Delayed contrast enhanced MRI of meniscus with ionic and non-ionic agents

Purpose:

To evaluate the potential difference in post‐contrast T₁ relaxation time of the meniscus (T_1Gd) between osteoarthritic patients (OA) and healthy subjects (HS), and to verify if charge density has any influence on meniscal T_1Gd.

Materials and Methods:

We performed a retrospective analysis of meniscal T₁ relaxation time on data previously acquired for studying articular cartilage with both ionic and non‐ionic contrast media. MR imaging was performed in 10 OA and 8 HS at 120 min following administration of double‐dose ionic Gd‐DTPA^2? on one day and non‐ionic Gd‐DTPA‐BMA on a different day. A three‐dimensional Look‐Locker sequence with echo time of 2 ms was used for data acquisition to allow T₁ mapping of the meniscus.

Results:

Compared with HS, significantly lower meniscal T_1Gd was observed in OA with either ionic Gd‐DTPA^2? (P < 0.01) or non‐ionic Gd‐DTPA‐BMA (P < 0.001) contrast agent. There was a correlation between meniscal T₁(Gd‐DTPA^2?) versus T₁(Gd‐DTPA‐BMA). Meniscal T₁(Gd‐DTPA‐BMA) showed a larger difference and smaller overlap between OA and HS. No significant differences in either pre‐contrast T₁ or post‐contrast T_1Gd were observed between inner and outer zones of the meniscus with either agent.

Conclusion:

Significant differences in meniscal T_1Gd between OA and HS were observed with both ionic and non‐ionic contrast agents, suggesting that charge density is not responsible for the observed differences. J. Magn. Reson. Imaging 2011;33:731–735. © 2011 Wiley‐Liss, Inc.

     

Impact of motion on T1 mapping acquired with inversion recovery fast spin echo and rapid spoiled gradient recalled‐echo pulse sequences for delayed gadolinium‐enhanced MRI of cartilage (dGEMRIC) in volunteers

Purpose:

To evaluate the impact of motion on T1 values acquired by using either inversion‐recovery fast spin echo (IR‐FSE) or three‐dimensional (3D) spoiled gradient recalled‐echo (SPGR) sequences for delayed gadolinium‐enhanced magnetic resonance imaging of cartilage (dGEMRIC) in volunteers.

Materials and Methods:

Single‐slice IR‐FSE and 3D SPGR sequences were applied to perform dGEMRIC in five healthy volunteers. A mutual information‐based approach was used to correct for image misregistration. Displacements were expressed as averaged Euclidean distances and angles. Averages of differences in goodness of fit (Δχ²) tests and averages of relative differences in T1 values (ΔT1) before and after motion correction were computed.

Results:

Maximum Euclidean distance was 3.5 mm and 1.2 mm for IR‐FSE and SPGR respectively. Mean ± SD of Δχ² were 10.18 ± 8.4 for IR‐FSE and ?1.37 ± 5.5 for SPGR. Mean ± SD of ΔT1 were 0.008 ± 0.0048 for IR‐FSE and ?0.002 ± 0.019 for FSPGR. Pairwise comparison of Δχ² values showed a significant difference for IR‐FSE, but not for 3D‐SPGR. Significantly greater variability in T1 values was also noted for IR‐FSE than for 3D‐SPGR.

Conclusion:

Involuntary motion has a significant influence on T1 values acquired with IR‐FSE, but not with 3D‐SPGR in healthy volunteers. J. Magn. Reson. Imaging 2010;32:394–398. © 2010 Wiley‐Liss, Inc.

     

Quantitative T2 mapping of femoral head cartilage in systemic lupus erythematosus patients with noncollapsed osteonecrosis of the femoral head associated with corticosteroid therapy

Purpose:

To evaluate articular cartilage degeneration with transverse relaxation time (T2) mapping in systemic lupus erythematosus (SLE) patients with noncollapsed and asymptomatic osteonecrosis of the femoral head associated with corticosteroids.

Materials and Methods:

T2 mapping with a 1.5‐T magnetic resonance imaging system was prospectively performed for 28 normal hips from 14 healthy volunteers (control group) and 15 hips from 10 SLE patients that met the inclusion criteria of noncollapsed and asymptomatic osteonecrosis of the femoral head (osteonecrosis group). Exclusion criteria were past experience of pain, trauma, infection, or prior hip joint surgery. Distribution of T2 values of the femoral head cartilage were compared between the control group and the osteonecrosis group with respect to acetabular dysplasia by center‐edge angle (CEA).

Results:

T2 values of the femoral head cartilage were significantly higher in the osteonecrosis group than in the control group (34.4 msec vs. 30.8 msec, P = 0.001). Multiple regression analysis revealed that the osteonecrosis group and decreased CEA was significantly associated with high T2 values (T2 value = 34.6 + 3.6 × [osteonecrosis] ? 0.14 × CEA, R² = 0.52, P = 0.003).

Conclusion:

Degeneration of articular cartilage was associated with osteonecrosis of the femoral head in SLE patients and acetabular dysplasia. J. Magn. Reson. Imaging 2011;. © 2011 Wiley Periodicals, Inc.

     

Weight-bearing MRI of patellofemoral joint cartilage contact area

Purpose

To measure contact area of cartilage in the patellofemoral joint during weight bearing using an open MRI scanner.

Materials and Methods

We developed an MR‐compatible back support that allows three‐dimensional imaging of the patellofemoral cartilage under physiologic weight‐bearing conditions with negligible motion artifact in an open MRI scanner. To measure contact areas, we trained observers using a phantom of known area and tested intra‐ and interobserver variability. We measured in vivo contact areas between the patella and femoral cartilage with the knee in 30 degrees of flexion, loaded and unloaded, in six volunteers.

Results

We were able to measure the contact area of the patellofemoral cartilage with small interobserver (CV 7.0%) and intraobserver (CV 3.0%) variation. At 30 degrees of knee flexion, mean contact area increased from 400 mm² (unloaded) to 522 mm² (loaded to 0.45 times body weight per leg).

Conclusion

Using an open magnet and specially designed apparatus, it is possible to image the patellar cartilage during physiologic loading. Knowledge of patellar cartilage contact area is needed to assess patellofemoral stress, which may be increased in patients with patellofemoral pain syndrome. J. Magn. Reson. Imaging 2004;20:526–530. Published 2004 Wiley‐Liss, Inc.

     

Delayed gadolinium‐enhanced MRI of cartilage in the ankle at 3 T: Feasibility and preliminary results after matrix‐associated autologous chondrocyte implantation

Purpose:

To demonstrate the feasibility of delayed gadolinium‐enhanced magnetic resonance imaging (MRI) of cartilage (dGEMRIC) in the ankle at 3 T and to obtain preliminary data on matrix associated autologous chondrocyte (MACI) repair tissue.

Materials and Methods:

A 3D dual flip angle sequence was used with an eight‐channel multipurpose coil at 3 T to obtain T1 maps both pre‐ and postintravenous contrast agent (Magnevist, 0.2 mM/kg). Postcontrast T1 over time was evaluated in three volunteers; a modified dGEMRIC protocol was then used to assess 10 cases after MACI in the ankle.

Results:

Forty‐five minutes were found sufficient for maximum T1 decrease. MACI cases had a precontrast mean T1 of 1050 ± 148.4 msec in reference cartilage (RC) and 1080 ± 165.6 msec in repair tissue (RT). Postcontrast T1 decreased to 590 ± 134.0 msec in RC and 554 ± 133.0 msec in RT. There was no significant difference between the delta relaxation rates in RT (9.44 × 10^?4 s^?1) and RC (8.04 × 10^?4 s^?1, P = 0.487). The mean relative delta relaxation rate was 1.34 ± 0.83.

Conclusion:

It is feasible to assess the thin cartilage layers of the ankle with dGEMRIC at 3 T; MACI can yield RT with properties similar to articular cartilage. J. Magn. Reson. Imaging 2010;31:732–739. © 2010 Wiley‐Liss, Inc.

     

In vivo MR imaging tracking of transplanted mesenchymal stem cells in a rabbit model of acute peripheral nerve traction injury

Purpose

To investigate in vivo MRI tracking mesenchymal stem cells (MSCs) in peripheral nerve injures using a clinically available paramagnetic contrast agent (Gd‐DTPA) and commercially available rhodamine‐incorporated transfection reagents (PEI‐FluoR).

Materials and Methods

After bone marrow MSCs were labeled with Gd‐DTPA and PEI‐FluoR complex, the labeling efficacy and longevity of Gd‐DTPA maintenance were measured and cell viability, proliferation, and apoptosis were assessed. Thirty‐six rabbits with acute sciatic nerve traction injury randomly received 1 × 10⁶ labeled (n = 12) or unlabeled MSCs (n = 12) or vehicle alone injection. The distribution and migration of implanted cells was followed by MRI and correlated with histology. The relative signal intensity (RSL) of the grafts was measured.

Results

The labeling efficiency was 76 ± 4.7% and the labeling procedure did not in?uence cell viability, proliferation, and apoptosis. A persistent higher RSL in grafts was found in the labeled group compared with the unlabeled and vehicle groups until 10 days after transplantation (P < 0.05). The distribution and migration of labeled cells could be tracked by MRI until 10 days after transplantation. Transplanted MSCs were not found to transdifferentiate into Schwann‐like cells within 14‐day follow‐up.

Conclusion

Labeling MSCs with the dual agents may enable cellular MRI of the engraftment in the experimental peripheral nerve injury. J. Magn. Reson. Imaging 2010;32:1076–1085. © 2010 Wiley‐Liss, Inc.

     

Gd‐EOB‐DTPA‐enhanced MR imaging: Prediction of hepatic fibrosis stages using liver contrast enhancement index and liver‐to‐spleen volumetric ratio

Purpose:

To develop and evaluate a quantitative parameter for staging hepatic fibrosis by contrast enhancement signal intensity and morphological measurements from gadoxetic acid (Gd‐EOB‐DTPA)‐enhanced MR imaging.

Materials and Methods:

MR images were obtained in 93 patients; 75 patients had histopathologically proven hepatic fibrosis and 18 patients who had healthy livers were evaluated. The liver‐to‐muscle signal intensity ratio (SI_post = SIliver/SImuscle), contrast enhancement index (CEI = SIpost/SIpre), and liver‐to‐spleen volumetric ratio (VR = Vliver/Vspleen) were evaluated for staging hepatic fibrosis.

Results:

VR was most strongly correlated with fibrosis stage (7.21; r = ?0.83; P < 0.001). Sensitivity, specificity, and area under the ROC curve demonstrated by linear regression formula generated by VR and CEI in predicting fibrous scores were 100%, 73%, and 0.91, respectively, for the detection of hepatic fibrosis F1 or greater (≥ F1),100%, 87%, and 0.96 for ≥ F2, 74%, 98%, and 0.93 for ≥ F3 and 91%, 100%, and 0.97 for F4.

Conclusion:

The liver‐to‐spleen volumetric ratio and contrast enhancement index were reliable biomarkers for the staging of hepatic fibrosis on Gd‐EOB‐DTPA‐enhanced MR imaging. J. Magn. Reson. Imaging 2012;36:1148–1153. © 2012 Wiley Periodicals, Inc.

     

Water-silicone separated volumetric MR acquisition for rapid assessment of breast implants

Purpose:

To develop a robust T₂‐weighted volumetric imaging technique with uniform water‐silicone separation and simultaneous fat suppression for rapid assessment of breast implants in a single acquisition.

Materials and Methods:

A three‐dimensional (3D) fast spin echo sequence that uses variable refocusing flip angles was combined with a three‐point chemical‐shift technique (IDEAL) and short tau inversion recovery (STIR). Phase shifts of ?π/6, +π/2, and +7π/6 between water and silicone were used for IDEAL processing. For comparison, two‐dimensional images using 2D‐FSE‐IDEAL with STIR were also acquired in axial, coronal, and sagittal orientations.

Results:

Near‐isotropic (true spatial resolution—0.9 × 1.3 × 2.0 mm³) volumetric breast images with uniform water‐silicone separation and simultaneous fat suppression were acquired successfully in clinically feasible scan times (7:00–10:00 min). The 2D images were acquired with the same in‐plane resolution (0.9 × 1.3 mm²), but the slice thickness was increased to 6 mm with a slice gap of 1 mm for complete coverage of the implants in a reasonable scan time, which varied between 18:00 and 22:30 min.

Conclusion:

The single volumetric acquisition with uniform water and silicone separation enables images to be reformatted into any orientation. This allows comprehensive assessment of breast implant integrity in less than 10 min of total examination time. J. Magn. Reson. Imaging 2012;35:1216‐1221. © 2012 Wiley Periodicals, Inc.

     

T1ρ and T2 mapping reveal the in vivo extracellular matrix of articular cartilage

Purpose:

To determine the relationship between changes in the extracellular matrix (ECM) and T_1ρ and T₂ values in vivo. The ECM is composed of proteoglycan (PG), collagen, and water. It has been unclear which of the ECM constituents affects T_1ρ and T₂ mapping in living human cartilage.

Materials and Methods:

Sagittal T_1ρ and T₂ maps were preoperatively obtained from 20 knee osteoarthritis patients. Osteochondral samples harvested from the resected tibial plateaus during total knee arthroplasty were consistent with the MRIs of the patients' knees. Parameters that included histological grading of cartilage degeneration, glycosaminoglycan (GAG) content (which constitutes PG), presence of collagen anisotropy and water content were evaluated along with T_1ρ and T₂ values, and statistical analysis was performed using multiple regression analysis.

Results:

T_1ρ and T₂ values were significantly correlated with the degree of cartilage degeneration (β = 0.397 and 0.357, respectively) and the GAG content (β = ?0.340 and ?0.244, respectively).

Conclusion:

The present study demonstrated that T_1ρ and T₂ values reflect the GAG content of the cartilage and can indicate cartilage degeneration in vivo. Use of these parameters can facilitate the noninvasive diagnosis and evaluation of cartilage degeneration. J. Magn. Reson. Imaging 2012;35:147‐155. © 2011 Wiley Periodicals, Inc.

     

Polydisulfide manganese(II) complexes as non-gadolinium biodegradable macromolecular MRI contrast agents

Purpose:

To develop safe and effective manganese(II) ‐based biodegradable macromolecular MRI contrast agents.

Materials and Methods:

In this study, we synthesized and characterized two polydisulfide manganese(II) complexes, Mn‐DTPA cystamine copolymers and Mn‐EDTA cystamine copolymers, as new biodegradable macromolecular MRI contrast agents. The contrast enhancement of the two manganese‐based contrast agents were evaluated in mice bearing MDA‐MB‐231 human breast carcinoma xenografts, in comparison with MnCl₂.

Results:

The T₁ and T₂ relaxivities were 4.74 and 10.38 mM^?1s^?1 per manganese at 3T for Mn‐DTPA cystamine copolymers (M_n = 30.50 kDa) and 6.41 and 9.72 mM^?1s^?1 for Mn‐EDTA cystamine copolymers (M_n = 61.80 kDa). Both polydisulfide Mn(II) complexes showed significant liver, myocardium and tumor enhancement.

Conclusion:

The manganese‐based polydisulfide contrast agents have a potential to be developed as alternative non‐gadolinium contrast agents for MR cancer and myocardium imaging. J. Magn. Reson. Imaging 2012;35:737‐744. © 2011 Wiley Periodicals, Inc.

     

Single breathhold cardiac CINE imaging with multi‐echo three‐dimensional hybrid radial SSFP acquisition

Purpose:

To achieve single breathhold whole heart cardiac CINE imaging with improved spatial resolution and temporal resolution by using a multi‐echo three‐dimensional (3D) hybrid radial SSFP acquisition.

Materials and Methods:

Multi‐echo 3D hybrid radial SSFP acquisitions were used to acquire cardiac CINE imaging within a single breathhold. An optimized interleaving scheme was developed for view ordering throughout the cardiac cycle.

Results:

Whole heart short axis views were acquired with a spatial resolution of 1.3 × 1.3 × 8.0 mm³ and temporal resolution of 45 ms, within a single 17 s breathhold. The technique was validated on eight healthy volunteers by measuring the left ventricular volume throughout the cardiac cycle and comparing with the conventional 2D multiple breathhold technique. The left ventricle functional measurement bias of our proposed 3D technique from the conventional 2D technique: end diastolic volume ?3.3 mL ± 13.7 mL, end systolic volume 1.4 mL ± 6.1 mL, and ejection fraction ?1.7% ± 4.3%, with high correlations 0.94, 0.97, and 0.91, accordingly.

Conclusion:

A multi‐echo 3D hybrid radial SSFP acquisition was developed to allow for a whole heart cardiac CINE exam in a single breathhold. Cardiac function measurements in volunteers compared favorably with the standard multiple breathhold exams. J. Magn. Reson. Imaging 2010;32:434–440. © 2010 Wiley‐Liss, Inc.

     

MR prediction of liver fibrosis using a liver-specific contrast agent: Superparamagnetic iron oxide versus Gd-EOB-DTPA

Purpose:

To examine whether the uptake of a liver‐specific contrast agent in the liver parenchyma was correlated with the degree of liver fibrosis.

Materials and Methods:

This retrospective study included 54 and 63 patients who underwent superparamagnetic iron oxide (SPIO)‐ and gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid (Gd‐EOB‐DTPA)‐enhanced MRI before liver surgery, respectively. For each patient, we calculated ΔR2* and ΔR2, which represent differences in R2* and R2 values of the liver parenchyma before and after administration of SPIO; and the increase rate of liver‐to‐spleen signal intensity ratio (LSR) on the hepatobiliary phase compared with the precontrast image. The correlation of each MR parameter with the degree of liver fibrosis (F0 to F4) was assessed using Spearman's rank correlation test.

Results:

The increase rate of LSR was best correlated with the degree of liver fibrosis and significantly decreased as the liver fibrosis progressed (rho = ?0.641; P < 0.0001). It showed sensitivity of 76.9% and specificity of 83.3% in differentiating F3 or greater fibrosis when 1.126 or less was set up as a cut‐off value. No significant correlation was obtained between ΔR2* or ΔR2 and the degree of liver fibrosis.

Conclusion:

The uptake of Gd‐EOB‐DTPA in the liver parenchyma decreased as the liver fibrosis progressed. J. Magn. Reson. Imaging 2012;36:664–671. © 2012 Wiley Periodicals, Inc.

     

Quantitative cerebral MR perfusion imaging: preliminary results in stroke

Purpose:

To demonstrate that OKN007, a disulfonyl derivative of phenyl‐tert‐butyl nitrone (PBN), has anti‐glioma activity in the clinically relevant C6 rat glioma model using multi‐parametric magnetic resonance imaging.

Materials and Methods:

Twenty‐one rats were intracerebrally implanted with C6 cells and administered OKN007 or kept as controls. Animals were monitored with MRI at 7 Tesla (T), using morphologic, diffusion‐weighted and perfusion imaging, followed by histology and Western blots of angiogenesis and inflammatory markers.

Results:

OKN007 was found to decrease tumor volumes and increase survival. The glioma tissues of OKN007‐treated rats were found to have longitudinal apparent diffusion coefficients (ADC_z) of 0.76 ± 0.06 × 10^?3 mm²/s, similar to the contralateral tissue and significantly smaller than untreated gliomas (0.97 ± 0.13 × 10^?3 mm²/s). They had higher perfusion rates (66 ± 4 mL/100 g·min) than untreated gliomas (26 ± 7 mL/100 g·min). All examined molecular markers were decreased in OKN007‐treated rat gliomas, compared with elevated levels in untreated rats.

Conclusion:

MRI assessment was successfully used to monitor a decrease in tumor growth, and corresponding alterations in ADC and perfusion rates in rat C6 gliomas treated with the anti‐glioma agent, OKN007. J. Magn. Reson. Imaging 2010;31:796–806. ©2010 Wiley‐Liss, Inc.

     

Different signal intensity at Gd-EOB-DTPA compared with Gd-DTPA-enhanced MRI in hepatocellular carcinoma transgenic mouse model in delayed phase hepatobiliary imaging

Purpose:

To evaluate hyperintense Gd‐DTPA‐ compared with hyper‐ and hypointense Gd‐EOB‐DTPA‐enhanced magnet resonance imaging (MRI) in c‐myc/TGFα transgenic mice for detecting hepatocellular carcinoma (HCC).

Materials And Methods:

Twenty HCC‐bearing transgenic mice with overexpression of the protooncogene c‐myc and transforming growth factor‐alpha (TGF‐α) were analyzed. MRI was performed using a 3‐T MRI scanner and an MRI coil. The imaging protocol included Gd‐DTPA‐ and Gd‐EOB‐DTPA‐enhanced T1‐weighted images. The statistically evaluated parameters are signal intensity (SI), signal intensity ratio (SIR), contrast‐to‐noise ratio (CNR), percentage enhancement (PE), and signal‐to‐noise ratio (SNR).

Results:

On Gd‐DTPA‐enhanced MRI compared with Gd‐EOB‐DTPA‐enhanced MRI, the SI of liver was 265.02 to 573.02 and of HCC 350.84 to either hyperintense with 757.1 or hypointense with 372.55 enhancement. Evaluated parameters were SNR of HCC 50.1 to 56.5/111.5 and SNR of liver parenchyma 37.8 to 85.8, SIR 1.32 to 1.31/0.64, CNR 12.2 to 26.1/?30.08 and PE 42.08% to 80.5/?98.2%, (P < 0.05).

Conclusion:

Gd‐EOB‐DTPA is superior to Gd‐DTPA for detecting HCC in contrast agent‐enhanced MRI in the c‐myc/TGFα transgenic mouse model and there was no difference between the hyperintense or hypointense appearance of HCC. Either way, HCCs can easily be distinguished from liver parenchyma in mice. J. Magn. Reson. Imaging 2012;35:1397–1402. © 2012 Wiley Periodicals, Inc.

     

PEG coating reduces NMR relaxivity of Mn(0.5)Zn(0.5)Gd(0.02)Fe(1.98)O4 hyperthermia nanoparticles

Purpose:

To investigate both T1 and T2 MR relaxation enhancement of Gd substituted Zn‐Mn ferrite magnetic nanoparticles. Both uncoated and polyethylene glycol (PEG) coated particles were used.

Materials and Methods:

Chemical co‐precipitation was used to synthesize particles in the form Mn_0.5Zn_0.5Gd_0.2Fe_1.98O₄ suitable for hyperthermia applications. Physical characterization of the magnetic nanoparticles included SEM, TEM, ICP, and SQUID. T1 and T2 measurements were performed at 1.5 Tesla (T).

Results:

The saturation magnetization was 12.86 emu/g while the particle's magnetic moment was 1.86 × 10^?19 J/T. The particle size increased due to coating, while 1/T1 and 1/T2 relaxivities (26°C) decreased from 2.5 to 0.7 and from 201.3 to 76.6 s^?1 mM^?1, respectively, at a magnetic field 1.5T.

Conclusion:

The reduction in both 1/T1 and 1/T2 is attributed to increased distance of closest approach between the protons and the magnetic core caused by the shielding provided by the high molecular weight PEG. 1/T2 data are compared with existing theoretical models using a modified radius that takes into account both possible agglomeration of the particles and increased inter‐particle separation induced by PEG coating. J. Magn. Reson. Imaging 2011;. © 2011 Wiley Periodicals, Inc.

     

Microperfusion‐induced elevation of ADC is suppressed after contrast in breast carcinoma

Purpose

To investigate the effect of gadolinium (Gd)‐DTPA on the apparent diffusion coefficient (ADC) of breast carcinoma and to analyze the relationship between pre/postcontrast ADC and the degree of contrast enhancement.

Materials and Methods

Nineteen histopathologically confirmed breast carcinomas (mean size = 22 mm) were analyzed. Their ADCs before and after contrast administration were measured. The contrast‐to‐noise ratios (CNRs) of the tumors were measured on fat‐suppressed 3D T1‐weighted images in precontrast, early, and late postcontrast phases. These results were correlated with the measured ADC values.

Results

A significant decrease in the measured ADC was noted after contrast administration (?23%, P = 0.01). Lesions with relatively high ADC before contrast (>1.3 × 10^?3 mm²/sec; n = 12) demonstrated a larger degree of ADC reduction (mean 34%) than lesions with low ADC (≤1.3 × 10^?3 mm²/sec; n = 7) (mean 4.5%). When an early postcontrast image was used as a surrogate marker of malignant potential, we found a significant inverse correlation with postcontrast ADC (γ = ?0.57, P = 0.02).

Conclusion

Postcontrast ADC exhibited lower values than precontrast ADC, which is thought to reflect suppression of the microperfusion‐induced effect on diffusion‐weighted imaging. Postcontrast ADC may be a better indicator than precontrast ADC to reflect malignant potential of tumors. J. Magn. Reson. Imaging 2009;29:1080–1084. © 2009 Wiley‐Liss, Inc.

     

T(2) preparation method for measuring hyperemic myocardial O(2) consumption: in vivo validation by positron emission tomography

Purpose

To validate a new T₂‐prepared method for the quantification of regional myocardial O₂ consumption during pharmacologic stress with positron emission tomography (PET).

Materials and Methods

A T₂ prepared gradient‐echo sequence was modified to measure myocardial T₂ within a single breath‐hold. Six beagle dogs were randomly selected for the induction of coronary artery stenosis. Magnetic resonance imaging (MRI) experiments were performed with the T₂ imaging and first‐pass perfusion imaging at rest and during either dobutamine‐ or dipyridamole‐induced hyperemia. Myocardial blood flow (MBF) was quantified using a previously developed model‐free algorithm. Hyperemic myocardial O₂ extraction fraction (OEF) and consumption (MVO₂) were calculated using a two‐compartment model developed previously. PET imaging using ¹¹C‐acetate and ¹⁵O‐water was performed in the same day to validate OEF, MBF, and MVO₂ measurements.

Results

The T₂‐prepared mapping sequence measured regional myocardial T₂ with a repeatability of 2.3%. By myocardial segment‐basis analysis, MBF measured by MRI is closely correlated with that measured by PET (R² = 0.85, n = 22). Similar correlation coefficients were observed for hyperemic OEF (R² = 0.90, n = 9, mean difference of PET – MRI = ?2.4%) and MVO₂ (R² = 0.83, n = 7, mean difference = 4.2%).

Conclusion

The T₂‐prepared imaging method may allow quantitative estimation of regional myocardial oxygenation with relatively good accuracy. The precision of the method remains to be improved. J. Magn. Reson. Imaging 2011;33:320–327. © 2011 Wiley‐Liss, Inc.

     

Use of conventional MR imaging and diffusion‐weighted imaging for evaluating the risk grade of gastrointestinal stromal tumors

Purpose:

To study the risk grade of gastrointestinal stromal tumors (GISTs) with conventional MR imaging and diffusion‐weighted imaging (DWI).

Materials and Methods:

The abdominal MR images with DWI of 23 patients with pathologically proven GISTs during January 2010 to May 2011 were retrospectively reviewed. The conventional MR imaging findings and apparent diffusion coefficient (ADC) values of the tumors related to the risk grade were analyzed.

Results:

In the 23 patients, there were 13 patients with high‐risk, 5 with medium‐risk, 5 with low‐risk, and 0 with very low‐risk GISTs. Most of the conventional MR findings of the tumors did not correlate with the risk grade. The only exception to this was the correlation between risk grade and the enhancement degree of the tumor after Gd‐DTPA. The ADC values were, respectively, (1.04 ± 0.13) × 10^?3 mm²·s^?1, (1.59 ± 0.06) × 10^?3 mm²·s^?1 and (1.94 ± 0.08) × 10^?3 mm²·s^?1 (P < 0.05) in the high‐, medium‐, and low‐risk grade groups. The ADC values of GISTs decreased with the increase of the risk grade of the tumors (r = ?0.957; P < 0.05).

Conclusion:

DWI can be used to assess the risk grade of GISTs, but conventional MR imaging is of limited use. J. Magn. Reson. Imaging 2012; 36:1395–1401. © 2012 Wiley Periodicals, Inc.

     

Intermuscular adipose tissue (IMAT): Association with other adipose tissue compartments and insulin sensitivity

Purpose

To quantify intermuscular adipose tissue (IMAT) of the lower leg as well as to investigate associations with other adipose tissue (AT) compartments. The relationship between IMAT and insulin sensitivity was also examined.

Materials and Methods

Standardized quantification of IMAT was performed in a large cohort (N = 249) at increased risk for type 2 diabetes in the right calf by T1‐weighted fast spin‐echo imaging at 1.5T (Magnetom Sonata; Siemens Healthcare). Additionally, whole‐body AT distribution was assessed. Insulin sensitivity was determined by glucose clamp.

Results

Males showed significantly more IMAT than females (2.1 ± 1.1 cm² vs. 1.5 ± 0.9 cm²; P < 0.001). IMAT correlated well with other AT depots, especially with visceral AT (VAT; r_females = 0.52, P < 0.0001 vs. r_males = 0.42, P < 0.0001). Moreover, IMAT showed a negative correlation with the glucose infusion rate (GIR; r_females = ?0.43, P = 0.0002 vs. r_males = ?0.40, P = 0.0007).

Conclusion

Quantification of IMAT is possible by standard MR techniques. AT distribution of the lower leg is comparable to the visceral compartment with males having higher IMAT/VAT but lower subcutaneous AT (SCAT). IMAT seems to be involved in the pathogenesis of insulin resistance, as shown by the significant negative correlation with GIR. J. Magn. Reson. Imaging 2009. © 2009 Wiley‐Liss, Inc.

     

Comparison and reproducibility of ADC measurements in breathhold, respiratory triggered, and free-breathing diffusion-weighted MR imaging of the liver

Purpose

To compare and determine the reproducibility of apparent diffusion coefficient (ADC) measurements of the normal liver parenchyma in breathhold, respiratory triggered, and free‐breathing diffusion‐weighted magnetic resonance imaging (DWI).

Materials and Methods

Eleven healthy volunteers underwent three series of DWI. Each DWI series consisted of one breathhold, one respiratory triggered, and two free‐breathing (thick and thin slice acquisition) scans of the liver, at b‐values of 0 and 500 s/mm². ADCs of the liver parenchyma were compared by using nonparametric tests. Reproducibility was assessed by the Bland–Altman method.

Results

Mean ADCs (in 10^?3 mm²/sec) in respiratory triggered DWI (2.07–2.27) were significantly higher than mean ADCs in breathhold DWI (1.57–1.62), thick slice free‐breathing DWI (1.62–1.65), and thin slice free‐breathing DWI (1.57–1.66) (P < 0.005). Ranges of mean difference in ADC measurement ± limits of agreement between two scans were ?0.02–0.05 ± 0.16–0.24 in breathhold DWI, ?0.14–0.20 ± 0.59–0.60 in respiratory triggered DWI, ?0.03–0.03 ± 0.20–0.29 in thick slice free‐breathing DWI, and ?0.01–0.09 ± 0.21–0.29 in thin slice free‐breathing DWI.

Conclusion

ADC measurements of the normal liver parenchyma in respiratory triggered DWI are significantly higher and less reproducible than in breathhold and free‐breathing DWI. J. Magn. Reson. Imaging 2008;28:1141–1148. © 2008 Wiley‐Liss, Inc.