T2 mapping of hip articular cartilage in healthy volunteers at 3T: a study of topographic variation

PURPOSE: To perform baseline T(2) mapping of the hips of healthy volunteers, focusing on topographic variation, because no detailed study has involved hips. T(2) mapping is a quantitative magnetic resonance imaging (MRI) technique that evaluates cartilage matrix components. MATERIALS AND METHODS: Hips of 12 healthy adults (six men and six women; mean age = 29.5 +/- 4.9 years) were studied with a 3.0-Tesla MRI system. T(2) measurement in the oblique-coronal plane used a multi-spin-echo (MSE) sequence. Femoral cartilage was divided into 12 radial sections; acetabular cartilage was divided into six radial sections, and each section was divided into two layers representing the superficial and deep halves of the cartilage. T(2) of these sections and layers were measured. RESULTS: Femoral cartilage T(2) was the shortest (-20 degrees to 20 degrees and -10 degrees to 10 degrees , superficial and deep layers), with an increase near the magic angle (54.7 degrees ). Acetabular cartilage T(2) in both layers was shorter in the periphery than the other parts, especially at 20 degrees to 30 degrees . There were no significant differences in T(2) between right and left hips or between men and women. CONCLUSION: Topographic variation exists in hip cartilage T(2) in young, healthy adults. These findings should be taken into account when T(2) mapping is applied to patients with degenerative cartilage. J. Magn. Reson. Imaging 2007;26:165-171. (c) 2007 Wiley-Liss, Inc.

Effect of multislice acquisition on T1 and T2 measurements of articular cartilage at 3T

PURPOSE: The aim of this study was to investigate the effect of magnetization transfer on multislice T(1) and T(2) measurements of articular cartilage. MATERIALS AND METHODS: A set of phantoms with different concentrations of collagen and contrast agent (Gd-DTPA(2-)) were used for the in vitro study. A total of 20 healthy knees were used for the in vivo study. T(1) and T(2) measurements were performed using fast-spin-echo inversion-recovery (FSE-IR) sequence and multi-spin-echo (MSE) sequence, respectively, in both in vitro and in vivo studies. We investigated the difference in T(1) and T(2) values between that measured by single-slice acquisition and that measured by multislice acquisition. RESULTS: Regarding T(1) measurement, a large drop of T(1) in all slices and also a large interslice variation in T(1) were observed when multislice acquisition was used. Regarding T(2) measurement, a substantial drop of T(2) in all slices was observed; however, there was no apparent interslice variation when multislice acquisition was used. CONCLUSION: This study demonstrated that the adaptation of multislice acquisition technique for T(1) measurement using FSE-IR methodology is difficult and its use for clinical evaluation is problematic. In contrast, multislice acquisition for T(2) measurement using MSE was clinically applicable if inaccuracies caused by multislice acquisition were taken into account. J. Magn. Reson. Imaging 2007;26:109-117. (c) 2007 Wiley-Liss, Inc.

Coronary plaque composition of culprit/target lesions according to the clinical presentation: a virtual histology intravascular ultrasound analysis

AIMS: To evaluate the plaque composition obtained by virtual histology (VH) IVUS according to the clinical presentation and to compare those data to previously published histopathology data. METHODS AND RESULTS: VH was performed on 95 de novo significant lesions (>75% stenosis) in 85 patients [28 acute coronary syndrome (ACS) patients, 30 lesions; 57 stable angina pectoris (SAP) patients, 65 lesions]. There were a higher prevalence of positive remodelling (47 vs. 22%, P=0.013), thrombus (20 vs. 1.5%, P=0.0037), and echo-lucent area (23.3 vs. 7.7%, P=0.047) in ACS patients. At the minimal lumen site, fibrous plaque area was significantly larger in ACS lesions than in SAP lesions (66.0+/-10.7 vs. 61.4+/-8.9%, P=0.034), whereas necrotic core and dense calcium plaque area were smaller in ACS lesions (Necrotic core: 6.8+/-6.0 vs. 11.0+/-8.3%, P=0.02; Dense calcium: 2.6+/-3.0 vs. 4.9+/-5.8%, P=0.03). No differences in rate of thin cap fibroatheroma, thick fibrotheroma, or for the presence of multiple necrotic core layers were observed between both groups. CONCLUSION: Plaque composition obtained by VH-IVUS shows less necrotic core and more fibrous tissue in ACS compared to SAP lesions, which is in contradiction with previously published histopathologic data.

MRI follow-up of TNF-dependent differential progression of atherosclerotic wall-thickening in mouse aortic arch from early to advanced stages

OBJECTIVES: An optimized, longitudinal in vivo magnetic resonance vessel wall-imaging protocol was evaluated regarding its capability of detecting differences in the time-dependent atherosclerotic lesion progression in the aortic arch between ApoE(-/-) and double-deficient ApoE(-/-)/TNF(-/-) mice at comparatively early plaque development stages. MATERIALS AND METHODS: Seven ApoE(-/-) and seven ApoE(-/-)/TNF(-/-) female mice underwent MRI at 11.75 teslas at four stages up to 26 weeks of age. A double-gated spin-echo MRI sequence was used with careful perpendicular slice positioning to visualize the vessel wall of the ascending aortic arch. RESULTS: Wall-thickness progression measured with MRI was significant at 11 weeks of age in ApoE(-/-) mice, but only at 26 weeks in ApoE(-/-)/TNF(-/-) mice. A significant correlation was found between MRI wall-thickness and lesion area determined on histology. CONCLUSION: MRI was shown to be sensitive enough to reveal subtle genetically-induced differences in lesion progression at ages earlier than 25 weeks.

Oxygen-sensitive 3He-MRI in bronchiolitis obliterans after lung transplantation

Oxygen-sensitive 3He-MRI was studied for the detection of differences in intrapulmonary oxygen partial pressure (pO2) between patients with normal lung transplants and those with bronchiolitis obliterans syndrome (BOS). Using software developed in-house, oxygen-sensitive 3He-MRI datasets from patients with normal lung grafts (n = 8) and with BOS (n = 6) were evaluated quantitatively. Datasets were acqiured on a 1.5-T system using a spoiled gradient echo pulse sequence. Underlying diseases were pulmonary emphysema (n = 10 datasets) and fibrosis (n = 4). BOS status was verified by pulmonary function tests. Additionally, 3He-MRI was assessed blindedly for ventilation defects. Median intrapulmonary pO2 in patients with normal lung grafts was 146 mbar compared with 108 mbar in patients with BOS. Homogeneity of pO2 distribution was greater in normal grafts (standard deviation pO2 34 versus 43 mbar). Median oxygen decrease rate during breath hold was higher in unaffected patients (-1.75 mbar/s versus -0.38 mbar/s). Normal grafts showed fewer ventilation defects (5% versus 28%, medians). Oxygen-sensitive 3He-MRI appears capable of demonstrating differences of intrapulmonary pO2 between normal lung grafts and grafts affected by BOS. Oxygen-sensitive 3He-MRI may add helpful regional information to other diagnostic techniques for the assessment and follow-up of lung transplant recipients.

MR imaging of the adrenal glands: 1.5T versus 3T

MR imaging at 1.5T is considered the prime cross-sectional imaging modality for characterization of adrenal lesions. This is of utmost clinical importance, because non-functioning adenoma and adrenal metastasis are fairly common. The differentiation of these two tumor entities primarily is based on chemical shift imaging, also known as dual echo in-phase and opposed-phase imaging. At 3.0 T, the echo time pairs for in-phase and opposed-phase MR imaging need to be adjusted because the frequency difference is double that of standard 1.5T MR systems. Unfortunately, the acquisition of the first opposed-phase echo at 1.1 milliseconds and the first in-phase echo at 2.2 milliseconds within the same breath-hold requires unacceptably high receiver bandwidths at 3.0 T. Therefore, alternative data collection schemes have been implemented. This article reviews the current literature regarding adrenal imaging at 3.0 T with a focus on the chemical shift technique.

Magnetic resonance (MR) cholangiography: quantitative and qualitative comparison of 3.0 Tesla with 1.5 Tesla

OBJECTIVES: To determine quantitative and qualitative image quality in patients undergoing magnetic resonance (MR) cholangiography at 3.0 Tesla (T) compared with 1.5 T. MATERIALS AND METHODS: Fifty patients (30 women; mean age, 51 years) underwent MR cholangiography at 1.5 T; another 50 patients (25 women; mean age 51 years) were scanned at 3.0 T. MR sequence protocol consisted of breath-hold single-slice rapid acquisition with relaxation enhancement (RARE) and a respiratory-triggered 3D turbo spin echo (3D TSE) sequence. Maximum intensity projections were generated from the 3D TSE datasets. Contrast-to-noise ratio (CNR) measurements between the common bile duct (CBD), left and right intrahepatic duct (LHD, RHD), and periductal tissue were performed. Three radiologists assessed qualitatively the visibility of the CBD, LHD, and RHD and the overall diagnostic quality. RESULTS: Mean gain in CNR at 3.0 T versus 1.5 T in all 3 locations ranged for the RARE sequence from 7.7% to 38.1% and for the 3D TSE from 0.5% to 26.1% (P > 0.05 for all differences). Qualitative analysis did not reveal any significant difference between the 2 field strengths (P > 0.05). CONCLUSIONS: MR cholangiography at 3.0 T shows a trend toward higher CNR without improving image quality significantly.

Evaluation of magnetic resonance colonography at 3.0 Tesla regarding diagnostic accuracy and image quality

OBJECTIVES: To assess magnetic resonance (MR)-colonography (MRC) for detection of colorectal lesions using two different T1w three-dimensional (3D)-gradient-recalled echo (GRE)-sequences and integrated parallel data acquisition (iPAT) at a 3.0 Tesla MR-unit. MATERIALS AND METHODS: In this prospective study, 34 symptomatic patients underwent dark lumen MRC at a 3.0 Tesla unit before conventional colonoscopy (CC). After colon distension with tap water, 2 high-resolution T1w 3D-GRE [3-dimensional fast low angle shot (3D-FLASH), iPAT factor 2 and 3D-volumetric interpolated breathhold examination (VIBE), iPAT 3] sequences were acquired without and after bolus injection of gadolinium. Prospective evaluation of MRC was performed. Image quality of the different sequences was assessed qualitatively and quantitatively. The findings of the same day CC served as standard of reference. RESULTS: MRC identified all polyps >5 mm (16 of 16) in size and all carcinomas (4 of 4) correctly. Fifty percent of the small polyps 0.6). CONCLUSIONS: MRC using 3D-GRE-sequences and iPAT is feasible at 3.0 T-systems. The high-resolution 3D-FLASH was slightly preferred over the 3D-VIBE because of better image quality, although both used sequences showed no statistical significant difference.

[Pediatric cardiac disease: indications for family screening and risk stratification]

In some forms of cardiac disease in childhood, familial occurrence is frequent. This implies the question whether family members should undergo cardiologic screening examinations. For cardiomyopathies the familiarity is so frequent and morbidity so important that examination by echo of all first degree relatives is recommended. As these cardiomyopathies may develop its phenotype all along a lifetime, repetitive examinations usually are indicated. For the primary electrical diseases the so called channelopathies the same is true, as for the high rate of familial occurrence and the high morbidity. Thus ECG screening of first degree relatives is recommended. In a child with congenital heart disease there are no recommendations with regard to familial screening and cardiological examinations usually are indicated only in case of clinical suspicion for heart disease.

Intrapulmonary 3He gas distribution depending on bolus size and temporal bolus placement

OBJECTIVE: Dynamic ventilation (3)He-MRI is a new method to assess pulmonary gas inflow. As differing airway diameters throughout the ventilatory cycle can influence gas inflow this study intends to investigate the influence of volume and timing of a He gas bolus with respect to the beginning of the tidal volume on inspiratory gas distribution. MATERIALS AND METHODS: An ultrafast 2-dimensional spoiled gradient echo sequence (temporal resolution 100 milliseconds) was used for dynamic ventilation (3)He-MRI of 11 anesthetized and mechanically ventilated pigs. The applied (3)He gas bolus was varied in volume between 100 and 200 mL. A 150-mL bolus was varied in its application time after the beginning of the tidal volume between 0 and 1200 milliseconds. Signal kinetics were evaluated using an in-house developed software after definition of parameters for the quantitative description of (3)He gas inflow. RESULTS: The signal rise time (time interval between signal in the parenchyma reaches 10% and 90% of its maximum) was prolonged with increasing bolus volume. The parameter was shortened with increasing delay of (3)He application after the beginning of the tidal volume. Timing variation as well as volume variation showed no clear interrelation to the signal delay time 10 (time interval between signal in the trachea reaches 50% of its maximum and signal in the parenchyma reaches 10% of its maximum). CONCLUSIONS: Dynamic ventilation (3)He-MRI is able to detect differences in bolus geometry performed by volume variation. Pulmonary gas inflow as investigated by dynamic ventilation (3)He-MRI tends to be accelerated by an increasing application delay of a (3)He gas bolus after the beginning of the tidal volume.

Steady-state diffusion imaging for MR in-vivo evaluation of reparative cartilage after matrix-associated autologous chondrocyte transplantation at 3 tesla--preliminary results

OBJECTIVES: To demonstrate the feasibility of time-reversed fast imaging with steady-state precession (FISP) called PSIF for diffusion-weighted imaging of cartilage and cartilage transplants in a clinical study. MATERIAL AND METHODS: In a cross-sectional study 15 patients underwent MRI using a 3D partially balanced steady-state gradient echo pulse sequence with and without diffusion weighting at two different time points after matrix-associated autologous cartilage transplantation (MACT). Mean diffusion quotients (signal intensity without diffusion-weighting divided by signal intensity with diffusion weighting) within the cartilage transplants were compared to diffusion quotients found in normal cartilage. RESULTS: The global diffusion quotient found in repair cartilage was significantly higher than diffusion values in normal cartilage (p<0.05). There was a decrease between the earlier and the later time point after surgery. CONCLUSIONS: In-vivo diffusion-weighted imaging based on the PSIF technique is possible. Our preliminary results show follow-up of cartilage transplant maturation in patients may provide additional information to morphological assessment.

Experimental model to evaluate in vivo and in vitro cartilage MR imaging by means of histological analyses

OBJECTIVES: Implementation of an experimental model to compare cartilage MR imaging by means of histological analyses. MATERIAL AND METHODS: MRI was obtained from 4 patients expecting total knee replacement at 1.5 and/or 3T prior surgery. The timeframe between pre-op MRI and knee replacement was within two days. Resected cartilage-bone samples were tagged with Ethi((R))-pins to reproduce the histological cutting course. Pre-operative scanning at 1.5T included following parameters for fast low angle shot (FLASH: TR/TE/FA=33ms/6ms/30 degrees , BW=110kHz, 120mmx120mm FOV, 256x256 matrix, 0.65mm slice-thickness) and double echo steady state (DESS: TR/TE/FA=23.7ms/6.9ms/40 degrees , BW=130kHz, 120x120mm FOV, 256x256 matrix, 0.65mm slice-thickness). At 3T, scan parameters were: FLASH (TR/TE/FA=12.2ms/5.1ms/10 degrees , BW=130kHz, 170x170mm FOV, 320x320, 0.5mm slice-thickness) and DESS (TR/TE/FA=15.6ms/4.5ms/25 degrees , BW=200kHz, 135mmx150mm FOV, 288x320matrix, 0.5mm slice-thickness). Imaging of the specimens was done the same day at 1.5T. MRI (Noyes) and histological (Mankin) score scales were correlated using the paired t-test. Sensitivity and specificity for the detection of different grades of cartilage degeneration were assessed. Inter-reader and intra-reader reliability was determined using Kappa analysis. RESULTS: Low correlation (sensitivity, specificity) was found for both sequences in normal to mild Mankin grades. Only moderate to severe changes were diagnosed with higher significance and specificity. The use of higher field-strengths was advantageous for both protocols with sensitivity values ranging from 13.6% to 93.3% (FLASH) and 20.5% to 96.2% (DESS). Kappa values ranged from 0.488 to 0.944. CONCLUSIONS: Correlating MR images with continuous histological slices was feasible by using three-dimensional imaging, multi-planar-reformat and marker pins. The capability of diagnosing early cartilage changes with high accuracy could not be proven for both FLASH and DESS.

Magnetization transfer contrast and T2 mapping in the evaluation of cartilage repair tissue with 3T MRI

PURPOSE: To use magnetization transfer (MT) imaging in the visualization of healthy articular cartilage and cartilage repair tissue after different cartilage repair procedures, and to assess global as well as zonal values and compare the results to T2-relaxation. MATERIALS AND METHODS: Thirty-four patients (17 after microfracture [MFX] and 17 after matrix-associated autologous cartilage transplantation [MACT]) were examined with 3T MRI. The MT ratio (MTR) was calculated from measurements with and without MT contrast. T2-values were evaluated using a multiecho, spin-echo approach. Global (full thickness of cartilage) and zonal (deep and superficial aspect) region-of-interest assessment of cartilage repair tissue and normal-appearing cartilage was performed. RESULTS: In patients after MFX and MACT, the global MTR of cartilage repair tissue was significantly lower compared to healthy cartilage. In contrast, using T2, cartilage repair tissue showed significantly lower T2 values only after MFX, whereas after MACT, global T2 values were comparable to healthy cartilage. For zonal evaluation, MTR and T2 showed a significant stratification within healthy cartilage, and T2 additionally within cartilage repair tissue after MACT. CONCLUSION: MT imaging is capable and sensitive in the detection of differences between healthy cartilage and areas of cartilage repair and might be an additional tool in biochemical cartilage imaging. For both MTR and T2 mapping, zonal assessment is desirable.

In vivo biochemical 7.0 Tesla magnetic resonance: preliminary results of dGEMRIC, zonal T2, and T2* mapping of articular cartilage

INTRODUCTION: Ultra-high-field whole-body systems (7.0 T) have a high potential for future human in vivo magnetic resonance imaging (MRI). In musculoskeletal MRI, biochemical imaging of articular cartilage may benefit, in particular. Delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) and T2 mapping have shown potential at 3.0 T. Although dGEMRIC, allows the determination of the glycosaminoglycan content of articular cartilage, T2 mapping is a promising tool for the evaluation of water and collagen content. In addition, the evaluation of zonal variation, based on tissue anisotropy, provides an indicator of the nature of cartilage ie, hyaline or hyaline-like articular cartilage.Thus, the aim of our study was to show the feasibility of in vivo dGEMRIC, and T2 and T2* relaxation measurements, at 7.0 T MRI; and to evaluate the potential of T2 and T2* measurements in an initial patient study after matrix-associated autologous chondrocyte transplantation (MACT) in the knee. MATERIALS AND METHODS: MRI was performed on a whole-body 7.0 T MR scanner using a dedicated circular polarization knee coil. The protocol consisted of an inversion recovery sequence for dGEMRIC, a multiecho spin-echo sequence for standard T2 mapping, a gradient-echo sequence for T2* mapping and a morphologic PD SPACE sequence. Twelve healthy volunteers (mean age, 26.7 +/- 3.4 years) and 4 patients (mean age, 38.0 +/- 14.0 years) were enrolled 29.5 +/- 15.1 months after MACT. For dGEMRIC, 5 healthy volunteers (mean age, 32.4 +/- 11.2 years) were included. T1 maps were calculated using a nonlinear, 2-parameter, least squares fit analysis. Using a region-of-interest analysis, mean cartilage relaxation rate was determined as T1 (0) for precontrast measurements and T1 (Gd) for postcontrast gadopentate dimeglumine [Gd-DTPA(2-)] measurements. T2 and T2* maps were obtained using a pixelwise, monoexponential, non-negative least squares fit analysis; region-of-interest analysis was carried out for deep and superficial cartilage aspects. Statistical evaluation was performed by analyses of variance. RESULTS: Mean T1 (dGEMRIC) values for healthy volunteers showed slightly different results for femoral [T1 (0): 1259 +/- 277 ms; T1 (Gd): 683 +/- 141 ms] compared with tibial cartilage [T1 (0): 1093 +/- 281 ms; T1 (Gd): 769 +/- 150 ms]. Global mean T2 relaxation for healthy volunteers showed comparable results for femoral (T2: 56.3 +/- 15.2 ms; T2*: 19.7 +/- 6.4 ms) and patellar (T2: 54.6 +/- 13.0 ms; T2*: 19.6 +/- 5.2 ms) cartilage, but lower values for tibial cartilage (T2: 43.6 +/- 8.5 ms; T2*: 16.6 +/- 5.6 ms). All healthy cartilage sites showed a significant increase from deep to superficial cartilage (P < 0.001). Within healthy cartilage sites in MACT patients, adequate values could be found for T2 (56.6 +/- 13.2 ms) and T2* (18.6 +/- 5.3 ms), which also showed a significant stratification. Within cartilage repair tissue, global mean values showed no difference, with 55.9 +/- 4.9 ms for T2 and 16.2 +/- 6.3 ms for T2*. However, zonal assessment showed only a slight and not significant increase from deep to superficial cartilage (T2: P = 0.174; T2*: P = 0.150). CONCLUSION: In vivo T1 dGEMRIC assessment in healthy cartilage, and T2 and T2* mapping in healthy and reparative articular cartilage, seems to be possible at 7.0 T MRI. For T2 and T2*, zonal variation of articular cartilage could also be evaluated at 7.0 T. This zonal assessment of deep and superficial cartilage aspects shows promising results for the differentiation of healthy and affected articular cartilage. In future studies, optimized protocol selection, and sophisticated coil technology, together with increased signal at ultra-high-field MRI, may lead to advanced biochemical cartilage imaging.

Magnetic resonance imaging for diagnosis and assessment of cartilage defect repairs

Clinical magnetic resonance imaging (MRI) is the method of choice for the non-invasive evaluation of articular cartilage defects and the follow-up of cartilage repair procedures. The use of cartilage-sensitive sequences and a high spatial-resolution technique enables the evaluation of cartilage morphology even in the early stages of disease, as well as assessment of cartilage repair. Sequences that offer high contrast between articular cartilage and adjacent structures, such as the fat-suppressed, 3-dimensional, spoiled gradient-echo sequence and the fast spin-echo sequence, are accurate and reliable for evaluating intrachondral lesions and surface defects of articular cartilage. These sequences can also be performed together in reasonable examination times. In addition to morphology, new MRI techniques provide insight into the biochemical composition of articular cartilage and cartilage repair tissue. These techniques enable the diagnosis of early cartilage degeneration and help to monitor the effect and outcome of various surgical and non-surgical cartilage repair therapies.