Diffusion-weighted imaging in the abdomen and pelvis: concepts and applications

Characteristic MRI findings of sarcomatoid renal cell carcinoma dedifferentiated from clear cell renal carcinoma: radiological-pathological correlation

PURPOSE

To evaluate MRI findings of sarcomatoid renal cell carcinoma (SRCC).

MATERIAL AND METHODS

Eleven patients with pathologically proven SRCC dedifferentiated from clear cell renal carcinoma (CCRC) underwent preoperative renal MRI. The MRI findings were compared with histological findings. On MRI, the following findings were evaluated: the presence and distribution of areas showing heterogeneous iso to high signal intensity (SI) on T2-weighted images (T2HIA) and conspicuously low SI areas (T2LIA) compared to normal renal cortex, areas showing high SI on T1-weighted images and unenhanced areas on dynamic contrast-enhanced images, disruption of pseudocapsule, and the SIs of T2HIA and T2LIA on diffusion-weighted imaging (DWI). The apparent diffusion coefficient (ADC) values and SI ratios to muscle on dynamic contrast-enhanced imaging (DCE) were compared between T2HIA and T2LIA using the t test.

RESULTS

The distribution of T2HIA and T2LIA was as follows: a mixed pattern alone in five, nodular T2LIA pattern alone in one, both mixed and nodular T2LIA patterns in four, and a separated pattern in one. Disruption of the pseudocapsule was seen in all cases. The imaging findings suggesting intratumoral hemorrhage and necrosis were seen in 18% and 63%, respectively. The SIs of T2HIA and T2LIA were low intermediate and high on DWI, respectively. T2LIA and T2HIA corresponded to the components of SRCC with abundant fibrosis and CCRC, respectively. T2LIA showed significantly lower enhancement at all DCE phases and a lower ADC value than T2HIA.

CONCLUSION

The presence of T2LIA corresponding to the area showing a hypovascular nature and markedly restricted diffusion might be characteristic findings of SRCC. Intratumoral hemorrhage and necrosis were seen, but they were not specific findings.

Diffusion-weighted MRI of the abdomen: current value in clinical routine

Magnetic resonance imaging (MRI) provides high tissue contrast without ionizing radiation exposure and unenhanced images are often diagnostic. Therefore, MRI is especially an attractive tool for patients with allergies for gadolinium-based contrast agents or renal failure. Technical advantages have led to the increasing use of diffusion-weighted (DW) MRI in abdominal imaging, which provides qualitative and quantitative information of tissue cellularity and the integrity of cellular membranes. This review article presents the current status of noncontrast MRI with the focus of DW-MRI. Technical background and clinical applications are explained and discussed.

Diseases of the female pelvis: advances in imaging evaluation

Magnetic resonance (MR) imaging has been widely accepted as a powerful imaging modality for the evaluation of the pelvis because of its intrinsic superior soft tissue contrast compared with that of computed tomography. In certain cases, however, the morphologic study provided by MR imaging may not be enough. Functional evaluation with perfusion and diffusion, which allow estimation of the microvascular characteristics and cellularity of the lesions, favors the differentiation of benign from malignant lesions. This article focuses on new magnetic resonance techniques and their contribution to the differentiation and characterization of pelvic pathologies.

The added role of MR imaging in treatment stratification of patients with gynecologic malignancies: what the radiologist needs to know

Many treatment options are available to patients with endometrial, cervical, or ovarian cancer. Magnetic resonance (MR) imaging plays an important role in the patient journey from the initial evaluation of the extent of the disease to appropriate treatment selection and follow-up. The purpose of this review is to highlight the added role of MR imaging in the treatment stratification and overall care of patients with endometrial, cervical, or ovarian cancer. Several MR imaging techniques used in evaluation of patients with gynecologic malignancies are described, including both anatomic MR imaging sequences (T1- and T2-weighted sequences) and pulse sequences that characterize tissue on the basis of physiologic features (diffusion-weighted MR imaging), dynamic contrast agent-enhanced MR imaging, and MR spectroscopy. MR imaging findings corresponding to the 2009 revised International Federation of Gynecology and Obstetrics staging of gynecologic malignancies are also described in detail, highlighting possible pearls and pitfalls of staging. With the growing role of the radiologist as a core member of the multidisciplinary treatment planning team, it is crucial for imagers to recognize that MR imaging has become central in tailoring treatment options and therapy in patients with gynecologic malignancies.

Cardiac diffusion-weighted MR imaging in recent, subacute, and chronic myocardial infarction: a pilot study

PURPOSE

To investigate the clinical feasibility of diffusion-weighted imaging (DWI) to detect recent myocardial infarction (MI) and to differentiate it from subacute and chronic MI, with late-gadolinium enhancement (LGE) sequence as reference. Furthermore, to measure variation of the myocardial apparent diffusion coefficient (ADC) according to the age of MI.

MATERIALS AND METHODS

Seventy-four MI patients were separated in 3 groups. Group A included 34 recent (< 8 days) MI patients; group B, 22 subacute (9-90 days) MI patients; group C, 18 chronic (> 90 days) MI patients; a fourth group (group D) included 24 controls. DWI and LGE images were acquired on a 1.5T system. DWI and LGE matched images were assessed visually by two blinded observers for hyperintense areas in corresponding segments.

RESULTS

Qualitative assessment of DWI compared with LGE images yielded a sensitivity of 97% and a specificity of 61%/14% to differentiate recent from chronic/subacute MI, respectively. The absolute ADCs (recent 0.00632 ± 0.00037 mm(2) /s, subacute 0.00639 ± 0.00035 mm(2) /s, chronic 0.00743 ± 0.00056 mm(2) /s, remote or normal 0.00895 ± 0.00019 mm(2) /s) and relative ADCs were significantly different between groups (P < 0.001) except between recent and subacute MIs.

CONCLUSION

DWI is a sensitive technique to diagnose recent MI. DWI MR sequences could help differentiate recent from chronic MI. From these preliminary results, one should expect DWI to be used in the triage of emergency patients with atypical chest pain, to clarify if an MI is present or not in just a few minutes.

Modern imaging evaluation of the liver: emerging MR imaging techniques and indications

Modern MR imaging evaluation of the liver allows for a comprehensive morphologic and functional assessment of the liver parenchyma, hepatic vessels, and biliary tree, thus aiding in the diagnosis of both focal and diffuse liver diseases.

Magnetic resonance imaging of rectal cancer

Optimal treatment decisions for patients with rectal cancer are based on knowledge of tumor characteristics and prognostic features and any initial treatment must aim to reduce the risk of both local and distant recurrence. The radiologist has become an increasingly important part of multidisciplinary team managing rectal cancer. The primary goal of MRI staging of rectal tumors is to identify prognostic factors in order to offer patients a tailored treatment based on individual risks. Restaging of rectal tumors using MRI after chemoradiation therapy is becoming more relevant issue, since further tailoring of treatment is increasingly being considered after the treatment.

MRI findings of granulomatous prostatitis developing after intravesical Bacillus Calmette-Guérin therapy

AIM

To evaluate magnetic resonance imaging (MRI) findings of granulomatous prostatitis (GP) developing after intravesical Bacillus Calmette-Guérin (BCG) therapy.

MATERIALS AND METHODS

Ten patients with pathologically proven GP underwent prostatic MRI. Lesion shape and signal intensity (SI) were evaluated on T2-weighted (T2WI), T1WI, and diffusion-weighted imaging (DWI).

RESULTS

Polygonal nodular lesions with notches, diffuse lesions, and cystic lesions with mural nodules were seen in two, six, and one patients, respectively. The remaining patient had a diffuse and cystic lesion. All diffuse lesions showed higher SI than muscle on T1WI and higher SI than the normal peripheral zone (PZ) on DWI. On T2WI, six of seven diffuse lesions showed a slightly lower SI than bone marrow and the remaining one lesion was iso-intense. All nodular lesions showed a low SI similar to muscle on T2WI and were iso-intense to muscle on T1WI. On DWI, two each of the four nodular lesions showed slightly lower SI and slightly higher SI than the normal PZ, respectively. All contents within the cyst and mural nodules showed markedly high and low SI on T2WI, respectively. On DWI, all fluids within cysts showed markedly high SI. One each of the mural nodules showed slightly higher SI and slightly lower SI than the normal PZ on DWI.

CONCLUSION

Three main MRI patterns of GP were identified: diffuse, nodular, and cystic with mural nodule; among them, the diffuse type was the most common. Cystic lesions with mural nodules could accompany the lesion.

Diffusion-weighted MR imaging for the differentiation of malignant from benign strictures in the periampullary region

OBJECTIVES

To investigate the value of DWI for differentiating malignant from benign strictures in the periampullary region.

METHODS

We retrospectively analysed data from 78 patients who had undergone magnetic resonance cholangiopanreatography (MRCP) and diffusion-weighted imaging (DWI), in whom biliary strictures in the periampullary region were suspected. Twenty-two malignant and 56 benign lesions were included. One radiologist compared the signal intensity of malignant and benign periampullary lesions on DWI using b = 500 and 800 s/mm(2). The signal intensity of bile was also compared, and an optimal b value was determined for periampullary lesions. Two other radiologists reviewed MRCP alone and combined DWI and MRCP for the possibility of malignant periampullary lesions. Diagnostic accuracy was calculated for each reviewer by receiver operating characteristic (ROC) curve analysis.

RESULTS

Malignant periampullary lesions more frequently appeared hyperintense than benign lesions on DWI using the two b values (P < 0.001). Bile more frequently appeared hyperintense on DWI using b = 500 s/mm(2) (87.2 %) than b = 800 s/mm(2) (24.4 %). Therefore, b = 800 s/mm(2) was determined as the preferred sequence. Diagnostic accuracy for malignant periampullary lesions improved for both reviewers after adding DWI; from 0.714 to 0.924 (P = 0.006, for reviewer 1) and from 0.714 to 0.919 (P = 0.007, reviewer 2).

CONCLUSIONS

Combined DWI with MRCP can improve the diagnostic accuracy for differentiating malignant from benign strictures in the periampullary region.

KEY POINTS

• Diffusion-weighted magnetic resonance imaging provides yet more information about hepatobiliary structures. • Diffusion-weighted imaging (DWI) has now been applied to the biliary tree. • Most periampullary carcinomas appear hyperintense on high b value DWI. • DWI can help differentiate between malignant and benign periampullary lesions.

Diffusion-weighted magnetic resonance imaging for staging liver fibrosis is less reliable in the presence of fat and iron

OBJECTIVES

To investigate the reliability of diffusion-weighted magnetic resonance imaging (DW-MRI) for staging liver fibrosis in the presence of fat and iron.

METHODS

Ninety-five patients, including 48 men and 47 women, aged 57.0 ± 14.2 years, underwent liver biopsy. Ninety-six samples were histologically staged for liver fibrosis (0-Ishak score 0; 1-Ishak score 1-4; 2-Ishak score 5-6) and semiquantitatively graded for hepatic iron (0, no; 1, low; 2, moderate; 3, high iron) and for hepatic steatosis. Within 72 h after biopsy, navigator-triggered DW-MRI using b-values of 50/400/800 s/mm(2) was performed in a 1.5-T system, and apparent diffusion coefficients (ADC) were analysed. ADCs were correlated with fibrosis stage, steatosis grade, and iron grade using linear regression.

RESULTS

ADC did not correlate with fibrosis stages in either the overall group (n = 96; R (2) = 0.38; P = 0.17) or in the subgroup without liver iron and steatosis (n = 40; R (2) = 0.01; P = 0.75). ADC decreased significantly with steatosis grade in cases without iron and fibrosis (n = 42; R (2) = 0.28; ß = -5.3; P < 0.001). Liver iron was modestly correlated with ADC in patients without fibrosis and steatosis (n = 33; R (2) = 0.29; P = 0.04), whereas high iron concentrations were associated with low ADC values (group 3: β = -489; P = 0.005; reference:group 0) but intermediate levels were not (group 1/group 2: P = 0.93/P = 0.54; reference group: 0).

CONCLUSIONS

ADC values are confounded by fat and iron. However, even in patients without fat or iron, DW-MRI does not adequately discriminate the stage of fibrosis.

KEY POINTS

• Diffusion-weighted magnetic resonance imaging (DW-MRI) is increasingly used to evaluate liver disease. • DWI using b-values of 50/400/800 s/mm (2) does not adequately quantify fibrosis. • Assessment of the apparent diffusion coefficient (ADC) is confounded by fat and iron. • Fat may influence ADCs by altering water diffusion. • Iron may influence ADCs by signal decay and noise floor effects.

PET/MR in oncology: an introduction with focus on MR and future perspectives for hybrid imaging

After more than 20 years of research, a fully integrated PET/MR scanner was launched in 2010 enabling simultaneous acquisition of PET and MR imaging. Currently, no clinical indication for combined PET/MR has been established, however the expectations are high. In this paper we will discuss some of the challenges inherent in this new technology, but focus on potential applications for simultaneous PET/MR in the field of oncology. Methods and tracers for use with the PET technology will be familiar to most readers of this journal; thus this paper aims to provide a short and basic introduction to a number of different MRI techniques, such as DWI-MR (diffusion weighted imaging MR), DCE-MR (dynamic contrast enhanced MR), MRS (MR spectroscopy) and MR for attenuation correction of PET. All MR techniques presented in this paper have shown promising results in the treatment of patients with solid tumors and could be applied together with PET increasing the amount of information about the tissues of interest. The potential clinical benefit of applying PET/MR in staging, radiotherapy planning and treatment evaluation in oncology, as well as the research perspectives for the use of PET/MR in the development of new tracers and drugs will be discussed.

Diffusion-weighted imaging of the liver: usefulness of ADC values in the differential diagnosis of focal lesions and effect of ROI methods on ADC measurements

OBJECT

By measuring the apparent diffusion coefficient (ADC) of liver parenchyma and focal hepatic lesions (FHL) we proposed to investigate the utility of ADC in the differential diagnosis of hepatic disease and to determine the influence of region of interest (ROI) characteristics in those measurements.

MATERIALS AND METHODS

Ninety-three patients with at least one supracentimetric FHL, or parenchymal abnormality, were retrospectively evaluated. Diagnosis was based on histopathologic data or, alternatively, on a combination of consensus between imaging methods and 24 months of follow-up. Ninety lesions were evaluated with respiratory-triggered diffusion-weighted imaging (b values: 50 and 700 s/mm(2)): 14 hepatocellular carcinomas, 18 metastases, 10 focal nodular hyperplasias, four adenomas, 30 hemangiomas and 14 cysts. ADC of hepatic parenchyma was measured by placing ROIs in four different segments, and in FHLs by using three circular 1 cm(2) ROIs and one ROI encompassing the full lesion. Data was statistically analyzed (p < 0.05 considered significant), and a receiver operating characteristic curve was assessed to evaluate the accuracy for the diagnosis of malignancy.

RESULTS

Our measurements showed that parenchyma ADC was significantly higher in segment II and that ADCs of malignant lesions were significantly lower than those of benign lesions (p < 0.001). There was significant overlap between benign solid lesions and malignant lesions and the area under the curve for malignancy was 0.939 (sensitivity 89.7 %, specificity 90.6 %), using a cutoff of 1.43 × 10(-3) mm(2)/s. No significant difference was found between ROIs of different characteristics.

CONCLUSION

ADC measurements can help to characterize FHLs and differentiate normal from pathological parenchyma. Any ROI above 1 cm(2) can provide accurate ADC measurements in homogenous lesions.

Usefulness of diffusion-weighted magnetic resonance imaging in the diagnosis of prostate cancer

RATIONALE AND OBJECTIVES

The aim of this study was to evaluate the diagnostic accuracy of diffusion-weighted magnetic resonance imaging (DWI) in prostate cancer.

MATERIALS AND METHODS

The MEDLINE, Embase, CANCERLIT, and Cochrane Library databases were searched for studies published from January 2001 to August 2011 evaluating the diagnostic performance of DWI in detecting prostate carcinoma. Sensitivities and specificities were determined across studies, and summary receiver-operating characteristic curves were constructed using hierarchical regression models.

RESULTS

Sixteen studies (18 subsets) with a total of 852 patients were included. Six studies (seven subsets) examining men with pathologically confirmed prostate cancer (260 patients) had pooled sensitivity and specificity of 0.88 (95% confidence interval [CI], 0.76-0.95) and 0.84 (95% CI, 0.76-0.90), respectively. Compared to patients at high risk for clinically relevant cancer, sensitivity was higher in low-risk patients (0.94 [95% CI, 0.89-0.97] vs 0.62 [95% CI, 0.54-0.70], P < .05), but specificity was lower (0.86 [95% CI, 0.72-0.94] vs 0.89 [95% CI, 0.83-0.93], P < .05). Ten studies (11 subsets) examining patients with suspected prostate cancer (592 patients) had pooled sensitivity and specificity of 0.76 (95% CI, 0.68-0.84) and 0.86 (95% CI, 0.79-0.91). Sensitivity was lower in high-risk patients (0.74 [95% CI, 0.57-0.87] vs 0.78 [95% CI, 0.70-0.84], P > .05), but specificity was higher (0.92 [95% CI, 0.89-0.94] vs 0.78 [95% CI, 0.70-0.84], P < .05).

CONCLUSIONS

A limited number of small studies suggest that DWI could be a rule-in test for high-risk patients. Further prospective studies including larger populations are necessary to confirm the actual value of DWI in this field.

MR imaging of hypervascular lesions in the cirrhotic liver: a diagnostic dilemma

Cirrhosis is characterized by a spectrum of hepatocellular nodules that mark the progression from regenerative nodules to low- and high-grade dysplastic nodules, followed by small and large hepatocellular carcinomas (HCCs). Characterization of small nodules on the basis of imaging and histopathologic findings is complicated by an overlap in findings associated with each type of nodule, a reflection of their multistep transitions. Vascularity patterns change gradually as the nodules evolve, with an increasing shift from predominantly venous to predominantly arterial perfusion. Regenerative and low-grade dysplastic nodules demonstrate predominantly portal perfusion and contrast enhancement similar to that of surrounding parenchyma. Differentiation of high-grade dysplastic nodules and well-differentiated HCCs on the basis of dynamic imaging and histologic findings is challenging, with a high rate of false-negative results. Some small nodules that lack hypervascularity may be early HCCs. Progressed small and large HCCs usually present no diagnostic difficulty because of their characteristic findings. Although characterization of hypervascular lesions in the cirrhotic liver is difficult, it is a key step in disease management and is the radiologist's responsibility.

Diffusion-weighted MRI of the liver-Interpretative pearls and pitfalls

Diffusion-weighted magnetic resonance imaging (DW MRI) is an established technique in neuroradiology and more recently has emerged as a useful adjunct to various oncological applications of MRI. It has an expanding role in the evaluation of liver lesions, offers higher detection rates for small lesions, and can increase confidence in differentiating between benign and malignant lesions. Other applications include assessment of tumour response to therapy, differentiating tumour from bland thrombus, and assessment of liver fibrosis. DW sequences can be performed on most modern MRI machines with relative ease, in a short time period and without the need for contrast medium. DW MRI can be of value in the detection and characterization of hepatic lesions but there are pitfalls, which can potentially cause interpretative difficulty. This article will review the rationale for DW MRI in liver imaging, demonstrate the clinical utility of the technique in a spectrum of hepatic diseases, and illustrate key interpretative pearls and pitfalls.

The clinical value of diffusion-weighted imaging in combination with T2-weighted imaging in diagnosing prostate carcinoma: a systematic review and meta-analysis

OBJECTIVE

We aimed to explore the role of diffusion-weighted imaging (DWI) in combination with T2-weighted imaging (T2WI) in detecting prostate carcinoma through a systematic review and meta-analysis.

MATERIALS AND METHODS

The MEDLINE, EMBASE, Cancerlit, and Cochrane Library databases were searched for studies published from January 2001 to July 2011 evaluating the diagnostic performance of T2WI combined with DWI in detecting prostate carcinoma. We determined sensitivities and specificities across studies, calculated positive and negative likelihood ratios, and constructed summary receiver operating characteristic curves. We also compared the performance of T2WI combined with DWI with T2WI alone by analyzing studies that had also used these diagnostic methods on the same patients.

RESULTS

Across 10 studies (627 patients), the pooled sensitivity of T2WI combined with DWI was 0.76 (95% CI, 0.65-0.84), and the pooled specificity was 0.82 (95% CI, 0.77-0.87). Overall, the positive likelihood ratio was 4.31 (95% CI, 3.12-5.92), and the negative likelihood ratio was 0.29 (95% CI, 0.20-0.43). In seven studies in which T2WI combined with DWI and T2WI alone were performed, the sensitivity and specificity of T2WI combined with DWI were 0.72 (95% CI, 0.67-0.82) and 0.81 (95% CI, 0.76-0.86), respectively, and the sensitivity and specificity of T2WI alone were 0.62 (95% CI, 0.55-0.68) and 0.77 (95% CI, 0.71-0.82), respectively.

CONCLUSION

T2WI combined with DWI may be a valuable tool for detecting prostate cancer in the overall evaluation of prostate cancer, compared with T2WI alone. High-quality prospective studies of T2WI combined with DWI to detect prostate carcinoma still need to be conducted.

Diffusion-weighted imaging of biliopancreatic disorders: correlation with conventional magnetic resonance imaging

Diffusion-weighted magnetic resonance imaging (DWI) is a well established method for the evaluation of intracranial diseases, such as acute stroke. DWI for extracranial application is more difficult due to physiological motion artifacts and the heterogeneous composition of the organs. However, thanks to the newer technical development of DWI, DWI has become increasingly used over the past few years in extracranial organs including the abdomen and pelvis. Most previous studies of DWI have been limited to the evaluation of diffuse parenchymal abnormalities and focal lesions in abdominal organs, whereas there are few studies about DWI for the evaluation of the biliopancreatic tract. Although further studies are needed to determine its performance in evaluating bile duct, gallbladder and pancreas diseases, DWI has potential in the assessment of the functional information on the biliopancreatic tract concerning the status of tissue cellularity, because increased cellularity is associated with impeded diffusion, as indicated by a reduction in the apparent diffusion coefficient. The detection of malignant lesions and their differentiation from benign tumor-like lesions in the biliopancreatic tract could be improved using DWI in conjunction with findings obtained with conventional magnetic resonance cholagiopancreatography. Additionally, DWI can be useful for the assessment of the biliopancreatic tract in patients with renal impairment because contrast-enhanced computed tomography or magnetic resonance scans should be avoided in these patients.

Acute appendicitis on abdominal MR images: training readers to improve diagnostic accuracy

PURPOSE

To determine if training with direct feedback helps to improve the diagnostic performance of inexperienced readers in the detection of appendicitis on magnetic resonance (MR) images.

MATERIALS AND METHODS

The institutional review board approved this retrospective study and waived the requirement for informed consent. Nine radiologists and eight residents without experience in evaluating MR images for acute abdominal conditions evaluated a training set of images from 100 MR imaging examinations of patients suspected of having appendicitis and received direct feedback after each evaluation. An expert panel made a diagnosis of appendicitis in 45 patients and an alternative diagnosis in 55 patients on the basis of histopathologic examination and follow-up. Readers recorded two diagnoses: the first after viewing images from conventional MR sequences (half-Fourier rapid acquisition with relaxation enhancement and true fast imaging with steady-state precession) and the second after viewing diffusion-weighted (DW) MR images. Reader sensitivity and specificity were calculated per set of 25 cases.

RESULTS

The average reader sensitivity for detecting appendicitis improved significantly after training (0.82 vs 0.92, P = .003); the average specificity improved nonsignificantly (0.82 vs 0.88, P = .10). Sensitivity for radiologists increased from 0.81 in the first set of 25 cases to 0.91 in the last set, and specificity improved from 0.82 to 0.85. For residents, sensitivity increased from 0.82 to 0.94, and specificity increased from 0.82 to 0.91. Sensitivity improved from 0.80 to 0.87 (P < .001) in all readings combined when DW images were read in addition to conventional MR images.

CONCLUSION

Diagnostic accuracy of inexperienced readers in the evaluation of abdominal MR images for acute appendicitis improved after training with direct feedback, and the addition of DW images improved reader sensitivity.

Differentiation between pelvic abscesses and pelvic tumors with diffusion-weighted MR imaging: a preliminary study

PURPOSE

Use diffusion-weighted magnetic resonance imaging (MRI) in differentiating pelvic abscess from pelvic cystic tumor.

MATERIALS AND METHODS

Patients with pelvic abscess (n=23) or pelvic cystic tumor (n=15) who underwent diffusion-weighted MRI were reviewed.

RESULTS

Pelvic abscesses showed hyperintensity on diffusion-weighted MRI and hypointensity on apparent diffusion coefficient (ADC) map. The mean ADC values of fluid in pelvic abscess and pelvic tumors were 0.73 ± 0.15 × 10(-3) and 2.27 ± 0.45 × 10(-3) mm(2)/s, respectively. Pelvic abscesses had significantly lower ADC values than pelvic cystic tumors (P<.001).

CONCLUSION

Diffusion-weighted MRI provides a noncontrast method for interpreting pelvic cystic lesions.

CT, MRI, and PET findings of gastric schwannoma

Gastric schwannoma is a rare tumor that accounts for only 0.2 % of all gastric tumors. We report a case of gastric schwannoma that underwent computed tomography (CT), magnetic resonance imaging (MRI), and [(18)F]-fluorodeoxyglucose positron emission tomography (FDG-PET), and its histological confirmation was acquired. Gastric schwannoma showed high intensity on T2-weighted and diffusion-weighted MRI and high maximum standardized uptake on [(18)F]-FDG-PET. Lymphadenopathy close to the tumor was also found. Although diffusion-weighted MRI, [(18)F]-FDG-PET, and the presence of lymphadenopathy could suggest malignant tumors, the detail interpretation of the other CT and MRI findings may give a clue for the diagnosis of gastric schwannoma.

Diffusion-weighted MRI of focal cystic pancreatic lesions at 3.0-Tesla: preliminary results

PURPOSE

To determine the utility of 3.0-Tesla diffusion-weighted (DW) magnetic resonance imaging (MRI) for focal cystic pancreatic lesion (FCPL) characterization.

MATERIALS AND METHODS

55 FCPL (34 IPMN, 5 serous cystadenoma, and 16 inflammatory) were evaluated. Two radiologists reviewed in consensus DW-MRI images. Reference standard was obtained from patient history, cytological and histopathology data, FCPL fluid analysis, and follow-up imaging results. Signal intensity (SI) and apparent diffusion coefficient values (ADC) of FCPL and normal pancreas were measured. FCPL-to-pancreas SI and ADC ratios were also calculated.

RESULTS

Qualitatively, 11 of 21 non-mucinous vs. 4 of 34 mucinous lesions appeared hyperintense at b value of 1,000 s/mm(2) (P = 0.02). Three FCPL demonstrated restricted diffusion: all inflammatory. Significant differences in mean ADC between neoplastic vs. non-neoplastic (P = 0.009), and mucinous vs. non-mucinous (P = 0.013) lesions were demonstrated. FCPL-to-pancreas ADC and SI ratios demonstrated significant differences between neoplastic vs. non-neoplastic lesions [ADC, (P = 0.019); SI for b values 750 (P = 0.010) and 1,000 s/mm(2) (P = 0.017)] and mucinous vs. non-mucinous lesions [ADC (P = 0.018); SI for b values 750 (P = 0.013) and 1,000 s/mm(2) (P = 0.015)].

CONCLUSION

Although mean ADC values and FCPL-to-pancreas SI and ADC ratios may be helpful in differentiating FCPL, characterization of individual FCPL by means of 3.0-Tesla DW-MRI appears limited.

Role of apparent diffusion coefficient values and diffusion-weighted magnetic resonance imaging in differentiation between benign and malignant thyroid nodules

OBJECTIVE

The purpose of the study was to differentiate between benign and malignant thyroid nodules using nodule-spinal cord signal intensity and nodule apparent diffusion coefficient (ADC) ratios on diffusion-weighted magnetic resonance imaging (DW-MRI).

MATERIALS AND METHODS

Forty-four patients (27 females, 17 males; mean age, 49 years) with nodules who underwent DW-MRI were included in this study. The images were acquired with 0, 50, 400 and 1000 s/mm(2)b values. ADC maps were calculated afterwards. Fine needle aspiration biopsies (FNAB) were performed at the same day with DW-MRI acquisition. The diagnosis in patients where malignity was detected after FNAB was confirmed by histopathologic analysis of the operation material. The signal intensities of the spinal cord and the nodule were measured additionally, over b-1000 diffusion-weighted images. Nodule/cord signal intensity (SI) ratios were obtained and the digital values were calculated by dividing to ADC values estimated for each nodule. Statistical analysis was performed.

RESULTS

The (nodule SI-cord SI)/nodule ADC ratio is calculated in the DW images, and a statistically significant relationship was found between this ratio and the histopathology of the nodules (P<.001). The ratio was determined as 0.27 in benign and 0.86 in malignant lesions. The result of receiver operating characteristic (ROC) analysis was statistically significant, and the area under curve (100%) was considerably high. The threshold value was calculated as 0.56 according to the ROC analysis. According to this threshold value, the sensitivity, specificity, positive predictive value, negative predictive value, and accuracy rates for (nodule SI/cord SI)/ADC ratios in differentiating benign from malignant thyroid nodules are calculated as 100%, 97%, 83%, 100%, and 98%, respectively.

CONCLUSION

We have found that (nodule/cord SI)/nodule ADC ratio has the highest values for sensitivity and specificity among the tests defined for characterization of nodules.

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.

[Benign focal hepatic lesions]

A profound knowledge of the various benign focal hepatic lesions and selection of the most suitable radiological examination modality is essential for achieving an accurate characterization of a hepatic lesion and in turn will determine the further patient management. This will avoid unnecessary agitation to both patient and the referring clinician and limits time-consuming, costly and risky biopsies to an absolute minimum. The following article will discuss the typical and atypical appearances of the most frequent and clinically relevant benign focal hepatic lesions with ultrasound, computed tomography and magnetic resonance imaging.

Diffusion-weighted MR imaging of normal and abnormal scrotum: preliminary results

Magnetic resonance (MR) imaging of the scrotum represents an important supplemental diagnostic tool in the evaluation of scrotal diseases. Diffusion-weighted (DW) MR imaging is a developing technique, proved to improve tissue characterization. We evaluated the feasibility and diagnostic performance of DW MR imaging in the detection and characterization of scrotal lesions. We retrospectively evaluated 31 scrotal lesions (23 intratesticular and 8 extratesticular) in 26 men. All MR examinations were performed on a 1.5-T unit, using a pelvic-phased array coil. DW sequences were obtained using a single shot, multislice spin echo planar diffusion pulse sequence and a b factor of 0 and 900 s mm(-2). The DW MR characteristics and the apparent diffusion coefficient (ADC) values of normal scrotal contents and scrotal diseases were evaluated. Comparison between the ADC values of normal scrotum, benign lesions and scrotal malignancies was performed. The accuracy of conventional sequences, DW images alone and DW imaging combined with conventional images in differentiating benign from malignant scrotal lesions was calculated. The ADC values of testicular malignancies were different from those of normal testis and benign intratesticular lesions, and the ADC values of benign extratesticular lesions from those of normal epididymis (P<0.05). The overall accuracy of conventional imaging, DW imaging alone and DW MR combined with conventional sequences in the characterization of intratesticular lesions was 91%, 87% and 100%, respectively. Our findings suggest that DW MR imaging and ADC values may provide valuable information in the diagnosis and characterization of scrotal diseases.

Principles and applications of diffusion-weighted imaging in cancer detection, staging, and treatment follow-up

Diffusion-weighted imaging relies on the detection of the random microscopic motion of free water molecules known as Brownian movement. With the development of new magnetic resonance (MR) imaging technologies and stronger diffusion gradients, recent applications of diffusion-weighted imaging in whole-body imaging have attracted considerable attention, especially in the field of oncology. Diffusion-weighted imaging is being established as a pivotal aspect of MR imaging in the evaluation of specific organs, including the breast, liver, kidney, and those in the pelvis. When used in conjunction with apparent diffusion coefficient mapping, diffusion-weighted imaging provides information about the functional environment of water in tissues, thereby augmenting the morphologic information provided by conventional MR imaging. Detected changes include shifts of water from extracellular to intracellular spaces, restriction of cellular membrane permeability, increased cellular density, and disruption of cellular membrane depolarization. These findings are commonly associated with malignancies; therefore, diffusion-weighted imaging has many applications in oncologic imaging and can aid in tumor detection and characterization and in the prediction and assessment of response to therapy.

Diffusion-weighted MRI of fatty liver

PURPOSE

To investigate the effect of fat infiltration on the apparent diffusion coefficient (ADC) of liver, and assess the relationship between ADC and hepatic fat fraction (HFF).

MATERIALS AND METHODS

MRI scans of 120 consecutive patients were included in this retrospective study. Of these, 42 patients were included in the fatty liver group and 78 in the control group. ADC values were measured from a pair of diffusion-weighted (DW) images (b = 0 mm(2) /s and 1000 mm(2) /s). HFFs were measured using T1W GRE dual-echo images. The difference between the ADCs of the two groups was assessed with the t-test. The relationship between HFF and ADC was determined using linear regression analysis and the Pearson correlation coefficient (r).

RESULTS

Mean HFFs were 0.85 ± 2.86 and 13.67 ± 8.62 in the control and fatty liver groups, respectively. The mean ADC of fatty liver group 1.20 ± 0.22 × 10(-3) mm(2) /s was significantly lower than that of the control group 1.32 ± 0.23 × 10(-3) mm(2) /s (P = 0.02). Linear regression analysis revealed an inverse relationship between ADC and HFF (r = -0.39, P < 0.0001).

CONCLUSION

ADC significantly decreases in patients with >5% HFF, and ADC and HFF exhibit an inverse relationship.

Diffusion-weighted MR imaging in gynecologic cancers

Diffusion-weighted imaging (DWI) reflects changes in proton mobility caused by pathological alterations of tissue cellularity, cellular membrane integrity, extracellular space perfusion, and fluid viscosity. Functional imaging is becoming increasingly important in the evaluation of cancer patients because of the limitations of morphologic imaging. DWI is being applied to the detection and characterization of tumors and the evaluation of treatment response in patients with cancer. The advantages of DWI include its cost-effectiveness and brevity of execution, its complete noninvasiveness, its lack of ionizing radiation, and the fact that it does not require injection of contrast material, thus enabling its use in patients with renal dysfunction. In this article, we describe the clinical application of DWI to gynecological disorders and its diagnostic efficacy therein.

High-b-value diffusion-weighted MR imaging of benign hepatocellular lesions: quantitative and qualitative analysis

PURPOSE

To analyze the signal intensity (SI) of benign hepatocellular lesions in high-b-value diffusion-weighted (DW) magnetic resonance (MR) images and to compare the apparent diffusion coefficient (ADC) values of focal nodular hyperplasias (FNHs) with those of hepatocellular adenomas (HCAs).

MATERIALS AND METHODS

This retrospective study was approved by institutional review board, with waiver of informed consent. Inclusion criteria were consecutive patients with diagnosed FNH or HCA who underwent MR imaging with a DW sequence of the liver at three b values, 0, 150, and 600 sec/mm2. The final study population included 67 patients (seven men, 60 women) with 90 hepatocellular lesions (54 FNHs, 36 HCAs). The mean ADC was compared between the lesions and the liver. Receiver operating characteristic analysis was performed to evaluate the diagnostic value of ADC for differentiating HCAs and FNHs.

RESULTS

The mean ADC value of all FNHs and HCAs was significantly lower than that of the liver (P=.004). An ADC ratio below 15% was observed in 50 of 54 (93%) FNHs and in 29 of 36 (81%) HCAs. The mean ADC value of FNHs was significantly higher than that of HCAs (P<.001). The area under the receiver operating characteristic curve was 0.760. With a cutoff value of 1.37×10(-3) mm2/sec, the sensitivity and specificity for differentiating HCA from FNH were 70% and 76%, respectively. There was no significant difference in ADC values between HCA subtypes. The SI of most FNHs and HCAs (78 of 90, 87%) increased with increasing b values, whereas none showed a decrease in SI with increasing b values. When the DW MR criteria for benign and malignant liver tumors were applied, 44 of 90 (49%) lesions would have been considered malignant lesions, whereas the other lesions (46 of 90, 51%) would have been considered indeterminate.

CONCLUSION

On DW MR images, benign hepatocellular lesions often show findings that suggest restricted diffusion.

MR imaging of the abdomen and pelvis in infants, children, and adolescents

Recent developments in magnetic resonance (MR) imaging have profoundly changed the investigation of abdominal and pelvic disease in pediatrics. Motion reduction techniques, such periodically rotated overlapping parallel lines with enhanced reconstruction, or PROPELLER, have resulted in reliable imaging with quiet breathing. Faster imaging sequences minimize artifact and allow for more efficient studies. Diffusion-weighted imaging has become increasingly important in the evaluation of neoplastic disease, depicting disease with increased cellularity and helping to differentiate benign from malignant masses. MR enterography helps visualize intra- and extraluminal bowel pathologic conditions. MR cholangiopancreatography can depict congenital and acquired causes of pancreatic and biliary abnormalities. MR urography is an effective technique for a one-stop-shop evaluation of structural urinary tract abnormality and renal function. Three-dimensional acquisitions allow volumetric display of structures from multiple angles. Specialized techniques allow quantification of iron and fat in the viscera in children with hemolytic anemia and obesity, respectively. This article covers current techniques and strategies to perform and optimize MR imaging of the abdomen and pelvis in infants, children, and adolescents and describes important practical applications.

Perfusion fraction of diffusion-weighted MRI for predicting the presence of blood supply in ovarian masses

PURPOSE

To evaluate whether perfusion fraction (PF) calculated with diffusion-weighted magnetic resonance imaging (MRI) predicts the presence of blood supply in ovarian masses.

MATERIALS AND METHODS

PFs of 92 ovarian lesions in 53 patients administered gadolinium were retrospectively calculated with diffusion-weighted images at b-values of 0, 500, and 1000 sec/mm(2). PFs were compared between ovarian lesions, except for fat, with (n = 21) or without contrast enhancement (n = 57), using Student's t-test and receiver operating characteristics (ROC) curve analysis. Lesion enhancement rates of contrast-enhanced images at 30 and 180 seconds after gadolinium injection (ER(30sec) and ER(180sec)) and PFs were compared using Pearson's correlation coefficient.

RESULTS

PFs of the lesions with contrast enhancement were significantly higher than those without contrast enhancement (0.22 ± 0.09 and 0.02 ± 0.08, respectively, P < 0.0001). The ROC curve identified the best cutoff point for PF at 0.135 (95.2% sensitivity and 94.7% specificity) as a predictor of the contrast enhancement effect. The area under the ROC curve was 0.984. PF correlated moderately with ER(30sec) (0.62, y = 0.13x + 0.04, P < 0.0001) and ER(180sec) (0.74, y = 0.13x + 0.03, P < 0.0001).

CONCLUSION

PF calculated with diffusion-weighted images can potentially predict blood supply in ovarian masses.

Prostate MRI: diffusion-weighted imaging at 1.5T correlates better with prostatectomy Gleason Grades than TRUS-guided biopsies in peripheral zone tumours

OBJECTIVES

To investigate the usefulness of Apparent Diffusion Coefficients (ADC) in predicting prostatectomy Gleason Grades (pGG) and Scores (GS), compared with ultrasound-guided biopsy Gleason Grades (bGG).

METHODS

Twenty-four patients with biopsy-proven prostate cancer were included in the study. Diffusion-weighted images were obtained using 1.5-T MR with a pelvic phased-array coil. Median ADC values (b0,500,1000 s/mm²) were measured at the most suspicious areas in the peripheral zone. The relationship between ADC values and pGG or GS was assessed using Pearson's coefficient. The relationship between bGG and pGG or GS was also evaluated. Receiver operating characteristic (ROC) curve analysis was performed to assess the performance of each method on a qualitative level.

RESULTS

A significant negative correlation was found between mean ADCs of suspicious lesions and their pGG (r = -0.55; p < 0.01) and GS (r = -0.63; p < 0.01). No significant correlation was found between bGG and pGG (r = 0.042; p > 0.05) or GS (r = 0.048; p > 0.05). ROC analysis revealed a discriminatory performance of AUC = 0.82 for ADC and AUC = 0.46 for bGG in discerning low-grade from intermediate/high-grade lesions.

CONCLUSIONS

The ADC values of suspicious areas in the peripheral zone perform better than bGG in the correlation with prostate cancer aggressiveness, although with considerable intra-subject heterogeneity.

KEY POINTS

• Prostate cancer aggressiveness is probably underestimated and undersampled by routine ultrasound-guided biopsies. • Diffusion-weighted MR images show good linear correlation with prostate cancer aggressiveness. • DWI information may be used to improve risk-assessment in prostate cancer.

[Contribution of new MRI sequences in the exploration of the pelvic gynaecological disease]

MRI has emerged for several years as the imaging examination of second-line indications in the majority of female pelvic imaging, after ultrasonography. Recent technical advances have allowed the widespread use of new MRI sequences, allowing a morphological and functional analysis of the pelvic organs. Diffusion weighted-imaging has a definite interest for the detection, characterization and staging of uterine and adnexal lesions. Dynamic contrast-enhanced imaging is an essential tool for characterizing adnexal lesions and to optimize the staging of uterine cancers. The 3D morphological imaging allows multiplanar reconstructions and is particularly useful in mapping fibroids, uterine malformations and in endometriosis.

Confident non-invasive diagnosis of pseudolesions of the liver using diffusion-weighted imaging at 3T MRI

PURPOSE

Pseudolesions of the liver including focal steatosis or non-steatosis and THID (transient hepatic intensity differences) are often challenging, especially when imaging patients with underlying malignant disease. We evaluated the efficacy of diffusion-weighted imaging (DWI) in the diagnostic work-up of pseudolesions.

MATERIALS AND METHODS

Forty-eight patients with pseudolesions of the liver were consecutively examined and the images were retrospectively analyzed. MRI was performed on a clinical 3T scanner using T1-GRE in-phase and opposed phase images, T2-TSE-FS, diffusion-weighted sequences (b-value 50, 300, 600), ADC mapping, and dynamic post-contrast T1-VIBE-FS sequences (32 patients received Gd-EB-DTPA and 16 patients received gadolinium chelates). All images were analyzed by two experienced radiologists in consensus. As a standard of reference, we used the T1-w GRE, in-phase and out of phase, and the contrast enhanced series, as well as long-term follow-up.

RESULTS

In the 48 patients, a total of 116 liver lesions were found. Of these, 40 were benign and eleven were malignant focal lesions. Benign lesions included one FNH, 26 simple cysts, and twelve hemangiomas. In addition, 65 pseudolesions (20 focal steatosis, 13 focal non-steatosis, and 32 THIDs) were found. All pseudolesions could be identified either on the T1-GRE in-phase and opposed phase images or on the contrast-enhanced series, or on both. However, none of them were visible on the diffusion-weighted images.

CONCLUSION

Pseudolesions are invisible on DWI (negative predictive value = 1); therefore, DWI can be used as an additional sequence to significantly increase diagnostic confidence in the differentiation between pseudolesions and other focal liver lesions.

Diffusion-weighted magnetic resonance imaging in the upper abdomen: technical issues and clinical applications

Recent technological achievements have enabled the transposition of diffusion-weighted imaging (DWI) with good diagnostic quality into other body regions, especially the abdomen and pelvis. Many emerging and established applications are now being evaluated on the upper abdomen, the liver being the most studied organ. This article discusses imaging strategies for DWI on the upper abdomen, describes the clinical protocol, and reviews the most common clinical applications of DWI on solid abdominal organs.

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.