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.

Functional imaging in head and neck squamous cell carcinoma: correlation of PET/CT and diffusion-weighted imaging at 3 Tesla.

PURPOSE: The purposes of this study were: (a) to prospectively assess the correlation between apparent diffusion coefficient (ADC) values and maximum standardized uptake values (SUVmax) in patients with head and neck squamous cell carcinomas (SCC); and (b) to assess ADC and SUVmax values in relation to different tumour grades and stages in our patient population. METHODS: The study group comprised 31 consecutive patients with biopsy-proven head and neck squamous cell carcinoma who were examined using a 3T MRI scanner with a 16-channel head and neck coil. In addition to routine sequences, axial (DWIBS) and sagittal (DW-EPI) diffusion-weighted sequences were obtained using b-values of 0 mm(2)/s and 800 mm(2)/s. The ADC maps were calculated automatically. The ADC values of the tumours were measured with three regions of interest (ROIs) of standard size, and an ROI covering the entire tumour. In all patients, contrast-enhanced, whole-body (18)F-FDG PET/CT was performed within 2 weeks of the MRI examination. SUVmax was measured for every tumour using a 3-D freehand ROI that covered the entire tumour. Two-way repeated measures ANOVA was used for group comparisons. The Spearman rank correlation test was performed for ADC values. RESULTS: Mean ADC values in the 31 SCC were 0.902 (± 0.134) with a ROI of standard size, and 0.928 (± 0.160) with the large ROI measurements on the axial DWIBS sequence. The ADC values of the tumours were significantly higher when measured with the sagittal DW-EPI sequence: 1.051 (± 0.211) and 1.082 (± 0.208). We observed no significant differences in ADC values and SUVmax between the various T stages or histological grades of the tumours. SUVmax values (26.5 ± 12) did not correlate with ADC values on DWIBS or EPI. CONCLUSION: There is no correlation between the FDG uptake and the ADC value in head and neck SCC. The three different tumour grades and four tumour stages present in our study population could not be differentiated based on ADC values or SUV.

Diagnostic value of sonography, ultrasound-guided fine-needle aspiration cytology, and diffusion-weighted MRI in the characterization of cold thyroid nodules.

INTRODUCTION: The purpose of this prospective study was to assess the diagnostic value of different modalities for the characterization of cold thyroid nodules. METHODS: In 35 patients with cold nodules, thyroid carcinoma was suspected on scintigraphy. These patients were prospectively investigated with sonography, ultrasound-guided fine-needle aspiration (USgFNA), and quantitative diffusion-weighted imaging magnetic resonance imaging (DWI) (navigated echo-planar imaging; maximum b-value 800s/mm(2)) prior to surgery. The sonographic findings, USgFNA cytology, and the apparent diffusion coefficient (ADC) values of DWI were correlated with the postoperative histology of benign and malignant lesions. Statistical analysis was performed with the Kruskal-Wallis test and the Fisher's exact test. P<.05 denoted statistical significance. RESULTS: The accuracy of sonography and USgFNA was 64% and 68.8%, respectively. The sensitivity was 86.7% and 80%, respectively. Specificity was only 57.2% and 50%, respectively. The median ADC values for carcinoma and adenoma were 2.73 x 10(-3)mm(2)/s and 1.93 x 10(-3)mm(2)/s, respectively (P<.001). There was no significant difference between the median ADC value for Hashimoto thyroiditis (3.46 x 10(-3)mm(2)/s) and carcinoma. An ADC value of 2.25 x 10(-3)mm(2)/s or higher was proven to be the cut-off value for differentiating between benign and malignant cold thyroid nodules, with an accuracy of 88%, a sensitivity of 85%, and a specificity of 100%. CONCLUSIONS: These results show that quantitative DWI is a more reliable diagnostic method for differentiation between benign and malignant thyroid lesions than sonography or USgFNA. However, further studies including a larger study population are necessary to confirm our study results.

Diffusion-weighted magnetic resonance imaging of head and neck squamous cell carcinomas.

OBJECTIVE: To evaluate whether diffusion-weighted imaging (DWI) is a reliable technique to quantify microstructural differences between head and neck squamous cell carcinomas (SCC) and tumour-free soft tissue. MATERIALS AND METHODS: DWI was obtained from 20 patients with histologically proven, untreated head and neck SCC. DWI was acquired using a diffusion-weighted, navigated echo-planar imaging sequence with a maximum b-value of 800 s/mm2. For an objective assessment of image quality, the signal-to-noise ratio (SNR) was calculated. Microstructural differences between vital tumour tissue and tumour-free soft tissue were quantified by calculating the apparent-diffusion-coefficients (ADC) on a pixel by pixel method. RESULTS: Echo-planar DWI provided good image quality in all patients (mean SNR 18.4). The mean ADC of SCC, (0.64+/-0.28 x 10(-3) mm2/s), was significantly (P<0.0001) lower than that of the tumour-free soft tissue, (2.51+/-0.82 x 10(-3) mm2/s). CONCLUSION: DWI is a reliable diagnostic tool to quantify the microstructural differences between vital tumour tissue and tumour-free soft tissue in patients with head and neck SCC.

Diffusion weighted imaging in osteoradiology.

Diffusion weighted imaging gained attention as an imaging modality, which provides information on the microstructure of a tissue, which can be used for tissue characterization. This is of importance in patients where other diagnostic tools provide equivocal or unspecific information. In addition quantitative diffusion measurements provide objective parameters for unbiased comparison of treatment response, which is mandatory for therapy monitoring. Technical restriction limited the use of Diffusion Weighted Imaging to the brain. However, with the improvement in scanner technology and the availability of new MR sequences investigation of the Muskulo Skeletal System was made possible. We describe the potential of Diffusion Weighted Imaging as a non-invasive technique to evaluate pathological, inflammatory and physiological processes in osteoradiology.

Magnetic resonance imaging of liver malignancies.

The histological structure of the liver is complex, consisting of hepatocytes, biliary epithelium, and mesenchymal cells. From this large variety of cells, a broad spectrum of benign and malignant liver lesions in originate. An accurate diagnosis of these lesions is mandatory for choosing an appropriate therapeutic approach. With the recent developments in hardware and software, magnetic resonance imaging (MRI) has emerged as the method of choice in the diagnostic workup of focal liver lesions, in particular in the pretherapeutic stage. The introduction of high-field MRI at 3.0 T in the routine workup and the selective use of liver-specific contrast agents, including hepatobiliary and reticuloendothelial agents, have also strengthened the role of MRI in liver imaging. In this overview article, we will review the recent developments in 3.0-T MRI and MRI contrast agents in the diagnostic workup of the most common malignant liver tumors.

Perineural tumor spread in malignant head and neck tumors.

Perineural tumor spread (PNS) of head and neck malignancies is a course of disease in which tumor metastasizes along the endoneurium or perineurium. Perineural tumor spread is a potentially devastating complication of head and neck cancer and has a high impact on the therapeutical management and overall prognosis. Imaging plays an important role in the detection of this condition, especially in view of a large number of clinically asymptomatic patients with PNS. Magnetic resonance imaging is the modality of choice in the assessment of PNS because of its multiplanar capability and its superior soft-tissue contrast. Knowledge of normal cranial nerve anatomy and the imaging appearance of perineural tumor extension is imperative in the evaluation of PNS which represents a special challenge in head and neck radiology.

Diffusion weighted imaging of bone marrow pathologies.

Diffusion weighted imaging of non-CNS tissue has attracted much attention during the last years. Its capability of probing the microstructure of a biologic tissue at a sub-millimeter range is used to evaluate its diffusion capacity, which is tissue specific and can be used for tissue characterization. Processes involving bone marrow where the primary target for DWI during the last years. Most experience has been gained for differentiating benign from pathologic vertebral compression fractures, which can be reliably done when quantitative diffusion measurements are available. However, preliminary results exist indicating that this non-invasive technique may be a potential tool for therapy monitoring, which will revise the management of cancer patients. Moreover, this will be the first non-invasive and quantifiable tool for evaluating the effectiveness of modern tumor treatment. In this article, we will give an overview on the current status of DWI in the evaluation of bone marrow alterations; on currently available DWI techniques and a short out-look on future aspects of DWI in bone marrow pathologies.

Asymmetric closure of ischiopubic synchondrosis in pediatric patients: correlation with foot dominance.

OBJECTIVE: The enlarged ischiopubic synchondrosis is a well-known anatomic structure; however, little is known about its physiology. In early childhood, enlargement of this synchondrosis occurs bilaterally, whereas before complete ossification, it is frequently found unilaterally. In most children, the unilateral enlarged ischiopubic synchondrosis is observed in the left hemipelvis, a finding that was hitherto unexplained. During common athletic activities, increased ground reaction forces are exerted on the weight-bearing nondominant limb, which in up to 87% of the general population is the left leg. The asymmetric exertion of these forces may explain the distinct closure sequence of this temporary joint. The purpose of this study was to correlate unilateral enlarged ischiopubic synchondrosis with foot dominance. MATERIALS AND METHODS: The study cohort comprised 32 children who had undergone unenhanced radiography, CT, or MRI for reasons other than bone disorders and who presented with enlarged ischiopubic synchondroses. In these children, the distribution of enlarged ischiopubic synchondrosis and foot dominance were evaluated either retrospectively (n = 11) or prospectively (n = 21). RESULTS: In this cohort, 78% of patients were right-footed and 22% were left-footed. Nine of the 32 children presented with unilateral enlarged ischiopubic synchondrosis (left, seven [78%] of nine; right, two [22%] of nine). All children with enlarged left ischiopubic synchondrosis were right-footed, and all children with enlarged right ischiopubic synchondrosis were left-footed. CONCLUSION: Unilateral enlarged ischiopubic synchondrosis is closely correlated with foot dominance. The asymmetric ossification pattern of the ischiopubic synchondrosis indicates delayed ossification of this anatomic structure due to asymmetrically applied mechanical forces to the nondominant limb.

Acute colonic pseudo-obstruction (Ogilvie's-syndrome) and pneumatosis intestinalis in a kidney recipient patient.

Acute colonic pseudo-obstruction (Ogilvie's syndrome) is a clinical entity characterized by massive nontoxic dilatation of the colon in the absence of mechanical obstruction and is associated with increased morbidity and mortality in the immunosuppressed patient. We present a case of a kidney transplant recipient developing a life-threatening condition with acute colonic pseudo-obstruction associated with radiologic findings of a linear pneumatosis intestinalis (PI). Urgent laparotomy and resection of the dilated cecum, colon ascendens and transversum was performed because of bowel necrosis with multiple serosal defects. Stool cultures and special stains for microorganisms were all negative, and there was no evidence for viral or fungal infection. The patient was discharged 31 days after transplantation with normal renal function. In conclusion, this steroid-induced ileus (pseudo-obstruction) is a potentially malignant early form of colonic dysmotility rarely reported in transplant recipients. Awareness and early recognition of the condition are critical for a successful outcome. Colonoscopic decompression can achieve reversal of colonic dilatation in most cases, but in some patients prophylactic laparotomy is indicated for prevention of the catastrophic consequences of perforation.

Four-channel multidetector CT in facial fractures: do we need 2 x 0.5 mm collimation?

OBJECTIVE: Our aim was to optimize acquisition protocols and multiplanar reformation algorithms for the evaluation of facial fractures using multidetector CT (MDCT) and to determine whether 2 x 0.5 mm collimation is necessary. MATERIALS AND METHODS: A cadaveric head with artificial blunt facial trauma was examined using a four-channel MDCT scanner. The influence of acquisition parameters (collimation, 2 x 0.5 mm, 4 x 1 mm, 4 x 2.5 mm; tube current, 120 mAs, 90 mAs, 60 mAs), image reconstruction algorithms (standard vs ultra-high-resolution modes; reconstructed slice thicknesses, 0.5 mm, 1 mm, 3 mm; increment, 0.3 mm, 0.6 mm, 1.5 mm), and reformation algorithms (slice thicknesses, 0.5 mm, 1 mm, 3 mm; overlap, 0.5 mm, 1 mm, 3 mm) on detectability of facial fractures in multiplanar reformations with MDCT was analyzed. RESULTS: Fracture detection was significantly higher with thin multiplanar reformations (0.5 and 0.5 mm, 1 and 0.5 mm, and 1 and 1 mm) (p < or = 0.014) acquired with 2 x 0.5 mm collimation (p < or = 0.046) in ultra-high-resolution mode (p < 0.0005) with 120 mAs (p < or = 0.025). Interobserver variability showed very good agreement (kappa > or = 0.942). Non-ultra-high-resolution mode, lower milliampere-seconds, and thick multiplanar reformations (3 and 0.5 mm, 3 and 1 mm, and 3 and 0.5 mm) showed significantly decreased fracture detectability. CONCLUSION: Although thin multiplanar reformations obtained from thin collimation (2 x 0.5 mm) are statistically superior for the detection of subtle fractures, 4 x 1 mm collimation is sufficient for routine diagnostic evaluation. Ultra-high-resolution mode with 120 mAs is mandatory for detection of clinically relevant fractures.

Apparent diffusion coefficient: a quantitative parameter for in vivo tumor characterization.

PURPOSE: The purpose of the this study was to evaluate the potential of diffusion weighted imaging (DWI) to distinguish different tissue compartments in early, intermediate and advanced tumor stages. MATERIALS AND METHODS: Twenty-two male mice were induced with squamous cell tumor (SCCVII) and scanned with a clinical 1.5 T scanner. T1-SE, T2-FSE, diffusion weighted Line-Scan-MRI and contrast enhanced T1-SE were obtained from mice with early (tumor volume 10-100 mm(3)), intermediate (200-600 mm(3)), advanced tumors (600-1000 mm(3)) and tumor necrosis (>1500 mm(3)). The apparent diffusion coefficient (ADC) of different tumor compartments was calculated offline with a pixel-by-pixel method. The animals were sacrificed immediately after scanning and histopathologic correlation was performed. RESULTS: In early stages of tumor development, tumors appeared homogeneous on diffusion weighted images with an ADC of 0.64+/-0.06 x 10(-3) mm(2)/s. With tumor progression the ADC in the rim areas of tumor increased significantly (intermediate stage: 0.70+/-0.11 x 10(-3) mm(2)/s; advanced stage: 0.88+/-0.11 x 10(-3) mm(2)/s; tumor necrosis 1.03+/-0.06 x 10(-3) mm(2)/s), whereas the ADC in viable tumor remained constant. Histologically the areas with an increased ADC correlated well with areas of necrosis (reduced cell density). CONCLUSION: The ADC is a non-invasive technique to monitor changes in the biological structure of tumor tissue during tumor progression. Thus, DWI is a potential diagnostic tool for in-vivo tissue characterization.

Line scan diffusion imaging of the spine.

BACKGROUND AND PURPOSE: Recent findings suggest that diffusion-weighted imaging might be an important adjunct to the diagnostic workup of disease processes in the spine, but physiological motion and the challenging magnetic environment make it difficult to perform reliable quantitative diffusion measurements. Multi-section line scan diffusion imaging of the spine was implemented and evaluated to provide quantitative diffusion measurements of vertebral bodies and intervertebral disks. METHODS: Line scan diffusion imaging of 12 healthy study participants and three patients with benign vertebral compression fractures was performed to assess the potential of line scan diffusion imaging of the spinal column. In a subgroup of six participants, multiple b-value (5-3005 s/mm(2)) images were obtained to test for multi-exponential signal decay. RESULTS: All images were diagnostic and of high quality. Mean diffusion values were (230 +/- 83) x 10(-6) mm(2)/s in the vertebral bodies, (1645 +/- 213) x 10(-6) mm(2)/s in the nuclei pulposi, (837 +/- 318) x 10(-6) mm(2)/s in the annuli fibrosi and ranged from 1019 x 10(-6) mm(2)/s to 1972 x 10(-6) mm(2)/s in benign compression fractures. The mean relative intra-participant variation of mean diffusivity among different vertebral segments (T10-L5) was 2.97%, whereas the relative difference in mean diffusivity among participants was 7.41% (P <.0001). The estimated measurement precision was <2%. A bi-exponential diffusion attenuation was found only in vertebral bodies. CONCLUSION: Line scan diffusion imaging is a robust and reliable method for imaging the spinal column. It does not suffer as strongly from susceptibility artifacts as does echo-planar imaging and is less susceptible to patient motion than are other multi-shot techniques. The different contributions from the water and fat fractions need to be considered in diffusion-weighted imaging of the vertebral bodies.

Vertebral metastases: assessment with apparent diffusion coefficient.

The authors evaluated the apparent diffusion coefficient (ADC) in the assessment of vertebral metastases and acute vertebral compression fractures in 22 patients with known or suspected vertebral metastases. On the basis of significantly (P <.03) different ADCs, vertebral metastases (0.69 x 10(-3) mm2/sec) and pathologic compression fractures (0.65 x 10(-3) mm2/sec) can be safely distinguished from vertebral bodies (1.66 x 10(-3) mm2/sec) and benign compression fractures (1.62 x 10(-3) mm2/sec). Thus, the use of ADCs may increase the specificity of magnetic resonance imaging in these patients.

Imaging articular cartilage defects in the ankle joint with 3D fat-suppressed echo planar imaging: comparison with conventional 3D fat-suppressed gradient echo imaging.

PURPOSE: To shorten the examination time for articular cartilage imaging, using a recently developed three-dimensional (3D) multishot echo planar imaging (EPI) sequence with fat saturated (FS), compared to a conventional 3D fat-saturated spoiled gradient echo sequence (3D FS GRE). MATERIAL AND METHODS: There were 32 consecutive patients with ankle joint disorders who underwent magnetic resonance imaging (MRI) in a 1.0-T unit. Hyaline cartilage was imaged with a 3D FS EPI sequence and a 3D FS GRE sequence. Image assessment criteria included lesion conspicuity, contrast between different types of normal tissue, and image artifacts. In addition, contrast-to-noise ratios (CNRs) of cartilage vs. joint fluid and bone marrow were measured. RESULTS: The 3D FS EPI sequence provided a high CNR between cartilage and subchondral bone, similar to that of the 3D FS GRE sequence. The CNR between cartilage and effusion was significantly lower on the 3D EPI sequence due to the higher signal intensity of fluid. Both sequences were equal in lesion detection ability. The image quality of the 3D FS GRE sequence was slightly higher than that of the 3D FS EPI, but the difference was not statistically significant. CONCLUSION: We conclude that the 3D FS EPI sequence is comparable to the 3D FS GRE sequence in the detection of cartilage lesions, with the additional advantage of reduction in scan time by a factor of 4.