Multicenter validation of the magnetic resonance t2* technique for segmental and global quantification of myocardial iron

Purpose

To assess the transferability of the magnetic resonance imaging (MRI) multislice multiecho T2* technique for global and segmental measurement of iron overload in thalassemia patients.

Materials and Methods

Multiecho T2* sequences were installed on six MRI scanners. Five healthy subjects (n = 30) were scanned at each site; five thalassemia major (TM) patients were scanned at the reference site and were rescanned locally (n = 25) within 1 month. T2* images were analyzed using previously validated software.

Results

T2* values of healthy subjects showed intersite homogeneity. On TM patients, for global heart T2* values the correlation coefficient was 0.97, coefficients of variation (CoV_s) ranged from 0.04–0.12, and intraclass coefficients (ICC_s) ranged from 0.94–0.99. The mean CoV and ICC for segmental T2* distribution were 0.198 and 88, respectively.

Conclusion

The multislice multiecho T2* technique is transferable among scanners with good reproducibility. J. Magn. Reson. Imaging 2009;30:62–68. © 2009 Wiley‐Liss, Inc.     

Standardization of the quantification of iron concentration in the liver by magnetic resonance imaging

ObjectiveTo calibrate 1.5 tesla magnetic resonance scanners for the quantification of the concentration of iron in the liver.Material and methodsWe analyzed twenty-eight 1.5 tesla magnetic resonance scanners using a phantom with four tubes containing different concentrations of iron (III) chloride and one tube without iron. The phantom represented two typical patients: one with moderate iron overload and one with high iron overload. We measured the signal intensity ratio between each iron-containing tube and the tube without iron; then we calculated the theoretical levels of iron concentration in each scanner according to the model for the two levels of overload. We compared the results of each scanner with those of the reference scanner in which the model and the phantom had been designed, and we calculated the percentage of difference between the two scanners.ResultsThe mean difference in the ratios compared to the reference center was 11% (0.3-39). The mean concentration of iron was 71 μmol Fe/g for moderate overload and 193 μmol Fe/g for high overload. The mean difference was 6% (1.2- 7%) and 3.4% (0-16%). respectively.In two scanners, we applied a correction factor so that the difference was below 25% in all cases.ConclusionWe calibrated twenty-eight 1.5 tesla scanners for the concentration of iron in the liver and achieved variability less than 25%.     

A single breath-hold multiecho T2* cardiovascular magnetic resonance technique for diagnosis of myocardial iron overload

PURPOSE: To assess tissue iron concentrations by the use of a gradient echo T2* multiecho technique. MATERIALS AND METHODS: We compared the results of measurements of heart T2* from 32 patients using the established multiple breath-hold variable TR technique with a new multiecho sequence that acquires all images within a single breath-hold with constant TR. RESULTS: There was good agreement of myocardial T2* values between both methods in the abnormal range of T2* < 20 msec (mean difference 0.2 msec, 95% CI -1.3 to 0.9 msec, r = 0.97, P < 0.0001). The coefficient of variability between the methods was 3.5%. The interstudy reproducibility using the multiecho sequence had a variability coefficient of 2.3% in the abnormal T2* range and 5.8% over all T2* values. There was good agreement between the techniques for the liver T2* values. CONCLUSIONS: The use of the single breath-hold, multiecho acquisition allowed reliable quantification of myocardial T2*. The good reproducibility, speed, and T1 independence of this technique allows greater accuracy, faster patient throughput, and, therefore, reduced costs (which is important in developing countries where thalassemia is most prevalent).     

Multislice multiecho T2* cardiovascular magnetic resonance for detection of the heterogeneous distribution of myocardial iron overload

PURPOSE: To assess the tissue iron concentration of the left ventricle (LV) using a multislice, multiecho T2* MR technique and a segmental analysis. MATERIALS AND METHODS: T2* multiecho MRI was performed in 53 thalassemia major patients. Three short-axis views of the LV were obtained and analyzed with custom-written software. The myocardium was automatically segmented into 12 segments. The T2* value on each segment as well as the global T2* value were calculated. Cine dynamic images were also obtained to evaluate biventricular function parameters by quantitative analysis. RESULTS: For the T2* global value, the coefficient of variation (CoV) for intra-/interobserver and interstudy reproducibility was 3.9% (r = 0.98), 5.5% (r = 0.98), and 4.7% (r = 0.99) respectively. Three groups were identified based on analysis of myocardial T2*: homogeneous (21%), heterogeneous (38%), and no myocardial iron overload (41%). The mean serum ferritin, liver iron concentration, and urinary iron excretion were significantly different among the groups. We did not find significant differences among groups in biventricular function. There was a correlation between the global T2* value and the T2* value in the mid-ventricular septum (r = 0.95, P < 0.0001). CONCLUSION: Multislice multiecho T2* MRI provides a noninvasive, fast, reproducible means of assessing myocardial iron distribution. The single measurement of mid-septal T2* correlated well with the global T2* value.     

MR T2*加权成像和磁敏感加权成像在慢性肝病中的应用现状

肝纤维化是各种慢性肝病的共同特征。在肝纤维化-肝硬化-肝癌进程中,目前认为肝纤维化只有处于特定阶段时经抗纤维化治疗才可以逆转。早期诊断肝纤维化并对其严重程度进行评价,有利于抓住抗纤维化时机及时治疗,有望促进病程逆转。慢性肝病病人肝内存在异常铁沉积,MR T2*加权成像和磁敏感加权成像能检测铁沉积,可评估肝纤维化严重程度及诊断肝硬化和肝癌。就T2*加权成像和磁敏感加权成像在慢性肝病中的研究进展进行综述。     

Superparamagnetic iron oxide-enhanced liver magnetic resonance imaging: comparison of 1.5 T and 3.0 T imaging for detection of focal malignant liver lesions

OBJECTIVES: We sought to compare the image quality, lesion conspicuity, and the diagnostic performance of 1.5 T and 3.0 T superparamagnetic iron oxide-enhanced liver magnetic resonance imaging (MRI) for detecting focal malignant hepatic lesions. MATERIALS AND METHODS: A total of 35 patients with pathologically proven liver malignancy underwent both 1.5 and 3.0 T SPIO-enhanced MRI. The diagnostic accuracy was evaluated using the alternative-free response receiver operating characteristic method. Image artifacts, quality, and the lesion conspicuity were analyzed. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of the lesion were calculated. RESULTS: No significant difference of area under ROC curve (Az value) was noted. The mean SNR and CNR of the lesions was higher in the 3.0 T sets. There was no difference between the 1.5 T and the 3.0 T image sets for lesion conspicuity, but the image quality was better on 1.5 T. Motion and susceptibility artifacts were more frequent on 3.0 T. CONCLUSION: Diagnostic accuracies of the SPIO-enhanced MRI were equivalent on the 1.5 T and 3.0 T image sets. More prominent artifacts on 3.0 T superparamagnetic iron oxide-enhanced liver MRI counteracted advantage of higher SNR and CNR of 3.0 T.     

Distribution of cardiac iron measured by magnetic resonance imaging (MRI)-R*2

Purpose

To assess regional iron distribution by magnetic resonance imaging (MRI)‐R₂* within the heart of patients with β‐thalassemia major (TM) and other iron overload diseases.

Materials and Methods

Breathhold electrocardiogram (ECG)‐gated MRI (1.5 T) of the heart was used for the measurement of transverse relaxation rates R₂* in 32 patients (11–79 years). In a mid‐papillary short‐axis slice divided into septal, anterior, lateral, and posterior quadrants, R₂* was analyzed from region of interest (ROI)‐based signal intensities from 12 echo times (TE = 1.3–26 msec). Typical boundary effects were evaluated in detail.

Results

The segmentation of the cardiac wall resulted in highly significant correlations of R₂* between septal and all other quadrants. In the patient group with R₂* < 50 s^?1 (normal), all quadrants show higher normalized median rates (126%–174%) than the septum (P < 10^?4), while this was relatively smaller in the group with septal R₂* > 50 s^?1. Typical boundary effects on segmental R₂* from blood, lung tissue, epicardial fat, and hepatic iron could not be easily separated from segmental iron distribution.

Conclusion

The measurement of MRI‐R2* in the interventricular septum is the least affected method by boundary effects to detect patients with iron overload at risk of developing heart failure. J. Magn. Reson. Imaging 2010;32:1104–1109. © 2010 Wiley‐Liss, Inc.

     

Cine phase-contrast magnetic resonance imaging as a tool for quantification of skeletal muscle motion

In recent years, biomechanics researchers have increasingly used dynamic magnetic resonance imaging techniques, such as cine phase contrast (cine PC), to study muscle and bone motion in vivo. Magnetic resonance imaging provides a non-invasive tool to visualize the anatomy and measure musculoskeletal tissue velocities during joint motion. Current application of cine PC magnetic resonance imaging in biomechanics includes study of knee joint kinematics, tendon strain, and skeletal muscle displacement and shortening. This paper article reviews the use of cine PC magnetic resonance imaging for quantification of skeletal muscle motion. The imaging studies presented examine the relative motion of the knee flexor and extensor muscles after orthopedic surgery and examine the uniformity of shortening within the biceps brachii muscle. The current challenges and limitations of using cine PC magnetic resonance imaging in biomechanics research are addressed as well as opportunities for future studies of skeletal muscle motion using dynamic magnetic resonance imaging.     

Reproducibility and biological basis of in vivo T2* magnetic resonance imaging of liver metastasis of colorectal cancer

In this study, the reproducibility of MR imaging in colorectal liver metastases was assessed and values were correlated with the expression of the hypoxia‐related markers GLUT‐1 and CA‐IX as well as the relative vascular area, and the vessel density in resected tumors. The reproducibility of was analyzed in 18 patients with in total 22 colorectal liver metastases using the Bland and Altman method for the 16th, 50th, and 84th percentile values. Immunohistochemical staining was performed on 17 resected tumors obtained from 16 patients. The median of all liver metastases was 25.0 ± 5.6 ms vs. 23.0 ± 4.1 ms (median ± st.dev.) in normal liver. The coefficient of repeatability was 11.2 ms and the limits of agreement were ?13.2 ms and 9.1 ms for median values. On average, showed fair reproducibility. No correlations between values, hypoxia‐ and vascularity‐related markers were observed. Magn Reson Med, 70:1145–1152, 2013. © 2012 Wiley Periodicals, Inc.     

Hepatic magnetic resonance imaging with T2* mapping of ovariectomized rats: correlation between iron overload and postmenopausal osteoporosis

Objective

To explore the correlation between liver iron overload and bone mineral density (BMD) in an ovariectomy (OVX) rat model, using liver magnetic resonance (MR)-T2* and dual-energy X-ray absorptiometry (DEXA).

Methods

Sprague–Dawley rats received deferoxamine (DFO) or phosphate-buffered saline 3 months after bilateral OVX. MRI and DEXA were performed pre- and postoperatively. Five rats per group were killed every month for micro-CT, histopathology and biochemical examinations. Statistical analysis was performed with independent-samples t tests, box plots and Pearson’s correlation analysis.

Results

At 2 months postoperatively, BMD was significantly lower in the OVX group than in the control group (P?<?0.01), corresponding to the increased serum ferritin concentration (SFC; P?<?0.01) and liver iron concentration (LIC; P?<?0.01). Liver T2* values significantly differed between the two groups at 1 month postoperatively (P?<?0.001) and improved 1 month after DFO injection (P?<?0.05). These values were significantly and positively correlated with BMD in the control (r?=?0.527, P?<?0.001) and OVX (r?=?0.456, P?<?0.001) groups.

Conclusion

Liver MRI T2* changed markedly earlier than BMD, LIC and SFC, and correlated well with osteoporosis; it may thus be a valuable early indicator of osteoporosis.

Key Points

? Iron overload plays a vital role in the pathogenesis of postmenopausal osteoporosis. ? Liver T2* relaxation time is a sensitive value in reflecting iron overload. ? Liver T2* mapping elucidates changes in postmenopausal osteoporosis earlier than BMD. ? Iron chelation increases BMD in ovariectomized rats. ? Liver T2* has a moderate positive correlation with BMD.     

Hepatocellular carcinoma with marginal superparamagnetic iron oxide uptake on T2*-weighted magnetic resonance imaging: histopathologic correlation

Purpose

To evaluate the characteristics of hepatocellular carcinomas (HCCs) with marginal superparamagnetic iron oxide (SPIO) uptake on T2*-weighted MRI.

Materials and methods

The study group consisted of 73 patients with 83 surgically resected HCCs. Preoperative SPIO-enhanced MRI studies were retrospectively reviewed. Marginal SPIO uptake was considered positive if a rim-like or band-like low intensity area was present on SPIO-enhanced T2*-weighted images. The prevalence of marginal SPIO uptake was evaluated. Pathological specimens with hematoxylin and eosin staining and immunohistochemical staining of CD68 were reviewed in HCCs with marginal SPIO uptake and 33 HCCs without marginal SPIO uptake (control group).

Results

Ten of 83 (12%) HCCs showed marginal SPIO uptake. All HCCs were hypervascular, and only one nodule showed a nodule-in-nodule appearance on imaging findings. The pathology specimens suggested possible causes of marginal SPIO uptake, including marginal macrophage infiltration in moderately or poorly differentiated HCC (n = 4), residual normal hepatic tissue at the marginal area of confluent multinodular or single nodular with extranodular growth type HCC (n = 3), and a well-differentiated HCC component in nodule-in-nodule type HCC (n = 3). Marginal macrophage infiltration was not seen in the control group.

Conclusion

SPIO-enhanced MRI may be able to demonstrate marginal macrophage infiltration in HCC.     

Automatic motion correction for quantification of myocardial perfusion with dynamic magnetic resonance imaging.

Respiratory motion makes it difficult to quantify myocardial perfusion with dynamic magnetic resonance imaging (MRI). The purpose of this study was to evaluate an automatic registration method for motion correction for quantification of myocardial perfusion with dynamic MRI. The present method was based on the gradient-based method with robust estimation of displacement parameters. For comparison, we also corrected for motion with manual registration as the benchmark. The myocardial kinetic parameters, K1 (rate constant for transfer of contrast agent from blood to myocardium) and k2 (rate constant for transfer from myocardium to blood), were calculated from dynamic images with a two-compartment model. The images corrected by the present method were similar to those corrected by manual registration. The kinetic parameters obtained after motion correction with the present method were close to those obtained after motion correction with manual registration. These results suggest that the present method is useful for motion correction for quantification of myocardial perfusion with dynamic MRI.     

Hypointensities in the brain on T2*-weighted gradient-echo magnetic resonance imaging

The objectives of this review are to present various entities that can result in hypointensity on brain T2*-weighted gradient-echo (GE) images and to show the usefulness of this sequence. There are six etiologies, resulting in hypointensity on T2*-weighted GE images, ie, the presence of hemosiderin, deoxyhemogrobin, ferritin, calcium, other metals, and air. This sequence is sensitive to magnetic susceptibility effect and useful for detecting some kinds of small brain lesions and for differential diagnosis in some special conditions.     

Motion suppression improves quantification of rat liver volume in vivo by magnetic resonance imaging

In response to the presence of certain compounds, rat liver weight can increase. Under the assumption that the liver density does not change, the liver volume will increase as well. To develop the capability to monitor this process noninvasively over time, we used liver volumes determined from MR images to estimate the in vivo liver volumes and weights of normal rats. We acquired multislice, spin-echo images from 18 rats using several protocols for suppression of motion artifacts. We found that volumes determined from data obtained using a combination of gradient moment mulling and respiratory gating, or a combination of signal averaging and “retarded” (after the π pulse) phase-encoding, produced the most accurate estimates of in vivo liver volume and weight.     

Left ventricular diastolic function compared with T2* cardiovascular magnetic resonance for early detection of myocardial iron overload in thalassemia major

PURPOSE: To compare left ventricular (LV) diastolic function with myocardial iron levels in beta thalassemia major (TM) patients, using cardiovascular magnetic resonance (CMR). MATERIALS AND METHODS: We studied 67 regularly transfused patients with TM and 22 controls matched for age, gender, and body surface area. The early peak filling rate (EPFR) and atrial peak filling rate (APFR) were determined from high-temporal-resolution ventricular volume-time curves. Myocardial iron estimation was achieved using myocardial T2* measurements. RESULTS: Myocardial iron loading was found in 46 TM patients (69%), in whom the EPFR correlated poorly with T2* (r = -0.20, P = 0.19). The APFR (r = 0.49, P < 0.001) and EPFR/APFR ratio (r = -0.62, P < 0.001) correlated better with T2*. The sensitivity of the diastolic parameters for detecting myocardial iron loading ranged from 4% (EPFR and APFR) to 17% (EPFR/APFR ratio). CONCLUSION: Myocardial iron overload results in diastolic myocardial dysfunction, but low sensitivity limits the use of a single estimation for early detection of iron overload, for which T2* has a superior categorical limit of normality.     

Estimation of liver function using T2* mapping on gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid enhanced magnetic resonance imaging

Purpose

To investigate the usefulness of T2* mapping of liver on gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid (Gd-EOB-DTPA)-enhanced MRI for estimating liver function.

Materials and methods

33 patients were classified into 3 groups as follows: normal liver function (NLF) (n = 7); mild liver damage (MLD) (n = 16) with Child-Pugh A; severe liver damage (SLD) (n = 10) with Child-Pugh B. T2*-weighted gradient-echo (T2*W-GRE) and T1-weighted gradient-echo (T1W-GRE) images were obtained before and after Gd-EOB-DTPA administration (3, 8, 13, and 18 min; 5, 10,15, and 20 min; respectively). T2* mapping of liver was calculated from T2*W-GRE, then T2* values of liver and T2* reduction rates of T2* value between pre- and post-contrast enhancement were measured. The increase rates of liver-to-muscle signal intensity (LMS) ratio on T1W-GRE between pre- and post-contrast enhancement were calculated.

Results

T2* values on pre- and post-contrast showed no significant differences among three groups. Significant differences in T2* reduction rates were found among groups, and those of LCB were lower than those of other groups (NLF:MLD:SLD, 3.8:6.0:0.6% at 3 min, 8.2:10.3:1.0% at 8 min, 10.7:11.5:1.2% at 13 min, and 16.1:13.2:3.5% at 18 min, respectively) (P < 0.05). Significant differences in increase rates of LMS ratio on T1W-GRE were identified (NLF:MLD:SLD, 1.53:1.46:1.35 at 5 min, 1.68:1.64:1.37 at 10 min, 1.79:1.76:1.44 at 15 min, and 1.89:1.78:1.49 at 20 min, respectively).

Conclusion

T2* reduction rate and increase rate of LMS ratio on T1W-GRE may allow us estimation of liver function according to Child-Pugh score.     

An animal model for the study of liver regeneration by magnetic resonance imaging

Liver regeneration after partial hepatectomy was studied in rats by means of magnetic resonance (MR) imaging and T1 relaxation time. Fourteen hepatectomized rats were compared to sham operated ones and to controls which had not undergone any surgical treatment. The animals were imaged at 0.5 T, and inversion recovery (IR) technique was employed at the T-null of liver before surgery. T1 was determined in vitro with spectroscopy. Regenerating rat liver exhibited a significantly high increase in MR signal intensity and T1 values (p less than 0.05) 24 hours after surgery, returning to baseline values at 2 weeks. Sham operated animals and controls did not exhibit significant changes in signal intensity from baseline values (p greater than 0.05). These findings suggest that MR imaging is able to detect the pathophysiological changes occurring in liver parenchyma during the regenerating process and to monitor different stages of the hyperplastic process.     

Interscanner reproducibility of cardiovascular magnetic resonance T2* measurements of tissue iron in thalassemia

PURPOSE: To assess interscanner reproducibility of tissue iron measurements in patients with thalassemia using gradient echo T2* measurements on two different MRI scanners. MATERIALS AND METHODS: Twenty-five patients with thalassemia major had liver and myocardial T2* assessment using a Picker Edge 1.5T Scanner and a Siemens Sonata 1.5T scanner, with similar gradient echo sequences. In a subset of 13 patients, two scans on the Siemens scanner were performed to assess interstudy reproducibility. RESULTS: There was a highly significant, linear correlation between T2* values obtained for both the heart (r = 0.95) and the liver (r = 0.99) between scanners. The mean difference, coefficient of variability, and 95% confidence intervals between scanners were 0.8 msec, 9.4% and -5.0 to 6.7 msec for the heart; and 0.9 msec, 7.9% and -2.0 to 3.9 msec for the liver. The interstudy mean difference and coefficient of variability on the Siemens scanner was 0.3 msec and 4.8% (r = 0.99) for the heart, and 0.04 msec and 1.9% (r = 0.99) for the liver. CONCLUSION: The T2* technique for measuring tissue iron is reproducible between the two manufacturers' scanners. This suggests that the widespread implementation of the technique is possible for clinical assessment of myocardial iron loading in thalassemia.