MRI临床应用新进展

磁共振成像设备的飞速发展为许多高端新技术在临床的应用奠定了基础，很好地解决了临床应用过程中的伪影和心血管成像等难题，在心脏的冠脉成像、血管造影成像、弥散和灌注成像、磁共振波谱、以及功能磁共振成像等方面均取得了令人瞩目的进展，大大地满足了临床与科研的需要。     

Comparison of different MRI sequences in lesion detection and early response evaluation of diffuse large B‐cell lymphoma – a whole‐body MRI and diffusion‐weighted imaging study

To compare different MRI sequences for the detection of lesions and the evaluation of response to chemotherapy in patients with diffuse large B‐cell lymphoma (DLBCL), 18 patients with histology‐confirmed DLBCL underwent 3‐T MRI scanning prior to and 1 week after chemotherapy. The MRI sequences included T₁‐weighted pre‐ and post‐contrast, T₂‐weighted with and without fat suppression, and a single‐shot echo‐planar diffusion‐weighted imaging (DWI) with two b values (0 and 800 s/mm²). Conventional MRI sequence comparisons were performed using the contrast ratio between tumor and normal vertebral body instead of signal intensity. The apparent diffusion coefficient (ADC) of the tumor was measured directly on the parametric ADC map. The tumor volume was used as a reference for the evaluation of chemotherapy response. The mean tumor volume was 374 mL at baseline, and decreased by 65% 1 week after chemotherapy (p < 0.01). The T₂‐weighted image with fat suppression showed a significantly higher contrast ratio compared with images from all other conventional MRI sequences, both before and after treatment (p < 0.01, respectively). The contrast ratio of the T₂‐weighted image with fat suppression decreased significantly (p < 0.01), and that of the T₁‐weighted pre‐contrast image increased significantly (p < 0.01), after treatment. However, there was no correlation between the change in contrast ratio and tumor volume. The mean ADC value was 0.68 × 10^–3 mm²/s at baseline; it increased by 89% after chemotherapy (p < 0.001), and the change in ADC value correlated with the change in tumor volume (r = 0.66, p < 0.01). The baseline ADC value also correlated inversely with the percentage change in ADC after treatment (r = ?0.62, p < 0.01). In conclusion, this study indicates that T₂‐weighted imaging with fat suppression is the best conventional sequence for the detection of lesions and evaluation of the efficacy of chemotherapy in DLBCL. DWI with ADC mapping is an imaging modality with both diagnostic and prognostic value that could complement conventional MRI. Copyright © 2013 John Wiley & Sons, Ltd.     

Imaging update on soft tissue sarcoma

Soft tissue sarcomas (STS) are rare tumours presenting as soft tissue lumps. Ultrasound is often the primary modality for the initial assessment, with MRI the mainstay for lesion characterisation. PET/CT along with other emerging MRI sequences are used in certain situations as an adjunct and problem solving tool in STS staging and assessment of disease recurrence. Recent advances include the promise of whole body MRI, hybrid PET/MRI, diffusion weighted imaging, dynamic contrast enhanced MRI and advances in artificial intelligence. This article discusses current concepts in extremity STS imaging and highlights recent advances.     

磁共振弥散加权成像DWI及动态增强扫描诊断前列腺癌的价值探讨

目的 研究分析磁共振弥散加权成像DWI及动态增强扫描对前列腺癌患者的诊断价值.方法 选择我院收治的经病理学检查确诊为前列腺癌的患者40例作为研究对象,对所有患者进行磁共振弥散加权成像DWI检查及动态增强扫描,并与病理学检查结果对比,分析其临床诊断效果.结果 前列腺癌患者的ADC为（0.81±0.09）,最大强化率为（138.98±36.34）,1 min强化率为（132.87±35.35）,2 min强化率为（133.09±41.21）,流出分数为（17.72±7.88）.与病理学检查诊断结果对比,2种检查方法对前列腺癌的检出率差异无统计学意义（P＞0.05）.结论 使用磁共振弥散加权成像DWI及动态增强扫描诊断前列腺癌效果较为理想,与病理学诊断较为接近,可以在临床上推广应用.     

Stratification of the aggressiveness of prostate cancer using pre‐biopsy multiparametric MRI (mpMRI)

Risk stratification, based on the Gleason score (GS) of a prostate biopsy, is an important decision‐making tool in prostate cancer management. As low‐grade disease may not need active intervention, the ability to identify aggressive cancers on imaging could limit the need for prostate biopsies. We assessed the ability of multiparametric MRI (mpMRI) in pre‐biopsy risk stratification of men with prostate cancer. One hundred and twenty men suspected to have prostate cancer underwent mpMRI (diffusion MRI and MR spectroscopic imaging) prior to biopsy. Twenty‐six had cancer and were stratified into three groups based on GS: low grade (GS ≤ 6), intermediate grade (GS = 7) and high grade (GS ≥ 8). A total of 910 regions of interest (ROIs) from the peripheral zone (PZ, range 25–45) were analyzed from these 26 patients. The metabolite ratio [citrate/(choline + creatine)] and apparent diffusion coefficient (ADC) of voxels were calculated for the PZ regions corresponding to the biopsy cores and compared with histology. The median metabolite ratios for low‐grade, intermediate‐grade and high‐grade cancer were 0.29 (range: 0.16, 0.61), 0.17 (range: 0.13, 0.32) and 0.13 (range: 0.05, 0.23), respectively (p = 0.004). The corresponding mean ADCs (×10^–3 mm²/s) for low‐grade, intermediate‐grade and high‐grade cancer were 0.99 ± 0.08, 0.86 ± 0.11 and 0.69 ± 0.12, respectively (p < 0.0001). The combined ADC and metabolite ratio model showed strong discriminatory ability to differentiate subjects with GS ≤ 6 from subjects with GS ≥ 7 with an area under the curve of 94%. These data indicate that pre‐biopsy mpMRI may stratify PCa aggressiveness noninvasively. As the recent literature data suggest that men with GS ≤ 6 cancer may not need radical therapy, our data may help limit the need for biopsy and allow informed decision making for clinical intervention. Copyright © 2015 John Wiley & Sons, Ltd.     

Whole body MRI: Improved lesion detection and characterization with diffusion weighted techniques

Diffusion‐weighted imaging (DWI) is an established functional imaging technique that interrogates the delicate balance of water movement at the cellular level. Technological advances enable this technique to be applied to whole‐body MRI. Theory, b‐value selection, common artifacts and target to background for optimized viewing will be reviewed for applications in the neck, chest, abdomen, and pelvis. Whole‐body imaging with DWI allows novel applications of MRI to aid in evaluation of conditions such as multiple myeloma, lymphoma, and skeletal metastases, while the quantitative nature of this technique permits evaluation of response to therapy. Persisting signal at high b‐values from restricted hypercellular tissue and viscous fluid also permits applications of DWI beyond oncologic imaging. DWI, when used in conjunction with routine imaging, can assist in detecting hemorrhagic degradation products, infection/abscess, and inflammation in colitis, while aiding with discrimination of free fluid and empyema, while limiting the need for intravenous contrast. DWI in conjunction with routine anatomic images provides a platform to improve lesion detection and characterization with findings rivaling other combined anatomic and functional imaging techniques, with the added benefit of no ionizing radiation. J. Magn. Reson. Imaging 2013;38:253–268. © 2013 Wiley Periodicals, Inc.     

Diffusion‐prepared stimulated‐echo turbo spin echo (DPsti‐TSE): An eddy current‐insensitive sequence for three‐dimensional high‐resolution and undistorted diffusion‐weighted imaging

In this study, we present a new three‐dimensional (3D), diffusion‐prepared turbo spin echo sequence based on a stimulated‐echo read‐out (DPsti‐TSE) enabling high‐resolution and undistorted diffusion‐weighted imaging (DWI). A dephasing gradient in the diffusion preparation module and rephasing gradients in the turbo spin echo module create stimulated echoes, which prevent signal loss caused by eddy currents. Near to perfect agreement of apparent diffusion coefficient (ADC) values between DPsti‐TSE and diffusion‐weighted echo planar imaging (DW‐EPI) was demonstrated in both phantom transient signal experiments and phantom imaging experiments. High‐resolution and undistorted DPsti‐TSE was demonstrated in vivo in prostate and carotid vessel wall. 3D whole‐prostate DWI was achieved with four b values in only 6 min. Undistorted ADC maps of the prostate peripheral zone were obtained at low and high imaging resolutions with no change in mean ADC values [(1.60 ± 0.10) × 10^?3 versus (1.60 ± 0.02) × 10^?3 mm²/s]. High‐resolution 3D DWI of the carotid vessel wall was achieved in 12 min, with consistent ADC values [(1.40 ± 0.23) × 10^?3 mm²/s] across different subjects, as well as slice locations through the imaging volume. This study shows that DPsti‐TSE can serve as a robust 3D diffusion‐weighted sequence and is an attractive alternative to the traditional two‐dimensional DW‐EPI approaches.     

Diffusion-weighted magnetic resonance imaging in rat kidney using two-dimensional navigated,interleaved echo-planar imaging at 7.0 T

The purpose of this study was to investigate the feasibility of two-dimensional (2D) navigated, interleaved multishot echo-planar imaging (EPI) to enhance kidney diffusion-weighted imaging (DWI) in rats at 7.0 T. Fully sampled interleaved four-shot EPI with 2D navigators was tailored for kidney DWI (Sprague–Dawley rats, n = 7) on a 7.0-T small bore preclinical scanner. The image quality of four-shot EPI was compared with T₂-weighted rapid acquisition with relaxation enhancement (RARE) (reference) and single-shot EPI (ss-EPI) without and with parallel imaging (PI). The contrast-to-noise ratio (CNR) was examined to assess the image quality for the EPI approaches. The Dice similarity coefficient and the Hausdorff distance were used for evaluation of image distortion. Mean diffusivity (MD) and fractional anisotropy (FA) were calculated for renal cortex and medulla for all DWI approaches. The corticomedullary difference of MD and FA were assessed by Wilcoxon signed-rank test. Four-shot EPI showed the highest CNR among the three EPI variants and lowest geometric distortion versus T₂-weighted RARE (mean Dice: 0.77 for ss-EPI without PI, 0.88 for ss-EPI with twofold undersampling, and 0.92 for four-shot EPI). The FA map derived from four-shot EPI clearly identified a highly anisotropic region corresponding to the inner stripe of the outer medulla. Four-shot EPI successfully discerned differences in both MD and FA between renal cortex and medulla. In conclusion, 2D navigated, interleaved multishot EPI facilitates high-quality rat kidney DWI with clearly depicted intralayer and interlayer structure and substantially reduced image distortion. This approach enables the anatomic integrity of DWI-MRI in small rodents and has the potential to benefit the characterization of renal microstructure in preclinical studies.     

The stratification of severity of acute radiation proctopathy after radiotherapy for cervical carcinoma using diffusion-weighted MRI

ObjectiveTo determine whether diffusion-weighted imaging (DWI) can be used for quantitatively evaluating severity of acute radiation proctopathy after radiotherapy for cervical carcinoma.Materials and methodsOne hundred and twenty-four patients with cervical carcinoma underwent MR examination including DWI before and after radiotherapy. Acute radiation proctopathy was classified into three groups (grade 0, grade I–II and grade III–IV) according to Toxicity Criteria of the Radiation Therapy Oncology Group (RTOG). The pretreatment ADC (ADC_pre), ADC after treatment (ADC_post) and ADC change (ΔADC) were compared among three groups. In addition, acute radiation proctopathy was classified into good-prognosis group and poor-prognosis group. ADC_pre, ADC_post and ΔADC were compared between two groups. For DWI parameter that had significant difference, discriminatory capability of the parameter was determined using receiver operating characteristics (ROC) analysis.ResultsADC_post and ΔADC were higher in grade I–II group than in grade 0 group (p < 0.05), yielding a sensitivity of 79.3% and specificity of 69.4% for ADC_post, and 85.1%, 72.3% for ΔADC for discrimination between two groups. ADC_post and ΔADC were higher in grade III–IV group than in grade I–II group (p < 0.05), yielding a sensitivity of 80.3% and specificity of 72.5% for ADC_post, and 84.1%, 74.5% for ΔADC for discrimination between two groups. ADC_post and ΔADC were higher in poor-prognosis group than in good-prognosis group (p < 0.05), yielding a sensitivity of 79.5% and specificity of 73.4% for ADC_post, and 87.2%, 78.3% for ΔADC for discrimination between two groups.ConclusionDiffusion-weighted MRI can be used for quantitative stratification of severity of acute radiation proctopathy, which serves as an important basis for appropriate timely adjustment of radiotherapy for cervical carcinoma in order to maximally reduce the radiation injury of rectum.