Biomedical subjects

Ravinder Reddy

Publications and source records attributed to Ravinder Reddy.

At least 37 records · Page 2Linked to original sources

PubMed2004

Method for reduced SAR T1rho-weighted MRI.

A reduced specific absorption rate (SAR) version of the T(1rho)-weighted MR pulse sequence was designed and implemented. The reduced SAR method employs a partial k-space acquisition approach in which a full power spin-lock pulse is applied to only the central phase-encode lines of k-space, while the remainder of k-space receives a low-power spin-lock pulse. Acquisition of high- and low-power phase-encode lines are interspersed chronologically to minimize average power deposition. In this way, the majority of signal energy in the central portion of k-space receives full T(1rho)-weighting, while the average SAR of the overall acquisition can be reduced, thereby lowering the minimum safely allowable TR. The pulse sequence was used to create T(1rho) maps of a phantom, an in vivo mouse brain, and the brain of a human volunteer. In the images of the human brain, SAR was reduced by 40% while the measurements of T(1rho) differed by only 2%. The reduced SAR sequence enables T(1rho)-weighted MRI in a clinical setting, even at high field strengths.

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PubMed2004

Reduction of residual dipolar interaction in cartilage by spin-lock technique.

The influence of radiofrequency (RF) spin-lock pulse on the laminar appearance of articular cartilage in MR images was investigated. Spin-lock MRI experiments were performed on bovine cartilage plugs on a 4.7 Tesla small-bore MRI scanner, and on human knee cartilage in vivo on a 1.5 Tesla clinical scanner. When the normal to the surface of cartilage was parallel to B0, a typical laminar appearance was exhibited in T2-weighted images of cartilage plugs, but was absent in T1rho-weighted images of the same plugs. At the "magic angle" orientation (when the normal to the surface of cartilage was 54.7 degrees with respect to B0), neither the T2 nor the T1rho images demonstrated laminae. At the same time, T1rho values were greater than T2 at both orientations throughout the cartilage. T1rho dispersion (i.e., the dependence of the relaxation rate on the spin-lock frequency omega1) was observed, which reached a steady-state value of close to 2 kHz in both parallel and magic-angle orientations. These results suggest that residual dipolar interaction from motionally-restricted water and relaxation processes, such as chemical exchange, contribute to T1rho dispersion in cartilage. Further, one can reduce the laminar appearance in human articular cartilage by applying spin-lock RF pulses, which may lead to a more accurate diagnosis of degenerative changes in cartilage.

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PubMed2004

In vivo quantification of T1rho using a multislice spin-lock pulse sequence.

A multislice spin-lock (MS-SL) pulse sequence is implemented on a clinical scanner to acquire multiple images with spin-lock-generated contrast of the knee joints of six healthy human subjects. The MS-SL sequence produces images with T1rho contrast with an additional factor of intrinsic T2rho weighting, which hinders direct measurement of T1rho. A method is presented to compensate the MS-SL-generated data with regard to T2rho in an effort to accurately calculate multislice T1rho maps in a feasible experimental time. The T2rho-compensated multislice T1rho maps produced errors in the measurement of T1rho in healthy patellar cartilage of approximately 5% compared to the gold standard measurement of T1rho acquired with single-slice spin-lock pulse sequence. The MS-SL sequence has potential as an important clinical tool for the acquisition of multislice T1rho-weighted images and/or quantitative multislice T1rho maps.

Adult↗

PubMed2004

T2rho-weighted contrast in MR images of the human brain.

In this work, the feasibility of using T2rho weighting as an MR contrast mechanism is evaluated. Axial images of a human brain were acquired using a single-slice spin-lock T2rho-weighted pulse sequence and compared to analogous T2-weighted images of the same slice. The contrast between white matter and gray matter in T2rho-weighted images was approximately 40% greater than that from T2-weighted data. These preliminary data suggest that the novel contrast mechanism of T2rho can be used to yield high-contrast T2-like images.

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PubMed2004

3D-T1rho-relaxation mapping of articular cartilage: in vivo assessment of early degenerative changes in symptomatic osteoarthritic subjects.

RATIONALE AND OBJECTIVES: To determine the in vivo feasibility of quantifying early degenerative changes in patellofemoral joint of symptomatic human knee using spin-lattice relaxation time in the rotating frame (T(1rho)) magnetic resonance imaging (MRI). MATERIALS AND METHODS: All the MRI experiments were performed on a 1.5 T whole-body GE Signa clinical scanner using a custom built 15-cm diameter transmit-receive quadrature birdcage radiofrequency coil. The T(1rho)-prepared magnetization was imaged with a three-dimensional gradient-echo pulse sequence pre-encoded with a three-pulse cluster consisting of two hard 90 degrees pulses and a low power spin-lock pulse. Quantitative T(1rho) relaxation maps of asymptomatic (n = 8 males), and six symptomatic human volunteers (four men, two women) were computed using a appropriate signal expression. RESULTS: All six symptomatic volunteers showed elevation in T(1rho) relaxation times when compared with asymptomatic subjects. In symptomatic population, the T(1rho) relaxation times varied from 63 +/- 4 ms to 95 +/- 12 ms (mean +/- standard deviation) depending on the degree of cartilage degeneration. The increase in T(1rho) of symptomatic population was statistically significant (n = 6, P <.002) when compared with corresponding asymptomatic population. However, in asymptomatic population the relaxation times varied only from approximately 45 to 55 ms (n = 8, age range 22-45 years). CONCLUSION: Preliminary results demonstrated the in vivo feasibility of quantifying early biochemical changes in symptomatic osteoarthritis subjects employing T(1rho)-weighted MRI on a 1.5 T clinical scanner. This study on limited number of symptomatic population shows that T(1rho)-weighted MRI provides a noninvasive marker for quantitation of early degenerative changes of cartilage in vivo. However, further studies are needed to correlate early osteoarthritis determined from arthroscopy with T(1rho) in a large symptomatic population.

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PubMed2004

Cartilage volume quantification via Live Wire segmentation.

RATIONALE AND OBJECTIVES: A reduction in cartilage volume is characteristic of osteoarthritis and hence there exists a need for an accurate and reproducible method to measure in vivo cartilage volume. Quantification of cartilage volume from magnetic resonance (MR) images requires a segmentation technique such as the user-driven "Live Wire" strategy that can reliably delineate object volumes in a time-efficient manner. In the present work, the accuracy and reproducibility of the Live Wire method for the quantification of cartilage volume in MR images is evaluated. MATERIALS AND METHODS: The accuracy of the Live Wire method was assessed by comparing the MR-based volume measurement of a patellar cartilage-shaped phantom versus data calculated via water displacement. The inter- and intra-operator reproducibility of the technique was evaluated from Live Wire segmentation of the patellar cartilage volume from fat-suppressed 3-dimensional spoiled-gradient-echo images of five healthy human volunteers performed by three operators. To provide data for analysis of inter-scan reproducibility, the human scans were repeated five times with the aid of a leg-restraining jig to minimize repositioning error. RESULTS: The volume of the patellar cartilage-shaped phantom measured via Live Wire segmentation of MR images was within 97.8% of its true volume. The average inter- and intra-operator coefficients of variation of three operators were 3.0% and 0.4%, respectively. The average inter-scan coefficient of variation of five repeated scans of each volunteer was 2.7%. CONCLUSION: The data suggest that the Live Wire strategy is an accurate, reproducible, and efficient technique to measure cartilage volume in vivo in a feasible amount of operator time.

Adult↗

PubMed2004

T1rho-weighted MRI using a surface coil to transmit spin-lock pulses.

T1rho-weighted MRI is a novel basis for generating tissue contrast. However, it suffers from sensitivity to B1 inhomogeneity. First, excitation with a spatially varying B1 causes flip-angle artifacts and second, spin locking with an inhomogeneous B1 results in non-uniform T1rho contrast. In this study, we overcome the former complication with a specially designed spin-locking pulse sequence and we successfully obtain T1rho-weighted images with a surface coil. In this pulse sequence, the spin-lock pulse was divided into segments of equal duration and alternating phase. This "self-compensating" T1rho-preparatory pulse sequence was analyzed and the effect of an inhomogeneous B1 field was simulated using the Bloch equations. T1rho-weighted MR images of a phantom and a human knee joint in vivo were obtained on a clinical scanner with a surface coil to demonstrate the utility of the pulse sequence. The self-compensating T1rho-prepared pulses sequence resulted in substantially reduced image artifacts compared to the conventional, single-phase spin-lock pulse.

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PubMed2004

Proton MRI of metabolically produced H2 17O using an efficient 17O2 delivery system.

In vivo detection of H(2)(17)O produced via metabolic reduction of inhaled (17)O-enriched gas is demonstrated using proton magnetic resonance imaging (MRI). Specifically, (1)H T(1rho)-weighted MRI, which may be readily implemented on any MRI scanner, is applied as an indirect (17)O imaging method to quantitatively monitor the distribution of metabolically produced (17)O water (mpH(2)(17)O) in the rat brain. The delivery of (17)O(2) to rats is conducted via a specially designed closed respiration circuit that conserves the expensive gas. Quantitative mapping of H(2)(17)O performed via (1)H T(1rho)-weighted MRI is validated by direct (17)O-magnetic resonance spectroscopy. The MRI data show that a steady-state H(2)(17)O concentration of 25.7 +/- 1.66 mM (n = 4) is achieved in the rat brain within approximately 30 min under the (17)O inhalation paradigm used. From the first minute of the mpH(2)(17)O time courses, cerebral metabolic rate of oxygen (CMRO(2)) is estimated to be 2.10 +/- 0.44 micromol g(-1) min(-1) (n = 4), a value that is consistent with the literature.

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PubMed2004

Sodium magnetic resonance imaging of proteoglycan depletion in an in vivo model of osteoarthritis.

RATIONALE AND OBJECTIVES: The aim of the study was to investigate the feasibility of using sodium magnetic resonance imaging (MRI) as a noninvasive quantitative technique for measuring proteoglycan (PG) content in an in vivo porcine model of osteoarthritis (OA). MATERIALS AND METHODS: Biochemical conditions similar to those of OA were created by an intra-articular injection of recombinant porcine interleukin-1beta (IL-1beta) into the knee joint of pigs (n = 6) before performing MRI. The contralateral knee joint was given a saline injection to serve as an internal control. Sodium MRI data were acquired on a 4-T clinical MR scanner and used to compute quantitative sodium and fixed charge density (FCD) maps based on a previously established methodology. In vivo FCD maps were compared with FCD maps obtained using ex vivo patellae harvested from the specimens. The tissue and joint fluid were subjected to histologic and immunohistochemical analyses as independent measurements of IL-1beta activity and PG loss. RESULTS: The average FCD of IL-1beta-treated patellae was measured to be 49% lower than that of saline-treated patellae, indicating a loss of PG content. These results were supported by histologic and immunochemical findings, most notably a reduction in staining for PG and an increase in matrix metalloproteinases in the synovial fluid. CONCLUSION: Sodium MRI can serve as a quantitative method to measure in vivo changes in PG content in an animal model of OA. The use of a noninvasive quantitative in vivo PG measurement technique such as sodium MRI on an animal model would aid greatly in efforts to monitor the efficacy of treatments for OA. Furthermore, these results indicate that early degenerative events could be detected noninvasively in vivo in humans with PG-depleting diseases such as OA.

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PubMed2004

von Willebrand's disease and psychotic disorders: co-segregation and genetic associations.

OBJECTIVES: To evaluate co-segregation and genetic associations between von Willebrand's disease (vWD) and psychotic disorders. METHODS: The study was initiated following ascertainment of a nuclear family in which four members were diagnosed with vWD and psychotic/mood disorders. As co-segregation was uncertain in the extended pedigree, we also investigated population-based linkage and association using polymorphisms of vWF, the gene conferring susceptibility to vWD. Three common vWF polymorphisms were investigated among 194 patients with psychotic disorders (bipolar I disorder, BD I; schizoaffective disorder, SZA and schizophrenia, SZ) and their parents. The cases were also compared with unrelated population-based controls (n = 183). RESULTS: The transmission disequilibrium test and related analyses suggested nominally significant transmission distortion of one allele and related haplotypes to the probands from their parents. The most significant results were obtained among patients with BD I, and similar trends were also evident in the SZ sample. Comparisons between the cases and population-based controls did not reveal associations, though marginally significant case-control differences were obtained in the BD I sample. CONCLUSIONS: These studies are consistent with association and linkage between vWF and BD I. However, given the relatively small sample, stochastic variation is an alternative explanation.

Adult↗

PubMed2004

Proteoglycan loss in human knee cartilage: quantitation with sodium MR imaging--feasibility study.

The feasibility of using sodium magnetic resonance (MR) imaging to detect proteoglycan loss in early-stage osteoarthritis is evaluated. Fixed charge density (FCD) maps were calculated from sodium MR imaging data collected in nine healthy volunteers and three individuals with symptoms of early-stage osteoarthritis by using a 4.0-T clinical MR imaging unit. Data from the healthy individuals revealed a mean FCD of -182 mmol/L +/- 9. Data from the symptomatic subjects revealed focal regions of decreased FCD, with mean values ranging from -108 to -144 mmol/L, indicating proteoglycan loss from the cartilage matrix. The data suggest that sodium MR imaging has potential for use as a quantitative diagnostic tool to measure changes in proteoglycan content in early-stage osteoarthritis.

Adult↗

PubMed2003

Reduced plasma antioxidants in first-episode patients with schizophrenia.

Recent findings suggest that free radical-mediated pathological processes may underlie membrane deficits that have been observed in schizophrenia. We have previously demonstrated that both total antioxidant status (TAS) and individual antioxidants were significantly reduced in plasma of chronic schizophrenic patients, on and off haloperidol. To test whether reductions in plasma antioxidants are independent of treatment or illness progression, levels of plasma antioxidants were evaluated in 43 patients at first-episode of psychosis, 31 patients meeting DSM-IV criteria for schizophrenia or schizoaffective disorder (reconfirmed after 6 months) and 12 patients with primary mood (bipolar or depressive (BP/D)) disorder, at neuroleptic-naive baseline as well as 40 age- and sex-matched normal controls (NC). The major plasma antioxidants albumin, uric acid and bilirubin were all significantly lower in the first-episode schizophrenic, but not in the BP/D patients, than in normal controls. Factors that can affect these antioxidants-age, gender, diet and smoking-were examined. Body mass index (BMI) was significantly lower in patients, but was not correlated with plasma albumin and bilirubin; there was a trend for a correlation with uric acid in schizophrenic patients. Lower antioxidant levels were independent of smoking status of patients. The present data suggest that a defect in the antioxidant defense system (AODS), which may lead to oxidative damage, occurs early in the course of illness and is independent of treatment effects.

Adult↗

PubMed2003

Proton spin-lock ratio imaging for quantitation of glycosaminoglycans in articular cartilage.

PURPOSE: To quantify glycosaminoglycans (GAG) in intact bovine patellar cartilage using the proton spin-lock ratio imaging method. This approach exploits spin-lattice relaxation time in the rotating frame (T(1rho)) imaging and T(1rho) relaxivity (R(1rho)). MATERIALS AND METHODS: All the magnetic resonance imaging (MRI) experiments were performed on a 4-T whole-body GE Signa scanner (GEMS, Milwaukee, WI), and spectroscopy experiments of chondroitin sulfate (CS) phantoms were done on a 2-T custom-built spectrometer. A custom-built 11-cm-diameter transmit-receive birdcage coil, which was tuned to a proton frequency of 170 MHz, was employed for the imaging experiments. T(1rho) measurements were made using a fast spin echo (FSE) sequence pre-encoded with a three-pulse cluster consisting of two 90 degrees hard pulses separated by a low-power rectangle pulse for spin-locking. RESULTS: The methodology is first validated on CS phantoms and then used to quantify GAG content in intact bovine cartilage (N = 5). There is a good agreement between the GAG map calculated from the T(1rho) ratio imaging method (71 +/- 4%) and GAG measured from spectrophotometric assay (75 +/- 5%) in intact bovine tissue. CONCLUSION: We have demonstrated a proton spin-lock ratio imaging method to quantify absolute GAG distribution in the cartilage in a noninvasive and nondestructive manner.

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PubMed2003

Three-dimensional T1rho-weighted MRI at 1.5 Tesla.

PURPOSE: To design and implement a magnetic resonance imaging (MRI) pulse sequence capable of performing three-dimensional T(1rho)-weighted MRI on a 1.5-T clinical scanner, and determine the optimal sequence parameters, both theoretically and experimentally, so that the energy deposition by the radiofrequency pulses in the sequence, measured as the specific absorption rate (SAR), does not exceed safety guidelines for imaging human subjects. MATERIALS AND METHODS: A three-pulse cluster was pre-encoded to a three-dimensional gradient-echo imaging sequence to create a three-dimensional, T(1rho)-weighted MRI pulse sequence. Imaging experiments were performed on a GE clinical scanner with a custom-built knee-coil. We validated the performance of this sequence by imaging articular cartilage of a bovine patella and comparing T(1rho) values measured by this sequence to those obtained with a previously tested two-dimensional imaging sequence. Using a previously developed model for SAR calculation, the imaging parameters were adjusted such that the energy deposition by the radiofrequency pulses in the sequence did not exceed safety guidelines for imaging human subjects. The actual temperature increase due to the sequence was measured in a phantom by a MRI-based temperature mapping technique. Following these experiments, the performance of this sequence was demonstrated in vivo by obtaining T(1rho)-weighted images of the knee joint of a healthy individual. RESULTS: Calculated T(1rho) of articular cartilage in the specimen was similar for both and three-dimensional and two-dimensional methods (84 +/- 2 msec and 80 +/- 3 msec, respectively). The temperature increase in the phantom resulting from the sequence was 0.015 degrees C, which is well below the established safety guidelines. Images of the human knee joint in vivo demonstrate a clear delineation of cartilage from surrounding tissues. CONCLUSION: We developed and implemented a three-dimensional T(1rho)-weighted pulse sequence on a 1.5-T clinical scanner.

Adult↗

PubMed2003

T 1 rho-relaxation mapping of human femoral-tibial cartilage in vivo.

PURPOSE: To demonstrate the in vivo feasibility of measuring spin-lattice relaxation time in the rotating frame (T(1rho)); and T(1rho)-dispersion in human femoral cartilage. Furthermore, we aimed to compute the baseline T(1rho)-relaxation times and spin-lock contrast (SLC) maps on healthy volunteers, and compare relaxation times and signal-to-noise ratio (SNR) with corresponding T(2)-weighted images. MATERIALS AND METHODS: All MR imaging experiments were performed on a 1.5 T GE Signa scanner (GEMS, Milwaukee, WI) using a custom built 15-cm transmit-receive quadrature birdcage radio-frequency (RF) coil. The T(1rho)-prepared magnetization was imaged with a single-slice two-dimensional fast spin-echo (FSE) pulse sequence preencoded with a three-pulse cluster consisting of two hard 90 degrees pulses and a low power spin-lock pulse. T(1rho)-dispersion imaging was performed by varying the spin-lock frequency from 100 to 500 Hz in five steps in addition to varying the length of the spin-lock pulse. RESULTS: The average T(1rho)-relaxation times in the weight-bearing (WB) and nonweight-bearing (NWB) regions of the femoral condyle were 42.2 +/- 3.6 msec and 55.7 +/- 2.3 msec (mean +/- SD, N = 5, P < 0.0001), respectively. In the same regions, the corresponding T(2)-relaxation times were 31.8 +/- 1.5 msec and 37.6 +/- 3.6 msec (mean +/- SD, N = 5, P < 0.0099). T(1rho)-weighted images have approximately 20%-30% higher SNR than the corresponding T(2)-weighted images for similar echo time. The average SLC in the WB region of femoral cartilage was 30 +/-4.0%. Furthermore, SLC maps provide better contrast between fluid and articular surface of femoral-tibial joint than T(1rho)-maps. The T(1rho)-relaxation times varied from 32 msec to 42 msec ( approximately 31%) in the WB and 37 msec to 56 msec ( approximately 51%) in NWB regions of femoral condyle, respectively, in the frequency range 0-500 Hz (T(1rho)-dispersion). CONCLUSION: The feasibility of performing in vivo T(1rho) relaxation mapping in femoral cartilage at 1.5T clinical scanner without exceeding Food and Drug Administration (FDA) limits on specific absorption rate (SAR) of RF energy was demonstrated.

Adult↗

PubMed2003

Application of the keyhole technique to T1rho relaxation mapping.

PURPOSE: To demonstrate the feasibility of using the keyhole technique to minimize error in a least squares regression estimation of T(1rho) from magnetic resonance (MR) image data. MATERIALS AND METHODS: The keyhole method of partial k-space acquisition was simulated using data from a virtual phantom and MR images of ex vivo bovine and in vivo human cartilage. T(1rho) maps were reconstructed from partial k-space (keyhole) image data using linear regression, and error was measured with relation to T(1rho) maps created from the full k-space images. An error model was created based on statistical theory and fitted to the error measurements. RESULTS: T(1rho) maps created from keyhole images of a human knee produced levels of error on the order of 1% while reducing standard image acquisition time approximately by half. The resultant errors were strongly correlated with expectations derived from statistical theory. CONCLUSION: The error model can be used to analytically optimize the keyhole method in order to minimize the overall error in the estimation of the relaxation parameter of interest. The keyhole method can be generalized to significantly expedite all forms of relaxation mapping.

Animals↗

PubMed2003

High-resolution assessment of blood flow in murine RIF-1 tumors by monitoring uptake of H(2)(17)O with proton T(1rho)-weighted imaging.

Perfusion parameters, such as blood flow, are critical properties of tumors related to angiogenesis, drug delivery, radiosensitivity, bioenergetic status, and steady state levels of metabolites, such as lactate, that have been proposed as indices of tumor response to therapy. The existing MR methods for measuring tumor blood flow (TBF) have limitations related to sensitivity, spatial resolution, or dependence on other physiological properties such as vascular permeability. To address many of these difficulties, this study introduces the use of an (17)O-enriched tracer in conjunction with high-resolution, indirect MRI to measure TBF. To demonstrate the advantages of this technique, relative TBF was measured in subcutaneous RIF-1 tumors in C3H mice by monitoring the uptake of H(2) (17)O with a resolution of 0.16 x 0.31 x 3 mm in 13 sec. At this resolution, tumor heterogeneity with respect to blood flow is clearly visible. Measurement of the tracer arterial input function, which is necessary for determination of absolute blood flow, may be facilitated with improved temporal resolution.

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PubMed2003

Indirect 17(O)-magnetic resonance imaging of cerebral blood flow in the rat.

Proton T(1rho)-dispersion MRI is demonstrated for indirect, in vivo detection of (17)O in the brain. This technique, which may be readily implemented on any clinical MRI scanner, is applied towards high-resolution, quantitative mapping of cerebral blood flow (CBF) in the rat by monitoring the clearance of (17)O-enriched water. Strategies are derived and employed for 1) quantitation of absolute H(2) (17)O tracer concentration from a ratio of high- and low-frequency spin-locked T(1rho) images, and 2) mapping CBF without having to transform the T(1rho) signal to H(2) (17)O tracer concentration. Absolute regional blood flow was mapped in a single 3-mm brain slice at an in-plane resolution of 0.4 x 0.8 mm within a 5-min tracer washout time; these data are consistent with the less localized CBF measurements reported in the literature. T(1rho)-weighted imaging yields excellent signal-to-noise ratios, spatiotemporal resolution, and anatomical contrast for mapping CBF.

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