CT and radiography of bacterial respiratory infections in AIDS patients

OBJECTIVE: Acute vertebral collapse is common, and it is sometimes difficult to determine whether the cause is benign or malignant. Recently, diffusion-weighted imaging has been reported to be useful for differentiating the two types. The purpose of this study was to evaluate diffusion abnormalities quantitatively in benign and malignant compression fractures using line scan diffusion-weighted imaging. SUBJECTS AND METHODS. Line scan diffusion-weighted imaging was prospectively performed in 17 patients with 20 acute vertebral compression fractures caused by osteoporosis or trauma, in 12 patients with 16 vertebral compression fractures caused by malignant tumors, and in 35 patients with 47 metastatic vertebrae without collapse. Images were obtained at b values of 5 and 1,000 sec/mm(2). The apparent diffusion coefficient (ADC) was measured in vertebral compression fractures and metastatic vertebrae without collapse. RESULTS: The ADC (mean +/- SD) was 1.21 +/- 0.17 x 10(-3) mm(2)/sec in benign compression fractures, 0.92 +/- 0.20 x 10(-3) mm(2)/sec in malignant compression fractures, and 0.83 +/- 0.17 x 10(-3) mm(2)/sec in metastatic vertebral lesions without collapse. The ADC was significantly higher in benign compression fractures than in malignant compression fractures (p < 0.01), although the two types showed considerable overlap. CONCLUSION: Although the quantitative assessment of vertebral diffusion provides additional information concerning compressed vertebrae, the benign and malignant compression fracture ADC values overlap considerably. Therefore, even a quantitative vertebral diffusion assessment may not always permit a clear distinction between benign and malignant compression fractures.     

SSH-EPI diffusion-weighted MR imaging of the spine with low b values: is it useful in differentiating malignant metastatic tumor infiltration from benign fracture edema?

Objective  Conventional MR sequences are sometimes not helpful in differentiating benign from pathologic fractures. Our aim was to evaluate the usefulness of single-shot echo-planar imaging sequences (diffusion-weighted imaging (DWI)/SSH-EPI) with low b value in differentiating malignant metastatic tumor infiltration of vertebral bone marrow from benign vertebral fracture edema. Materials and methods  A total of 47 patients, 20 with benign fractures and 27 with tumor infiltration, were included in this prospective study. Diffusion-weighted MR images were obtained by single-shot echo-planar imaging technique with diffusion gradient (b = 300 s/mm²; TR/TE, 1,400/100), using a 1.5 T MR scanner. T1- and T2-weighted images and short inversion time inversion-recovery images were available for all 64 lesions. The lesions on DWI/SSH-EPI were categorized as having hypo-, iso-, or hyperintense signal intensity relative to normal vertebrae by two experienced radiologists. Results  We evaluated signal intensity patterns on DWI/SSH-EPI in 64 lesions, which showed low signal intensity on T1-weighted images in both benign fractures and metastasis. With the exception of sclerotic metastases in two patients, malignant metastatic tumor infiltration was hyperintense with respect to normal bone marrow on diffusion-weighted images; all but four benign vertebral fractures were isointense with respect to normal bone marrow. Conclusion  Single-shot echo-planar imaging sequences (DWI/SSH-EPI) with low b value provided excellent distinction between metastatic tumor infiltration and benign vertebral fracture edema. Hyperintense signal intensity on DWI/SSH-EPI was highly specific for the diagnosis of metastatic tumor infiltration of the spine.     

Evaluation of diffusion-weighted imaging for the differential diagnosis of poorly contrast-enhanced and T2-prolonged bone masses: Initial experience

PURPOSE: To determine whether quantitative diffusion-weighted imaging (DWI) is useful for characterizing poorly contrast-enhanced and T2-prolonged bone masses. MATERIALS AND METHODS: We studied 20 bone masses that showed high signal intensity on T2-weighted images and poor enhancement on contrast-enhanced T1-weighted images. These included eight solitary bone cysts, five fibrous dysplasias, and seven chondrosarcomas. To analyze diffusion changes we calculated the apparent diffusion coefficient (ADC) for each lesion. RESULTS: The ADC values of the two types of benign lesions and chondrosarcomas were not significantly different. However, the mean ADC value of solitary bone cysts (mean +/-SD, 2.57 +/- 0.13 x 10(-3) mm(2)/second) was significantly higher than that of fibrous dysplasias and chondrosarcomas (2.0 +/- 0.21 x 10(-3) mm(2)/second and 2.29 +/- 0.14 x 10(-3) mm(2)/second, respectively, P < 0.05). None of the lesions with ADC values lower than 2.0 x 10(-3) mm(2)/second were chondrosarcomas. CONCLUSION: Although there was some overlapping in the ADC values of chondrosarcomas, solitary bone cyst, and fibrous dysplasia, quantitative DWI may aid in the differential diagnosis of poorly contrast-enhanced and T2-prolonged bone masses.     

Diffusion-weighted MR imaging offers no advantage over routine noncontrast MR imaging in the detection of vertebral metastases

BACKGROUND AND PURPOSE: Diffusion-weighted MR imaging of the spine has been used to differentiate benign from pathologic vertebral body compression fractures. We sought to determine the utility of diffusion-weighted MR imaging in the detection of vertebral metastases and to compare it with conventional noncontrast T1- and T2-weighted MR imaging. METHODS: Fifteen patients with metastases to the spine were studied using conventional MR imaging and diffusion-weighted imaging. Blinded review of all images was undertaken, and patients were categorized according to whether they had focal or multiple lesions. The signal intensity of the lesions was compared on T1-, T2- (fast spin-echo), and diffusion-weighted images. RESULTS: In five patients with focal disease, metastases were hypointense on T1-weighted images; hypointense (n = 2), isointense (n = 1), or hyperintense (n = 2) on T2-weighted images; and hypointense (n = 3) or hyperintense (n = 2) on diffusion-weighted images with respect to presumed normal bone marrow. In 10 patients with disease in multiple sites, all lesions were hypointense on T1-weighted images; hypointense (n = 2), isointense (n = 4), hyperintense (n = 2), or mixed (n = 2) on T2-weighted images; and hypointense (n = 5), hyperintense (n = 3), or mixed (n = 2) on diffusion-weighted images with respect to presumed normal bone marrow. CONCLUSION: As used in this study, diffusion-weighted MR imaging of the spine showed no advantage in the detection and characterization of vertebral metastases as compared with noncontrast T1-weighted imaging, but was considered superior to T2-weighted imaging.     

Single shot fast spin echo diffusion-weighted MR imaging of the spine; Is it useful in differentiating malignant metastatic tumor infiltration from benign fracture edema?

PURPOSE: This study aims to evaluate the usefulness of single shot fast spin echo diffusion-weighted MR imaging (DWSSFSE) in differentiating malignant metastatic tumor infiltration of vertebral bone marrow from benign vertebral fracture edema. MATERIALS AND METHODS: Forty-six consecutive patients with 59 acute osteoporotic or traumatic vertebral fractures (mean age = 59) and 31 patients with 98 vertebral metastasis including 20 pathologic fractures (mean age = 53) were included in this study. Diffusion-weighted MR images were obtained by single-shot fast spin echo technique with diffusion gradient (b = 500 s/mm2, TR/TE: 5002/99) by using a 1.5 T MR scanner (Signa MR/i; GE Medical Systems, Milwaukee, WI, USA). T1- and T2-weighted images and short inversion time inversion-recovery (STIR) images were available in all 157 lesions, while contrast-enhanced images were available in 98 metastatic lesions. We evaluated signal intensity patterns on DWSSFSE in 157 lesions, which showed low signal intensity on T1-weighted images in both benign fractures and metastasis. The lesions on DWSSFSE were categorized as low, intermediate, and high signal intensity relative to presumed normal vertebra by concordant inspection of two experienced musculoskeletal radiologists. RESULTS: In benign fractures, DWSSFSE images showed low signal intensity in 56 vertebrae (95%) in 43 patients (93%) and intermediate signal intensity in only 3 vertebrae (5%) in 3 patients (7%). On the other hand, metastases most commonly had low signal intensity in 57 vertebrae (58%) in 25 patients (80%), intermediate signal intensity in 35 vertebrae (36%) in 16 patients (52%), and high signal intensity in 6 vertebrae (6%) in 3 patients (10%). Thus, intermediate and high signal intensities are far more common than benign fractures. Such differences in signal intensity were statistically significant (chi-square test, P < .05). High or intermediate signal intensity on DWSSFSE was highly specific for the diagnosis of metastatic tumor infiltration of the spine (sensitivity: 42%; specificity: 95%; true positive rate: 93%; false negative rate: 52%). CONCLUSIONS: DWSSFSE of the spine may be useful in differentiating metastatic tumor infiltration of vertebral bone marrow from benign fracture edema.     

Discrimination of metastatic cervical lymph nodes with diffusion-weighted MR imaging in patients with head and neck cancer

BACKGROUND AND PURPOSE: Metastasis to the regional cervical lymph nodes may be associated with alterations in water diffusivity and microcirculation of the node. We tested whether diffusion-weighted MR imaging could discriminate metastatic nodes. METHODS: Diffusion-weighted echo-planar and T1- and T2-weighted MR imaging sequences were performed on histologically proved metastatic cervical lymph nodes (25 nodes), benign lymphadenopathy (25 nodes), and nodal lymphomas (five nodes). The apparent diffusion coefficient (ADC) was calculated by using two b factors (500 and 1000 s/mm(2)). RESULTS: The ADC was significantly greater in metastatic lymph nodes (0.410 +/- 0.105 x 10(-3) mm(2)/s, P <.01) than in benign lymphadenopathy (0.302 +/- 0.062 x 10(-3) mm(2)/s). Nodal lymphomas showed even lower levels of the ADC (0.223 +/- 0.056 x 10(-3) mm(2)/s). ADC criteria for metastatic nodes (>/= 0.400 x 10(-3) mm(2)/s) yielded a moderate negative predictive value (71%) and high positive predictive value (93%). Receiver operating characteristic analysis demonstrated that the criteria of abnormal signal intensity on T1- or T2-weighted images (A(z) = 0.8437 +/- 0.0230) and ADC (A(z) = 0.8440 +/- 0.0538) provided similar levels of diagnostic ability in differentiating metastatic nodes. The ADC from metastatic nodes from highly or moderately differentiated cancers (0.440 +/- 0.020 x 10(-3) mm(2)/s, P <.01) was significantly greater than that from poorly differentiated cancers (0.356 +/- 0.042 x 10(-3) mm(2)/s). CONCLUSION: Diffusion-weighted imaging is useful in discriminating metastatic nodes.     

The role of diffusion-weighted imaging and the apparent diffusion coefficient (ADC) values for breast tumors.

OBJECTIVE: We wanted to evaluate the role of diffusion-weighted imaging (DWI) and the apparent diffusion coefficient (ADC) for detecting breast tumors, as compared with the T1- and T2-weighted images. MATERIALS AND METHODS: Forty-one female patients underwent breast MRI, and this included the T1-, T2-, DWI and dynamic contrast-enhanced images. Sixty-five enhancing lesions were detected on the dynamic contrast-enhanced images and we used this as a reference image for detecting tumor. Fifty-six breast lesions were detected on DWI and the histological diagnoses were as follows: 43 invasive ductal carcinomas, one mucinous carcinoma, one mixed infiltrative and mucinous carcinoma, seven ductal carcinomas in situ (DCIS), and four benign tumors. First, we compared the detectability of breast lesions on DWI with that of the T1- and T2-weighted images. We then compared the ADCs of the malignant and benign breast lesions to the ADCs of the normal fibroglandular tissue. RESULTS: Fifty-six lesions were detected via DWI (detectability of 86.2%). The detectabilities of breast lesions on the T1- and T2-weighted imaging were 61.5% (40/65) and 75.4% (49/65), respectively. The mean ADCs of the invasive ductal carcinoma (0.89+/-0.18 x 10(-3)mm(2)/second) and DCIS (1.17+/-0.18 x 10(-3)mm(2)/ second) are significantly lower than those of the benign lesions (1.41+/-0.56 x 10(-3)mm(2)/second) and the normal fibroglandular tissue (1.51+/-0.29 x 10(-3)mm(2)/ second). CONCLUSION: DWI has a high sensitivity for detecting breast tumors, and especially for detecting malignant breast tumors. DWI was an effective imaging technique for detecting breast lesions, as compared to using the T1- and T2-weighted images.     

Minimum apparent diffusion coefficients in the evaluation of brain tumors

OBJECTIVE: To determine whether diffusion-weighted imaging by using minimum apparent diffusion coefficient (ADC(min)) values could differentiate various brain tumors including gliomas, metastases, and lymphomas. MATERIALS AND METHODS: We examined 65 patients with histologically or clinically diagnosed brain tumors (12 low-grade gliomas, 31 high-grade gliomas, 14 metastatic tumors, and 8 lymphomas) using a 1.5 T MR unit. On diffusion-weighted imaging, the ADC(min) values were measured within the tumors and mean values were evaluated regarding statistical differences between groups. RESULTS: The ADC(min) values of low-grade gliomas (1.09+/-0.20 x 10(-3)mm(2)/s) were significantly higher (p<.001) than those of other tumors. There were no statistical significant differences between glioblastomas (0.70+/-0.16 mm(2)/s), anaplastic astrocytomas (0.77+/-0.21 mm(2)/s), metastases (0.78+/-0.21 mm(2)/s), and lymphomas. But, lymphomas had lower mean ADC(min) values (0.54+/-0.10mm(2)/s) than high-grade gliomas and metastases. CONCLUSION: The ADC measurements may help to differentiate low-grade gliomas from high-grade gliomas, metastases, and lymphomas. Although there is no statistical difference, lymphomas seem to have marked restriction in diffusion coefficients.     

Diffusion-weighted MR imaging of intracerebral masses: comparison with conventional MR imaging and histologic findings

BACKGROUND AND PURPOSE: The purposes of this study were to find the role of diffusion-weighted MR imaging in characterizing intracerebral masses and to find a correlation, if any, between the different parameters of diffusion-weighted imaging and histologic analysis of tumors. The usefulness of diffusion-weighted imaging and apparent diffusion coefficient (ADC) maps in tumor delineation was evaluated. Contrast with white matter and ADC values for tumor components with available histology were also evaluated. METHODS: Twenty patients with clinical and routine MR imaging/CT evidence of intracerebral neoplasm were examined with routine MR imaging and echo-planar diffusion-weighted imaging. The routine MR imaging included at least the axial T2-weighted fast spin-echo and axial T1-weighted spin-echo sequences before and after contrast enhancement. The diffusion-weighted imaging included an echo-planar spin-echo sequence with three b values (0, 300, and 1200 s/mm(2)), sensitizing gradient in the z direction, and calculated ADC maps. The visual comparison of routine MR images with diffusion-weighted images for tumor delineation was performed as was the statistical analysis of quantitative diffusion-weighted imaging parameters with histologic evaluation. RESULTS: For tumors, the diffusion-weighted images and ADC maps of gliomas were less useful than the T2-weighted spin-echo and contrast-enhanced T1-weighted spin-echo images in definition of tumor boundaries. Additionally, in six cases of gliomas, neither T2-weighted spin-echo nor diffusion-weighted images were able to show a boundary between tumor and edema, which was present on contrast-enhanced T1-weighted and/or perfusion echo-planar images. The ADC values of solid gliomas, metastases, and meningioma were in the same range. In two cases of lymphomas, there was a good contrast with white matter, with strongly reduced ADC values. For infection, the highest contrast on diffusion-weighted images and lowest ADC values were observed in association with inflammatory granuloma and abscess. CONCLUSION: Contrary to the findings of previous studies, we found no clear advantage of diffusion-weighted echo-planar imaging in the evaluation of tumor extension. The contrast between gliomas, metastases, meningioma, and white matter was generally lower on diffusion-weighted images and ADC maps compared with conventional MR imaging. Unlike gliomas, the two cases of lymphomas showed hyperintense signal on diffusion-weighted images whereas the case of cerebral abscess showed the highest contrast on diffusion-weighted images with very low ADC values. Further study is required to find out whether this may be useful in the differentiation of gliomas and metastasis from lymphoma and abscess.     

Restricted diffusion within ring enhancement is not pathognomonic for brain abscess.

BACKGROUND AND PURPOSE: Recent experience suggests that diffusion-weighted MR imaging may be decisive in the differential diagnosis of ring-enhancing cerebral lesions. Whether restricted diffusion within a ring-enhancing cerebral mass lesion is pathognomonic for abscess was studied. METHODS: Seventeen patients with ring-enhancing cerebral lesions (three abscesses, six glioblastomas, eight metastases) on conventional contrast-enhanced T1-weighted images were examined with echo-planar diffusion-weighted MR imaging. Apparent diffusion coefficient (ADC) maps and the ADCs were calculated for all lesions. Lesions with signs of intralesional hemorrhage on unenhanced T1-weighted images were excluded. RESULTS: The central portion of all six glioblastomas and seven of eight metastases showed unrestricted diffusion, whereas two of three abscesses showed restricted diffusion (low ADC values) in their cavity. However, restricted diffusion also was found in one metastasis, and one abscess within a postoperative cavity showed unrestricted diffusion within a larger nondependent portion. CONCLUSION: In patients with ring-enhancing cerebral mass lesions, restricted diffusion might be characteristic but is not pathognomonic for abscess, as low ADC values also may be found in brain metastases.     

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.     

Acute vertebral body compression fractures: discrimination between benign and malignant causes using apparent diffusion coefficients

Diffusion weighted MRI was performed on patients with acute vertebral body compression. The usefulness of the apparent diffusion coefficient (ADC) in differentiating between benign and malignant fractures was evaluated. A total of 49 acute vertebral body compression fractures were found in 32 patients. 25 fractures in 18 patients were due to osteoporosis, 18 fractures in 12 patients were histologically proven to be due to malignancy, and 6 fractures in 2 patients were due to tuberculosis. Signal intensities on T(1) weighted, short tau inversion recovery (STIR) and diffusion weighted images were compared. ADC values of normal and abnormal vertebral bodies were calculated. Except for two patients with sclerotic metastases, benign acute vertebral fractures were hypointense and malignant acute vertebral fractures were hyperintense with respect to normal bone marrow on diffusion weighted images. Mean combined ADCs (ADC(cmb); average of the combined ADCs in the x, y and z diffusion directions) were 0.23 x 10(-3) mm(2) s(-1) in normal vertebrae, 0.82 x 10(-3) mm(2) s(-1) in malignant acute vertebral fractures and 1.94 x 10(-3) mm(2) s(-1) in benign acute vertebral fractures. The differences between ADC(cmb) values were statistically significant (p<0.001). The ADC is useful in differentiating benign from malignant acute vertebral body compression fractures, but there may be overlapping ADC values between malignant fractures and tuberculous spondylitis.     

Role of diffusion-weighted MR in differential diagnosis of intracranial cystic lesions

AIM: The purpose of this study was to evaluate the role of diffusion-weighted imaging (DWI) in characterizing cerebral cystic lesions. The usefulness of the apparent diffusion coefficient (ADC) map in lesion characterization was also evaluated. METHODS: We compared the findings of conventional MR images with those of DWI: 63 cystic masses in 48 patients were examined with routine MR imaging and echo-planar DWI. The routine MR imaging included at least the axial T2- and T1-weighted sequences, and post-contrast T1 axial sequences. The DWI included an echo-planar spin-echo sequence with three values (0, 500 and 1000s/mm(2)) sensitizing gradient in the x, y, z direction, and it obtained an ADC map. RESULTS: The sensitivity of DWI for differentiating abscesses from primary brain tumours was 100%; for differentiating abscesses from metastatic tumours was 73%; for differentiating benign from malignant lesions was 90%. CONCLUSION: Although some metastatic lesions may appear hyperintense on DWI thus imitating an abscess, evaluation of the lesions with both DWI and conventional MRI may have an important contribution to the differentiation of tumours from abscesses.     

Diffusion-weighted imaging of the liver: optimizing b value for the detection and characterization of benign and malignant hepatic lesions

PURPOSE: To determine the optimal b values required for diffusion-weighted (DW) imaging of the liver in the detection and characterization of benign and malignant hepatic lesions. MATERIALS AND METHODS: MR images obtained in 76 patients including 28 malignant hepatic lesions (21 hepatocellular carcinomas and 7 metastases) and 27 benign lesions (12 hemangiomas and 15 cysts) were reviewed. DW-echo planner images (EPIs; b values with 100, 200, 400, and 800 s/mm2) were reviewed solely first, and then with T2-weighted EPIs (b=0 s/mm2). RESULTS: Sensitivity for malignant lesions (74%) was highest on DW-EPIs with b value of 100 s/mm2 and T2-weighted EPIs combined (P<0.05), and sensitivity for benign lesions (87%) was highest on DW-EPIs with b value of 800 s/mm2 and T2-weighted EPIs (P<0.05). Specificities were comparably high for all sequences. The Az values for malignant lesions were 0.94, 0.90, 0.87, and 0.89, and those for benign lesions were 0.91, 0.89, 0.87, and 0.94 on DW-EPIs with b values of 100, 200, 400, and 800 and T2-weighted EPIs combined, respectively. Hepatic cysts were clearly distinguished with the cutoff ADC value of 2.5x10(-3) mm2/s using a b value of 400 s/mm2 or greater. CONCLUSION: DW-EPIs with middle b values were not required in the detection and characterization of benign and malignant hepatic lesions.     

Malignant renal neoplasms: correlation between ADC values and cellularity in diffusion weighted magnetic resonance imaging at 3 T

PURPOSE: This study aimed at exploring the feasibility of high-field diffusion-weighted magnetic resonance imaging (DW-MRI) (3 T) and to correlate apparent diffusion coefficient (ADC) values with tumour cellularity in renal malignancies. MATERIALS AND METHODS: Thirty-seven patients (ten healthy volunteers and 27 patients with suspected renal malignancy) underwent T1-, T2-weighted and T1-weighted contrast-enhanced magnetic resonance imaging (MRI). Diffusion-weighted images were obtained with a single-shot spin-echo echo-planar imaging (SE-EPI) sequence with a b value of 500 s/mm(2). All lesions were surgically resected, and mean tumour cellularity was calculated. Comparison between tumour cellularity and mean ADC value was performed using simple linear regression analysis. RESULTS: The mean ADC value in normal renal parenchyma was 2.35+/-0.31 x 10(-3) mm(2)/s, whereas mean ADC value in renal malignancies was 1.72+/-0.21 x 10(-3) mm(2)/s. In our population, there were no statistically significant differences between ADC values of different histological types. The analysis of mean ADC values showed an inverse linear correlation with cellularity in renal malignancies (r=-0.73, p<0.01). CONCLUSIONS: DW-MRI is able to differentiate between normal and neoplastic renal parenchyma on the basis of tissue cellularity.     

Quantitative magnetic resonance techniques in the evaluation of intracranial tuberculomas

PURPOSE: To evaluate intracranial tuberculomas using quantitative magnetic resonance (MR) techniques such as T2 relaxometry, magnetization transfer (MT), and diffusion-weighted imaging (DWI). MATERIAL AND METHODS: Thirty-three patients with intracranial tuberculomas (histologically confirmed in 22) were evaluated using proton density/T2-weighted, T1-weighted (with and without MT), and echo-planar diffusion-weighted imaging sequences. T2 relaxation times, MT ratios (MTR), and apparent diffusion coefficient (ADC) values were calculated from the center of the lesion, the periphery, perilesional edema, and contralateral normal white matter. The mean and standard deviation values of each variable were calculated and correlated using Pearson's test (P = 0.05). RESULTS: The measured mean values of T2 relaxation time, MTR, and ADC in the center of lesions were 155.5 ms, 14.1, and 1.27 x 10(-3) mm(2)/s, respectively, compared to 117 ms, 23.72, and 0.74 x 10(-3) mm(2)/s in normal white matter, and a T2 relaxation time of 187.45 ms in normal gray matter. Significant inverse correlations were noted between T2 relaxation values and MTR (P<0.001) and between MTR and ADC (P = 0.046). Significant positive correlation was seen between T2 relaxation and ADC values (P = 0.03). CONCLUSION: Intracranial tuberculomas are characterized by relatively short T2 relaxation times (compared to normal gray matter), decreased MTR, and mostly no restriction of diffusion. A combination of these quantitative parameters could be of help in the noninvasive diagnosis of tuberculomas.     

Evaluation of liver diffusion isotropy and characterization of focal hepatic lesions with two single-shot echo-planar MR imaging sequences: prospective study in 66 patients

PURPOSE: To (a) evaluate liver diffusion isotropy, (b) compare two diffusion-weighted magnetic resonance (MR) imaging sequences for the characterization of focal hepatic lesions by using two or four b values, and (c) determine an apparent diffusion coefficient (ADC) threshold value to differentiate benign from malignant lesions. MATERIALS AND METHODS: Sixty-six patients were examined with two single-shot echo-planar diffusion-weighted MR sequences. In the first sequence, liver diffusion isotropy was evaluated by using diffusion gradients in three directions with two b values. In the second sequence, a unidirectional diffusion gradient was used with four b values. ADCs were measured in 43 patients with 52 focal hepatic lesions more than 1 cm in diameter and in 23 patients with 14 normal and nine cirrhotic livers and were compared by using nonparametric tests. RESULTS: Diffusion in the liver parenchyma was isotropic. ADCs of focal hepatic lesions were significantly different between sequences (P <.01). The mean (+/- SD) ADCs in the first sequence were 0.94 x 10(-3) mm(2)/sec +/- 0.60 for metastases, 1.33 x 10(-3) mm(2)/sec +/- 0.13 for HCCs, 1.75 x 10(-3) mm(2)/sec +/- 0.46 for benign hepatocellular lesions, 2.95 x 10(-3) mm(2)/sec +/- 0.67 for hemangiomas, and 3.63 x 10(-3) mm(2)/sec +/- 0.56 for cysts. There was a significant difference between benign (2.45 x 10(-3) mm(2)/sec +/- 0.96, isotropic value) and malignant (1.08 x 10(-3) mm(2)/sec +/- 0.50) lesions (P <.01 for both sequences). CONCLUSION: Diffusion-weighted MR imaging can help differentiate benign from malignant hepatic lesions. The use of two b values in one direction could be sufficient for the design of MR sequences in the liver.     

Quantitative assessment of diffusion abnormalities in posterior reversible encephalopathy syndrome

BACKGROUND AND PURPOSE: Previous studies have shown that lesions in posterior reversible encephalopathy syndrome are often isointense on diffusion-weighted MR images. We hypothesized that 1) apparent diffusion coefficient (ADC) maps using various thresholds would show larger abnormalities in posterior white matter (WM) and 2) isointense appearance of lesions on isotropic diffusion-weighted images results from a balance of T2 prolongation effects and diffusibility effects. METHODS: T2-weighted MR images from 11 patients were reviewed. Hyperintense lesions were located in both anterior and posterior WM in eight patients and solely in posterior WM in three patients. The ADC maps were produced by use of ADC values > or = 3 SD and > or = 10 SD above the mean value of normal WM. Lesions on diffusion-weighted images were classified as isointense or hypointense. ADC values within lesions (ADC(L)) were compared with those of normal WM (ADC(N)), and compared for isointense lesions and hypointense lesions. RESULTS: The distribution of lesions with ADC values > or = 3 SD was essentially identical to that on T2-weighted images. Regions with ADC values > or = 10 SD were found in both anterior WM and posterior WM in two patients and solely in posterior WM in nine patients. On diffusion-weighted images, lesions appeared isointense in seven patients and hypointense in four patients. Mean ADC(L)/ADC(N) for all lesions was 1.81; for hypointense lesions, 2.30. CONCLUSION: Vasogenic edema was more severe in posterior WM. Isointense lesions result from a balance of T2 effects and increased water diffusibility. Hypointense lesions have higher ADC values, which are not balanced by T2 effects.     

Can diffusion-weighted imaging be used to differentiate benign from pathologic fractures? A meta-analysis

OBJECTIVE: Conventional MR sequences are sometimes nonspecific in differentiating benign from pathologic fractures. To address this difficulty, diffusion-weighted images were conjectured to aid in this discrimination with variable results. As each of these studies contained somewhat small numbers of patients, we performed a meta-analysis to determine if this sequence may be used for this important diagnostic problem. MATERIALS AND METHODS: We reviewed and statistically analyzed the results of eight studies, performed between 1998 and 2003, comparing diffusion-weighted magnetic resonance signal intensity characteristics of benign and pathologic vertebral body fractures. Diffusion-weighted imaging (DWI) signal characteristics and apparent diffusion coefficient (ADC) values of 104 benign fractures and 161 combined malignant vertebral body lesions and pathologic fractures were statistically evaluated in terms of mean ADC, as well as percentage classified as either hypointense or isointense. The meta-analysis to compare benign fractures with the combined pathologic fractures and metastatic lesions in terms of mean ADC used Hedge's g statistic with a small sample bias adjustment; the comparison of the percentage hypo- or isointense used the Mantel-Haenszel method to calculate a weighted summary odds ratio. All summary effect sizes were computed under a random effects model to account for study heterogeneity. RESULTS: The mean ADC was significantly higher (p < 0.01) among benign fractures, with a standardized mean difference (SMD) of 2.8 and a 95% confidence interval (CI) for the SMD of 2.1 to 3.5. Lesions classified as hypointense were significantly more likely to be benign (p < 0.01), based on a summary odds ratio (OR) of 24.5 and 95% confidence that the OR exceeds 1.7. Lesions classified as isointense were not significantly more likely to be benign or malignant (p > 0.1), based on a summary OR of 3.6 and a 95% CI for the OR of 0.35 to 36.6. CONCLUSION: Even though the literature has been inconsistent, ADC maps appear to be a reliable method to differentiate benign from malignant fractures.     

Diffusion-weighted imaging of metastatic brain tumors: comparison with histologic type and tumor cellularity

BACKGROUND AND PURPOSE: On diffusion-weighted imaging (DWI), metastatic tumors of the brain may exhibit different signal intensities (SI) depending on their histology and cellularity. The purpose of our study was to verify the hypotheses (1) that SI on DWI predict the histology of metastases and (2) that apparent diffusion coefficient (ADC) values reflect tumor cellularity. MATERIALS AND METHODS: We assessed conventional MR images, DWI, and ADC maps of 26 metastatic brain lesions from 26 patients, 13 of whom underwent surgery after the MR examination. Two radiologists performed qualitative assessment by consensus of the SI on DWI in areas corresponding to their enhancing portions. We measured the contrast-to-noise ratio (CNR) on T2-weighted images and normalized ADC (nADC) values, and compared them with tumor cellularity. RESULTS: The mean SI on DWI and the CNR on T2-weighted images were significantly lower in well differentiated than in poorly differentiated adenocarcinomas and lesions other than adenocarcinoma. The mean nADC value was significantly higher in well differentiated than poorly differentiated adenocarcinomas and lesions other than adenocarcinoma. All 3 small-cell carcinomas and 1 large-cell neuroendocrine carcinoma exhibited high SI on DWI. The nADC value showed a significant inverse correlation with tumor cellularity. There was no significant correlation between the CNR and tumor cellularity. CONCLUSION: The SI on DWI may predict the histology of metastases; well differentiated adenocarcinomas tended to be hypointense, and small- and large-cell neuroendocrine carcinomas showed hyperintensity. Their ADC values reflect tumor cellularity.