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Biomedical subjects

Robert L Greenman

Publications and source records attributed to Robert L Greenman.

9 recordsLinked to original sources
PubMed2005

Early changes in the skin microcirculation and muscle metabolism of the diabetic foot.

BACKGROUND: Changes in the large vessels and microcirculation of the diabetic foot are important in the development of foot ulceration and subsequent failure to heal existing ulcers. We investigated whether oxygen delivery and muscle metabolism of the lower extremity were factors in diabetic foot disease. METHODS: We studied 108 patients (21 control individuals who did not have diabetes, 36 patients with diabetes who did not have neuropathy, and 51 patients with both diabetes and neuropathy). We used medical hyperspectral imaging (MHSI) to investigate the haemoglobin saturation (S(HSI)O2; % of oxyhaemoglobin in total haemoglobin [the sum of oxyhaemoglobin and deoxyhaemoglobin]) in the forearm and foot; we also used 31P-MRI scans to study the cellular metabolism of the foot muscles by measuring the concentrations of inorganic phosphate and phosphocreatine and calculating the ratio of inorganic phosphate to phosphocreatine (Pi/PCr). FINDINGS: The forearm S(HSI)O2 during resting was different in all three groups, with the highest value in controls (mean 42 [SD 17]), followed by the non-neuropathic (32 [8]) and neuropathic (28 [8]) groups (p<0.0001). In the foot at resting, S(HSI)O2 was higher in the control (38 [22]) and non-neuropathic groups (37 [12]) than in the neuropathic group (30 [12]; p=0.027). The Pi/PCr ratio was higher in the non-neuropathic (0.41 [0.10]) and neuropathic groups (0.58 [0.26]) than in controls (0.20 [0.06]; p<0.0001). INTERPRETATION: Our results indicate that tissue S(HSI)O2 is reduced in the skin of patients with diabetes, and that this impairment is accentuated in the presence of neuropathy in the diabetic foot. Additionally, energy reserves of the foot muscles are reduced in the presence of diabetes, suggesting that microcirculation could be a major reason for this difference.

Case-Control Studies↗
PubMed2005

Evaluation of the RF field uniformity of a double-tuned 31P/1H birdcage RF coil for spin-echo MRI/MRS of the diabetic foot.

PURPOSE: To evaluate the B1 field uniformity of a double-tuned birdcage coil designed for (31)P/(1)H MRI/MRS spin-echo (SE) imaging of the metatarsal head region of the foot in neuropathic diabetic patients. MATERIALS AND METHODS: A low-pass double-tuned (31)P/(1)H RF birdcage coil was constructed to fit over the adult forefoot. Flip angle (FA) maps were created from B1 data acquired at the 3T (31)P (four normal subjects) and (1)H (five normal subjects) frequencies. T2-weighted (T2-W) (1)H images, (31)P rapid acquisition with relaxation enhancement (RARE) images, and composite SE pulse CSI data were acquired to demonstrate the uniformity of the resulting images and data. RESULTS: The means and standard deviations (SDs) of the range of FAs across the feet of the volunteer subjects indicated good uniformity (the maximum coefficients of variation (CVs) for all of the (31)P and (1)H FA maps were 7.6% and 7.3%, respectively). The FA values across the metatarsal head region indicated a maximum signal intensity variation of +/-3% in a RARE image acquired using an echo train length of 32. CONCLUSION: A (31)P/(1)H birdcage coil constructed for MRI/MRS studies of the human forefoot provided sufficient signal uniformity of SE data to facilitate accurate (31)P concentration measurements in muscle.

Diabetic Foot↗
PubMed2005

Concentric coil arrays for parallel MRI.

A new type of coil array is proposed that consists of concentrically placed coil elements, each of which is characterized by symmetrically arranged lobes that have alternating current directions. Symmetries in the coil elements' conductor paths allow for the minimization of mutual inductance and noise correlations. In addition, the concentric arrangement of the coil elements provides spatial encoding capabilities in multiple directions, which is valuable when arrays are used with parallel MRI. Simulations are presented that describe the signal-to-noise ratio (SNR) properties of individual concentric array elements, and a four-element prototype concentric array is constructed. This prototype array is compared experimentally with three alternative four-element array designs. The overall SNR of the concentric array is comparable to the SNR of the competing arrays. Reconstruction of twofold undersampled data using the concentric array yields an average g-factor of less than 1.3 in all directions parallel to the plane of the array. There is some degradation in performance when threefold undersampled data are reconstructed, but the array still shows substantial directional invariance compared to alternative designs. Both fully-sampled and undersampled cardiac images acquired using the concentric array are shown. These results suggest that concentric structures can be useful tools for designing specialized coil arrays for parallel MRI.

Computer-Aided Design↗
PubMed2005

Strategies for shimming the breast.

There is evidence in the literature indicating a significant static field inhomogeneity in the human breast. A nonhomogenous field results in line broadening and frequency shifts in MRS and can cause intensity loss and spatial errors in MRI. Thus, there is a clear rationale for determining the regional variations in the static field homogeneity in the breast and providing strategies to correct them. Herein, the nature and extent of the static magnetic field at 3 T were measured in central planes of the human breast using both phase maps and multivoxel MRS techniques. In addition, the effect of first- and high-order shimming and of spatial saturation pulses on the static field inhomogeneity was evaluated. Both the theoretical and the measured field were found to be primarily linear in nature, with a reduction of 300 Hz from the nipple to the chest wall. First-order shimming reduced this inhomogeneity by 65%. Interestingly, the combination of spatial saturation pulses and first-order shimming was more effective than high-order shim alone. Since many clinical scanners do not have either higher-order shim or automated higher shimming algorithms that work in the presence of fat, the suggested combination provides an effective means to correct inhomogeneities in the breast.

Adult↗
PubMed2005

Foot small muscle atrophy is present before the detection of clinical neuropathy.

OBJECTIVE: To characterize structural changes and the metabolic profile of foot muscles and correlate them with diabetic neuropathy measurements using phosphorus-31 ((31)P) rapid acquisition with relaxation enhancement (RARE) magnetic resonance imaging (MRI). RESEARCH DESIGN AND METHODS: We studied 12 control subjects, 9 non-neuropathic diabetic patients, and 12 neuropathic diabetic patients using (31)P RARE and proton ((1)H) MRI at 3 Tesla. The ratio of the total cross-sectional area of the foot to that of the muscle tissue was calculated from transaxial (1)H and (31)P images. The average (31)P concentration across the metatarsal head region was measured from the (31)P images. RESULTS: The muscle area-to-total area ratio differed among all three groups (means +/- SD): 0.55 +/- 0.04 vs. 0.44 +/- 0.05 vs. 0.06 +/- 0.06 for control, non-neuropathic, and neuropathic subjects, respectively (P < 0.0001). The average (31)P concentration also differed among all groups: 27.7 +/- 3.8 vs. 21.7 +/- 4.8 vs. 7.9 +/- 8.8 mmol/l for control, non-neuropathic, and neuropathic subjects (P < 0.0001). The muscle area-to-total area ratio strongly correlated with clinical measurements: Neuropathy Disability Score, r = -0.83, P < 0.0001; vibration perception threshold, r = -0.79, P < 0.0001; and Semmes-Weinstein monofilaments, r = -0.87, P < 0.0001. CONCLUSIONS: Small muscle atrophy is present in diabetes before clinical peripheral neuropathy can be detected using standard clinical techniques. The (31)P RARE MRI method evaluates the severity of muscle atrophy, even in the early stages when neuropathy is absent. This technique may prove to be a useful diagnostic tool in identifying early-stage diabetic foot problems.

Atrophy↗
PubMed2004

Quantification of the 31P metabolite concentration in human skeletal muscle from RARE image intensity.

A method is described for quantifying the cellular phosphorus-31 (31P) concentration in human skeletal muscle based on RARE (rapid acquisition with relaxation enhancement) image intensities. The 31P concentrations were calculated using relaxation rates, RF coil spatial characteristics, and RARE signal intensities from foot muscle and an external 31P standard. 31P RARE and 1H T2-weighted images of the foot muscles in 11 normal subjects were acquired at 3.0 T using a double-tuned (31P/1H) birdcage coil. 31P PRESS (point-resolved spectroscopy) spectra were acquired to verify the measurable 31P concentrations in a multiecho acquisition. The mean measured concentration was 26.4 +/- 3.1 mM (mean +/- SD) from RARE signal intensities averaged over the entire imaged foot anatomy and 27.6 +/- 4.1 mM for a 3 x 3 pixel region-of-interest measurement. The 31P RARE image acquisition time was 4 min with a 0.55 cm3 voxel size. These results demonstrate that the 31P concentration can be accurately measured noninvasively in human muscle from RARE images acquired in short scan times with relatively high spatial resolution.

Foot↗
PubMed2003

Double inversion black-blood fast spin-echo imaging of the human heart: a comparison between 1.5T and 3.0T.

PURPOSE: To evaluate the effectiveness of blood suppression and the quality of black-blood cardiac images acquired at 3.0 Tesla using a double-inversion recovery fast spin-echo sequence by comparing data acquired at 3.0T to data acquired at 1.5T. MATERIALS AND METHODS: Black-blood T2-weighted fast spin-echo images of the heart were acquired from five normal volunteers at 1.5T and five normal volunteers at 3.0T. Region-of-interest signal intensity measurements were performed at several locations in the suppressed blood regions of the left and right ventricles and around the left ventricle walls to assess the effectiveness and uniformity of the blood suppression, the myocardial signal-to-noise ratio (SNR), and the signal uniformity at both field strengths. B1 field maps were produced in phantoms and in subjects at both field strengths. RESULTS: Blood suppression performance is equivalent at 1.5T and 3.0T. The improvement in SNR at 3.0T compared with 1.5T is less than has been predicted in previous studies. The signal uniformity is significantly poorer at 3.0T than at 1.5T due to dielectric effects and shorter radio frequency wavelengths (P < 0.005). CONCLUSION: Spin-echo and spin-echo echo-train sequences that perform well at 1.5T will produce large signal variations in the chest cavity at 3.0T without modifications. B1 insensitive methods must be explored and implemented for spin-echo sequences to fully realize the advantages of using these sequences for high-field MRI.

Blood↗
PubMed2002

Fast imaging of phosphocreatine in the normal human myocardium using a three-dimensional RARE pulse sequence at 4 Tesla.

PURPOSE: To investigate the use of a three-dimensional rapid acquisition with relaxation enhancement (RARE) pulse sequence for direct acquisition of phosphocreatine (PCr) images of the human myocardium. MATERIALS AND METHODS: A short elliptical birdcage radiofrequency (RF) body coil was constructed to produce a uniform flip angle throughout the chest cavity. In vivo images using a spectrally-selective RARE sequence with a spatial resolution of 1.2 cm x 1.2 cm x 2.5 cm (4 cm(3)) were acquired in nine minutes and 40 seconds. RESULTS: Scans of phantoms demonstrated excellent spectral selectivity. The signal-to-noise ratio in the myocardium ranged from 12.6 in the anterior wall to 5.3 in the mid septum. CONCLUSION: This study demonstrates that PCr data can be acquired using a three-dimensional RARE sequence with greater spatial and temporal resolution than spectroscopic techniques.

Humans↗