Biomedical subjects

M Henkelman

Publications and source records attributed to M Henkelman.

6 recordsLinked to original sources

PubMed2000

Brain tumor surgery with the Toronto open magnetic resonance imaging system: preliminary results for 36 patients and analysis of advantages, disadvantages, and future prospects.

OBJECTIVE: Frameless navigation systems represent a huge step forward in the surgical treatment of intracranial pathological conditions but lack the ability to provide real-time imaging feedback for assessment of postoperative results, such as catheter positions and the extent of tumor resections. An open magnetic resonance imaging system for intracranial surgery was developed in Toronto, by a multidisciplinary team, to provide real-time intraoperative imaging. METHODS: The preliminary experience with a 0.2-T, vertical-gap, magnetic resonance imaging system for intraoperative imaging, which was developed at the University of Toronto for the surgical treatment of patients with intracranial lesions, is described. The system is known as the image-guided minimally invasive therapy unit. RESULTS: Between February 1998 and March 1999, 36 procedures were performed, including 21 tumor resections, 12 biopsies, 1 transsphenoidal endoscopic resection, and 2 catheter placements for Ommaya reservoirs. Three complications were observed. All biopsies were successful, and the surgical goals were achieved for all resections. Problems included restricted access resulting from the confines of the magnet and the imaging coil design, difficulties in working in an operating room that is less spacious and familiar, inconsistent image quality, and a lack of nonmagnetic tools that are as effective as standard neurosurgical tools. Advantages included real-time imaging to facilitate surgical planning, to confirm entry into lesions, and to assess the extent of resection and intraoperative and immediate postoperative imaging to confirm the extent of resections, catheter placement, and the absence of postoperative complications. CONCLUSION: Intraoperative magnetic resonance imaging has great potential as an aid for intracranial surgery, but a number of logistic problems require resolution.

Adult↗

PubMed1998

Spatial localization combining projection presaturation with a two-dimensional excitation pulse.

Single-shot spatial localization of short T1 nuclei was achieved by outer volume suppression with projection presaturation followed by selective excitation of the desired volume with a two-dimensional (2D) pulse. After the projection, presaturation with a 2D pulse avoided signal contamination from magnetization regrowth in the outer volume, whereas preceding the 2D pulse with projection presaturation reduced any unwanted excitation in the outer volume caused by the 2D pulse. The improvement in outer volume suppression achieved by combining these two techniques was demonstrated by images collected after the application of projection presaturation alone, a 2D pulse alone, and the two combined.

Animals↗

PubMed1996

Quantification of cardiac and tissue iron by nuclear magnetic resonance relaxometry in a novel murine thalassemia-cardiac iron overload model.

OBJECTIVE: To determine whether nuclear magnetic resonance (NMR) relaxation parameters can be used to quantify iron in tissues, the relationship between NMR spectrometric T2 relaxation measurements and tissue iron concentration were verified in a novel murine cardiac iron overload model. METHODS: Congenital heterozygous thalassemic mice and controls were injected with intraperitoneal iron or saline and were sacrificed at three weeks. Samples of liver, heart and peripheral muscle were subjected to NMR relaxation measurements and continuous distribution analysis. Tissue ferritin levels were determined with immunoadsorbance techniques, and elemental iron was assayed by flame atomic absorption. Tissues were analyzed pathologically with hematoxylin and eosin and Prussian blue staining to confirm the localization of iron. RESULTS: This murine iron loading model was uniquely successful in loading iron into the major organs, especially the heart, and produced significant reductions in T1 and T2 NMR relaxation values. There was a good correlation between soluble ferritin and total iron levels (r=0.92), indicating that there is a constant and significant fraction of total iron present in ferritin irrespective of absolute iron concentrations. Regression analysis between total iron content and T2 relaxivity showed a linear relationship (r=0.96), suggesting that the T2 relaxation parameter is related to tissue iron concentration. The regression relationship suggested that NMR can detect iron levels as low as 0.1 mg/g of tissue. CONCLUSIONS: Parenteral iron loading in mice produces unique iron overload in major organs, including the heart. Local iron deposition is detectable by NMR relaxometry at 0.1 mg/g or higher. There is a linear relationship between iron concentration and T2 relaxivity. Thus, NMR may be an important and useful clinical tool to quantify iron excess in various pathobiological states of human disease due to iron overload, including heart disease.

Animals↗

PubMed1994

Optimization of gradient-echo MR for calcium detection.

PURPOSE: To determine optimal MR gradient-echo sequences for the visualization of calcium in neurologic MR. METHOD: The dependence of signal intensity and image contrast on the imaging parameters repetition time, echo time, flip angle, and spoiling were measured for hydroxyapatite samples. Calculations of signal intensity were shown to correspond to these measures. RESULTS: Optimum detectability was obtained with an echo time of 29 msec and was independent of spoiling. As repetition time ranged from 30 msec to 700 msec, the optimal flip angle ranged from 17 degrees to 66 degrees. CONCLUSIONS: Gradient-echo sequences that optimize the contrast for detection of calcium in neurologic imaging have been determined.

Brain Diseases↗

PubMed1990

Brain damage from 125I brachytherapy evaluated by MR imaging, a blood-brain barrier tracer, and light and electron microscopy in a rat model.

Changes in normal rat brain were studied acutely, and at 3, 6, 9, and 12 months following interstitial brachytherapy with high-activity 125I seeds. An 80-Gy radiation dose was administered to an area with a 5.5-mm radius. Effects were measured with magnetic resonance (MR) imaging (with and without gadolinium enhancement), leakage of horseradish peroxidase (HRP), electron microscopy, and light microscopy. Significant histological damage was seen at radiation doses above 295 Gy, and breakdown of the blood-brain barrier was observed only in tissue receiving a dose of 165 Gy or greater. Blood-brain barrier breakdown increased up to the 6-month time point, and thereafter appeared to stabilize or decrease. The area of blood-brain barrier disruption indicated by gadolinium-enhanced MR imaging was greater than that indicated by leakage of HRP.

Animals↗

PubMedDate not supplied

In vivo detection of applied electric currents by magnetic resonance imaging.

Magnetic resonance imaging is very sensitive to magnetic field variations. This inherent sensitivity can be exploited to measure small electric currents flowing in the human body. This report describes an experiment in which the magnetic fields produced by small currents applied to the forearm of a living subject have been detected in the tissue. It shows how such measurements have been used to measure current density. The suggested technique is used to measure one component of a current density in a saline solution in vitro.

Electric Conductivity↗