Diffusion-weighted magnetic resonance imaging for characterization of focal liver masses: impact of parallel imaging (SENSE) and b value

[Importance of diffusion imaging in liver metastases]

CLINICAL/METHODICAL ISSUE

Detection and characterization of focal liver lesions.

STANDARD RADIOLOGICAL METHODS

Due to its excellent soft tissue contrast, the availability of liver-specific contrast agents and the possibility of functional imaging, magnetic resonance imaging (MRI) is the method of choice for the evaluation of focal liver lesions.

METHODICAL INNOVATIONS

Diffusion-weighted imaging (DWI) enables generation of functional information about the microstructure of a tissue besides morphological information.

PERFORMANCE

In the detection of focal liver lesions DWI shows a better detection rate compared to T2w sequences and a slightly poorer detection rate compared to dynamic T1w sequences. In principle, using DWI it is possible to distinguish malignant from benign liver lesions and also to detect a therapy response at an early stage.

ACHIEVEMENTS

For both detection and characterization of focal liver lesions, DWI represents a promising alternative to the morphological sequences; however, a more detailed characterization with the use of further sequences should be carried out particularly for the characterization of solid benign lesions. For the assessment and prognosis of therapy response, DWI offers advantages compared to morphological sequences.

PRACTICAL RECOMMENDATIONS

For the detection of focal liver lesions DWI is in principle sufficient. After visual detection of a solid liver lesion a more detailed characterization should be carried out using further sequences (in particular dynamic T1w sequences). The DWI procedure should be used for the assessment and prognosis of a therapy response.

Application values of 3.0T magnetic resonance diffusion weighted imaging for distinguishing liver malignant tumors and benign lesions

The aim of the present study was to investigate the significance and values of 3.0T diffusion weighted imaging (DWI) to differentially diagnose benign and malignant space-occupying liver lesions. A total of 91 patients with liver space-occupying lesions (145 lesions) were admitted into Zhongnan Hospital of Wuhan University (Wuhan, China) from November 2015 to May 2016. Routine scanning, DWI and high-resolution T2-weighted imaging using spin-echo echo-planar imaging were performed on all patients, to compare the apparent diffusion coefficient (ADC) values of three regions of interest in lesions with normal liver tissue. The ADC values of malignant liver lesions compared with benign liver cysts demonstrated a statistically significant difference in low b-value (P<0.05) and there was also a significant difference between malignant lesion and hepatic cyst, hepatic hemangioma or hepatic abscess in middle b-value (P<0.05). The measured ADC value may be more conducive to identify the nature of the liver space-occupying lesions; as the ADC values of malignant liver lesion, liver cyst, and liver abscesses demonstrated a statistical significance in high b-value (P<0.05). The mean ADC values between malignant liver tumors compared with benign lesions indicated a statistically significant difference. In the present study, liver space-occupying lesions demonstrated different DWI features and ADC ranges, and 3.0T DWI may be a potential means to accurately determine the nature of lesions, identifying benign and malignant space-occupying lesions.

Standard-b-Value Versus Low-b-Value Diffusion-Weighted Imaging in Hepatic Lesion Discrimination: A Meta-analysis

OBJECTIVE

We sought to determine the comparative diagnostic performance of standard-b-value (500-1000s/mm) versus low-b-value (≤500 s/mm) diffusion-weighted imaging (DWI) in the discrimination of hepatic lesions.

METHODS

A total of 1775 hepatic malignant lesions and 1120 benign hepatic lesions from 21 studies were included.

RESULTS

(1) The global sensitivity was 0.86 (95% confidence interval [CI], 0.847-0.879), the specificity was 0.82 (95% CI, 0.797-0.842), the positive likelihood ratio (PLR) was 6.234 (95% CI, 4.260-9.123), the negative likelihood ratio (NLR) was 0.175 (95% CI, 0.135-0.227), and diagnostic odds ratio (DOR) was 42.836 (95% CI, 24.134-76.031). The area under the curve (AUC) and Q* index were 0.93 and 0.87. Publication bias was not present (P > 0.05). (2)The sensitivity of a subgroup meta-analysis of standard-b-value DWI was 0.858 (95% CI, 0.835-0.880), the specificity was 0.836 (95% CI, 0.807-0.863), the PLR was 6.527 (95% CI, 3.857-11.046), the NLR was 0.168 (95% CI, 0.123-0.239), and the DOR was 49.716 (95% CI, 22.897-107.98). The AUC and Q* index were 0.941 and 0.88. (3)The sensitivity of a subgroup meta-analysis of low-b-value DWI was 0.87 (95% CI, 0.84-0.89), the specificity was 0.80 (95% CI, 0.76-0.83), the PLR was 6.22 (95% CI, 3.29-11.76), the NLR was 0.19 (95% CI, 0.12-0.29), and the DOR was 37.14 (95% CI, 14.80-93.18). The AUC and Q* index were 0.922 and 0.86.

CONCLUSIONS

Hepatic DWI is useful in differentiating between malignant and benign hepatic lesions. Standard-b-value DWI displayed an overall superior diagnostic accuracy over low-b-value DWI. Further trials needed to determine whether increasing b values beyond 1000 s/mm affects the diagnostic accuracy of hepatic lesion discrimination.

Lesion discrimination with breath-hold hepatic diffusion-weighted imaging: A meta-analysis

AIM: To investigate the diagnostic capability of breath-hold diffusion-weighted imaging (DWI) for differentiation between malignant and benign hepatic lesions.

METHODS: A total of 614 malignant liver lesions (132 hepatocellular carcinomas, 468 metastases and 14 intrahepatic cholangiocarcinomas) and 291 benign liver lesions (102 hemangiomas, 158 cysts, 24 focal nodular hyperplasia, 1 angiomyolipoma and 6 hepatic adenomas) were included from seven studies (eight sets of data).

RESULTS: The pooled sensitivity and specificity of breath-hold DWI were 0.93 [95% confidence interval (CI): 0.91-0.95] and 0.87 (95%CI: 0.83-0.91), respectively. The positive likelihood ratio and negative likelihood ratio were 7.28 (95%CI: 4.51-11.76) and 0.09 (95%CI: 0.05-0.17), respectively. The P value for χ² heterogeneity for all pooled estimates was < 0.05. From the fitted summary receiver operating characteristic curve, the area under the curve and Q* index were 0.96 and 0.91, respectively. Publication bias was not present (t = 0.49, P = 0.64). The meta-regression analysis indicated that evaluated covariates including magnetic resonance imaging modality, echo time, mean age, maximum b factor, and number of b factors were not sources of heterogeneity (all P > 0.05).

CONCLUSION: Breath-hold DWI is useful for differentiating between malignant and benign hepatic lesions. The diffusion characteristics of benign lesions that mimic malignant ones have rarely been investigated.

Preoperative evaluation of the histological grade of hepatocellular carcinoma with diffusion-weighted imaging: a meta-analysis

OBJECTIVE

To evaluate the diagnostic performance of diffusion-weighted imaging (DWI) in the preoperative prediction of the histological grade of hepatocellular carcinoma (HCC).

MATERIALS AND METHODS

A comprehensive literature search was performed in several authoritative databases to identify relevant articles. QUADAS-2 was used to assess the quality of included studies. Data were extracted to calculate the pooled sensitivity, specificity, positive likelihood ratio (PLR) and negative likelihood ratio (NLR). Summary receiver operating characteristic (SROC) curves were derived and areas under the SROC curve (AUC) were computed to indicate the diagnostic accuracy. Heterogeneity test, meta-regression analysis and sensitivity analysis were performed to identify factors and studies contributed to the heterogeneity.

RESULTS

A total of 11 studies with 912 HCCs were included in this meta-analysis. The pooled sensitivity, specificity, PLR and NLR with corresponding 95% confidence intervals (CI) were 0.54(0.47-0.61), 0.90(0.87-0.93), 4.88(2.99-7.97) and 0.46(0.27-0.77) for the prediction of well-differentiated HCC (w-HCC), 0.84(0.78-0.89), 0.48(0.43-0.52), 2.29(1.43-3.69) and 0.30(0.22-0.41) for the prediction of poorly-differentiated HCC (p-HCC). The AUC were 0.9311 and 0.8513 in predicting w-HCC and p-HCC, respectively. Results were further evaluated according to the method of image interpretation. Significant heterogeneity was observed.

CONCLUSION

DWI had excellent and moderately high diagnostic accuracy for the detection of w-HCC and p-HCC, respectively. Nonetheless, further studies in larger populations and an optimized image acquisition and interpretation are required before DWI-derived parameters can be used as a useful image biomarker for the prediction of the histological grade of HCC.

Can a b value of 500 be substituted for a b value of 1000 in the characterization of focal liver lesions?

PURPOSE

Comparison of two different b values in diffusion-weighted magnetic resonance imaging (DWI) for characterization of focal liver lesions.

METHODS

A total of 174 focal liver lesions from 100 patients were analyzed using two different b values (500 and 1000 s/mm(2)). The DWI with b values of 500 s/mm(2) (DWI500) and 1000 s/mm(2) (DWI1000) were analyzed using the Mann-Whitney test, kappa statistic, and paired t test with respect to image quality. The statistically significant differences between DWI500 and DWI1000 in the characterization of the lesions with respect to the cutoff ADC values were evaluated via χ (2) test.

RESULTS

DWI500 had the highest mean score in the qualitative evaluation of image quality (p < 0.0001) and the highest signal-to-noise ratio (8.7 ± 2.1; p < 0.0001). The sensitivity, specificity, and AUC for discriminating malignant from benign focal lesions on DWI500 and DWI1000 using cutoff ADC values of 1.54 × 10(-3) and 1.38 × 10(-3) s/mm(2) were 95.8%, 92.3%, 0.98, and 93.8%, 92.3%, 0.97, respectively. There was no statistically significant difference in sensitivity, specificity, and AUC values between DWI500 and DWI1000 with respect to the cutoff ADC values (p > 0.05).

CONCLUSIONS

The image quality of DWI500 was better than that of DWI1000, and there was no significant difference between DWI500 and DWI1000 in the characterization of the lesions with respect to the cutoff ADC values. The b value of 500 s/mm(2) can be substituted for the b value of 1000 s/mm(2) in the characterization of focal liver lesions.

Diffusion-weighted imaging for the left hepatic lobe has higher diagnostic accuracy for malignant focal liver lesions

BACKGROUND

This study was conducted to investigate whether apparent diffusion coefficient (ADC) measurements by dividing the liver into left and right hepatic lobes may be utilized to improve the accuracy of differential diagnosis of benign and malignant focal liver lesions.

MATERIALS AND METHODS

A total of 269 consecutive patients with 429 focal liver lesions were examined by 3-T magnetic resonance imaging that included diffusion-weighted imaging. For 58 patients with focal liver lesions of the same etiology in left and right hepatic lobes, ADCs of normal liver parenchyma and focal liver lesions were calculated and compared using the paired t-test. For all 269 patients, ADC cutoffs for focal liver lesions and diagnostic accuracy in the left hepatic lobe, right hepatic lobe and whole liver were evaluated by receiver operating characteristic curve analysis.

RESULTS

For the group of 58 patients, mean ADCs of normal liver parenchyma and focal liver lesions in the left hepatic lobe were significantly higher than those in the right hepatic lobe. For differentiating malignant lesions from benign lesions in all patients, the sensitivity and specificity were 92.6% and 92.0% in the left hepatic lobe, 94.4% and 94.4% in the right hepatic lobe, and 90.4% and 94.7% in the whole liver, respectively. The area under the curve of the right hepatic lobe, but not the left hepatic lobe, was higher than that of the whole liver.

CONCLUSIONS

ADCs of normal liver parenchyma and focal liver lesions in the left hepatic lobe were significantly higher than those in the right hepatic lobe. Optimal ADC cutoff for focal liver lesions in the right hepatic lobe, but not in the left hepatic lobe, had higher diagnostic accuracy compared with that in the whole liver.

Chemotherapy-induced focal hepatopathy in patients with gastrointestinal malignancy: gadoxetic acid--enhanced and diffusion-weighted MR imaging with clinical-pathologic correlation

PURPOSE

To retrospectively evaluate findings of chemotherapy-induced focal hepatopathy (CIFH) on gadoxetic acid-enhanced magnetic resonance (MR) and diffusion-weighted (DW) images and to determine imaging features that are most helpful in differentiating CIFH from metastasis.

MATERIALS AND METHODS

This retrospective study was approved by the institutional review board, and informed consent was waived. MR images, including DW images and gadoxetic acid-enhanced images, from 12 patients (four men, eight women; age range, 25-64 years) with 15 CIFHs were reviewed independently and in consensus by two radiologists and were compared with those obtained in 20 control patients (12 men, eight women; age range, 32-84 years) with 30 hepatic metastasis who were matched for tumor size, primary organ, and chemotherapy regimen. Interobserver agreement was assessed with κ statistics, and univariate analysis was performed for comparisons. For quantitative analyses, apparent diffusion coefficients (ADCs) and lesion-to-liver contrast ratios (CRs) were measured. Histopathologic examinations were performed for CIFHs.

RESULTS

Histopathologic examination revealed that the development of CIFHs was attributable to accentuated manifestations of sinusoidal obstruction syndrome. Interobserver agreement was excellent (κ > 0.85). An ill-defined margin on hepatobiliary phase (HBP) images was the most discriminating independent variable in the differentiation of CIFH from metastasis (odds ratio, 16; P = .009). ADC and CR values in CIFH group were significantly higher than those in metastasis group (P < .001 and P = .041).

CONCLUSION

CIFH should be considered a mimicker of metastasis in patients with gastrointestinal malignancy during chemotherapy. CIFH can be differentiated from metastasis on the basis of gadoxetic acid-enhanced MR and DW imaging findings; an ill-defined margin on HBP images was especially characteristic.

Liver lesion detection and characterization: role of diffusion-weighted imaging

Diffusion-weighted imaging (DWI) plays an emerging role for the assessment of focal and diffuse liver diseases. This growing interest is due to that fact that DWI is a noncontrast technique with inherent high contrast resolution, with promising results for detection and characterization of focal liver lesions. Recent advances in diffusion image quality have also added interest to this technique in the abdomen. The purpose of this review is to describe the current clinical roles of DWI for the detection and characterization of focal liver lesions, and to review pitfalls, limitations, and future directions of DWI for assessment of focal liver disease.

Does diffusion-weighted imaging add diagnostic confidence in discriminating between benign and malignant solid focal liver lesions?

We investigated whether diffusion-weighted Imaging (DWI) adds diagnostic confidence in assessing focal liver lesions (FLLs). By reviewing FLLs without and with DWI at 1.5 T, two radiologists scored the confidence in diagnosing benignancy/malignancy (confidence score), and DWI usefulness (usefulness score). We showed that adding DWI significantly decreased the confidence score of the most experienced radiologist and increased his confidence in false-negative diagnoses showing atypical features on conventional magnetic resonance imaging.

High sensitivity of diffusion-weighted MR imaging for the detection of liver metastases from neuroendocrine tumors: comparison with T2-weighted and dynamic gadolinium-enhanced MR imaging

PURPOSE

To compare the sensitivity and specificity of diffusion-weighted (DW) magnetic resonance (MR) imaging for identifying liver metastases from neuroendocrine tumor (NET) to those of T2-weighted fast spin-echo (FSE) and three-dimensional dynamic gadolinium-enhanced MR imaging, with surgical and histopathologic findings as the reference standard.

MATERIALS AND METHODS

This retrospective study was approved by institutional review board, and informed consent was waived. Fifty-nine patients with NETs (41 patients with 162 liver metastases, and 18 control subjects with no liver metastases) underwent MR imaging that included DW, T2-weighted FSE, and dynamic gadolinium-enhanced MR sequences. Images were retrospectively reviewed by two abdominal radiologists, independently, for the detection and characterization of liver metastases. MR findings were compared with histopathologic and intraoperative ultrasonography findings for metastasis on a lesion-by-lesion basis to determine the sensitivity of each MR sequence alone and combined. Specificity was calculated by using the control population. Interreader agreement for each MR sequence and McNemar test were also calculated.

RESULTS

There was excellent agreement between observers 1 and 2 for characterizing liver metastases at per-lesion analysis (κ coefficient: 0.86-1.00). DW MR was more sensitive (observer 1: sensitivity, 71.6% [116 of 162], 95% confidence interval [CI]: 64.2%, 78.0%; observer 2: sensitivity, 71.0% [115 of 162], 95% CI: 63.6%, 77.4%) than T2-weighted FSE (observer 1: sensitivity, 55.6% [90 of 162], 95% CI: 47.9%, 63.0%; observer 2: sensitivity, 55.6% [90 of 162], 95% CI: 47.9%, 63.0%) and dynamic gadolinium-enhanced MR (observer 1: sensitivity, 47.5% [77 of 162], 95% CI: 34.0%, 55.2%; observer 2: sensitivity, 48.1% [78 of 162], 95% CI: 40.6%, 55.8%) (P < .001 for both, McNemar test). The specificity of these sequences ranged from 88.9% to 100% (DW MR vs T2-weighted FSE MR: P > .99, DW MR vs dynamic gadolinium-enhanced MR: P = .61, and T2-weighted FSE MR vs dynamic gadolinium-enhanced MR: P = .61, McNemar test).

CONCLUSION

DW MR imaging was more sensitive for the detection and characterization of liver metastases from NETs than T2-weighted FSE and dynamic gadolinium-enhanced MR imaging and should be systematically performed.

Diagnostic accuracy of diffusion-weighted imaging with conventional MR imaging for differentiating complex solid and cystic ovarian tumors at 1.5T

Background

Preoperative characterization of complex solid and cystic adnexal masses is crucial for informing patients about possible surgical strategies. Our study aims to determine the usefulness of apparent diffusion coefficients (ADC) for characterizing complex solid and cystic adnexal masses.

Methods

One-hundred and 91 patients underwent diffusion-weighted (DW) magnetic resonance (MR) imaging of 202 ovarian masses. The mean ADC value of the solid components was measured and assessed for each ovarian mass. Differences in ADC between ovarian masses were tested using the Student’s t-test. The receiver operating characteristic (ROC) was used to assess the ability of ADC to differentiate between benign and malignant complex adnexal masses.

Results

Eighty-five patients were premenopausal, and 106 were postmenopausal. Seventy-four of the 202 ovarian masses were benign and 128 were malignant. There was a significant difference between the mean ADC values of benign and malignant ovarian masses (p < 0.05). However, there were no significant differences in ADC values between fibrothecomas, Brenner tumors and malignant ovarian masses. The ROC analysis indicated that a cutoff ADC value of 1.20 x10^-3 mm²/s may be the optimal one for differentiating between benign and malignant tumors.

Conclusions

A high signal intensity within the solid component on T2WI was less frequently in benign than in malignant adnexal masses. The combination of DW imaging with ADC value measurements and T2-weighted signal characteristics of solid components is useful for differentiating between benign and malignant ovarian masses.

Diffusion-weighted MRI: a useful technique to discriminate benign versus malignant ovarian surface epithelial tumors with solid and cystic components

PURPOSE

To evaluate differences in apparent diffusion coefficient (ADC) values for the solid component of benign and malignant ovarian surface epithelial tumors with the goal of differentiating benign versus malignant ovarian tumors preoperatively.

MATERIALS AND METHODS

A total of 127 patients with 131 pelvic masses identified by ultrasound between January 2006 and January 2011 were enrolled in this study. 46 patients were diagnosed with benign tumors, and 85 patients were diagnosed with malignant pathologies. For all of the patients, routine spin-echo MRI and diffusion-weighted imaging were performed. ADC values were determined for all of the masses, and the mean ADC values for the benign and malignant tumors were analyzed using Student's t test. A P value <0.05 was considered statistically significant.

RESULTS

Mean ADC values associated with malignant ovarian surface epithelial tumors were significantly lower than the mean ADC values of the benign tumors. In addition, the range of ADC values associated with a 95% confidence interval did not overlap between the two groups. ROC analysis indicated that a cutoff ADC value of 1.25 × 10(-3) mm(2)/s was associated with 90.1% sensitivity and 89.9% specificity.

CONCLUSION

ADC values determined from 1.5 T MR DWI of benign and malignant ovarian masses were found to be significantly different.

Accuracy of visual analysis vs. apparent diffusion coefficient quantification in differentiating solid benign and malignant focal liver lesions with diffusion-weighted imaging

PURPOSE

The authors compared the accuracy of diffusion-weighted imaging (DWI) visual analysis (VA) vs. apparent diffusion coefficient quantification (ADC-Q) in assessing malignancy of solid focal liver lesions (FLLs).

MATERIALS AND METHODS

Using a 1.5-T system, two radiologists retrospectively assessed as benign or malignant 50 solid FLLs: (a) by VA of signal intensity on DWI images at b=800 s/mm(2) and ADC map; (b) by quantifying lesion ADC. Reference standard included histology or follow-up confirmation of diagnosis by a consensus panel. Receiver operating characteristic (ROC) curve analysis was performed.

RESULTS

because of 20 false-negative hepatocellular carcinomas, VA showed lower accuracy than ADC-Q (52.0% VS. 68.0%). however, stratified accuracy for metastases was higher with VA (75.0 VS. 66%). ADC and signal features of malignant and benign FLLs were found to largely overlap.

CONCLUSIONS

VA performed worse than ADC-Q for hepatocellular carcinoma and better for metastases. Overall, the accuracy of both methods was limited because of the overlap in visual appearance and ADC values between solid benign and malignant FLLs.

Motion artifact reduction of diffusion-weighted MRI of the liver: use of velocity-compensated diffusion gradients combined with tetrahedral gradients

PURPOSE

To assess the effect of motion artifact reduction on the diffusion-weighted magnetic resonance imaging (DWI-MRI) of the liver, we compared velocity-compensated DWI (VC-DWI) and VC-DWI combined with tetrahedral gradients (t-VC-DWI) to conventional DWI (c-DWI) in the assessment of apparent diffusion coefficients (ADCs) of the liver.

MATERIALS AND METHODS

In 12 healthy volunteers, the liver was scanned with c-DWI, VC-DWI, and t-VC-DWI sequences. The signal-to-noise ratio (SNR) and ADC of the liver parenchyma were measured and compared among sequences.

RESULTS

The image quality was visually better for t-VC-DWI than for the others. The SNR for t-VC-DWI was significantly higher than that for VC-DWI (P < 0.05) and comparable to that for c-DWI. ADCs in both hepatic lobes were significantly lower for t-VC-DWI than for c-DWI (P < 0.01). ADC in the left lobe was significantly lower for VC-DWI than for c-DWI (P < 0.01). Although ADC in the left lobe was significantly higher for c-DWI (P < 0.01), no significant differences in ADCs were found between the right and left lobes for VC-DWI and t-VC-DWI.

CONCLUSION

The use of a t-VC-DWI sequence enables us to correct ADCs of the liver for artificial elevation due to cardiac motion, with preserved SNR.

Diffusion-weighted MR imaging before and after contrast enhancement with superparamagnetic iron oxide for assessment of hepatic metastasis

PURPOSE

The purpose of our study was to validate diffusion-weighted MRI (DWI) before and after superparamagnetic iron oxide (SPIO) injection for assessment of hepatic metastases.

MATERIALS AND METHODS

Eighty-six hepatic metastases (size range, 0.3-4.7 cm; mean, 1.5 cm) verified pathologically or by follow-up imaging studies in 22 consecutive patients (17 men and 5 women; 44-83 years; mean age, 60 years) during a 13-month period were enrolled. Hepatic MRI, including DWI (b-factors=50, 400, 800 s/mm²) with breath-holding technique of single-shot spin-echo echo-planar imaging (TR/TE=1000/69 ms, average=2) before and after SPIO administration, were retrospectively reviewed by two independent radiologists with a 5-point scale confidence score for each hepatic lesion on pre-contrast DWI (pre-DWI), SPIO-enhanced DWI (SPIO-DWI), and SPIO-enhanced T2*-weighted imaging (SPIO-T2*wI).

RESULTS

For all lesions, SPIO-T2*wI showed significantly higher confidence score in the diagnosis of hepatic metastases than pre-contrast or SPIO-DWI regardless of the size of b-factors (p<0.05) with only one exception; using b-factor=50 s/mm², the score of SPIO-T2*wI was still higher than SPIO-DWI but there was no statistical significance given by observer 1 (p=0.730). For the subcentimeter lesions (n=37), SPIO-T2*wI showed the highest score, and using b-factor= 50 or 400 s/mm² SPIO-DWI showed similar confidence scores to SPIO-T2*wI by both observers (p>0.05). Pre-DWI using b-factor=50 sec/mm² was also comparable with SPIO-T2*wI by observer 1 (p=0.060).

CONCLUSION

Pre-DWI has a limited value for the assessment of hepatic metastases, however, the repetition of DWI after SPIO injection using small b-factors could complement SPIO-T2*wI, especially for subcentimeter lesions.

Oncologic applications of diffusion-weighted MRI in the body

Diffusion-weighted MRI (DWI) allows the detection of malignancies in the abdomen and pelvis. Lesion detection and characterization using DWI largely depends on the increased cellularity of solid or cystic lesions compared with the surrounding tissue. This increased cellularity leads results in restricted diffusion as indicated by reduction in the apparent diffusion coefficient (ADC). Low pretreatment ADC values of several malignancies have been shown to be predictive of better outcome. DWI can assess response to systemic or regional treatment of cancer at a cellular level and will therefore detect successful treatment earlier than anatomical measures. In this review, we provide a brief technical overview of DWI, discuss quantitative image analysis approaches, and review studies which have used DWI for the purpose of detection and characterization of malignancies as well as the early prediction of treatment response.

Diffusion-weighted imaging of the abdomen at 3.0 Tesla: image quality and apparent diffusion coefficient reproducibility compared with 1.5 Tesla

PURPOSE

To compare single-shot echo-planar imaging (SS EPI) diffusion-weighted MRI (DWI) of abdominal organs between 1.5 Tesla (T) and 3.0T in healthy volunteers in terms of image quality, apparent diffusion coefficient (ADC) values, and ADC reproducibility.

MATERIALS AND METHODS

Eight healthy volunteers were prospectively imaged in this HIPAA-compliant IRB-approved study. Each subject underwent two consecutive scans at both 1.5 and 3.0T, which included breathhold and free-breathing DWI using a wide range of b-values (0 to 800 s/mm²). A blinded observer rated subjective image quality (maximum score= 8), and a separate observer placed regions of interest within the liver, renal cortices, pancreas, and spleen to measure ADC at each field strength. Paired Wilcoxon tests were used to compare abdominal DWI between 1.5T and 3.0T for specific combinations of organs, b-values, and acquisition techniques.

RESULTS

Subjective image quality was significantly lower at 3.0T for all comparisons (P = 0.0078- 0.0156). ADC values were similar at 1.5T and 3.0T for all assessed organs, except for lower liver ADC at 3.0T using b0-500-600 and breathhold technique. ADC reproducibility was moderate at both 1.5T and 3.0T, with no significant difference in coefficient of variation of ADC between field strengths.

CONCLUSION

Compared with 1.5T, SS EPI at 3.0T provided generally similar ADC values, however, with worse image quality. Further optimization of abdominal DWI at 3.0T is needed.

Magnetic resonance imaging of the liver: sequence optimization and artifacts

The liver is one of the most challenging organs of the body to image with magnetic resonance because it is large and mobile, receives a dual blood supply, and is surrounded by organs and structures that contribute to artifacts from flow and susceptibility. Recent advances in imaging hardware, in addition to improvements in temporal resolution and development of hepatocyte-specific contrast agents, make imaging of the liver more approachable than in the past; however, it remains a complex process that requires compromise. In this article the authors discuss development and optimization of a liver imaging protocol at 1.5 T, with common variations in each element of the protocol, as well as the strengths and weaknesses associated with the relevant sequences.

Real-time ultrasonography-computed tomography fusion imaging for staging of hepatic metastatic involvement in patients with colorectal cancer: initial results from comparison to US seeing separate CT images and to multidetector-row CT alone

OBJECTIVES

To prospectively evaluate the role of real-time ultrasonography (US)-computed tomography (CT) fusion imaging (US-CT) in comparison with US seeing separate CT images (US + CT) and multidetector-row CT (MDCT) for the correct staging of hepatic metastatic involvement in patients with colorectal cancer.

METHODS

Sixty-four patients with newly diagnosed colorectal cancer and who were referred for abdominopelvic staging before primary tumor resection underwent same-day MDCT, US + CT, and US-CT. Examinations were evaluated on-site by 2 investigators in consensus. Investigators recorded the size and location of detected lesions on segmental liver maps, classified them as being benign, malignant, or indeterminate, and finally assessed the M stage of the liver as being M0, M1, or Mx (indeterminate). All patients underwent surgical exploration including intraoperative US. Reference standard diagnosis was based on findings at surgery, intraoperative US, histopathology, and MDCT follow-up imaging. Differences among investigated modalities were analyzed using McNemar's test.

RESULTS

The reference standard verified 109 (45 < or = 1 cm) hepatic lesions in 25 patients, including 65 (25 < or = 1 cm) metastases in 16 patients (M1). Regarding the 45 < or = 1 cm liver lesions, rates for detection were significantly higher (P < 0.05) for MDCT (80%, 36/45) and US-CT (77.8%, 35/45) than for US + CT (64.4%, 29/45); the rate for correct classification by US-CT (71.1%, 32/45) was significantly higher than for US + CT (48.9%, 22/45) and MDCT (31.1%, 14/45) (all P < 0.05). On patient-based analysis, specificity of MDCT (85.4%, 41/48) was significantly lower (P < 0.05) than for US-CT (97.9%, 47/48) and US + CT (93.7%, 45/48); the positive predictive value of MDCT (63.1%, 12/19) was not significantly different (P = 0.27) compared with US + CT (82.3%, 14/17) but significantly lower (P < 0.05) than for US-CT (93.7%, 15/16). In 13 patients (59 lesions) with only benign (stage M0) or coexistent benign and malignant lesions (stage M1), indeterminate lesion ratings and indeterminate liver stagings (Mx) occurred both significantly lower (P < 0.05) with US-CT (3.4%, 2/59; and 0%, 0/13) than with US + CT (11.9%, 7/59; and 23.1%, 3/13) or with MDCT (30.5%, 18/59; and 53.8%, 7/13).

CONCLUSIONS

Based on these initial diagnostic experiences, complementary US-CT fusion imaging of small CT-indeterminate liver lesions may have value in staging patients with colorectal cancer, focusing on patients who were likely to harbor only benign or coexisting benign and malignant liver lesions and in whom change of M staging would change the clinical management.

Diagnosis of liver metastases: can diffusion-weighted imaging (DWI) be used as a stand alone sequence?

OBJECTIVES

To evaluate if diffusion-weighted MRI (DWI) can replace gadolinium-enhanced MRI (Gd-MRI) for diagnosing liver metastases. The diagnostic accuracy of both techniques alone and in combination are compared.

MATERIALS AND METHODS

Sixty-eight patients with histologically proven primary extrahepatic tumors were included in this retrospective study. Lesions included 62 metastases and 130 benign lesions. Three image sets (unenhanced T1 and T2/gadolinium enhanced T1 (Gd-MRI), DWI and combination of both) were reviewed independently by 3 observers. The areas under the receiver operating characteristic curves (A(z)), sensitivity and specificity for the 3 image sets were compared. The standard of reference was either histopathology or multi-modality and clinical follow-up.

RESULTS

Pooled data showed higher diagnostic accuracy for the combined set (A(z)=0.93) compared to Gd-MRI (p=0.001) and DWI (p<0.0001). No difference was found between the performance of Gd-MRI and DWI (p=0.09). Sensitivity for the combined set was higher than Gd-MRI (p=0.0003) and DWI (p=0.0034). Specificity for DWI was lower than Gd-MRI (p<0.0001) and the combined set (p<0.0001).

CONCLUSION

The diagnostic performance of DWI is equal to that of Gd-MRI. DWI alone can be used in patients where gadolinium contrast administration is not allowed. Combination of Gd-MRI and DWI significantly increases diagnostic accuracy.

Focal eosinophilic infiltration of the liver: gadoxetic acid-enhanced magnetic resonance imaging and diffusion-weighted imaging

OBJECTIVES

Using gadoxetic acid-enhanced magnetic resonance imaging (MRI) and diffusion-weighted imaging (DWI), the purpose of this study was to evaluate findings of focal hepatic eosinophilic infiltration.

METHODS

This retrospective study included 8 patients with 7 histologically confirmed focal eosinophilic infiltration (FEI) of the liver. One case was considered as FEI by using clinical findings and follow-up imaging. Gadoxetic acid-enhanced MRI and DWI were reviewed by 2 radiologists. We evaluated the signal intensity of focal lesions on T1-weighted, T2-weighted, and DW images and the pattern of enhancement in arterial, portal, equilibrium, and hepatobiliary phases of the gadoxetic acid-enhanced MRI. Apparent diffusion coefficient (ADC) value for focal eosinophilic infiltration was also calculated.

RESULTS

On T2-weighted images, 7 (88%) of 8 cases (7/8 lesions) showed mixed hyperintensity with irregular margins. Six (75%) of the 8 cases showed rim enhancement in the arterial phase. Most cases (5/8 lesions [63%]) showed isointensity or hypointensity in the portal and equilibrium phases. In the hepatobiliary phase, all cases (8/8) showed mixed hypointensity with irregular margins and nonspherical shapes. All cases showed hyperintensity in both low and high b-value ranges on DWI. The ADCs for 6 cases showed less than 1.05 × 10(-3) mm2/s (0.74 × 10(-3) to 1.03 × 10(-3) mm2/s).

CONCLUSIONS

Focal eosinophilic infiltration showed mixed hypointensity, irregular margins, and nonspherical shapes with excellent lesion-to-liver contrast in the hepatobiliary phase of the gadoxetic acid-enhanced MRI. Diffusion-weighted imaging and ADCs may not be helpful for characterizing these benign hepatic lesions.

Value of diffusion-weighted magnetic resonance images for discrimination of focal benign and malignant hepatic lesions: a meta-analysis

PURPOSE

To evaluate the ability of DW-MRI in differentiating malignant hepatic tumors from benign lesions.

MATERIALS AND METHODS

Meta-analysis of 14 diagnostic studies was used. A systematic search in Medline, Embase, Web of Science (from January, 1966, to October, 2009), and Cochrane Controlled Clinical Trials Register Database (through third Quarter 2009) was used with screening of the literature.

RESULTS

A meta-analysis of all 95 published studies was performed. Fourteen studies fulfilled the inclusion criteria (804 patients with 1665 hepatic lesions). The global sensitivity was 0.91 (95% confidence interval [CI], 0.86-0.94), the specificity was 0.93 (95% CI, 0.86-0.97), the positive likelihood ratio (PLR) was 13.10 (95% CI, 6.30-27.26), the negative likelihood ratio (NLR) was 0.10 (95% CI, 0.06-0.15), and the diagnostic odds ratio (DOR) was 133.76 (95% CI, 49.77-359.45). The area under the curve of the summary receiver operator characteristic (SROC) was 0.96 (95% CI 0.94-0.98).

CONCLUSION

Diffusion-weighted magnetic resonance imaging is potential technically feasible to differentiate malignant from benign focal liver lesions. Apparent diffusion coefficient measurements can be useful in providing rapid quantifiable information.

Contribution of diffusion-weighted magnetic resonance imaging in the characterization of hepatocellular carcinomas and dysplastic nodules in cirrhotic liver

OBJECTIVES

To evaluate the diagnostic value of diffusion-weighted magnetic resonance imaging (DWI) for the characterization of hepatocellular carcinoma (HCC) and dysplastic nodule (DN) in cirrhotic liver, compared with contrast material-enhanced magnetic resonance imaging (CE-MRI).

METHODS

A total of 54 patients with 40 HCC and 19 DN lesions were included in our study, and all lesions were histopathologically confirmed. All lesions were evaluated with CE-MRI, and breath-hold DWI was performed with b = 500 s/mm. The signal intensity (SI) of the lesions were classified as low, iso-, slightly high, and strongly high SI compared with that of the surrounding liver parenchyma on DWI for qualitative assessment. Apparent diffusion coefficients (ADCs) and lesion-to-liver ADC ratio of HCCs and DNs were measured and compared by using the Mann-Whitney U test. The lesions were characterized with the use of CE-MRI criteria and DWI, respectively. Receiver operating characteristic analysis was performed to assess the diagnostic value of DWI, CE-MRI, and these techniques combined in the differentiation of HCCs from DNs.

RESULTS

In the qualitative analysis, among 40 HCCs, 39 (97.5%) had slightly high or strongly high SI on DWI, and 1 (2.5%) had low SI; only 4 (21.5%) of 19 DNs had slightly high SI, and 15 (78.95%) had iso-SI or low SI. The mean (SD) ADC and ADC ratio for HCCs (1.28 x 10 [0.25] mm/s and 0.88 [0.15], respectively) were significantly lower (P < 0.01 and P < 0.001, respectively) than those for DNs (1.53 x 10 [0.33] mm/s and 1.00 [0.08], respectively). The area, Az, under the receiver operating characteristic curve for the SI feature, the ADC ratio, and the ADCs based on the diagnosis of HCC versus DN were 0.88, 0.81, and 0.68, respectively. When the slightly high SI of lesion with a cutoff ADC ratio less than 0.92 was applied as a criterion, the Az, the sensitivity, the specificity, and the accuracy of DWI for the diagnosis of HCC versus DN were 0.81, 67.50%, 94.74%, and 76.27%, respectively. The corresponding Az, sensitivity, specificity, and accuracy of CE-MRI were 0.70, 82.50%, 57.89%, and 74.58%, respectively. Combined DWI plus CE-MRI had 0.91 Az, 97.50% sensitivity, and 93.22% accuracy, which increased significantly compared with those of CE-MRI alone.

CONCLUSIONS

Diffusion-weighted MRI can provide additional information to differentiate HCC from DN. Combined with CE-MRI, DWI allows improved characterization of HCC versus DN in cirrhotic liver.