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Biomedical subjects

P R Harvey

Publications and source records attributed to P R Harvey.

At least 19 recordsLinked to original sources
PubMed2001

Navigator motion correction of diffusion weighted 3D SSFP imaging.

Diffusion weighted (DW) 3D steady state MR (SSFP) head imaging technique using navigator echo's motion correction is presented. This new scheme enables acquisition of DW images even at regions where severe susceptibility is present. Another advantage is the moderate gradient performance requirements. DW imaging methods are sensitive to any kind of motion, thus, most of these methods might suffer from bulk motion artifacts. The common solution to avoid motion artifacts in a 2D DW SSFP acquisition is multi averaging. To avoid the time consuming multi averaging, the new scheme, described here, utilizes navigator echo's motion correction to remove respiratory bulk motion artifacts. At some brain regions, where the motion is governed by blood or CSF pulsation, the navigator motion correction fails. At these regions the correction is an interpolation of corrections from regions where the motion is particularly of the respiratory type. The combination of a 3D sequence with a navigator echo motion correction, enables acquisition of 10 DW slices within a time of 0:50-2:30 min.

Artifacts↗
PubMed2000

Genetic diversity and biological control activity of novel species of closely related pseudomonads isolated from wheat field soils in South Australia.

Rhizobacteria closely related to two recently described species of pseudomonads, Pseudomonas brassicacearum and Pseudomonas thivervalensis, were isolated from two geographically distinct wheat field soils in South Australia. Isolation was undertaken by either selective plating or immunotrapping utilizing a polyclonal antibody raised against P. brassicacearum. A subset of 42 isolates were characterized by amplified 16S ribosomal DNA restriction analysis (ARDRA), BIOLOG analysis, and gas chromatography-fatty acid methyl ester (GC-FAME) analysis and separated into closely related phenetic groups. More than 75% of isolates tested by ARDRA were found to have >95% similarity to either Pseudomonas corrugata or P. brassicacearum-P. thivervalensis type strains, and all isolates had >90% similarity to either type strain. BIOLOG and GC-FAME clustering showed a >70% match to ARDRA profiles. Strains representing different ARDRA groups were tested in two soil types for biological control activity against the soilborne plant pathogen Gaeumannomyces graminis var. tritici, the causative agent of take-all of wheat and barley. Three isolates out of 11 significantly reduced take-all-induced root lesions on wheat plants grown in a red-brown earth soil. Only one strain, K208, was consistent in reducing disease symptoms in both the acidic red-brown earth and a calcareous sandy loam. Results from this study indicate that P. brassicacearum and P. thivervalensis are present in Australian soils and that a level of genetic diversity exists within these two novel species but that this diversity does not appear to be related to geographic distribution. The result of the glasshouse pot trial suggests that some isolates of these species may have potential as biological control agents for plant disease.

Bacterial Typing Techniques↗
PubMed1999

Rapid iterative reconstruction for echo planar imaging.

A rapid automated method for reconstructing echo planar imaging (EPI) data has been developed and is shown to improve image quality by suppressing the troublesome ghost artifact. The algorithm can be applied without prior knowledge obtained from either reference scans or operator intervention. It first estimates, then improves iteratively, the parameters for a linear phase correction applied directly to the complex image data derived from odd and even echoes. The theory used to derive the criteria employed in the iteration provides insight into mechanisms that allow the process to work. Magn Reson Med 42:541-547, 1999.

Algorithms↗
PubMed1999

Modular gradient coil: A new concept in high-performance whole-body gradient coil design.

A new concept in high-performance MR gradient coil design is presented which we have called the Modular Gradient Coil (MGC). This novel design approach results in an actively shielded whole-body gradient coil containing multiple and independent elements, integrated onto a single former, for generating gradient fields along each of the three axes (x, y, and z). These elements can be energized in a number of configurations, using a single gradient power supply unit (PSU), to generate a whole range of gradient performance levels. The design criteria for the MGC also include a requirement to prohibit peripheral nerve stimulation in all of its modes of operation. This requirement is achieved, while simultaneously providing high performance, by specifying different volumes of gradient linearity for each of the operating modes. Magn Reson Med 42:561-570, 1999.

Biophysical Phenomena↗
PubMed1999

The modular (twin) gradient coil--high resolution, high contrast, diffusion weighted EPI at 1.0 Tesla.

The modular (twin) gradient coil is a novel and effective approach to obtaining flexible and high power gradient performance without (i) peripheral nerve stimulation and (ii) the need for resonant or expensive high voltage gradient power supply units (PSU). This whole-body gradient system contains, on the same former, two independent sets of gradient coils, the conventional coil set and the short-body coil set. Each gradient axis is able to operate, independently, in any one of three modes. The third, combined, mode is realized by connecting the conventional coils and short-body coils in series. Through careful design of the shape and size of the linear volume of each mode of operation, the modular gradient coil is able to utilize the power, from a single gradient PSU, more efficiently and more appropriately, as determined by the application. In the short-body and combined modes the gradient fields are linear over a volume suitable for whole head/neck, liver and cardiovascular applications. In the conventional mode, a reduced performance is possible but over a much larger (conventional) imaging volume. Utilizing a semi-conductor switching arrangement it is possible to switch between modes in as little as 1 ms. By mixing different modes of operation on different gradient axes it is possible to utilize more efficiently, and safely, the properties of gradient performance best suited to the sequence requirements. Diffusion weighted EPI (DW-EPI) is a particular technique that demands the extremes of gradient system performance in terms of both amplitude and slew rate. DW-EPI has been implemented, using the modular gradient system, on a 1.0 Tesla whole-body MRI system. The preliminary results presented here serve to illustrate the advantages of the modular gradient coil in of itself as well as the direct benefits it provides for DW imaging at 1.0 Tesla.

Brain↗
PubMed1999

A keyhole echo planar hybrid imaging technique.

A hybrid keyhole imaging method is presented which demonstrates the combination of two distinctly different MR imaging techniques. In this work single shot EPI was used as a dynamic update scan for a conventional high resolution gradient echo acquisition. Problems associated with the integration of MR data from distinctly different imaging techniques are addressed. Illustration is provided by way of diffusion weighted imaging. This novel development requires further investigation which need not be limited to the hybridization of strictly Cartesian based scanning methods.

Brain↗
PubMed1996

The influence of prostaglandin E1 on platelet adherence and injury in preserved rat liver allografts.

We have previously shown that part of the injury sustained by cold-preserved livers on reperfusion is the consequence of platelet adhesion to sinusoidal endothelium. The purpose of the present study was to determine whether prostaglandin E1 (PGE1) can reduce the injury and if so, how to maximize this beneficial effect. Rat livers were cold-preserved in University of Wisconsin solution for 30 hours then subjected to 1-hour warm ischemia after which they were reperfused at 37 degrees C with oxygenated Krebs-Henseleit solution with or without isolated platelets. PGE1 was used to treat the donor liver during harvesting, cold preservation, and reperfusion. In some studies, PGE1 was used to pretreat platelets before exposing them to the liver, and in other studies, both liver and platelets were treated. Pretreatment of platelets with paraformaldehyde, which inactivates them, or ADP, which activates them, was also studied. Treatment of livers with PGE1 significantly decreased preservation injury when livers were reperfused in the absence of platelets. However, when platelets were added to the perfusate, prior treatment of the liver with PGE1 had relatively minor beneficial effects. Pretreatment of platelets alone with PGE1 was also beneficial, but again the effect was small. However, when both liver and platelets were treated with PGE1 there was a highly significant decrease in the extent of liver injury and platelet adhesion. Perfusate transaminase levels were lower, bile flow was improved, and histologically, livers appeared less injured. Pretreatment of platelets with paraformaldehyde produced similar results to pretreatment with PGE1. When platelets were preactivated with adenosine diphosphate, extensive hepatic injury occurred upon reperfusion despite PGE1 treatment of the liver. PGE1 can lessen preservation-reperfusion injury impressively when administered to both liver and platelets but has little effect when platelets have been preactivated.

Alprostadil↗
PubMed1996

Echo-volumar imaging (EVI) at 0.5 T: first whole-body volunteer studies.

Improvements in the echo-volumar imaging (EVI) technique and its application in whole-body studies are described. Using an in-house built 0.5 T echo-planar imaging system, complete modulus three-dimensional image data are acquired in 102 ms with real-time display. Hardware limitations have restricted the maximum array size achievable to 64 x 32 x 8 voxels. Representative voxel dimensions are x = 6.0 mm; y = 4.0 mm, and z = 10.0 mm. Results on human volunteers are presented, showing cardiac, liver, and bladder images. Also shown are the first EVI gastric filling and emptying results.

Echo-Planar Imaging↗
PubMed1996

Accumulation of unconjugated bilirubin in cholesterol pellets implanted in swine gallbladders.

BACKGROUND & AIMS: Most cholesterol gallstones have a pigmented center, but it is unclear whether its presence is primary or secondary. This study was performed to determine if bilirubin would accumulate in a gallstone model consisting of cholesterol pellets. METHODS: Cholesterol was compressed into pellets at 2500 psi, producing a pellet that behaved like human cholesterol gallstones in regard to penetration of solutes into the stone. Pellets were implanted into gallbladders of pigs and harvested after 4 weeks. Bilirubin species were measured by high-performance liquid chromatography. RESULTS: The proportions of bilirubin species in bile were not changed by the presence of pellets, i.e., diconjugates (mean +/- SD, 1.9% +/- 1.0% vs. 0.7% +/- 0.8%), monoconjugates (83.8% +/- 5.5% vs. 87.8% +/- 6.6%), and unconjugated bilirubin (14.2% +/- 5.3% vs. 11.5% +/- 5.6%) were similar at the time of implantation and removal. The cut surfaces of the pellets were pigmented. Pellets contained 5.46 +/- 1.38 micrograms bilirubin/g sample at harvesting, and 98.6% +/- 2.3% of bilirubin in pellets was unconjugated. In in vitro studies, there was a large increase in unconjugated bilirubin in the bile. Pellets also became pigmented in vitro, but there was considerable variability in the bilirubin species present in the pellets. CONCLUSIONS: Unconjugated bilirubin accumulates in cholesterol pellets and pigments them. This provides a mechanism by which cholesterol gallstones could become secondarily pigmented.

Analysis of Variance↗
PubMed1995

Active acoustic screening: reduction of noise in gradient coils by Lorentz force balancing.

We have designed and constructed a quiet gradient set with restricted access for the combined purposes of evaluating the principles of active acoustic screening, recently introduced by Mansfield, Glover, and Bowtell, and for EPI studies of the head at 3.0 T. The design utilizes the return paths of the conductors in a closed arc loop arrangement to eliminate net Lorentz forces thereby attenuating acoustic noise especially at low frequency. This design should significantly reduce the dangers to patients of high noise levels, especially in high field magnetic resonance imaging systems.

Acoustics↗
PubMed1995

Evidence of preservation injury to bile ducts by bile salts in the pig and its prevention by infusions of hydrophilic bile salts.

Preservation injury to bile ducts is a serious problem in liver transplantation, especially when preservation exceeds 12 hours. The authors hypothesized that the injury was caused by contact of bile ducts with bile salts during cold preservation and might be preventable by infusion of more hydrophilic bile salts. Swine livers were harvested after intraportal infusions of saline (control), of the hydrophobic bile salt taurodeoxycholate, or of the hydrophilic bile salts tauroursodeoxycholate or dehydrocholate. The effect of infusing a combination of hydrophilic and hydrophobic bile acids was also studied. Bile samples were taken before and during the infusions. Then livers were perfused with UW solution, ducts were flushed retrograde with UW, and livers were stored at 0 to 1 degree C for 20 hours. Bile ducts were harvested after preservation, and coded microscopic slides of the specimens were examined by light microscopy. There was large variability in baseline bile salt concentration. Injury after preservation consisted of sloughing and pyknosis of surface and glandular epithelium. The histologic injury score determined after preservation was directly related to bile salt concentration in bile ducts at the time of flushing. During bile salt infusions, the infused bile salt replaced most or all of the other bile salts present in bile. Severe postpreservation injury of intrahepatic ducts occurred after taurodeoxycholate infusions, but injury was minimal when either of the two hydrophilic bile salts was infused. The mixture of bile acids produced intermediate results. Retrograde flushing with UW does not prevent injury to intrahepatic ducts. The authors conclude that the injury is caused by contact with bile salts, is dependent on bile salt concentration and composition, and is preventable.

Adenosine↗
PubMed1995

Effect of deoxycholate on immunoglobulin G concentration in bile: studies in humans and pigs.

Because an increase in biliary deoxycholate levels seems to be a risk factor for cholesterol gallstone formation, we determined the relationship between deoxycholate levels and levels of the pronucleating protein, immunoglobulin G (Ig) in human gallbladder bile. Patients with cholesterol gallstones had a higher concentration of biliary IgG compared with a pigmented stone group and control patients. This was associated with the simultaneous presence of two conditions in the cholesterol stone group, supersaturated bile and a high deoxycholate/cholate ratio. The other patient groups met only one of the two conditions. Next, animal studies were performed to determine if model biles mimicking the two conditions could affect IgG secretion by the gallbladder. Gallbladders were exposed in vivo and then in an Ussing chamber to model biles. The voltage clamp technique was used to monitor functional integrity of the preparation. Three different model biles were tested: (1) taurodeoxycholate (TDC), 80%; taurocholate (TC), 20%; and cholesterol saturation index (CSI), 1.2; (2) TDC, 20%; TC, 80%; and CSI, 1.2; and (3) TDC, 80%; TC, 20%; and CSI, 0.6. IgG concentrations became significantly higher in group 1 than in the other two groups. The concentration of mucous glycoprotein was also significantly greater in group 1 when compared with group 2. Plasma cells were increased in number in mucosal and submucosal layers in group 1. We conclude that cholesterol supersaturated model bile with high content of TDC induces gallbladder epithelial alterations, which increase the luminal concentration of IgG and mucous glycoprotein.

Animals↗
PubMed1995

A rapid, simple high capacity cholesterol crystal growth assay.

Cholesterol crystal "nucleation time", more recently referred to as cholesterol crystal observation time, is defined as the first appearance of cholesterol crystals from isotropic crystal-free biles on light microscopy. This test is used to assess the potency of nucleating agents. Crystal appearance has conventionally been determined by polarizing light microscopy and crystal growth by counting the number of crystals. In this study we adapted a spectrophotometric method to a microtiter plate reader to generate cholesterol crystal growth curves. Model biles were prepared with a cholesterol saturation of 1.2 to 1.3 and total lipid concentration of 10.7 g/dl (taurocholate, 125 mM; cholesterol, 16.8-18.4 mM; phospholipid, 43 mM). Pronucleating IgM samples were used to establish and validate the assay. Cholesterol crystal growth curves were generated by reading absorption at 630 nm daily on a Dynatech microplate reader. Results were correlated to cholesterol crystal counts as determined by polarizing light microscopy. Standard curves generated from absorbencies of known masses of cholesterol crystals were used to quantify the mass of cholesterol crystals formed over the observation period. The assay was applied to known pronucleating biliary immunoglobulins. Results obtained were similar to our previous report that biliary IgM is more potent than biliary IgG. We conclude that using microplates and a microtiter plate reader provides a rapid high capacity method for detecting cholesterol crystal growth to assess potential nucleating agents in nucleation assays.

Bile↗
PubMed1995

Cholesterol microcrystals associated with concanavalin A-binding glycoproteins contribute artifactually to nucleating activity assays.

Concanavalin A (Con A) affinity chromatography is the standard procedure to separate cholesterol nucleating biliary proteins from lipids and pigment. We observed that even after extensive washing following application of bile, lipid contaminants remain. We have determined the contribution of lipid contamination to cholesterol nucleation and assessed a modified procedure to remove lipids from the column. Human gallbladder bile was spiked with [3H]cholesterol and [14C]phospholipid and applied to two sets of Con A-Sepharose columns. One column was washed in the usual manner with Tris-HCl buffer and the other with buffer containing 10 mM taurocholate prior to eluting bound glycoproteins with alpha-D-methylmannopyranoside. Eluted proteins were added to heated abnormal bile at a final concentration of 250 micrograms/ml to study the effect on cholesterol nucleation. A separate aliquot (20 microliter) of the protein solutions was counted for radioactivity. Cholesterol nucleating activity was less in samples from columns washed with 10 mM taurocholate than in samples from columns not washed with the bile salt. Lipid radioactivity was associated with Con A-binding proteins prepared without taurocholate, but not in those prepared with taurocholate wash. Light microscopy revealed the presence of cholesterol microcrystals and vesicles in some Con A-binding protein preparations prepared without a taurocholate wash. However, pellets from ultracentrifuged Con A preparations prepared without a bile salt wash revealed cholesterol crystals in all samples (n = 6). Washing with taurocholate did not affect recovery of protein mass and appearance of bands on SDS-PAGE gel showed an identical pattern in the two groups. This modified procedure to prepare potential nucleating proteins from gallbladder bile should eliminate erroneous results that may arise due to lipid contamination.

Artifacts↗
PubMed1994

Fetal weight estimation by echo-planar magnetic resonance imaging.

Fetal weight was estimated in utero in eleven singleton pregnancies by measurement of fetal volume with echo-planar imaging (EPI), a form of magnetic resonance imaging, and by ultrasound measurements. EPI estimates of fetal volume were closely correlated with actual birthweight (R = 0.97). The median difference (expressed as a percentage of actual birthweight) between actual and EPI-estimated birthweights was 3.0% (range 0.6-9.9); this discrepancy was significantly smaller than that found for ultrasonographic estimates (6.5% [1.7-17.8]; p < 0.01).

Birth Weight↗
PubMed1994

Avoiding peripheral nerve stimulation: gradient waveform criteria for optimum resolution in echo-planar imaging.

Adaptation of Mansfield and Harvey's theory of magnetically induced neural stimulation indicates that, for trapezoidal gradient waveforms and at the relatively low modulation frequencies commonly used in echo-planar imaging, an increase in rise time even to the point of creating a triangular waveform can prove advantageous over the use of simple sinusoidal modulation. For example, a higher image resolution is in principle possible before the neural stimulation limit is reached. For higher modulation frequencies and fast ramp trapezoidal waveforms, the peak gradient can be lower than that for a sinusoidal waveform by a factor approaching 2/pi for equal resolution. This means that by using a multimode resonant gradient drive, the amplifier power requirements are greatly relaxed. The signal sampling bandwidth required is also lower, because, due to the trapezoidal nonlinear sample pattern, sample points are spaced linearly during the waveform plateaus.

Echo-Planar Imaging↗
PubMed1994

The effects of hepatic preservation at 0 degrees C compared to 5 degrees C: influence of antiproteases and periodic flushing.

The optimal preservation temperature for liver allografts is unknown. We evaluated the effect of small differences in preservation temperature, 5 degrees C vs 0 degrees C, on outcome of prolonged preservation. Livers of Wistar rats were preserved at these temperatures in UW solution for 40 h. Function was studied during reperfusion on the isolated perfused rat liver system at 37 degrees C. To compare the effects of a small reduction in temperature with known beneficial strategies, the effects of including antiproteases and periodic flushing of the graft with UW solution during cold preservation at 5 degrees C were also studied. Aspartate transaminase (AST) and alanine transaminase release after 4 h of reperfusion were much higher in the livers stored at 5 than at 0 degrees C (P < 0.0005). Addition of antiproteases to the preservation solution or periodic flushing reduced AST release but neither treatment at 5 degrees C was as good as simple storage at 0 degrees C. Cumulative bile production after 4 h of reperfusion was significantly greater in the 0 degrees C preserved group than in liver at 5 degrees C or 5 degrees C with periodic flushing. The addition of antiproteases resulted in slightly increased bile production (not significant). Platelets and WBCs in the perfusate decreased during reperfusion. This effect was more pronounced in the 5 degrees C preserved livers than in those stored at 0 degrees C. Antiproteases in the preservation solution appeared to inhibit platelet and WBC loss. Perfusate flow was significantly higher in the 0 degrees C group. We conclude that small differences in preservation temperature even at these low temperatures are important in postreperfusion liver function.

Adenosine↗