Rapid T1 mapping of mouse myocardium with saturation recovery look‐locker method

Dynamic contrast‐enhanced MRI using gadolinium or manganese provides unique characterization of myocardium and its pathology. In this study, an electrocardiography (ECG) triggered saturation recovery Look‐Locker method was developed and validated for fast cardiac T₁ mapping in small animal models. By sampling the initial portion of the longitudinal magnetization recovery curve, high temporal resolution (～3 min) can be achieved at a high spatial resolution (195 × 390 μm2) in mouse heart without the aid of parallel imaging or echo‐planar imaging. Validation studies were performed both in vitro on a phantom and in vivo on C57BL/6 mice (n = 6). Our results showed a strong agreement between T₁ measured by saturation recovery Look‐Locker and by the standard saturation recovery method in vitro or inversion recovery Look‐Locker in vivo. The utility of saturation recovery Look‐Locker in dynamic contrast‐enhanced MRI studies was demonstrated in manganese‐enhanced MRI experiments in mice. Our results suggest that saturation recovery Look‐Locker can provide rapid and accurate cardiac T₁ mapping for studies using small animal models. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Breast lesions with high signal intensity on T1-weighted MR images

Magnetic resonance imaging of the breast supplies much information concerning the signal characteristics of a lesion. Among these, high signal intensity on non-fat saturated T1-weighted imaging (WI) is a special finding. Such a finding may result from different causes, such as a paramagnetic substance or fatty, bloody or proteinaceous content. In this article, we present hyperintense breast lesions on T1-WI.     

Gd-DTPA bolus tracking in the myocardium using T1 fast acquisition relaxation mapping (T1 FARM).

MRI methods currently used for bolus tracking in the myocardium, such as saturation recovery turbo-fast low-angle shot (FLASH) (srTFL), are limited by signal intensity (SI) saturation at high contrast agent (CA) concentrations. By using T1 fast acquisition relaxation mapping (T1 FARM), a Gd-DTPA bolus (0.075 vs. 0.025 mmol/kg) may be injected without causing saturation. This study tested the feasibility of in vivo T1 FARM bolus tracking under rest/stress conditions in seven beagles with multiple permanently occluded branches of the left anterior descending (LAD) coronary artery. Although it underestimated the myocardial perfusion reserve (MPR) measured ex vivo using radioactive microspheres (mean +/- SEM; 3.60 +/- 0.26), the MPR determined upon application of the modified Kety model (1.86 +/- 0.10) enabled distinction between normal and infarcted tissue. The partition coefficient (lambda) estimated at rest and stress using the modified Kety model underestimated ex vivo radioactive measurements in infarcted tissue (0.25 +/- 0.01 vs. 0.26 +/- 0.01 vs. 0.79 +/- 0.08 ml/g, P < 0.0001) yet was accurate in normal tissue (0.28 +/- 0.01 vs. 0.30 +/- 0.01 vs. 0.33 +/- 0.01 ml/g, P = NS). Thus, although unsuitable for myocardial viability assessment, T1 FARM bolus tracking shows potential for assessment of myocardial perfusion.     

Breast MR imaging with high spectral and spatial resolutions: preliminary experience

The authors evaluated magnetic resonance (MR) imaging with high spectral and spatial resolutions (HSSR) of water and fat in breasts of healthy volunteers (n = 6) and women with suspicious lesions (n = 6). Fat suppression, edge delineation, and image texture were improved on MR images derived from HSSR data compared with those on conventional MR images. HSSR MR imaging data acquired before and after contrast medium injection showed spectrally inhomogeneous changes in the water resonances in small voxels that were not detectable with conventional MR imaging.     

Functional imaging with MR T1 contrast: a feasibility study with blood-pool contrast agent

The aim of this study was to prove the concept of using a long intravenous half-life blood-pool T1 contrast agent as a new functional imaging method. For each of ten healthy subjects, two dynamic magnetic resonance (MR) protocols were carried out: (1) a reference run with a typical T2* echo-planar imaging (EPI) sequence based on the blood oxygenation level-dependent (BOLD) effect and (2) a run with a T1-sensitive three-dimensional (3D) gradient-echo (GRE) sequence using cerebral blood volume (CBV) contrast after intravenous administration of a contrast agent containing a chelate of gadolinium diethylene-triamine-pentaacetate with a phosphono-oxymethyl substituent. All sequences were performed during the execution of a block-type finger-tapping paradigm. SPM5 software was used for statistical analysis. For both runs maximum activations (peak Z-score = 5.5, cluster size 3,449 voxels) were localized in the left postcentral gyrus. Visual inspection of respective signal amplitudes suggests the T1 contrast to be substantially smaller than EPI (0.5% vs 1%). A new functional imaging method with potentially smaller image artefacts due to the nature of CBV contrast and characteristics of the T1 sequence was proposed and verified.     

Hepatocellular tumors with high signal on T1-weighted MR images: chemical shift MR imaging and histologic correlation.

We reviewed conventional and chemical shift MR images and histologic findings of seven proven primary hepatic masses that had higher signal than liver on T1-weighted images to determine if this necessarily indicates fat and if the presence of fat indicates malignancy. These seven masses included five hepatocellular carcinomas (HCCs), one focal nodular hyperplasia (FNH), and one fatty dysplastic nodule. An eighth solitary high signal mass without histologic proof had evidence of abundant fat on each of two chemical shift MR images 25 months apart. Only one of the five HCCs had chemical shift or histologic evidence of fat, while the FNH and dysplastic nodule each had both chemical shift and histologic confirmation of fat. The dysplastic nodule became more dysplastic and grew significantly within 14 months, but remained benign. The unproven fatty lesion decreased in size over 25 months and is therefore presumably benign. Although no statistical inferences can be drawn from this small correlative study, we have shown that HCC may have higher signal intensity than liver on T1-weighted images, whether or not it contains fat. Chemical shift techniques can confirm the presence of intratumoral fat and thus indicate a mass of hepatocellular origin, but the mass may be benign or malignant.     

MR Lymphography with a Lymphotropic T1-Type MR Contrast Agent: Gd-DTPA-PGM

A model system of a paramagnetic lymphotropic MR contrast agent (Gd-DTPA labeled polyglucose associated macrocomplex, PGM) for T¹-weighted MR imaging of lymph nodes in rats and rabbits was evaluated. Pharmacokinetic (tissue accumulation) and MR imaging data (optimal dose and timing parameters) were obtained in normal rats (n = 88) after subcutaneous (SC) injection of paramagnetic, radiolabeled [111In]Gd-DTPA-PGM. A rabbit model of lymph node metastases (n = 8) was ultimately used to demonstrate the potential of MR imaging with Gd-DTPA-PGM for nodal tumor detection. Maximum concentrations of Gd-DTPA-PGM were found in popliteal and paraaortic lymph nodes within 24 h after SC administration, and highest lymph node SNR values were obtained by MR imaging at this time point. The optimum imaging dose was 6–12 μmol Gd/kg. Tumor-lymph node contrast increased from 0.0 ± 1.2 precontrast to 19.2 ± 6.5 (spoiled gradient echo sequence, TR 50/TE 7/flip angle 60°) postcontrast and conspicuity of nodal metastases was improved. Gd-DTPA-PGM accumulates in lymph nodes after SC administration and significantly enhances lymph node signal intensity of normal animals but not metastatic lymph nodes.     

Lung: spiral volumetric CT with single-breath-hold technique

The authors adapted the transport system of a computed tomographic (CT) scanner with continuous rotation capability to examine complete lung subvolumes during a single breath hold. Twenty-four adult patients underwent scanning with up to 12 continuous 1-second rotations, and data acquisition was synchronized with longitudinal patient motion at one section thickness per second. Interpolated planar raw data were obtained retrospectively from any level within the volume, and these afforded high-quality images that were comparable to standard images. Solitary pulmonary nodules were not omitted, their centers could always be depicted, and secondary reformations as well as three-dimensional reconstructions were obtained easily. The authors conclude that spiral volumetric CT, by completely surveying a subvolume of the lung, is an attractive new application of CT.     

T1 mapping of the gadolinium‐enhanced myocardium: Adjustment for factors affecting interpatient comparison

Quantitative T₁ mapping of delayed gadolinium‐enhanced cardiac magnetic resonance imaging has shown promise in identifying diffuse myocardial fibrosis. Despite careful control of magnetic resonance imaging parameters, comparison of T₁ times between different patients may be problematic because of patient specific factors such as gadolinium dose, differing glomerular filtration rates, and patient specific delay times. In this work, a model driven approach to account for variations between patients to allow for comparison of T₁ data is provided. Kinetic model parameter values were derived from healthy volunteer time‐contrast curves. Correction values for the factors described above were used to normalize T₁ values to a matched state. Examples of pre‐ and postcorrected values for a pool of normal subjects and in a patient cohort of type 1 diabetic patients shows tighter clustering and improved discrimination of disease state. Magn Reson Med, 2011. © 2010 Wiley‐Liss, Inc.     

High spatial resolution 3D MR cholangiography with high sampling efficiency technique (SPACE): comparison of 3T vs. 1.5T

Purpose

The aim of this study was to evaluate image quality of 3D MR cholangiography (MRC) using high sampling efficiency technique (SPACE) at 3 T compared with 1.5 T.

Methods and materials

An IRB approved prospective study was performed with 17 healthy volunteers using both 3 and 1.5 T MR scanners. MRC images were obtained with free-breathing navigator-triggered 3D T2-weighted turbo spin-echo sequence with SPACE (TR, >2700 ms; TE, 780 ms at 3 T and 801 ms at 1.5 T; echo-train length, 121; voxel size, 1.1 mm × 1.0 mm × 0.84 mm). The common bile duct (CBD) to liver contrast-to-noise ratios (CNRs) were compared between 3 and 1.5 T. A five-point scale was used to compare overall image quality and visualization of the third branches of bile duct (B2, B6, and B8). The depiction of cystic duct insertion and the highest order of bile duct visible were also compared. The results were compared using the Wilcoxon signed-ranks test.

Results

CNR between the CBD and liver was significantly higher at 3 T than 1.5 T (p = 0.0006). MRC at 3 T showed a significantly higher overall image quality (p = 0.0215) and clearer visualization of B2 (p = 0.0183) and B6 (p = 0.0106) than at 1.5 T. In all analyses of duct visibility, 3 T showed higher scores than 1.5 T.

Conclusion

3 T MRC using SPACE offered better image quality than 1.5 T. SPACE technique facilitated high-resolution 3D MRC with excellent image quality at 3 T.     

T2 mapping of human femorotibial cartilage with turbo mixed MR imaging at 1.5 T: feasibility

The feasibility of a high-spatial-resolution technique for mapping T1 and T2 in articular cartilage in the human knee was evaluated. The technique, turbo mixed magnetic resonance (MR) imaging, is based on a pulse sequence in which inversion-recovery and spin-echo measurements are interleaved. The sequence was first validated in a phantom experiment in which T1 and T2 values obtained with an accepted spectroscopic technique were correlated with those obtained by using a clinical magnetic resonance imager with the turbo mixed technique. T2 maps were obtained with turbo mixed imaging in 25 volunteers (17 men, eight women; mean age, 30.8 years; range, 23-45 years). A high correlation (r = 0.99) was found between T1 and T2 values obtained at spectroscopy and those obtained at turbo mixed imaging. Relative differences in the range of cartilage relaxation times between the two techniques were less than 20%. Turbo mixed imaging in human volunteers showed T2 cartilage relaxation times that corresponded with previously published data. Turbo mixed imaging, thus, is feasible for T2 mapping of cartilage.     

MR纵向弛豫时间定量成像评价肥厚型心肌病心肌纤维化的初步研究

目的 探讨纵向弛豫时间定量(T1mapping)成像对肥厚型心肌病(HCM)纤维化的诊断价值.方法 按诊断标准入选48例HCM患者和18名健康志愿者,分别行常规延迟强化(LGE)检查与T1 mapping成像,按HCM LGE有无及程度,分为LGE远处正常区、LGE边缘区、LGE区(分为晕状LGE与典型斑片状LGE),分别测量2组心肌对比剂增强后T1值的变化率并进行卡方检验、两两对比及ROC曲线分析.结果 健康志愿者T1值变化率与HCM远离LGE区差异无统计学意义(3.98 ±3.19和3.36 ±2.77,=0.98,p＞0.05),与LGE周边区(13.51±5.67)、晕状区(17.70±5.57)、斑片区(36.62±8.03)比较差异有统计学意义(t值分别为15.28、17.13和47.48,P值均＜0.01);远处正常区(3.36 ±2.77)与LGE周边区、晕状区及斑片区比较差异均有统计学意义(t值分别为19.64、20.76和56.64,P值均＜0.01);LGE周边区与LGE晕状区和斑片区比较差异均有统计学意义(t值分别为6.12和39.90,P值均＜0.01);LGE晕状区与斑片区比较差异有统计学意义(t=25.63,P＜0.01).ROC曲线提示T1 mapping成像较传统LGE成像有更大的曲线下面积(0.974±0.050和0.751±0.180).结论 HCM纤维化常见,且受累心肌的纤维化程度不一,T1 mapping成像能对HCM患者心肌纤维化的严重程度进行评价,能够发现处于纤维化早期的病变.     

In vivo proton MR three-dimensional T1rho mapping of human articular cartilage: initial experience

The purpose of this study was to demonstrate the feasibility of computing three-dimensional relaxation maps of spin-lattice relaxation time in the rotating frame (T1rho) from in vivo magnetic resonance (MR) images of the human patellofemoral joint. T1rho was measured by applying a three-dimensional gradient-echo pulse sequence in six healthy subjects and one symptomatic subject by using a 1.5-T MR imager and a 15-cm-diameter transmit-receive quadrature birdcage radiofrequency coil. Average T1rho measured in healthy patellar cartilage was 49.7 msec +/- 3.2 (mean +/- SD). Two-dimensional T1rho-weighted images were obtained with a fast spin-echo pulse sequence for comparison. There was good correlation between two-dimensional and three-dimensional T1rho values for the six healthy subjects (R2 = 0.88, slope = 1.16).