Comparative study of the sensitivity of ADC value and T2 relaxation time for early detection of Wallerian degeneration

Background and purpose

Wallerian degeneration (WD), the secondary degeneration of axons from cortical and subcortical injuries, is associated with poor neurological outcome. There is some quantitative MR imaging techniques used to estimate the biologic changes secondary to delayed neuronal and axonal losses. Our purpose is to assess the sensitivity of ADC value and T₂ relaxation time for early detection of WD.

Methods

Ten male Sprague-Dawley rats were used to establish in vivo Wallerian degeneration model of CNS by ipsilateral motor-sensory cortex ablation. 5 days after cortex ablation, multiecho-T₂ relaxometry and multi-b value DWI were acquired by using a 7 T MR imaging scanner. ADC-map and T₂-map were reconstructed by post-processing. ROIs are selected according to pathway of corticospinal tract from cortex, internal capsule, cerebral peduncle, pons, medulla oblongata to upper cervical spinal cord to measure ADC value and T₂ relaxation time of healthy side and affected side. The results were compared between the side with cortical ablation and the side without ablation.

Results

Excluding ablated cortex, ADC values of the corticospinal tract were significantly increased (P < 0.05) in affected side compared to the unaffected, healthy side; no difference in T₂ relaxation time was observed between the affected and healthy sides. Imaging findings were correlated with histological examinations.

Conclusion

As shown in this animal experiment, ADC values could non-invasively demonstrate the secondary degeneration involving descending white matter tracts. ADC values are more sensitive indicators for detection of early WD than T₂ relaxation time.     

MR T1 and T2 relaxations in cysts and abscesses measured by 1.5 T MRI

Objectives

The main objective of this study was to make a comparison between the relaxation rates in jaw cysts and abscesses. Such a comparison should provide quantitative information for MR image analysis.

Methods

A phantom containing 20 odontogenic jaw cysts and 11 jaw abscesses was imaged with 1.5 T MR. T₁ measurements were performed by using a mixed sequence of inversion recovery and spin echo, while T₂ measurements were carried out by the Carr–Purcell Meiboom–Gill (CPMG) sequence. Cystic fluids and abscesses were compared statistically.

Results

In cysts and abscesses, respectively, the mean 1/T₁ was 0.9355 s⁻¹ and 0.8245 s⁻¹ and the mean 1/T₂ was 2.4575 s⁻¹ and 4.7073 s⁻¹. The 1/T₂ in cysts was very highly significantly different from that in abscesses (p = 0.0001). Both T₁ and T₂ were linearly proportional to material contents. T₂ relaxivities [26.458 ml (g s)⁻¹ for abscesses and 21.455 ml (g s)⁻¹ for cysts] were higher than T₁ relaxivities [5.4766 ml (g s)⁻¹ for abscesses and 10.075 ml (g s)⁻¹ for cysts].

Discussion

Present T₂ measurements differentiate cysts from abscesses with a confidence interval of 95%. Because in vivo and in vitro image contrasts are changed by the same parameters, the T₂ findings should present valuable information for in vivo MRI. Hence the significant difference and the relaxivities may provide quantitative information for clinicians and researchers making image analyses.

Conclusion

T₂ may differentiate cysts from abscesses. The difference in T₂ is related to the material content of samples.     

Clinical Importance of Myocardial T2 Mapping and Texture Analysis

Late gadolinium enhancement (LGE) magnetic resonance imaging (MRI) is valuable for diagnosis and assessment of the severity of various myocardial diseases owing to its potential to visualize myocardial scars. T₁ mapping is complementary to LGE because it can quantify the degree of myocardial fibrosis or edema. As such, T₁-weighted imaging techniques, including LGE using an inversion recovery sequence, contribute to cardiac MRI. T₂-weighted imaging is widely used to characterize the tissue of many organs. T₂-weighted imaging is used in cardiac MRI to identify myocardial edema related to chest pain, acute myocardial diseases, or severe myocardial injuries. However, it is difficult to determine the presence and extent of myocardial edema because of the low contrast between normal and diseased myocardium and image artifacts of T₂-weighted images and the lack of an established method to quantify the images. T₂ mapping quantifies myocardial T₂ values and help identify myocardial edema. The T₂ values are significantly related to the clinical symptoms or severity of nonischemic cardiomyopathy. Texture analysis is a postprocessing method to quantify tissue alterations that are reflected in the T₂-weighted images. Texture analysis provides a variety of parameters, such as skewness, entropy, and grey-scale non-uniformity, without the need for additional sequences. The abnormal signal intensity on T₂-weighted images or T₂ values may correspond to not only myocardial edema but also other tissue alterations. In this review, the techniques of cardiac T₂ mapping and texture analysis and their clinical relevance are described.     

Evaluation of T2 values and apparent diffusion coefficient of the masseter muscle by clenching

Objective

: The aim of this study was to evaluate the changes in T₂ values and apparent diffusion coefficient (ADC) in the masseter muscle by clenching in healthy volunteers.

Methods

: 37 volunteers were enrolled in the study. We measured bite force using pressure-sensitive paper and a T₂ map. The ADC map was obtained at rest, during clenching, immediately after and 5 min after clenching. The spin-echo sequence was used to calculate T₂, and single-shot spin-echo echo planar imaging was used to calculate the ADC. The motion-probing gradients (MPGs) were applied separately along the posterior-to-anterior (PA), right-to-left (RL) and superior-to-inferior (SI) directions, with b values of 0, 300 and 600 s mm^–2 in each direction. ADC-PA, ADC-RL, and ADC-SI values were obtained, and we calculated the ADC-iso for the mean diffusivity.

Results

: There were no significant differences between the stronger and weaker sides of bite force before, during or 5 min after clenching for T₂ and ADC. The bite force had little effect on these parameters; thus, we used the average of the two sides for the following analyses. Time course analysis of ADC-iso, ADC-PA, ADC-RL and ADC-SI demonstrated a marked increase after clenching and a rapid decrease immediately after clenching, although they did not completely return to the initial values; however, the change in ADC-RL was significantly greater than those in ADC-PA or ADC-SI (P < 0.001 each). The changes in T₂ were similar to those of ADC, although not as marked.

Conclusions

: ADC (especially ADC-RL) was altered by contraction of the masseter muscle.     

Histological correlation of 7 T multi-parametric MRI performed in ex-vivo Achilles tendon

Introduction

The goal of this in vitro validation study was to investigate the feasibility of biochemical MRI techniques, such as sodium imaging, T₂ mapping, fast imaging with steady state precession (FISP), and reversed FISP (PSIF), as potential markers for collagen, glycosaminoglycan and water content in the Achilles tendon.

Materials and methods

Five fresh cadaver ankles acquired from a local anatomy department were used in the study. To acquire a sodium signal from the Achilles tendon, a 3D-gradient-echo sequence, optimized for sodium imaging, was used with TE = 7.71 ms and TR = 17 ms. The T₂ relaxation times were obtained using a multi-echo, spin-echo technique with a repetition time (TR) of 1200 ms and six echo times. A 3D, partially balanced, steady-state gradient echo pulse sequence was used to acquire FISP and PSIF images, with TR/TE = 6.96/2.46 ms. MRI parameters were correlated with each other, as well as with histologically assessed glycosaminoglycan and water content in cadaver Achilles tendons.

Results

The highest relevant Pearson correlation coefficient was found between sodium SNR and glycosaminoglycan content (r = 0.71, p = 0.007). Relatively high correlation was found between the PSIF signal and T₂ values (r = 0.51, p = 0.036), and between the FISP signal and T₂ values (r = 0.56, p = 0.047). Other correlations were found to be below the moderate level.

Conclusion

This study demonstrated the feasibility of progressive biochemical MRI methods for the imaging of the AT. A GAG-specific, contrast-free method (sodium imaging), as well as collagen- and water-sensitive methods (T₂ mapping, FISP, PSIF), may be used in fast-relaxing tissues, such as tendons, in reasonable scan times.     

Global and regional reproducibility of T2 relaxation time measurements in human patellar cartilage.

Seven T2 maps (multiecho (ME) sequence: 3000 ms, eight echoes with 13.2 ms of echo spacing, 20 sections) and T1-weighted (T1-w) fast low-angle shot (FLASH-water excitation (WE)) data sets from four imaging sessions (right patellae of 10 healthy volunteers) were obtained. A segmentation of cartilage (WE sequence) was overlaid on the ME data and T2 values were calculated for total cartilage, three layers, three facets (global), and 240 ROIs (regional). Reproducibility (precision error) was calculated as the root mean square average (RMSA) of the individual coefficients of variation (COVs, %) and standard deviations (SDs, ms) for intra- and intersession reproducibility. The precision error was 3-7% and 6-29% for global and regional T2, respectively. There was no difference between intra- and intersession reproducibility, but there was worse reproducibility in the superficial layers compared to the deeper layers. Peripheral ROI reproducibility (mean=13%) was worse than in the central portions (mean=11%), but omission of the periphery did not positively affect the globally calculated T2 reproducibility. The precision errors were small compared to reported changes in diseased cartilage, suggesting good discriminatory power of the technique. Our data provide a first estimate of global and regional reproducibility errors of T2 in healthy cartilage, and may serve as a basis for sample size calculations and aid study designs for longitudinal and cross-sectional trials in osteoarthritis (OA).     

Bladder tumour staging: comparison of diffusion- and T2-weighted MR imaging

The aim of this work was to evaluate the clinical feasibility of diffusion-weighted (DW) MRI in detection and staging of urinary bladder tumour and to compare DW MRI with the T₂-weighted technique. One hundred and six patients with bladder tumour were prospectively included in our study. All patients were evaluated with MR imaging. We started with axial T₂-weighted high resolution MR of the urinary bladder, then DW MRI. Two radiologists independently interpreted the MR images, and discrepancies were resolved by consensus. The accuracy of DW MRI in staging of bladder tumour was evaluated using the final histopathological findings. In DW imaging (DWI) staging accuracy was 63.6% and 69.6% in differentiating superficial from invasive tumours and organ-confined from non-organ-confined tumours, respectively. On a stage by a stage basis, DWI accuracy was 63.6% (21/33), 75.7% (25/33), 93.7% (30/32) and 87.5% (7/8) for stages T1, T2, T3 and T4, respectively. In the T₂-weighted technique, the overall staging accuracy was only 39.6% and accuracy for differentiating superficial from invasive tumours and organ-confined from non-organ-confined tumours was 6.1% and 15.1%, respectively. DW is superior to T₂-weighted MRI in staging of organ-confined tumours (≤T2) and both techniques are comparable in the evaluation of higher-stage tumours.     

Multiexponential T2 relaxation in degenerating peripheral nerve

The multiexponential T₂ relaxation spectrum of peripheral nerve undergoing Wallerian degeneration has been measured both in vivo and in vitro. Degeneration of the sciatic nerve of the amphibian Xenopus laevis was induced by crush injury, and T₂ relaxation spectra of the nerve were measured at several times up to 35 days following injury. Histologic evidence verified that the nerve underwent Wallerian degeneration. Relaxation spectra were observed to undergo measurable changes as degeneration progressed, the most evident being a reduction from three well-resolved T₂ components to one and a decline in the fraction of the spectra associated with the shortest T₂ component The former appears to reflect the collapse and loss of myelinated fibers, while the latter a combination of interstitial edema and myelin loss.     

结直肠癌肝转移瘤的CT动态增强强化特点及病灶分布规律

目的：探讨结直肠癌肝转移瘤的 CT 动态增强强化特点和病灶分布规律。方法：回顾性分析120例结直肠癌肝转移瘤患者的 CT 动态增强图像及临床资料,记录肿瘤原发灶部位、肝转移瘤的位置和数目、肝转移瘤的不同时相的强化特点及肠系膜下静脉汇入门静脉的位置。结果：CT 动态增强共检出肝内病灶486个,其中表现为环状强化灶245个（50．4％）,结节状强化灶183个（37．7％）,其他不典型强化灶58个（11．9％）。原发病灶位于右半结肠（右半结肠组）时,其转移灶在肝左、右叶的分布差异有统计学意义（P ＜0．05）。原发病灶位于左半结肠（左半结肠组）时,其转移灶在肝左、右叶的分布差异无统计义（P ＞0．05）。排除转移灶均匀分布于肝左、右叶的病例后,右半结肠组与左半结肠组肝转移灶的分布差异无统计学意义（P ＞0．05）。左半大肠癌肝转移患者中,肠系膜下静脉（IMV）汇入脾静脉（SPV）者34例,其转移灶在肝左、右叶的分布差异有统计学意义（P ＜0．05）。IMV 汇入肠系膜上静脉（SMV）者32例,其转移灶在肝左、右叶的分布差异有统计学意义（P ＜0．05）。IMV 汇入 SPV 与 SMV 汇合处者11例,其转移灶在肝左、右叶的分布差异无统计学意义（P ＞0．05）。结论：结直肠癌肝转移瘤的 CT 动态增强图像有一定特点,结直肠癌肝转移瘤的病灶分布有一定规律,了解这些情况有助于提高结直肠癌肝转移瘤的检出率和诊断符合率,减少误诊率。     

经门静脉栓塞化疗术与经肝动脉化疗栓塞术治疗结直肠癌肝转移瘤临床效果比较

目的：研究经门静脉栓塞化疗术（PVCE）治疗结直肠癌肝转移瘤的疗效、生存期及并发症。 方法：80例明确诊断的结直肠癌肝转移瘤患者,分成两组,PVCE组40例,行PVCE术。另外40例行经肝动脉化疗栓塞术（TACE组）。 结果：PVCE组临床有效率为82.5%,高于TACE组的55.0%,差异有统计学意义。PVCE组40例患者6、12、24个月的生存率分别为：92.5%、62.5%及40.0%,TACE组40例患者6、12、24个月的生存率分别为75.0%、52.5%及22.5%。PVCE组生存情况优于TACE组。 结论：经门静脉介入治疗结直肠癌肝转移瘤疗效确切,生存期优于经肝动脉介入治疗。     

T2-FLAIR Mismatch Sign Is Caused by Long T1 and T2 of IDH-mutant, 1p19q Non-codeleted Astrocytoma

T₂-fluid-attenuated inversion recovery images (FLAIR) mismatch sign is now known to be a specific yet insensitive image feature for IDH-mutant, 1p19q non-codeleted astrocytoma. The current study revealed that lesion presenting T₂-FLAIR mismatch exhibited extremely long T₁- and T₂-relaxation time while T₂-FLAIR matched lesions showed low to moderate values. On the other hand, IDH-wildtype tumors presented noticeably short T₁- and T₂-relaxation time. These different relaxation time characteristics seemed to render T₂-FLAIR mismatch sign of becoming such a unique and specific image feature for IDH-mutant, 1p19q non-codeleted astrocytoma.     

帕金森病患者脑灰质核团T_2弛豫时间的初步研究

目的:通过对比正常对照组与帕金森病患者脑灰质核团T2弛豫时间,定量分析帕金森病T2弛豫时间的变化规律。方法:选取17例帕金森病患者及20例健康志愿者,定量测量脑双侧CA、PM、GP、SNc的T2弛豫时间,将帕金森病患肢对侧和未出现症状肢体对侧相对应部位的CA、PM、GP、SNc的T2弛豫时间进行对比分析,并分别与正常对照组进行比较。结果:帕金森病组SNc的T2弛豫时间较正常对照组缩短(P0.05),GP的T2弛豫时间较正常对照组升高(P0.05),但在PD患者患肢对侧和同侧之间无显著性差异(P值0.05)。结论:帕金森病患者脑SNc的T2弛豫时间降低,GP的T2弛豫时间升高,T2弛豫时间定量测量可以作为PD的一种无创性检测方法。     

Comparison of acquired diffusion weighted imaging and computed diffusion weighted imaging for detection of hepatic metastases

Objective

To compare the accuracy of acquired diffusion weighted imaging (DWI) (b = 1000 s/mm²) with that of computed DWI (b = 1000 s/mm²) for the detection of hepatic metastases.

Methods

Two hundred and sixty patients underwent abdominal magnetic resonance imaging (MRI) at 3.0 T for the evaluation of hepatic metastasis, including T1-weighted imaging (T1WI), T2-weighted imaging (T2WI), heavily T2WI, DWI with b-values of 0, 500, 1000 s/mm², and three-dimensional dynamic contrast-enhanced MRI with gadolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid (Gd-EOB-DTPA), and 190 patients were included in the final study. Computed DWI (=1000 s/mm²) was synthesized from lower b-values (b = 0 and 500 s/mm²). Two groups were assigned and compared: group A (acquired DWI) and group B (computed DWI). Diagnostic performance using each imaging set was evaluated by receiver operating characteristic (ROC) curve analysis.

Results

A total of 76 hepatic metastases were confirmed. The area under the ROC curve (Az) of group A was larger than that of group B (Observer 1; 0.919–0.915, Observer 2; 0.926–0.901), but there were no significant differences (observer 1, P = 0.500; observer 2, P = 0.190). There were 5 metastases visualized in group A, but these were difficult to detect in group B. However, there were 2 metastases that were better visualized in group B than in group A.

Conclusion

There were no significant differences between acquired DWI and computed DWI in the detection of hepatic metastasis.     

Interleaved T1 and T2 relaxation time mapping for cardiac applications

Purpose

To diagnose acute myocardial infarction (MI) with MRI, T₁‐weighted and T₂‐weighted images are required to detect necrosis and edema. The calculation of both T₁ and T₂ maps can be relevant for quantitative diagnosis. In this work, we present a simultaneous quantification of T₁‐T₂ relaxation times of a short‐axis view of the heart in a single scan.

Materials and Methods

An electrocardiograph (ECG)‐triggered, navigator‐gated, interleaved T₁ and T₂ mapping sequence was implemented for the quantification of the T₁ and T₂ values of phantoms, healthy volunteers, and three patients with acute MI. The proposed acquisition scheme consisted of an interleaved two‐dimensional (2D) steady‐state free precession (SSFP) sequence with three different modules: an inversion‐recovery (IR) sequence with multiple time delays, followed by a delay of one cardiac cycle for magnetization recovery and a T₂‐preparation pulse with multiple echo‐times for T₂ quantification.

Results

Measurements of in vivo relaxation times were in good agreement with literature values. The interleaved sequence was able to measure T₁ and T₂ relaxation times of the myocardium.

Conclusion

The interleaved sequence acquires data for the calculation of T₁ and T₂ maps in only one scan without the need for registration. This technique has the potential to differentiate between acute and chronic MI by estimating the concentration of gadolinium diethylenetriamine pentaacetic acid (Gd‐DTPA) in the necrotic tissue and to assess the extent of edema from T₂ maps. J. Magn. Reson. Imaging 2009;29:480–487. © 2009 Wiley‐Liss, Inc.     

Long component time constant of 23Na T*2 relaxation in healthy human brain.

Signal intensity in 23Na images is altered in pathologic conditions such as ischemia and may provide information regarding tissue viability complementary to MR diffusion and perfusion imaging. However, the multicomponent transverse relaxation of 23Na (spin 3/2) complicates the determination of tissue sodium concentration from 23Na images with nonzero echo-time. The purpose of this study was to measure the long component time constant of tissue sodium T*2 relaxation in the healthy human brain at 4 T. Multiecho gradient-echo 23Na images (10 echo-times ranging from 3.8-68.7 ms) were acquired in five healthy human volunteers. T*2 was quantified on a pixel-by-pixel basis using a nonnegative least squares fitting routine using 100 equally spaced bins between 0.5-99.5 ms and parametric maps were produced representing components between 0.5-3, 3.1-50, 50.1-98, and 98.1-99.5 ms. The long T*2 component of tissue sodium (average +/- standard deviation) varied between cortex (occipital = 22.0 +/- 2.4 ms), white matter (parietal = 18.2 +/- 1.9 ms), and subcortical gray matter (thalamus = 16.9 +/- 2.4 ms). These results demonstrate considerable regional variability and establish a foundation for future characterization of 23Na T*2 in conditions such as cerebral ischemia and cancer.