Biomedical subjects

Pottumarthi V Prasad

Publications and source records attributed to Pottumarthi V Prasad.

18 recordsLinked to original sources

PubMed2006

Evaluation of intra-renal oxygenation by BOLD MRI.

This is a review of blood oxygenation level-dependent (BOLD) MRI as applied to the kidney. It has been shown that BOLD MRI measurements reflect changes in renal oxygenation, especially in the medulla. Renal medulla functions in a hypoxic milieu and is extremely sensitive to further decrease in blood flow or increase in oxygen consumption. Availability of a non-invasive technique such as BOLD MRI should allow for better understanding of the factors involved in the maintenance of renal oxygenation status, not only in animal models, but also in humans.

Humans↗

PubMed2006

Magnetic resonance imaging of myocardial infarction using a manganese-based contrast agent (EVP 1001-1): preliminary results in a dog model.

PURPOSE: To investigate the MRI characteristics of an intracellular manganese-based contrast agent, EVP 1001-1 (Eagle Vision Pharmaceutical Corp.), in a canine model of myocardial infarction. MATERIALS AND METHODS: Three dogs were imaged 14-37 days following permanent ligation of the left anterior descending coronary artery (LAD). Measurements of the longitudinal relaxation rate R(1) were made prior to EVP 1001-1 administration (20 micromol/kg i.v.) and for one hour thereafter. Triphenyl tetrazolium chloride (TTC) staining was used to document infarction. RESULTS: In normal myocardium, EVP 1001-1 produced a substantial increase in the longitudinal relaxation rate, which remained fairly constant over the postcontrast imaging period (DeltaR1= 1.47 +/- 0.58 sec(-1) (mean +/- SD) at 35 minutes, P < 0.05). In the infarct, the response to EVP 1001-1 was small or negligible (DeltaR1= 0.27 +/- 0.28 sec(-1)). This resulted in a significant postcontrast difference in relaxation rate between normal and infarcted tissue (R1(normal) - R1(infarct) = 1.08 +/- 0.26 sec(-1), P < 0.05). The infarct remained clearly delineated in all animals throughout the steady-state imaging period, and qualitatively matched TTC results. CONCLUSION: The persistent enhancement pattern revealed by MRI following EVP 1001-1 administration may be beneficial for identifying and characterizing myocardial infarction.

Animals↗

PubMed2006

Three-dimensional delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) at 1.5T and 3.0T.

PURPOSE: To implement and validate a three-dimensional (3D) T1 measurement technique that is suitable for delayed gadolinium (Gd)-enhanced MRI of cartilage (dGEMRIC) and can be easily implemented with clinically available pulse sequences at 1.5T and 3.0T. MATERIALS AND METHODS: A 3D inversion-recovery prepared spoiled gradient-echo (IR-SPGR) imaging pulse sequence with variable TR was used to implement a 3D T1 measurement protocol. The 3D T1 measurements were validated against a gold-standard single-slice 2D IR T1 measurement protocol in both phantoms and in vivo, in both asymptomatic volunteers and volunteers with osteoarthritis (OA). RESULTS: T1 measurements in phantoms showed a statistically significant correlation between the 2D and 3D measurements at 1.5T (R2=0.993, P<0.001) and 3.0T (R2=0.996, P<0.001). In vivo application demonstrated the feasibility of using this 3D IR-SPGR sequence to evaluate the molecular status of articular cartilage throughout the knee joint with 0.63x0.63x3.0 mm spatial resolution within a 20-minute acquisition, even with the measurement parameters set for the higher T1(Gd) of cartilage at 3T (range=400-900 msec mean T1 within a region of interest (ROI) in cartilage, compared to 200-600 msec mean T1 at 1.5T). CONCLUSION: This 3D T1 measurement protocol may prove useful for the evaluation and follow-up of cartilage dGEMRIC indices in clinical studies of OA.

Cartilage, Articular↗

PubMed2006

Evaluation of intrarenal oxygenation at 3.0 T using 3-dimensional multiple gradient-recalled echo sequence.

OBJECTIVE: The objective of this study was to validate quantitation of R2* and DeltaR2* measurements obtained with a 3-dimensional (3-D) multiple gradient-recalled echo (mGRE) sequence for evaluating intrarenal oxygenation in humans. MATERIALS AND METHODS: Validation was accomplished (1) by comparing R2* values with previously established 2-D techniques (n = 5, mean age = 33.6 years) and (2) by measuring change in DeltaR2* after furosemide (20 mg intravenously) administration (n = 5, mean age = 22 years). Additional pre- and postfurosemide scans were done at 1.5 T for comparison purposes. RESULTS: R2* measurements with the 3-D technique showed good agreement with the 2-D techniques. The baseline medullary R2* at 3.0 T was about twice the value found at 1.5 T. Furosemide-induced change in R2* was observed within 5 minutes after administration. CONCLUSIONS: R2* measurements with 3-D mGRE were comparable with those reported using 2-D techniques. The 3-D implementation facilitates observation of temporal changes in the medullary oxygenation without compromising spatial coverage.

Adult↗

PubMed2006

Functional MRI of the kidney: tools for translational studies of pathophysiology of renal disease.

Magnetic resonance imaging (MRI) provides exquisite anatomic detail of various organs and is capable of providing additional functional information. This combination allows for comprehensive diagnostic evaluation of pathologies such as ischemic renal disease. Noninvasive MRI techniques could facilitate translation of many studies performed in controlled animal models using technologies that are invasive to humans. Such a translation is being recognized as essential because many proposed interventions and drugs that prove efficacious in animal models fail to do so in humans. In this article, we review the state-of-the-art functional MRI technique as applied to the kidneys.

Animals↗

PubMed2006

Functional magnetic resonance imaging of the kidney.

In addition to exquisite anatomical detail, magnetic resonance imaging (MRI) provides a variety of avenues to study functional status of tissue. These functional parameters could either provide additional information, in terms of pathophysiology, or may improve the specificity of the diagnosis. This chapter reviews some current state-of-the-art functional MRI (fMRI) methods as applied to the kidney. Three parameters, renal perfusion, filtration or excretory function, and oxygenation are reviewed in depth. Illustrative examples are provided and advantages discussed.

Animals↗

PubMed2005

Delayed gadolinium-enhanced magnetic resonance imaging of cartilage in knee osteoarthritis: findings at different radiographic stages of disease and relationship to malalignment.

OBJECTIVE: Delayed gadolinium-enhanced magnetic resonance imaging (MRI) of cartilage (dGEMRIC) is used to examine the distribution of glycosaminoglycan in cartilage. This study sought to characterize dGEMRIC in the evaluation of knee osteoarthritis (OA) according to various radiographically determined disease parameters, and to examine the relationship between alignment of the knee joint and the lateral:medial dGEMRIC ratio. METHODS: Thirty-one patients with knee OA underwent MRI with a dGEMRIC protocol at 1.5T. Semiflexed knee radiographs and full-limb radiographs were also obtained for assessment of alignment. RESULTS: Compartments of the knee joint without joint space narrowing had a higher dGEMRIC index than those with any level of narrowing (mean 408 msec versus 365 msec; P = 0.001). In knees with 1 unnarrowed (spared) and 1 narrowed (diseased) compartment, the dGEMRIC index was greater in the spared versus the diseased compartment (mean 395 msec versus 369 msec; P = 0.001). In spared compartments, there was a trend toward a lower dGEMRIC index with increasing Kellgren/Lawrence (K/L) radiographic severity grade; the spared compartments of knees with a K/L grade 2 had a higher dGEMRIC index than those of knees with a K/L grade 4 (mean 425 msec versus 371 msec; P < 0.05). There was a range of dGEMRIC values in the spared compartments within a given K/L grade, demonstrating biochemical differentiation of disease in radiographically comparable compartments. Almost all compartments with narrowing had dGEMRIC indices of <400 msec. Valgus-aligned knees tended to have lower dGEMRIC values laterally, and varus-aligned knees tended to have lower dGEMRIC values medially; as a continuous variable, alignment correlated with the lateral:medial dGEMRIC ratio (Pearson's R = 0.43, P = 0.02). CONCLUSION: The biochemical information provided by dGEMRIC scans may augment radiography by improving the differentiation of disease status within a given radiographic grade, especially in early OA.

Aged↗

PubMed2005

First-pass contrast-enhanced magnetic resonance angiography in humans using ferumoxytol, a novel ultrasmall superparamagnetic iron oxide (USPIO)-based blood pool agent.

PURPOSE: To evaluate the feasibility of first-pass contrast-enhanced magnetic resonance angiography (MRA) using ferumoxytol in humans. MATERIALS AND METHODS: First-pass and equilibrium phase MRA were performed using ferumoxytol in one healthy volunteer and 11 patients with a fast three-dimensional spoiled gradient recalled (SPGR) pulse sequence. The examined vessels included carotid arteries, thoracic aorta, abdominal aorta, and peripheral arteries. A dose of either 71.6 micromol Fe/kg (n = 9), or 35.8 micromol Fe/kg (n = 3) was used. Based on a phantom study, the agent with initial concentration of 537.2 micromol Fe/mL was diluted by either four-fold (134.3 micromol Fe/mL) or eight-fold (67.1 micromol Fe/mL) for first-pass MRA. RESULTS: All subjects completed their studies without adverse events. First-pass MRA showed selective arterial enhancement, with both arterial and venous enhancement on delayed acquisitions. Selective venous enhancement could be obtained by subtraction of arterial phase images from equilibrium phase images. The findings in ferumoxytol MRA were consistent with the results of original vascular tests. CONCLUSION: Our preliminary experience supports the feasibility of first-pass MRA with ferumoxytol. Satisfactory arterial enhancement during first-pass imaging is obtained with injection of diluted contrast agent. With ferumoxytol, arteries and veins can be selectively depicted in a single exam.

Adult↗

PubMed2005

Feasibility of blood oxygenation level-dependent MR imaging to monitor hepatic transcatheter arterial embolization in rabbits.

Blood oxygenation level-dependent (BOLD) magnetic resonance (MR) imaging is a noninvasive method to assess changes in oxygen delivery to tissues. It was hypothesized that BOLD MR imaging can detect changes in rabbit VX2 liver tumor oxygenation after hepatic artery embolization with polyvinyl alcohol particles. In four discrete VX2 liver tumors, a statistically significant mean reduction in apparent transverse relaxation time was shown, from 55 milliseconds before embolization to 41 milliseconds after embolization (P < .01). This reduction corresponded to a decrease in hepatic tumor oxygenation. The use of BOLD MR imaging to monitor changes in hepatic tumor oxygenation after embolization is feasible. These functional MR imaging measurements of hypoxia may be targeted as an endpoint for therapy in future studies.

Angiography, Digital Subtraction↗

PubMed2004

Myocardial delayed enhancement imaging using inversion recovery single-shot steady-state free precession: initial experience.

PURPOSE: To evaluate the feasibility of using an inversion recovery single-shot steady-state free precession (SS_SSFP) sequence for myocardial delayed enhancement (MDE) imaging, and to compare SS_SSFP with the conventional inversion recovery segmented fast gradient echo (IR_FGRE) technique. MATERIALS AND METHODS: Ten subjects (four volunteers and six patients with suspected or known coronary disease) were included in this study. All subjects were scanned with both IR_FGRE and SS_SSFP sequences 15-25 minutes after gadopentetate dimeglumine injection. Overall image quality, signal-to-noise ratios (SNRs), and contrast-to-noise ratios (CNRs) between the two techniques were compared. RESULTS: Compared to IR_FGRE, SS_SSFP exhibited adequate image quality (average scores = 3.8 for IR_FGRE and 3.9 for SS_SSFP) with much shorter acquisition time (14.4 seconds for IR_FGRE and 1.3 seconds for SS_SSFP). SS_SSFP images showed higher SNRs (P < 0.05) and less motion artifact from breathing. Enhanced myocardium was detected by both techniques in three patients, but the image sharpness is compromised in SS_SSFP images. CONCLUSION: SS_SSFP provides adequate image quality compared to IR_FGRE, while requiring a much shorter acquisition time. It is feasible to use SS_SSFP as an alternative method for MDE imaging, especially in patients who have difficulty with holding their breath.

Aged↗

PubMed2004

Evaluation of intrarenal oxygenation by BOLD MRI at 3.0 T.

PURPOSE: To examine the benefit of using higher field strengths for BOLD MRI to detect changes in renal medullary oxygenation following pharmacological maneuvers. MATERIALS AND METHODS: Renal BOLD MRI, primarily at 1.5 T, has been shown to be useful for monitoring changes in medullary oxygenation status. We performed the present studies on a 3.0 T scanner using a multiple gradient-echo (mGRE) sequence with a multicoil array to acquire 16 T2*-weighted images within a single breath-hold. Data were obtained before and after administration of furosemide (20 mg iv). RESULTS: The baseline renal R2* (mean +/- SE) at 3.0 T was 37.4+/-1.2 Hz in the medulla, and 21.8 +/- 1.2 Hz in the cortex. The BOLD response to furosemide (DeltaR2*) at 3.0 T was 11.8 +/- 1.1 Hz in the medulla, and 3.0 +/- 0.5 Hz in the cortex. CONCLUSION: Higher magnetic field strength is beneficial for renal BOLD MRI studies. The cortico-medullary contrast on the R2* map was significantly improved at 3.0 T, with no evidence of increased bulk susceptibility artifacts. Baseline R2* and DeltaR2* in the renal medulla at 3.0 T were both significantly higher compared to our previously reported data obtained at 1.5 T.

Adult↗

PubMed2004

Dark flow artifacts with steady-state free precession cine MR technique: causes and implications for cardiac MR imaging.

Steady-state free precession cine images from cardiac magnetic resonance imaging studies of 24 patients were reviewed retrospectively to identify dark flow artifacts. The cause and features of the artifacts were studied in flow phantom experiments. Dark flow artifacts were recognized in eight of the 24 cases and were characterized by low or inhomogeneous signal intensity in blood pools with little change in adjacent tissues. The artifacts could be mimicked in flow phantom experiments by deliberately deshimming the gradients and appeared periodically during imaging with off-centered frequencies. These artifacts appeared to be caused by spins moving within an inhomogeneous magnetic field.

Adult↗

PubMed2003

Computing oxygen-enhanced ventilation maps using correlation analysis.

Correlation maps of oxygen-enhanced ventilation were obtained in nine healthy volunteers using complete and selected image series. The complete series included all images acquired with the subjects alternately inhaling room air and 100% oxygen. The selected series were the subsets of the complete series and included only co-registered images that showed matched diaphragmatic position at maximal expiration. Cross-correlation was computed between the time response function of each pixel and the input function representing the alternation between periods of room air and 100% oxygen inhalation. The confidence level for the correlation analysis was set to 0.01. Pulmonary parenchymal anatomy was consistently reproduced throughout the lung, even in anterior slices where published data have reported correlation problems. The overall average correlation coefficient was 0.66 +/- 0.07 for the complete series and 0.75 +/- 0.08 for the selected series. It was concluded that correlation analysis could be used to reconstruct qualitative oxygen-enhanced ventilation maps.

Adult↗

PubMed2003

Simultaneous magnetic resonance gadolinium-enhanced 2D perfusion and 3D angiographic imaging.

A method was implemented and tested that allows the simultaneous acquisition of magnetic resonance 2D slice selective perfusion and 3D angiographic data during a single bolus injection of a contrast agent. High quality contrast-enhanced perfusion images and angiograms of the lung, kidney and heart were obtained in healthy volunteers. Combined perfusion and angiography provided additional information with an acceptable increase in acquisition time. No image artifacts were attributed to the technique. The combined information may be useful in detecting, as well as characterizing, vascular abnormalities.

Adult↗

PubMed2003

Preliminary evaluation of EVP 1001-1: a new cardiac-specific magnetic resonance contrast agent with kinetics suitable for steady-state imaging of the ischemic heart.

RATIONALE AND OBJECTIVES: To investigate the potential of a novel manganese-based magnetic resonance (MR) contrast agent, EVP 1001-1 for the evaluation of myocardial ischemia. METHODS: MR imaging with EVP 1001-1 was performed on 6 Yorkshire pigs, and T1 relaxation times were calculated. One animal served as a control, 2 were subjected to an acute coronary artery occlusion and 3 provided a model of chronic ischemia. RESULTS: Administration of the agent in the control and acute coronary occlusion model demonstrated a short plasma half-life (approximately 1.5 minutes) and rapid myocardial uptake in nonoccluded regions, with long retention times in the myocardium (>1 hour) and no evidence of redistribution. In the chronic ischemia model, differential enhancement was observed between normal and ischemic tissue, particularly under dobutamine-induced stress. CONCLUSIONS: These properties suggest the use of EVP 1001-1 for steady-state imaging of myocardial perfusion. Contrast administration could be performed under stress conditions outside the scanner, with high-resolution MR images reflecting the stress condition acquired after the stress has subsided.

Animals↗

PubMed2002

MR assessment of left ventricular function: quantitative comparison of fast imaging employing steady-state acquisition (FIESTA) with fast gradient echo cine technique.

PURPOSE: To evaluate the agreement of fast imaging employing steady-state acquisition (FIESTA) cine technique with segmented k-space fast gradient echo (GRE) cine technique when using them for assessment of cardiac function. MATERIALS AND METHODS: Eleven MR cine studies were performed on six healthy volunteers and five patients, using FIESTA and fast GRE techniques. The quantitative measurements of ventricular function obtained from the two techniques were compared. The data analysis was performed by two observers independently. RESULTS: Compared to fast GRE cine technique, FIESTA cine technique consistently resulted in higher end-diastolic volume (10.2%) and end-systolic volume (21.6%), but lower myocardial mass of left ventricle (19.2%) and ejection fraction (9.9%). The stroke volume obtained from the two techniques was very close. The primary explanation for this variability is that the two techniques have different mechanisms on establishing signal contrast. CONCLUSION: Compared to fast GRE technique, FIESTA provides significantly different results when using it for assessment of left ventricular function. It is important to consider this difference in the assessment of cardiac function.

Adult↗

PubMed2002

Band artifacts due to bulk motion.

Band artifacts due to bulk motion were investigated in images acquired with fast gradient echo sequences. A simple analytical calculation shows that the width of the artifacts has a square-root dependence on the velocity of the imaged object, the time taken to acquire each line of k-space and the field of view in the phase-encoding direction. The theory furthermore predicts that the artifact width can be reduced using parallel imaging by a factor equal to the square root of the acceleration parameter. The analysis and results are presented for motion in the phase- and frequency-encoding directions and comparisons are made between sequential and centric ordering. The theory is validated in phantom experiments, in which bulk motion is simulated in a controlled and reproducible manner by rocking the scan table back and forth along the bore axis. Preliminary cardiac studies in healthy human volunteers show that dark bands may be observed in the endocardium in images acquired with nonsegmented fast gradient echo sequences. The fact that the position of the bands changes with the phase-encoding direction suggests that they may be artifacts due to motion of the heart walls during the image acquisition period.

Artifacts↗

PubMed2002

Effect of diabetes on renal medullary oxygenation during water diuresis.

OBJECTIVES: To study the effect of water diuresis on renal medullary and cortical oxygenation in patients with diabetes using blood oxygenation level--dependent magnetic resonance imaging (BOLD MRI). RESEARCH DESIGN AND METHODS: Nine mild diabetic subjects (48 +/- 2.7 years of age, six women) and nine nondiabetic subjects of similar age and sex, all without known vascular or renal disease, were studied noninvasively by MRI before and during water diuresis. RESULTS: Water diuresis induced an increase in medullary oxygenation in control subjects, producing a decrease in R2* (apparent spin-spin relaxation time) of 1.89 +/- 0.27 (P < 0.01), but no significant change in the group of diabetic subjects. CONCLUSIONS: These findings in middle-aged diabetic subjects, which resembled those previously described in elderly subjects >65 years of age, suggest early impairment of adaptive vasodilatation within the renal medulla in diabetes.

Adult↗