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Biomedical subjects

R R Price

Publications and source records attributed to R R Price.

At least 19 recordsLinked to original sources
PubMed1992

Magnetic resonance perfusion/diffusion imaging of the excised dog kidney.

RATIONALE AND OBJECTIVES: The authors developed a model of tissue capillary beds applicable to perfusion/diffusion imaging with magnetic resonance imaging (MRI). The model consists of a formalin-fixed excised dog kidney attached to a variable speed pump. With this system, it is possible to perfuse the kidney at selected rates. METHODS: Using the intravoxel incoherent motion model (IVIM), the apparent diffusion coefficient (ADC), diffusion coefficient (D), and perfusion fraction (f) were computed for a region of interest (ROI) in the renal cortex and in the medulla of seven kidneys, one of which was injected with a vasodilator before fixation. ADC and D values were computed for both cortex and medulla. These values were normalized to zero flow and plotted against renal perfusion. The perfusion fraction f was expressed in percent and was not normalized to zero flow. RESULTS: Normalized ADC and f were correlated with tissue perfusion rates using the Spearman rank-sum test (n = 18, rs greater than 0.5, P less than or equal to .02 for the standard preparation in both cortex and medulla), whereas normalized D (rs much less than 0.5) was uncorrelated for both preparations in cortex and medulla. CONCLUSIONS: The isolated perfused dog kidney is a useful model of tissue capillary beds for perfusion imaging technique development. The perfusion/diffusion-related parameters ADC and f increase as flow increases in the tissues, whereas D does not.

Animals↗
PubMed1992

Magnetic resonance angiography techniques.

After a radio frequency pulse, the decay of the magnetic resonance (MR) signal is described by two relaxation processes, T1 and T2. T1 describes the rate at which the magnetization realigns itself along the external magnetic field direction (ML), and T2 describes the rate of decay of the magnetization component along the transverse axis (MT). Magnetic resonance angiography (MRA) sequences have been developed that encode flow as changes in the apparent T1 or T2 of the moving blood relative to stationary tissues. MRA sequences typically use either time-of-flight (TOF) techniques to encode T1 or phase-contrast techniques to encode T2. TOF techniques encode flow as an apparent T1 shortening through the wash-in of fully relaxed blood from outside the image volume. The shorter T1 produces an enhancement of vascular structures relative to stationary tissues. TOF methods may use either sequential two-dimensional, three-dimensional, or multi-slab three-dimensional imaging sequences to produce a three-dimensional MRA data set. Phase-contrast methods use additional magnetic field gradients to encode flow as shifts in the phase of MT. Both TOF and phase-contrast methods use maximum intensity projection (MIP) images displayed in a cine format to aid in the visualization of three-dimensional vascular structures.

Animals↗
PubMed1991

Magnetic resonance diffusion/perfusion phantom experiments.

Recently, several models for determining microcirculatory parameters using magnetic resonance imaging have been proposed. These include the intravoxel incoherent motion (IVIM) model, the intravoxel coherent motion (IVCM) model, and various tracer models. In order to evaluate these models before extension into physiological systems, phantom studies were used to assess model assumptions, measurement uncertainties, and sensitivity to changes in perfusion. Emphasis is placed on the IVIM model, but the techniques discussed could be extended to evaluation of other models as well. An overview of considerations in pulse sequence development, phantom design, and data interpretation is presented for a variety of phantoms ranging in complexity from stationary volumes of fluid and mechanically pumped phantoms to isolated animal kidneys and finally to an in vivo animal model.

Animals↗
PubMed1991

Renal artery stenosis: in vivo perfusion MR imaging.

The intravoxel incoherent motion (IVIM) model of perfusion and diffusion imaging was applied to an in vivo canine model of unilateral renal artery stenosis and was compared with relative renal blood flow determination with radioactive microspheres. The percentage relative renal blood flow as determined with radioactive microspheres correlated closely with the percentage apparent diffusion coefficient. If this method can be adapted to human imaging, it may provide a noninvasive means for detecting renal artery stenosis.

Animals↗
PubMed1990

Near-monochromatic X-ray beams produced by the free electron laser and Compton backscatter.

The intense photon output of a free electron laser may be made to collide with its own high energy electron beam to create nearly monochromatic x-rays using Compton backscatter techniques. These x-rays can be used for imaging and non-imaging diagnostic and therapeutic experiments. The initial configuration of the Vanderbilt Medical Free Electron Laser (Sierra Laser Systems, Sunnyvale, CA) produces intense x-rays up to 17.9 keV, although higher energies are easily attainable through the use of frequency doubling methods, alteration of the energy of the electron beam and coupling to conventional laser inputs.

Electrons↗
PubMed1990

Gadolinium-enhanced MR angiography.

Experience in three patients (one each with meningioma, pineal tumor, and prominent jugular bulb) illustrates that magnetic resonance (MR) angiography can benefit from the administration of gadolinium diethylenetriaminepentaacetic acid. Data were acquired with a three-dimensional velocity-compensated (fast imaging with steady-state precession) sequence. MR angiograms were obtained with a ray projection algorithm by using maximum intensity values. Portions of the vascular anatomy--particularly venous structures and smaller arteries--were better portrayed on the postcontrast than on the precontrast angiograms. Enhancing lesions were also seen on the projection images. Enhancement of dura and extracranial tissues (sinus and nasal mucosa) can obscure vascular detail.

Adult↗
PubMed1990

Dermatomyositis: correlative MR imaging and P-31 MR spectroscopy for quantitative characterization of inflammatory disease.

Magnetic resonance (MR) imaging and phosphorus-31 MR spectroscopy were used to examine four patients with dermatomyositis and five control subjects. T2-weighted images of the thigh muscles of patients showed increased signal intensity, with focal and inhomogeneous involvement predominantly in the vastus lateralis and secondarily in the vastus intermedius and vastus medialis. T1 and T2 values of the vastus lateralis in patients were significantly higher than those of the control subjects. T1 values of the rectus femoris and biceps femoris with more generalized inflammation were moderately elevated but still significantly higher than those of the control subjects. P-31 MR spectra of the quadriceps muscles were obtained during rest, during exercise at two graded levels, and in recovery. Concentrations of adenosine triphosphate and phosphocreatine (PCr) in the diseased muscles were 30% below normal values, and the inorganic phosphate/PCr ratios were increased in the patients' muscles at rest and throughout exercise. The T1 and T2 values as well as the P-31 metabolite data correlated with symptoms and clinical assessment.

Adult↗
PubMed1989

AUR memorial award--1988. MRI enhancement of perfused tissues using chromium labeled red blood cells as an intravascular contrast agent.

It has been demonstrated that chromium (Cr) labeling significantly decreases the relaxation times of packed red blood cells (RBCs). In this study, the spin-lattice relaxation time (T1) of human red cells was shortened from 836 ms to 29 ms and the spin-spin relaxation time (T2) shortened from 134 ms to 18 ms, when the cells were labeled at a Cr incubation concentration of 50 mM. Labeling of canine cells at 50 mM resulted in a T1 of 36 ms and a T2 of 26 ms. A labeling concentration of 10 mM produced similar relaxation enhancement, with uptake of 47% of the available Cr, and was determined to be optimal. The enhancement of longitudinal and transverse relaxation rates (1/T1,-1/T2) per amount of hemoglobin-bound Cr are 6.9 s-1 mM-1 and 9.8 s-1 mM-1 respectively, different from those of a pure Cr+3 solution. Labeling cells at 10 mM decreased the survival half-time in vivo from 16.6 days to 4.7 days in dogs. No difference in red cell survival was found with the use of hetero-transfusion versus auto-transfusion of labeled RBCs. Significant shortening of the T1 (912 ms to 266 ms, P = .03) and T2 (90 ms to 70 ms, P = .006) of spleen and the T1 (764 ms to 282 ms, P = .005) and the T2 (128 ms to 86 ms, P = .005) of liver occurred when 10% of the RBC mass of dogs was exchanged with Cr labeled cells. Liver and spleen spin density changes (P greater than 0.23) and muscle spin density and relaxation changes (P greater than 0.4) were insignificant. The in vivo T1 of a canine spleen which had been infarcted did not change following transfusion with labeled cells, where the T1 of liver did shorten. We believe this preliminary study suggests that Cr labeled red cells may have the potential to become an intravascular magnetic resonance imaging contrast agent.

Animals↗
PubMed1988

Rapid local rectangular views and magnifications: reduced phase encoding of orthogonally excited spin echoes.

A method is described for rapid, artifact-free imaging and magnification of small regions within a larger sample. This combines a rectangular window, reconstructed from a reduced number of phase-encoding steps, and confinement of spin echoes to a similar rectangular strip by orthogonal pi/2 and pi excitations. Phase encoding is along the width of the strip (along Y). Off-center strips are excited by offsetting the Y slice-selecting gradient, and the reconstruction window is kept coincident with excitation by similarly offsetting the Y phase-encoding gradient. The excited strip is centered in the reconstruction window by setting the radiofrequency transmitter on resonance. The method is shown to be useful for long narrow structures such as the spine where the acquisition time is reduced by over a factor of 5 determined by the image aspect ratio.

Humans↗
PubMed1988

Differential scanning calorimetric study of the thermotropic phase behavior of a polymerizable, tubule-forming lipid.

A comparative study of the polymorphism exhibited by the polymerizable, tubule-forming phospholipid 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3- phosphocholine (DC23PC) and its saturated analog 1,2-ditricosanoyl-sn-glycero-3-phosphocholine (DTPC) in aqueous suspension is reported. Differential scanning calorimetry (DSC), as well as freeze-fracture electron microscopy and Raman spectroscopy, have been used to study the influence on phase behavior of rigid diacetylene groups in the fatty acyl chains of a phosphatidylcholine. DTPC large multilamellar vesicle (MLV) and small unilamellar vesicle (SUV) suspensions were found to retain liposome morphology after chain crystallization had occurred. In marked contrast, diacetylenic DC23PC suspensions do not maintain liposomal morphology in converting to the low temperature phase. Large MLVs of DC23PC with outer diameters in excess of 1 micron convert to a gel phase with cylindrical or tubular morphology at 38 degrees C, just a few degrees below the lipid's chain melting temperature (TM(H), i.e. temperature of an endothermic event observed during a heating scan) of 43.1 degrees C. Unlike the large MLVs, small MLVs or SUVs of DC23PC, with diameters of 0.4 +/- 0.3 micron and 0.04 +/- 0.02 micron, respectively, exhibit metastability in the liquid-crystalline state for several tens of degrees below the chain melting temperature prior to converting to a gel phase which, by electron microscopy, manifests itself as extended multilamellar sheets. Raman data collected at TM(H) -40 degrees C demonstrate that the gel state formed by DC23PC is very highly ordered relative to that of DTPC, suggesting that special chain packing requirements are responsible for the novel phase behavior of DC23PC.

Calorimetry, Differential Scanning↗
PubMed1988

Bony demineralization following urinary intestinal diversion.

The effect of urinary intestinal diversion on bone mineral metabolism was investigated in 78 rats. The animals were divided into sham-operated controls and diverted animals. The diverted animals were given either no supplement, sodium bicarbonate or ascorbic acid for an eight month period. Dual photon densitometry and bone mineral content were determined. Urinary intestinal diversion resulted in a minimal systemic acidosis and little alteration in baseline renal function but a significant decrease in bone calcium content. Oral bicarbonate and ascorbic acid administration prevented the demineralization.

Acidosis↗
PubMed1987

Simplified mathematical description of longitudinal recovery in multiple-echo sequences.

The intensity of multiple echoes separated by a time 2 tau has been modeled using the closed form of a finite geometric series. This eliminates long exponential series, introduces the number of echoes as an independent parameter, and corrects for the net T1 relaxation during the echo train. Other sequences having echo trains can be modeled similarly.

Magnetic Resonance Spectroscopy↗
PubMed1987

Techniques of non-orthogonal magnetic resonance imaging and its clinical application.

A technique to obtain non-orthogonal magnetic resonance (MR) images in the body has been developed using a simple three-dimensional model (3-DM). Images were obtained with multiple non-orthogonal planes, without subjecting patients to uncomfortable oblique positions. Eighty-two patients were studied using non-orthogonal planes. Euler angle determinations (EAD) were developed for different anatomical locations as well as for multiple clinical situations. One or all three Euler angles were changed using the EAD to define any plane of orientation relative to reference orthogonal frame. In a series of 12 patients for postoperative evaluation of Mustard and Senning procedure, the demonstration of anastomotic site was superior with angled coronal planes when compared to the routine coronal views in 83% of the studies. With the use of EAD, acquisition time for non-orthogonal planes can be reduced. 3-DM aids in the understanding of the Euler angles and leads to multiple non-orthogonal planes.

Child, Preschool↗