Low b-value diffusion-weighted imaging: emerging applications in the body

Thanks to recent advances in magnetic resonance imaging technology, it has become possible to perform intravoxel incoherent motion (IVIM) diffusion-weighted imaging (DWI) in any part of the body. Extracranial applications of DWI are currently under active investigation, especially for oncological imaging. However, the use of non-quantitative low b-value (10-100 s/mm(2)) DWI in the body is still a relatively unexplored field, and its potential is not fully recognized. Non-quantitative low b-value DWI may especially be useful for the evaluation of structures that have an inherently low signal at high b-value DWI, including (but not limited to) the liver, heart, and small bowel. This article will review and discuss the basic principles and potential applications of nonquantitative low b-value DWI in the body.     

Comparison of quantitative T2 mapping and diffusion-weighted imaging in the normal and pathologic prostate.

In this study, diffusion-weighted images of the human prostate were successfully obtained, enabling quantification of apparent diffusion coefficients (ADCs) in normal and pathologic regions. A dual acquisition fast spin-echo sequence was used for accurate T2 calculation. T2 values were significantly higher in the peripheral zone than the central gland (P = 0.015). No significant correlations were found in either normal or pathologic tissue between ADC values and relaxation rates for all three gradient directions and the orientationally averaged water diffusion coefficient. Evidence suggesting that diffusional anisotropy is present in normal prostatic tissue is also detailed, with significant differences noted between the z-component and both the x- and y-components of the ADC for peripheral zone (P < 0.040) and central gland (P < 0.001).     

Endorectal diffusion-weighted imaging in prostate cancer to differentiate malignant and benign peripheral zone tissue

PURPOSE: To determine if the apparent diffusion coefficient (ADC) can discriminate benign from malignant peripheral zone (PZ) tissue in patients with biopsy-proven prostate cancer that have undergone endorectal diffusion-weighted imaging (DWI) of the prostate. MATERIALS AND METHODS: Ten patients with prostate cancer underwent endorectal magnetic resonance imaging (MRI) in addition to DWI. A two-dimensional grid was placed over the axial images, and each voxel was graded by a 4-point rating scale to discriminate nonmalignant from malignant PZ tissue based on MR images alone. ADC was then determined for each voxel and plotted for nonmalignant and malignant voxels for the entire patient set. Second, with the radiologist aware of biopsy locations, any previously assigned voxel grade that was inconsistent with biopsy data was regrouped and ADCs were replotted. RESULTS: For the entire patient set, without and with knowledge of the biopsy data, the mean ADCs for nonmalignant and malignant tissue were 1.61 +/- 0.27 and 1.34 +/- 0.38 x 10(-3) mm2/second (P = 0.002) and 1.61 +/- 0.26 and 1.27 +/- 0.37 x 10(-3) mm2/second (P = 0.0005), respectively. CONCLUSION: DWI of the prostate is possible with an endorectal coil. The mean ADC for malignant PZ tissue is less than nonmalignant tissue, although there is overlap in individual values.     

Low b-value diffusion-weighted imaging for diagnosing strangulated small bowel obstruction: a feasibility study

Purpose:

To assess the feasibility of low b‐value diffusion‐weighted imaging (DWI) for diagnosing strangulated small bowel obstruction (SBO).

Materials and Methods:

Five volunteers and 14 patients with SBO underwent DWI at b‐values of 0 and 50 s/mm². Apparent diffusion coefficients (ADCs) and signal preservation ratios (SPRs) were measured in the distal jejunum in the volunteers before and after butylscopolamine administration, and in the (strangulated) closed loop, near the obstructive site, and far from the obstructive site in the patients. Low b‐value diffusion‐weighted images in the patients were quantitatively evaluated for diagnosing strangulation.

Results:

In the volunteers, mean ADC (10^?3 mm²/s) and SPR (%) before butylscopolamine administration (18.3 ± 5.9 and 41.4 ± 11.5) were significantly different (P < 0.05) from those after butylscopolamine administration (6.4 ± 3.6 and 73.7 ± 12.9). In the patients, mean ADCs and SPRs among the strangulated closed loop (3.8 ± 2.2 and 83.3 ± 9.3), near the obstructive site (12.1 ± 6.9 and 57.3 ± 18.5), and far from the obstructive site (26.8 ± 10.7 and 29.9 ± 16.4) were significantly different (P < 0.05). Areas under the receiver operating characteristic curve for the diagnosis of strangulation varied between 0.937 and 1.000.

Conclusion:

Low b‐value DWI is a feasible technique to distinguish the strangulated closed loop from nonstrangulated loops in SBO, and show promise for diagnosing strangulated SBO. J. Magn. Reson. Imaging 2011;. © 2011 Wiley Periodicals, Inc.

     

MRI扩散加权成像在前列腺癌及其邻近器官侵犯诊断中的价值

目的探讨MRI扩散加权成像(DWI)和ADC图在前列腺癌及其邻近器官侵犯诊断与鉴别诊断中的价值。方法回顾性分析经穿刺活检或手术病理证实的前列腺癌30例。所有患者均进行MRI常规扫描和DWI扫描,DWI序列取b值为0、100、800及200、1000两组分别扫描,分析DWI表现和表观扩散系数(ADC)图,并测量癌肿区及周围侵犯区的ADC值。结果前列腺癌病灶和邻近组织侵犯的病灶在两组扫描中5个序列DWI图上均呈高信号,ADC图呈低信号。所有病例的ADC值均低于(897.4±67.5)×10-6。结论 DWI成像检查在前列腺癌及其周围侵犯的诊断中具有特征性表现,在临床上有较高的应用价值。     

磁共振超高b值弥散序列指导前列腺穿刺的初步研究

目的探讨MR超高b值弥散序列指导前列腺穿刺的临床意义。方法前列腺穿刺病理证实患者共计48例,其中前列腺癌15例,前列腺增生33例。所有患者行MR常规扫描及弥散序列扫描,b=800,1500。以穿刺所得病理结果为金标准,分别观察前列腺癌及前列腺增生的常规b值及超高b值弥散图像特点。同时评价常规b值,超高b值及两组联合的诊断灵敏度、特异度、阳性预测值、阴性预测值。结果常规b值,超高b值及两组联合的诊断灵敏度分别为79.17%,62.5%,91.67%;特异度分别为75.61%,95.12%,95.12%;阳性预测分别为60%,88.24%,91.67%;阴性预测值分别为86.11%,81.25%,95.12%。前列腺癌在超高b值图像上呈高信号,具有明显的特征,在常规b值图像上前列腺癌及前列腺增生均可呈等信号或高信号影。在诊断效能方面,超高b值联合常规b值对比2种单独引导具有明显优越性。结论趟高b值弥散序列有助于前列腺癌的诊断,尤其在联合常规b值的情况下,明显提高诊断效能。     

Prostate cancer: utility of fusion of T2-weighted and high b-value diffusion-weighted images for peripheral zone tumor detection and localization

Purpose:

To retrospectively assess the utility of fusion of T2‐weighted images (T2WI) and high b‐value diffusion‐weighted images (DWI) for prostate cancer detection and localization.

Materials and Methods:

In this IRB‐approved HIPAA‐compliant study, 42 patients with prostate cancer underwent MRI including multiplanar T2WI and axial DWI before prostatectomy. Two independent radiologists first assessed multiplanar T2WI and axial DWI_b‐1000 images and recorded whether tumor was present in each sextant. Axial T2WI was then fused with axial DWI_b‐1000 images, and the radiologists re‐evaluated each sextant for tumor. Accuracy was compared using generalized estimating equations based on a binary logistic regression model.

Results:

The accuracy, sensitivity, specificity, PPV, and NPV for tumor detection on a sextant‐basis using separate and fused image sets was 65.1%, 50.8%, 78.0%, 67.8%, and 63.6% and 71.0%, 60.8%, 80.3%, 73.7%, and 69.3%, respectively, for reader 1, and 54.0%, 42.5%, 64.4%, 52.0%, and 55.2%, and 61.1%, 56.7%, 65.2%, 59.6%, and 62.3%, respectively, for reader 2. The improvements in accuracy, sensitivity, and NPV using fused images were statistically significant for both readers, as was the improvement in PPV for reader 2 (P ranging from <0.0001 to 0.041). With either separate or fused images, there was greater sensitivity for tumors of higher grade or larger size (P ranging from <0.001 to 0.099).

Conclusion:

Fusion of T2WI and high b‐value DWI resulted in significant improvements in sensitivity and accuracy for tumor detection on a sextant‐basis, with similar specificity. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

Diffusion-weighted MRI after cryosurgery of the canine prostate. Magnetic resonance imaging

PURPOSE: To evaluate the acute lesion created by cryosurgery with diffusion-weighted magnetic resonance imaging (DWI). MATERIALS AND METHODS: The appearance of the acute cryolesion was evaluated in four canine prostates DWI after they were warmed to original body temperature. The prostates were excised, stained with triphenyl tetrazolium chloride (TTC), photographed, prepared for hematoxylin and eosin (H&E) staining, and examined under a light microscope. RESULTS: A marked decrease in apparent diffusion coefficient of 38% was evident in the center of the previously frozen tissue, but not in all of the previously frozen tissue. Histologic results confirm differences between the iceball core and the periphery of the iceball, which have markedly different imaging characteristics on DWI. CONCLUSION: The core of the previously frozen tissue has a reduced apparent diffusion coefficient (ADC) compared to the periphery of the previously frozen tissue and previously unfrozen tissue.     

1.5T MR超高b值DWI对前列腺癌的诊断价值

目的 探讨1.5T MR 超高b值扩散加权成像(DWI)对前列腺癌(PCa)的诊断价值.方法 收集分析行常规MRI和DWI(b值为400、800、1 400 s/mm2)扫描,并经临床病理证实的PCa 12例,前列腺增生(BPH)17例,分别测量各b值DWI上感兴趣区(ROI)的信号强度,对ROI的可视化程度进行分级,比较其间是否存在差异.结果 超高b值与高b值DWI PCa病灶的信号强度差异有统计学意义(χ2=220.957,P=0.000<0.05);b值越高,DWI上PCa癌灶亮度对比越高,可视化程度差异有统计学意义(χ2=11.378,P=0.003<0.05).超高b值DWI上PCa癌灶与BPH和正常外周带信号强度有统计学意义(χ2=25.913,P=0.000<0.05),超高b值DWI PCa病灶亮度主要是亮和灰亮(占71.4%),BPH和正常外周带的亮度以暗和灰暗为主(BPH组占63.0%,正常外周带组占73.3%);可视化程度差异都有统计学意义(Z=-6.908、-6.110,P值均为0.000<0.017).b=1 400 s/mm2的DWI信号强度和可视化程度诊断效能最高.结论 1.5T MR超高b值DWI能提高PCa癌灶的显示率,易于观察和诊断.     

Diffusion‐weighted imaging of prostate cancer: Correlation between apparent diffusion coefficient values and tumor proliferation

Purpose

To investigate whether the apparent diffusion coefficient (ADC) values of prostate cancer (PCa) are able to reflect tumor proliferation.

Materials and Methods

The clinical and pathological information for 38 patients with PCa and 33 patients with benign prostate hyperplasia (BPH) were studied. Examination of the patients was performed using a 1.5 T superconducting magnetic scanner equipped with a pelvic phased‐array multicoil. Diffusion‐weighted images (DWIs) were acquired using an echo‐planar imaging sequence. The ADC values of PCa, BPH, and peripheral zone (PZ) were calculated. The cellularity of PCa was recorded based on hematoxylin and eosin staining. The proliferating cell nuclear antigen (PCNA) was detected using an immunohistochemical technique.

Results

The ADC values of PCa, BPH, and PZ were 49.32 ± 12.68 × 10^?5 mm²/s, 86.73 ± 26.75 × 10^?5 mm²/s, and 126.25 ± 27.21 × 10^?5 mm²/s, respectively. The ADC values of PCa were lower than those of BPH and PZ (P < 0.05). The cellularity and PCNA labeling index (LI) of PCa were higher than those of BPH (P < 0.05). The ADC values of PCa were negatively correlated with those of cellularity and PCNA LI (r = ?0.646 and ?0.446, respectively; P < 0.05).

Conclusion

The ADC values of PCa can reveal the differences in proliferative activity between PCa and BPH. These values are therefore able to predict the proliferative rate of variously differentiated prostate cancers. J. Magn. Reson. Imaging 2009;29:1360–1366. © 2009 Wiley‐Liss, Inc.

     

MR spectroscopic imaging and diffusion-weighted imaging of prostate cancer with Gleason scores

Purpose:

To investigate functional changes in prostate cancer patients with three pathologically proven different Gleason scores (GS) (3+3, 3+4, and 4+3) using magnetic resonance spectroscopic imaging (MRSI) and diffusion‐weighted imaging (DWI).

Materials and Methods:

In this study MRSI and DWI data were acquired in 41 prostate cancer patients using a 1.5T MRI scanner with a body matrix combined with an endorectal coil. The metabolite ratios of (Cho+Cr)/Cit were calculated from the peak integrals of total choline (Cho), creatine (Cr), and citrate (Cit) in MRSI. Apparent diffusion coefficient (ADC) values were derived from DWI for three groups of Gleason scores. The sensitivity and specificity of MRSI and DWI in patients were calculated using receiver operating characteristic curve (ROC) analysis.

Results:

The mean and standard deviation of (Cho+Cr)/Cit ratios of GS 3+3, GS 3+4, and GS 4+3 were: 0.44 ± 0.02, 0.56 ± 0.06, and 0.88 ± 0.11, respectively. For the DWI, the mean and standard deviation of ADC values in GS 3+3, GS 3+4, and GS 4+3 were: 1.13 ± 0.11, 0.97 ± 0.10, and 0.83 ± 0.08 mm²/sec, respectively. Statistical significances were observed between the GS and metabolite ratio as well as ADC values and GS.

Conclusion:

Combined MRSI and DWI helps identify the presence and the proportion of aggressive cancer (ie, Gleason grade 4) that might not be apparent on biopsy sampling. This information can guide subsequent rebiopsy management, especially for active surveillance programs. J. Magn. Reson. Imaging 2012;36:697–703. © 2012 Wiley Periodicals, Inc.     

Predicting response to neoadjuvant chemoradiation therapy in locally advanced rectal cancer: diffusion-weighted 3 Tesla MR imaging

Purpose:

To evaluate the efficacy of diffusion‐weighted imaging (DWI) on 3 Tesla (T) MR imaging to predict the tumor response to neoadjuvant chemoradiation therapy (CRT) in patients with locally advanced rectal cancer.

Materials and Methods:

Thirty‐five patients who underwent neoadjuvant CRT and subsequent surgical resection were included. Tumor volume was measured on T2‐weighted MR images before and after neoadjuvant CRT and the percentage of tumor volume reduction was calculated. The apparent diffusion coefficient (ADC) value was measured on the DWI before and after neoadjuvant CRT, and the change of ADC (Δ ADC) was calculated. The histopathologic response was categorized either as a responder to CRT or as a nonresponder. The relationship between the ADC parameters and the percentage of tumor volume reduction or histopathologic response was then evaluated.

Results:

There was a significant correlation between tumor volume reduction and pre‐CRT ADC and Δ ADC, respectively (r = ?0.352, r = 0.615). Pre‐CRT ADC of the histopathologic responders was significantly lower than that of the histopathologic nonresponders (P = 0.034). Δ ADC of the histopathologic responders was significantly higher than that of the histopathologic nonresponders (P < 0.005).

Conclusion:

DWI on 3T MR imaging may be a promising technique for helping to predict and monitor the treatment response to neoadjuvant CRT in patients with locally advanced rectal cancer. J. Magn. Reson. Imaging 2012;35:110‐116. © 2011 Wiley Periodicals, Inc.

     

Restriction spectrum imaging: An evolving imaging biomarker in prostate MRI

Restriction spectrum imaging (RSI) is a novel diffusion‐weighted MRI technique that uses the mathematically distinct behavior of water diffusion in separable microscopic tissue compartments to highlight key aspects of the tissue microarchitecture with high conspicuity. RSI can be acquired in less than 5 min on modern scanners using a surface coil. Multiple field gradients and high b‐values in combination with postprocessing techniques allow the simultaneous resolution of length‐scale and geometric information, as well as compartmental and nuclear volume fraction filtering. RSI also uses a distortion correction technique and can thus be fused to high resolution T2‐weighted images for detailed localization, which improves delineation of disease extension into critical anatomic structures. In this review, we discuss the acquisition, postprocessing, and interpretation of RSI for prostate MRI. We also summarize existing data demonstrating the applicability of RSI for prostate cancer detection, in vivo characterization, localization, and targeting. Level of Evidence: 5 J. Magn. Reson. Imaging 2017;45:323–336.     

Quantitative diffusion imaging in breast cancer: a clinical prospective study

PURPOSE: To study the correlation between apparent diffusion coefficient (ADC) and pathology in patients with undefined breast lesion, to validate how accurately ADC is related to histology, and to define a threshold value of ADC to distinguish malignant from benign lesions. MATERIALS AND METHODS: Seventy-eight patients (110 lesions) were referred for positive or dubious findings. Three-dimensional fast low-angle shot (3D-FLASH) with contrast injection was applied. EPI diffusion-weighted imaging (DWI) with fat saturation was performed, and ROIs were selected on subtraction 3D-FLASH images before and after contrast injection, and copied on an ADC map. Inter- and intraobserver analyses were performed. RESULTS: At pathology 22 lesions were benign, 65 were malignant, and 23 were excluded. The ADCs of malignant and benign lesions were statistically different. In malignant tumors the ADC was (mean +/- SEM) 0.95 +/- 0.027 x 10(-3)mm(2)/second, and in benign tumors it was 1.51 +/- 0.068 x 10(-3)mm(2)/second. According to receiver operating characteristic (ROC) curves, we found a threshold between malignant and benign lesions for highest sensitivity and specificity (both 86%) around 1.13 +/- 0.10 x 10(-3)mm(2)/second. For a threshold of 0.95 +/- 0.10 x 10(-3)mm(2)/second, specificity was 100% but sensitivity was very low. Inter- and intraobserver studies showed good reproducibility. CONCLUSION: The ADC may help to differentiate benign and malignant lesions with good specificity, and may increase the overall specificity of breast MRI.     

磁共振扩散加权成像在肝脓肿诊断中的价值

目的:探讨肝脓肿的磁共振扩散加权成像(DWI)影像特征,提高其影像诊断水平.方法:回顾性分析20例患者中30个肝脓肿的常规磁共振扫描加动态增强扫描及DWI图像,表观扩散系数(ADC)值定量分析肝脓肿的脓腔、脓肿壁及周围正常肝组织.结果:ADC图上,30个肝脓肿的脓腔中24个呈明显低信号,2个等信号,4个明显高信号,ADC值为(0.69～2.62)×10-3 mm2/s.30个肝脓肿中,8个未见明显脓肿壁形成; 22个脓肿壁在DWI图像上呈多样信号,在ADC图上均呈稍高信号,平均ADC值为(1.70 ± 0.23)×10-3 mm2/s.结论:肝脓肿的脓腔在DWI上常表现为明显高信号,ADC值较低;但部分脓腔ADC值较高,与肿瘤囊变坏死区难以鉴别;脓肿壁在ADC图上呈稍高信号的影像学特征有助于其诊断和鉴别诊断.     

Detection and localization of prostate cancer with the targeted biopsy strategy based on ADC map: a prospective large-scale cohort study

Purpose:

To investigate the usefulness of targeted biopsy strategy based on apparent diffusion coefficient (ADC) maps in the detection and localization of prostate cancer.

Materials and Methods:

Institutional review board approval and informed consent from all participants were obtained. This study included 1448 consecutive patients suspected of having prostate cancer based on PSA level, who were divided into two groups: Group A included 890 patients with low‐ADC lesions who underwent targeted and systematic biopsies; Group B included 558 patients with no low‐ADC lesions who underwent only systematic biopsies. The cancer detection rates (CDR) of each group, positive predictive value (PPV), and negative predictive value (NPV) of ADC maps were calculated.

Results:

The CDR was 70.1% for Group A, higher than those for overall patients (48.1%) and for Group B (13.1%) with significant difference (P < 0.001). In the serum, PSA range from 4 to 20 ng/mL, the CDR was higher for the Group A than for the Group B and overall patients with significant differences. PPV and NPV of MR findings were 70.1% and 86.9%, respectively. Especially, the PPV of the MR findings for the anterior portion was as high as 90.1%. Among the false negatives of MR findings, Gleason score proved 6 or smaller in 79.5%, and positive core number was merely one or two in 80.8%.

Conclusion:

The targeted biopsy strategy based on ADC maps can be useful in the detection and localization of prostate cancer with high PPV. J. Magn. Reson. Imaging 2012;35:1414–1421. © 2012 Wiley Periodicals, Inc.