Hepatic iron deposition on MR imaging in patients with chronic liver disease: correlation with serial serum ferritin concentration

Background: To evaluate the relationship between magnetic resonance (MR) imaging grading of iron deposition and serial serum ferritin concentration in patients with chronic viral liver diseases. Methods: In 80 patients with viral hepatitis and cirrhosis, MR images including T2*-weighted gradient echo images (echo time ≥ 6.5 ms) were reviewed. The grades of parenchymal iron deposition and iron-containing nodules in the liver and spleen and the liver-to-muscle and spleen-to-muscle signal intensity ratios were compared with the most recent, the mean, the lowest, and the highest values from all available serum ferritin levels. Results: The serum ferritin concentration was significantly correlated with the grades of iron deposition in liver and spleen and with the grades of iron-containing nodules seen on MR images (p < 0.05). Liver-to-muscle signal intensity ratio was weakly correlated with the ferritin concentrations. Among categories of ferritin concentration, correlation with MR grades was highest for mean ferritin concentration (r = 0.487, p < 0.001). Conclusion: MR imaging grades of hepatic iron and siderotic nodules correlate with serum ferritin, especially with the mean levels. Received: 9 May 2000/Accepted: 28 June 2000     

3.0T水脂分离梯度回波成像定量分析肝脏脂肪含量的可行性

目的 探讨3.0T水脂分离梯度回波序列在一次屏息内完成定量分析肝脏脂肪的可行性及其参数优化。方法 利用GE Signa HDx 3.0T MR系统对自制体模及42名受检者行迭代最小二乘法非对称采集水脂分离（IDEAL）梯度回波序列和单体素¹H-MRS,通过分析接收带宽（BW）、翻转角（FA）和矩阵（Matrix）的变化对体模脂肪定量分析的影响,确定以IDEAL梯度回波行脂肪定量分析的最优成像参数;以¹H-MRS测定的脂肪含量为参考标准,采用Spearman相关分析对IDEAL梯度回波序列测得数据进行相关性分析。结果 应用IDEAL梯度回波序列行体模脂肪定量分析时,BW和FA对结果的影响较大;BW为200 kHz、FA为12°时,体模脂肪定量分析结果与MRS的关联性最佳（r=0.997,P<0.05）,在此条件下,应用IDEAL梯度回波序列和¹H-MRS测得的肝脏脂肪含量分别为（9.48±5.42）%和（10.13±8.06）%,二者呈正相关（r=0.872,P<0.05）。结论 经参数优化的IDEAL梯度回波序列可在一次屏息内定量分析肝脏脂肪含量;成像时需合理调整FA和BW。     

Variable‐field relaxometry of iron‐containing human tissues: a preliminary study

Excess iron is found in brain nuclei from neurodegenerative patients (with Parkinson's, Alzheimer's and Huntington's diseases) and also in the liver and spleen of cirrhosis, hemochromatosis and thalassaemia patients. Ferritin, the iron‐storing protein of mammals, is known to darken T₂‐weighted MR images. Understanding NMR tissue behavior may make it possible to detect those diseases, to follow their evolution and finally to establish a protocol for non‐invasive measurement of an organ's iron content using MRI methods. In this preliminary work, the MR relaxation properties of embalmed iron‐containing tissues were studied as well as their potential correlation with the iron content of these tissues. Relaxometric measurements (T₁ and T₂) of embalmed samples of brain nuclei (caudate nucleus, dentate nucleus, globus pallidus, putamen, red nucleus and substantia nigra), liver and spleen from six donors were made at different magnetic fields (0.00023–14 T). The influence of the inter‐echo time on transverse relaxation was also studied. Moreover, iron content of tissues was determined by inductively coupled plasma atomic emission spectroscopy. In brain nuclei, 1/T₂ increases quadratically with the field and depends on the inter‐echo time in CPMG sequences at high fields, both features compatible with an outer sphere relaxation theory. In liver and spleen, 1/T₂ increases linearly with the field and depends on the inter‐echo time at all fields. In our study, a correlation between 1/T₂ and iron concentration is observed. Explaining the relaxation mechanism for these tissues is likely to require a combination of several models. The value of 1/T₂ at high field could be used to evaluate iron accumulation in vivo. In the future, confirmation of those features is expected to be achieved from measurements of fresh (not embalmed) human tissues. Copyright © 2009 John Wiley & Sons, Ltd.     

Compensated hepatitis C: unenhanced MR imaging correlated with pathologic grading and staging

Abstract Background We prospectively examined unenhanced MR imaging findings in relation to pathologic fibrosis, inflammation and steatosis in patients with compensated chronic hepatitis C viral infection (HCV). Methods Unenhanced MRI at 1.5 T was obtained within one month of core liver biopsy in 64 consecutive candidates for antiviral therapy for compensated HCV. Two pathologists independently graded inflammatory activity index (HAI) and steatosis, and staged fibrosis (grades 0–6). Morphologic MRI findings of cirrhosis, periportal lymph nodes, and MR fat signal ratio from dual gradient echo images were assessed independently by two radiologists blinded to clinical data. MRI and laboratory liver function results were correlated with pathologic results, using Spearman correlation coefficient and stepwise multiple regression. Results MR fat signal ratio correlation coefficient with pathologic steatosis was 0.71 (p < 0.0001). Coefficients with fibrosis stage were highest for surface nodularity (r _s = 47, p < 0.0001) and expanded gallbladder fossa (r _s = 0.42, p = 0.0006). Coefficients with HAI were highest for lymph node size (r _s = 0.355, p = 0.0040), surface nodularity (r = 0.47, p < 0.0001), expanded gallbladder fossa (r = 0.332, p = 0.0073), and caudate/right lobe ratio (r = 0.326, p = 0.0110). Combined lab and MRI variables provided the best prediction of fibrosis stage (r ² = 0.656) and HAI (r ² = 0.597). Conclusions A combination of MRI and laboratory findings was most predictive of fibrosis and inflammation.     

USPIO enhanced lymph node MRI using 3D multi‐echo GRE in a rabbit model

Ultrasmallsuperparamagnetic iron oxide (USPIO) has been suggested to be a negative MR contrast agent to detect metastatic lymph nodes. Previously reported studies have evaluated the diagnostic performance of USPIO‐enhanced MR lymph node imaging based on signal intensity. In this study, we investigate the specific performance of three different parametric approaches (normalized signal intensity, R₂* and susceptibility) using 3D multi‐echo gradient echo to quantify the USPIO particles in lymph nodes. Nine rabbits with VX2 tumor implants were scanned before and after USPIO injection. From 3D multi‐echo GRE magnitude and phase data, we generated multi‐echo combined T₂*‐weighted images, an R₂* map, and a quantitative susceptibility map. Eighteen lymph nodes (nine reactive and nine metastatic) were evaluated and showed remarkable signal drops in the area of USPIO accumulation. On parametric analysis, the R₂* difference before and after USPIO injection was significantly different (p < 0.05) between reactive and metastatic lymph nodes; in contrast, the normalized signal intensity and susceptibility were not significantly different between the nodes. Our study showed the potential utility of USPIO‐enhanced MRI using R2* mapping from 3D multi‐echo GRE for the detection of lymph node metastasis and parametric analysis of lymph node status in a rabbit model. Copyright © 2016 John Wiley & Sons, Ltd.     

同反相位图像减影技术及T2校正1H-MRS定量分析非酒精性脂肪肝的临床研究

目的：探讨双回波同反相位（IP-OP）减影法及T2校正1H-MRS定量分析非酒精性脂肪肝患者的肝脂肪含量（LFC）的可行性。方法：对42例临床怀疑脂肪肝的患者行3D T1WI IP-OP成像结合减影技术及1H-MRS检查。选取5名患者行多次回波PRESS序列以测量水、脂的T2值。采用非参数Spearman分析及Mann-Whitney U检验,比较评价两种影像方法定量分析脂肪肝的能力。结果：1H-MRS各峰值采用T2进行校正（T2水=33.1 ms,T2亚甲基=64.2 ms）。IP-OP减影法、1H-MRS对脂肪肝定性诊断的敏感度及特异度分别为89.2%、100%及91.2%、100%。IP-OP减影法及1H-MRS测得的脂肪含量与病理结果均呈显著的相关性（r=0.80,0.92;P＜0.01）。1H-MRS可有效区分无脂肪肝与轻度脂肪肝（Z=-2.97,P＜0.01）、轻度与中度脂肪肝（Z=-3.72,P＜0.01）、中度与重度脂肪肝（Z=-3.25,P＜0.01）,IP-OP减影法可有效区分无脂肪肝与轻度脂肪肝（Z=-2.54,P＜0.01）、轻度与中度脂肪肝（Z=-3.72,P＜0.01）,不能区分中度与重度脂肪肝（Z=-1.77,P=0.08）。1H-MRS、IP-OP减影法测得的LFC均低于病理结果（除无脂肪肝组外,Z≤-2.21,P＜0.05）。结论：IP-OP减影法可简单快速的诊断脂肪肝程度,1H-MRS对脂肪肝的定量诊断具有更高的准确性。     

Effect of magnetic field and iron content on NMR proton relaxation of liver,spleen and brain tissues

Iron accumulation is observed in liver and spleen during hemochromatosis and important neurodegenerative diseases involve iron overload in brain. Storage of iron is ensured by ferritin, which contains a magnetic core. It causes a darkening on T₂‐weighted MR images. This work aims at improving the understanding of the NMR relaxation of iron‐loaded human tissues, which is necessary to develop protocols of iron content measurements by MRI. Relaxation times measurements on brain, liver and spleen samples were realized at different magnetic fields. Iron content was determined by atomic emission spectroscopy. For all samples, the longitudinal relaxation rate (1/T₁) of tissue protons decreases with the magnetic field up to 1 T, independently of iron content, while their transverse relaxation rate (1/T₂) strongly increases with the field, either linearly or quadratically, or a combination thereof. The extent of the inter‐echo time dependence of 1/T₂ also varies according to the sample. A combination of theoretical models is necessary to describe the relaxation of iron‐containing tissues. This can be due to the presence, inside tissues, of ferritin clusters of different sizes and densities. When considering all samples, a correlation (r² = 0.6) between 1/T₁ and iron concentration is observed at 7.0 T. In contrast the correlation between 1/T₂ and iron content is poor, even at high field (r² = 0.14 at 7.0 T). Our results show that MRI methods based on T₁ or T₂ measurements will easily detect an iron overloading at high magnetic field, but will not provide an accurate quantification of tissue iron content at low iron concentrations. Copyright © 2014 John Wiley & Sons, Ltd.     

磁共振T1 mapping、T2 mapping评估大鼠肝纤维化和肝脂肪变性

目的 采用磁共振T1 mapping、T2 mapping评估大鼠肝纤维化和肝脂肪变性，观察其应用价值。方法 将80只大鼠随机分成实验组（n=70）对照组（n=10）， 分别于背部注射四氯化碳橄榄油溶液及生理盐水，制作大鼠肝纤维化模型。于注药后第4、6、8、10和12周，分别随机选取实验组14只和对照组2只大鼠采集MRI，测量肝实质T1值和T2值，并行组织病理检查。根据病理结果将大鼠肝纤维化划分为S₀~S₄期，脂肪变性划分为F₀~F₄度，比较肝纤维化各期T1值和T2值，分析其与肝纤维化及肝脂肪变性相关性。结果 S₀期大鼠肝脏T1值和T2值与肝纤维化各期差异有统计学意义（P均<0.05），S₁期[（402.01±57.14）ms]肝实质T1值较S₃期[（514.83±87.10）ms]和S₄期[（518.72±36.50）ms]短（P均<0.05），S₂期[（417.49±47.00）ms]肝实质T1值较S₄期短（P<0.05）；S₁期[（65.12±9.46）ms]肝实质T2值较S₄期[（55.33±7.30）ms]略延长（P<0.05）。T1值与肝纤维化程度呈正相关（r=0.68，P<0.01），T2值与脂肪变性程度呈正相关（r=0.72，P<0.01）。结论 磁共振T1 mapping可无创评估大鼠肝纤维化，T2 mapping可无创评估大鼠肝脂肪变性，有望为临床诊断肝纤维化和肝脂肪变性提供新的影像学方法。     

The efficacy of tissue Doppler imaging in predicting myocardial iron load in patients with beta-thalassemia major: correlation with T2* cardiovascular magnetic resonance

Tissue Doppler imaging (TDI) can detect myocardial dysfunction related to iron load in patients with beta-thalassemia major (TM). We aimed to assess the efficacy of pulsed-wave TDI (PW-TDI) in predicting myocardial iron load in patients with TM using T2* magnetic resonance (MR) as the gold-standard non-invasive diagnostic test. 33 asymptomatic TM patients, mean aged 18 ± 6 years (6–31) with normal left ventricular (LV) global systolic function were evaluated by conventional echocardiography and PW-TDI. Results were compared with 20 age and sex-matched controls. TDI measures included myocardial systolic (Sm), early (Em) and late (Am) diastolic velocities at basal and middle segments of septal and lateral LV wall. Myocardial iron deposition were measured in 29/33 patients by T2* MR. TM patients were also subgrouped according to those with iron load (T2* ≤ 20 ms) and those without (T2* > 20 ms). Mean T2* was 12.3 ± 7.8 ms (4–31.3). Abnormal myocardial iron load (T2* < 20 ms) was found in 25/29 (86%) patients. The following TDI measures were lower in patients than in controls: basal septal Em (P < 0.001) and Am (P < 0.05), mid-septal Am (P < 0.05), mid-lateral LV wall Sm (P < 0.05) and Am (P < 0.05). Regional myocardial dysfunction were more prominent in patients with T2* ≤ 20 ms. Mid-septal Sm and Em significantly correlated with mid-septal T2*(r = 0.44, P = 0.023 and r = 0.54, P = 0.004, respectively). The PW-TDI parameters and the cut-off values for predicting presence of myocardial iron load were determined. PW-TDI technique was found both sensitive and specific in predicting presence of myocardial iron load in TM patients with normal LV global systolic function. Therefore, it can be used for screening of TM patients.     

Ultrasound Attenuation Estimation in Harmonic Imaging for Robust Fatty Liver Detection

Accurate detection of liver steatosis is important for liver disease management. Ultrasound attenuation coefficient estimation (ACE) has great potential in quantifying liver fat content. The commonly used ACE methods (e.g., spectral shift methods, reference phantom methods) assume linear tissue response to ultrasound and were developed in fundamental imaging. However, fundamental imaging may be vulnerable to reverberation clutters introduced by the body wall. The clutters superimposed on liver echoes may bias the attenuation estimation. Here we propose a new ACE technique, the reference frequency method (RFM), in harmonic imaging to mitigate the reverberation bias. The accuracy of harmonic RFM was validated through a phantom study. In a pilot patient study, harmonic RFM performed more robustly in vivo compared with fundamental RFM, illustrating the potential of ACE in harmonic imaging.     

Detection of hepatocellular carcinoma and its metastases with various pulse sequences using superparamagnetic iron oxide (SHU-555-A)

Background: To identify the most useful combinations of various pre- and postcontrast magnetic resonance (MR) image sequences in detecting hepatocellular carcinoma (HCC) and its intrahepatic metastases before and after injection of SHU-555-A. Methods: Thirty-eight lesions in 16 patients were evaluated before and after administration of SHU-555-A by using fast spin echo (FSE), gradient echo (GRE), and echo planar (EP) imaging sequences using a 1.5-Tesla superconducting MR system. The signal intensity ratio (SIR) and contrast-to-noise ratio (CNR) of the lesions, signal-to-noise ratios, and other parameters were calculated. Results: Tumors were better detected after injection of SHU-555-A on all pulse sequences except on out-of-phase T1-weighted (T1W)-GRE sequences. Tumor detectability was higher for precontrast EP imaging and T2*-weighted (T2*W)-GRE sequences, whereas detectability at postcontrast was higher for T2*W-GRE, proton-density-weighted-FSE, and in-phase T1W-GRE sequences. The SIR and CNR at precontrast were highest for EP imaging, and those at postcontrast were highest for T2*W-GRE. Conclusion: SHU-555-A will increase the detectability of HCC and its liver metastases. T1W- and T2*W-GRE sequences would be the sequences of choice. Received: 21 December 1998/Revision accepted: 5 May 1999     

基于多回波肝脏内插容积激发成像评价大鼠非酒精性脂肪肝的初步研究

目的观察多回波肝脏内插容积激发成像(mLIVE)诊断非酒精性脂肪肝大鼠的价值。方法选取64只雌性SD大鼠,随机分为实验组(n=40)及对照组(n=24),实验组喂饲高脂饮食、对照组给予普通饲喂。于饲养4周后每周选取5只实验组和3只对照组大鼠行肝脏MR、组织病理检查及测定脂肪含量,对mLIVE成像测得的2组大鼠肝脏脂肪分数(FF)与病理结果及肝脏脂肪含量进行比较。结果对照组和实验组平均FF分别为(5.67±0.69)%和(10.48±3.24)%(P<0.05)。实验组11只轻度脂肪肝,16只中度脂肪肝,9只重度脂肪肝,平均FF分别为(7.99±1.48)%,(10.38±1.70)%和(13.71±4.33)%,两两比较差异均具有统计学意义(P<0.05)。2组大鼠肝脏平均脂肪含量分别为(18.83±6.29)nmol/mg和(50.44±20.24)nmol/mg(P<0.05),肝脏FF与脂肪含量呈显著正相关(r=0.74,P<0.001),直线回归方程为y=4.22+0.13 x。结论mLIVE成像可定量分析非酒精性脂肪肝大鼠肝脏脂肪含量,可用于评估脂肪肝。     

Myocardial and hepatic T2* magnetic resonance evaluation in ex-thalassemic patients after bone-marrow transplantation

Bone marrow transplantation (BMT) is the only complete cure for b-thalassemia. Iron depletion therapy is still required to remove excess iron, accumulated before BMT. Hepatic and myocardial iron load were evaluated using T2* magnetic resonance in 8 ex-thalassemic patients after BMT, aged 19.5 ± 4.25 years, who were in iron depletion therapy. Average hepatic T2* was 18.8 ± 11.0 msec (4.1–35.0 msec). In 4 out of 8 patients iron overload was detected, not exceeding however 4 mg/gr dry tissue. Average heart T2* was 31.0 ± 4.6 msec (25.6–35.2 msec), not significantly different (P = 0.18) from our age-matched normal population (33.0 ± 4.0). Normal left ventricular ejection fraction was found in 7 out of 8 patients (mean 64.5 ± 7.0%) with the remaining having a marginal value of 54.1%. Ferritin level before BMT was 1748 ± 451 μg/l and dropped to 536 ± 260 μg/l at the end of iron depletion therapy after BMT. Current ferritin level was 271 ± 253 μg/l and although it was significant lower compared to both ferritin before BMT (P < 0.001) and after iron depletion (P < 0.001), evidence of residual hepatic iron load was identified by T2*. Hepatic and myocardial T2* magnetic resonance can be used as a more reliable index than ferritin for evaluation of iron depletion therapy in ex-thalassemic patients after BMT.     

磁共振定量技术评估肝脏铁过载的研究进展

肝脏铁过载是遗传性血色素沉着症和输血性含铁血黄素沉着症的主要组织学特征,如果不进行治疗,过量的铁可导致肝损伤并缓慢发展为肝硬化和肝细胞癌。因此,肝铁浓度的评估对于铁过载的检测和定量分级以及铁螯合治疗的监测是至关重要的。金标准肝活检是有创性的,并且容易出现采样偏差,而MRI技术的非侵入性以及对铁的高敏感性使其成为广为使用的方法。本文将对信号强度比法、T2/R2弛豫法、磁共振波谱成像、T2*/R2*弛豫法、超短回波时间成像技术及定量磁化率成像评估肝铁定量的研究进展进行综述。     

Fat in liver metastasis from renal cell carcinoma detected by chemical shift MR imaging

A case with liver metastasis from papillary renal cell carcinoma (RCC) is presented, in which intratumoral fat was detected on dual-echo chemical shift magnetic resonance imaging (MRI). The preoperative chemical shift MR image of the primary RCC also suggested the presence of intratumoral fat. Liver metastasis from fat-containing RCC should be included in the differential diagnosis of fat-containing liver masses as observed on chemical shift MRI.     

Evaluation of the novel USPIO GEH121333 for MR imaging of cancer immune responses

Tumor‐associated macrophages (TAM) maintain a chronic inflammation in cancers, which is associated with tumor aggressiveness and poor prognosis. The purpose of this study was to: (1) evaluate the pharmacokinetics and tolerability of the novel ultrasmall superparamagnetic iron oxide nanoparticle (USPIO) compound GEH121333; (2) assess whether GEH121333 can serve as a MR imaging biomarker for TAM; and (3) compare tumor MR enhancement profiles between GEH121333 and ferumoxytol. Blood half‐lives of GEH121333 and ferumoxytol were measured by relaxometry (n = 4 each). Tolerance was assessed in healthy rats injected with high dose GEH121333, vehicle or saline (n = 4 each). Animals were monitored for 7 days regarding body weight, complete blood counts and serum chemistry, followed by histological evaluation of visceral organs. MR imaging was performed on mice harboring MMTV‐PyMT‐derived breast adenocarcinomas using a 7 T scanner before and up to 72 h post‐injection (p.i.) of GEH121333 (n = 10) or ferumoxytol (n = 9). Tumor R₁, R₂* relaxation rates were compared between different experimental groups and time points, using a linear mixed effects model with a random effect for each animal. MR data were correlated with histopathology. GEH121333 showed a longer circulation half‐life than ferumoxytol. Intravenous GEH121333 did not produce significant adverse effects in rats. All tumors demonstrated significant enhancement on T₁, T₂ and T₂*‐weighted images at 1, 24, 48 and 72 h p.i. GEH121333 generated stronger tumor T₂* enhancement than ferumoxytol. Histological analysis verified intracellular compartmentalization of GEH121333 by TAM at 24, 48 and 72 h p.i. MR imaging with GEH121333 nanoparticles represents a novel biomarker for TAM assessment. This new USPIO MR contrast agent provides a longer blood half‐life and better TAM enhancement compared with the iron supplement ferumoxytol. Copyright © 2013 John Wiley & Sons, Ltd.     

Prenatal diagnosis of idiopathic neonatal hemochromatosis with MRI

Intrauterine diagnosis of perinatal hemochromatosis is difficult. Noninvasive detection of hepatic iron deposition is crucial. We report the first case diagnosed intrauterine with magnetic resonance imaging (MRI). By visual analysis, if the fetal liver is less intense than maternal or fetal fat signal for T2* gradient echo image, hemochromatosis should be suggested.     

Can MR elastography be used to measure liver stiffness in patients with iron overload?

Untreated hepatic iron overload causes hepatic fibrosis and cirrhosis and can predispose to hepatocellular carcinoma. MR elastography (MRE) provides a non-invasive means to measure liver stiffness, which correlates with liver fibrosis but standard gradient recalled echo (GRE)-based MRE techniques fail in patients with high iron due to very low hepatic signal. Short echo time (TE) 2D spin echo echoplanar imaging (SE-EPI)-based MRE may allow measurement of stiffness in the iron loaded liver. The purpose of this study was to describe the use of such an MRE sequence in patients undergoing liver iron quantification by MRI. In our preliminary study of 43 patients with mean LIC of 9.3 mg/g (range 1.8–21.5 mg/g), liver stiffness measurements could be made in 77% (33/43) of patients with a short TE, SE-EPI based MRE sequence. On average, mean LIC in patients with failed MRE was higher than in those with successful MRE (15.9 mg/g dry weight vs. 7.3 mg/g), but a cut-off value for successful MRE could not be established. Seven patients (21% of those with successful MRE) had liver stiffness values suggestive of the presence of significant fibrosis (> 2.49 kPa). A short TE, SE-EPI based MR elastography sequence allows successful measurement of liver stiffness in a majority of patients with liver iron loading, potentially allowing non-invasive screening for fibrosis.

     

Susceptibility induced gray-white matter MRI contrast in the human brain

MR phase images have shown significantly improved contrast between cortical gray and white matter regions compared to magnitude images obtained with gradient echo sequences. A variety of underlying biophysical mechanisms (including iron, blood, myelin content, macromolecular chemical exchange, and fiber orientation) have been suggested to account for this observation but assessing the individual contribution of these factors is limited in vivo.For a closer investigation of iron and myelin induced susceptibility changes, postmortem MRI of six human corpses (age range at death: 56-80 years) was acquired in situ. Following autopsy, the iron concentrations in the frontal and occipital cortex as well as in white matter regions were chemically determined. The magnetization transfer ratio (MTR) was used as an indirect measure for myelin content. Susceptibility effects were assessed separately by determining R2* relaxation rates and quantitative phase shifts. Contributions of myelin and iron to local variations of the susceptibility were assessed by univariate and multivariate linear regression analysis.Mean iron concentration was lower in the frontal cortex than in frontal white matter (26 ± 6 vs. 45 ± 6 mg/kg wet tissue) while an inverse relation was found in the occipital lobe (cortical gray matter: 41 ± 10 vs. white matter: 34 ± 10 mg/kg wet tissue). Multiple regression analysis revealed iron and MTR as independent predictors of the effective transverse relaxation rate R2* but solely MTR was identified as source of MR phase contrast. R2* was correlated with iron concentrations in cortical gray matter only (r = 0.42, p < 0.05).In conclusion, MR phase contrast between cortical gray and white matter can be mainly attributed to variations in myelin content, but not to iron concentration. Both, myelin and iron impact the effective transverse relaxation rate R2* significantly. Magnitude contrast is limited because it only reflects the extent but not the direction of the susceptibility shift.     

Reproducibility of Semi-quantitative Parameters in FDG-PET Using Two Different PET Scanners: Influence of Attenuation Correction Method and Examination Interval

Purpose The aim of this study is to evaluate the reproducibility of semi-quantitative parameters obtained from two 2-deoxy-2-[F-18]fluoro-d-glucose-positron emission tomography (FDG–PET) studies using two different PET scanners. Methods Forty-five patients underwent FDG–PET examination with two different PET scanners on separate days. Two PET images with different attenuation correction method were generated in each patient, and three regions of interest (ROIs) were placed on the lung tumor and normal organs (mediastinum and liver) in each image. Mean and maximum standardized uptake values (SUVs), tumor-to-mediastinum and tumor-to-liver ratios (T/M and T/L), and the percentage difference in parameters between two PET images (% Diff.) were compared. Results All measured values except maximum SUV in the liver and tumor-related parameters (SUV in lung tumor, T/M, T/L) showed no significant difference between two PET images. Conclusion The mean measured values showed high reproducibility and demonstrate that follow-up study or measurement of tumor response to anticancer drugs can be undertaken by FDG–PET examination without specifying the particular type of PET scanner.