependent inversion recovery of highly T2 dependent spin echo sequences. This was observed in lipid containing tumors, malignant melanomas, tumors containing hemorrhage, acoustic neuromas, meningiomas, hamartomas, a pituitary prolactinoma, astrocytomas (grade I) treated with radiotherapy, pediatric tumors, and cases of unknown cause.

Adult↗
PubMedDate not supplied

MR imaging of the liver using short TI inversion recovery sequences.

Use of the short inversion time inversion recovery (STIR) sequence in magnetic resonance (MR) imaging of the liver is illustrated in 20 patients. The sequence provides high contrast images of the liver with relatively little degradation due to motion. Lesions appeared more extensive than with X-ray CT in 14 cases and equal in six. Additional areas of presumed atrophy, fatty infiltration, edema, or vascular insufficiency were only seen with MR. The STIR sequence may be valuable in screening of the liver for metastatic disease.

Evaluation Studies as Topic↗
PubMedDate not supplied

Comparative efficiency of different pulse sequences in MR imaging.

This article examines the relative performance of various sequences in terms of a figure of merit. The range of possible options is large but there are also major constraints on possible improvements by manipulating sequences. The performance of inversion recovery and partial saturation techniques is better than is often suggested.

Adult↗
PubMedDate not supplied

Clinical magnetic susceptibility mapping of the brain.

A field mapping technique was used to detect changes in the local magnetic field in 14 tumors, five hematomas, one lacunar infarct, and two cases of multiple sclerosis. These changes were attributed to variations in the tissue susceptibility. A partial or complete rim of changed susceptibility was detected at the margin of five of the tumors and localized changes were seen within two of the tumors. All five hematomas displayed susceptibility effects. These were seen at the rim of the hematoma in all cases but central effects were also seen in four cases. One area of probable lacunar infarction also displayed susceptibility effects. The effects described may be due to the paramagnetic contribution of species such as deoxyhemoglobin, methemoglobin, free ferric iron, hemosiderin, and other breakdown products of blood. Local field inhomogeneities due to changes in tissue susceptibility have implications for magnetic resonance (MR) image interpretation and the performance of MR spectroscopy.

Brain Diseases↗
PubMedDate not supplied

Clinical use of rapid T2 weighted partial saturation sequences in MR imaging.

Rapid T2 dependent field echo [partial saturation (PS)] sequences were used in 38 patients with brain tumors, intracerebral hematomas, and cerebral infarction as well as other neurological and abdominal disease. Reduction in the radiofrequency excitation angle (alpha) from 90 to 30 degrees produced an increase in lesion contrast as did change of echo time (TE) from 33 to 59 or 120 ms using repetition time (TR) values in the range of 120-500 ms. The PS sequence showing most lesion contrast was compared with conventional spin echo (SE 1,500/80 and SE 1,500/120) and inversion recovery (IR 1,500/500/44 and IR 1,500/100/44) sequences. Although PS sequences with TE = 39 ms were usually inferior to conventional SE sequences, those with TE = 59 or 120 ms were comparable and in some cases (particularly hematomas) superior. The PS sequences with alpha of approximately 30 degrees, TR of 80-250 ms, and TE of 60-120 ms offer considerable savings in time compared with conventional sequences although more work will be required to explore the limits of this approach and to optimize sequences at different field strengths.

Brain Diseases↗
PubMedDate not supplied

MR imaging with gadolinium-DTPA in the differentiation of tumor, syrinx, and cyst of the spinal cord.

Intravenous Gd-diethylenetriamine pentaacetic acid was used in 16 patients to differentiate between syringomyelia, syringomyelia in association with tumor, and cystic tumor in the spinal cord. Contrast enhancement occurred in all 12 histologically proven cases of tumor and enabled clear demarcation of neoplastic tissue from syrinx or cyst. Eleven of the twelve tumors seen in association with spinal cord cavitation were malignant; all tumors apart from one (a schwannoma) were intramedullary in location. Enhanced scans were more helpful than unenhanced scans in diagnosing and defining the extent of tumors associated with a syrinx or cyst.

Adolescent↗
PubMedDate not supplied

Assessment of brain perfusion with MR imaging.

A technique for assessing brain perfusion with magnetic resonance (MR) imaging is described. This technique uses two spin echo sequences that are identical except that the second is sensitised to blood flow by use of a pair of unipolar gradients on either side of the 180 degree pulse. Differences in phase between the two sequences are displayed with a sensitivity to flow rates of +/- 0.5, +/- 1, and +/- 2 mm/s per full scale (+/- pi radians) deflection. The technique was validated for measurement of flow at these rates with a water phantom. Ten patients with cerebrovascular disease, multiple sclerosis, cerebral tumor, periventricular leukomalacia, and meningitis were studied. Differences between grey and white matter were normally seen in adults. Infants displayed differences between central and peripheral regions of the brain. Abnormalities were seen in all clinical cases. The technique will require further validation but it appears to provide a totally noninvasive method for assessing brain perfusion.

Adult↗