Clinical single-shot diffusion-weighted MRI of the human brain on a short-bore medium-field imager

Diffusion-weighted MRI (DWI) is becoming important for assessment of acute stroke. Until recently single-shot DWI required expensive technology such as echo-planar imaging (EPI) available only at some research sites. A new medium-field (1.0 T) short-bore MR imager has been developed with which DWI data sets can be acquired. We prospectively studied 169 patients on this 1.0 T commercial system. After conventional imaging, DWI was performed with a single-shot multi-slice sequence with b values 0 an 900 s/mm², and with the gradients switched in three directions. The apparent diffusion coefficients were calculated with online calculation software. There were 50 patients with totally normal MRI, and 17 had strokes, these strokes were detected as areas of high signal on the images at a maximal b value. There was a drop in the ADC in ischaemic regions: in subacute infarcts, the values were between 0.41 and 0.531 × 10^{− 3} mm²/s. In old infarcts the ADC was 1.15 × 10^{− 3} mm²/s. Cerebrospinal fluid (CSF) gave low signal whereas areas in the brain had more intermediate intensities (CSF: 3.00; deep white matter: 0.75, cortical grey matter: 0.80, basal ganglia (thalamus): 0.70 and cerebellar white matter: 0.65 × 10^{− 3} mm²/s. Anisotropy was detected as areas of restricted diffusion along the tracts. These preliminary data show that DWI can be aquired successfully on a medium-field short-bore system. This should allow the technique to be implemented at more sites, therefore facilitating the diagnosis of acute stroke and rendering early intervention feasible. Received: 22 February 1999 Accepted: 27 April 1999     

CT Perfusion in Acute Lacunar Stroke: Detection Capabilities Based on Infarct Location

BACKGROUND AND PURPOSE:Recent studies demonstrated superiority of CTP to NCCT/CTA at detecting lacunar infarcts. This study aimed to assess CTP''s capability to identify lacunae in different intracranial regions.MATERIALS AND METHODS:Over 5.5 years, 1085 CTP examinations were retrospectively reviewed in patients with acute stroke symptoms with CTP within 12 hours and MRI within 7 days of symptom onset. Patients had infarcts ≤2 cm or no acute infarct on DWI; patients with concomitant infarcts >2 cm on DWI were excluded. CTP postprocessing was automated by a delay-corrected algorithm. Three blinded reviewers were given patient NIHSS scores and symptoms; infarcts were recorded based on NCCT/CTA, CTP (CBF, CBV, MTT, and TTP), and DWI.RESULTS:One hundred thirteen patients met inclusion criteria (53.1% female). On DWI, lacunar infarcts were present in 37 of 113 (32.7%), and absent in 76 of 113 (67.3%). On CTP, lacunar infarcts typically appeared as abnormalities larger than infarct size on DWI. Interobserver κ for CTP ranged from 0.38 (CBF) (P < .0001) to 0.66 (TTP) (P < .0001); interobserver κ for DWI was 0.88 (P < 0.0001). In all intracranial regions, sensitivity of CTP ranged from 18.9% (CBV) to 48.7% (TTP); specificity ranged from 97.4% (CBF and TTP) to 98.7% (CBV and MTT). CTP''s sensitivity was highest in the subcortical white matter with or without cortical involvement (21.7%–65.2%) followed by periventricular white matter (12.5%–37.5%); sensitivity in the thalami or basal ganglia was 0%.CONCLUSIONS:CTP has low sensitivity and high specificity in identifying lacunar infarcts. Sensitivity is highest in the subcortical white matter with or without cortical involvement, but limited in the basal ganglia and thalami.

Lacunar infarcts are ischemic insults that predominantly result from the occlusion of single perforating arteries.¹ Typically, lacunae occur within the thalami, basal ganglia, brain stem, corona radiata, or internal capsule.^2–4 Although lacunar infarcts predominantly occur secondary to small vessel disease, other etiologies such as cardiac emboli and vasculitis also have been described.⁵ Lacunar strokes are a common cause of morbidity and account for up to 25% of all ischemic strokes.^6,7 Classically, symptoms of lacunar infarcts include pure sensory syndrome, pure motor hemiparesis, sensorimotor stroke, ataxic hemiparesis, or dysarthria-clumsy hand syndrome.^2,8 Thrombolytic therapy has been shown to be effective in the treatment of acute lacunar stroke, making the timely and accurate diagnosis of lacunar infarcts of utmost importance.⁹NCCT is less sensitive than DWI in the detection of lacunar strokes, with reported sensitivities ranging from 0%–35% for NCCT and 75%–95% for DWI.^10–13 Nevertheless, because CT remains more accessible than MR imaging in emergency settings, its optimization in the diagnosis of stroke continues to be vital.¹⁴ Recently, CTP has been shown to be superior to NCCT and CTA in assessing for lacunar infarcts.^4,15 However, neither of the recent studies directly compared CTP with NCCT/CTA in the detection of lacunae: Rudilosso et al¹⁵ assessed the use of CTP in patients with clinical lacunar syndrome, and Das et al⁴ investigated the use of CTP as part of a multimodal approach in the setting of lacunar infarction, noting only that 61% of patients had an abnormality on CTP concordant with infarction on DWI. Furthermore, neither study investigated CTP''s capability to detect lacunae within specific regions of the brain.The purpose of this study was to compare the diagnostic performance of CTP with NCCT/CTA in the identification of acute lacunar infarcts and evaluate the diagnostic capabilities of CTP in the detection of lacunar strokes within different areas of the brain.     

Peripheral hyperintense pattern on T2-weighted magnetic resonance imaging (MRI) in breast carcinoma: correlation with early peripheral enhancement on dynamic MRI and histopathologic findings

Purpose

To assess the value of magnetic resonance (MR) diffusion‐weighted imaging (DWI) in the evaluation of deep infiltrating endometriosis (DIE).

Materials and Methods

In a prospective single‐center study, DWI was added to the standard MRI protocol in 56 consecutive patients with known or suspected endometriosis. Endometriotic lesions as well as (functional) ovarian cysts were analyzed for location, size, and signal intensity on T1, T2, and DWI. Apparent diffusion coefficient (ADC) values were calculated using b‐values of 50, 400, 800, and 1200 s/mm². Statistical analysis included the Spearman correlation coefficient, Mann–Whitney U, and Kruskal–Wallis tests.

Results

A total of 112 lesions (62 endometrial cysts and 48 DIE) were detected, 60 of which were large enough to analyze. Mean ADC values of endometrial cysts and functional ovarian cysts were 1.11 × 10^?3/mm²/s and 2.14 × 10^?3/mm²/s, respectively. Mean ADC values of DIE retrocervical, infiltrating the colon, and bladder were 0.70 × 10^?3/mm²/s, 0.79 × 10^?3/mm²/s, and 0.76 × 10^?3/mm²/s, respectively. ADC values of DIE did not show a significant difference between varying pelvic locations (P = 0.63).

Conclusion

Results of our study suggest that ADC values of DIE are consistently low, without significant difference between pelvic locations. J. Magn. Reson. Imaging 2010;31:1117–1123. © 2010 Wiley‐Liss, Inc.

     

Diffusion-weighted MRI in cystic or necrotic intracranial lesions

Our purpose was to investigate the signal intensities of cystic or necrotic intracranial lesions on diffusion-weighted MRI (DWI) and measure their apparent diffusion coefficients (ADC). We examined 39 cystic or necrotic intracranial lesions in 33 consecutive patients: five malignant gliomas, seven metastases, two other necrotic tumours, a haemangioblastoma, three epidermoids, an arachnoid cyst, seven pyogenic abscesses, 12 cases of cysticercosis and one of radiation necrosis. DWI was performed on a 1.5 T unit using a single-shot echo-planar spin-echo pulse sequence with b 1000 s/mm². The signal intensity of the cystic or necrotic portion on DWI was classified by visual assessment as markedly low (as low as cerebrospinal fluid), slightly lower than, isointense with, and slightly or markedly higher than normal brain parenchyma. ADC were calculated in 31 lesions using a linear estimation method with measurements from b of 0 and 1000 s/mm². The cystic or necrotic portions of all neoplasms (other than two metastases) gave slightly or markedly low signal, with ADC of more than 2.60 × 10⁻³ mm²/s. Two metastases in two patients showed marked high signal, with ADC of 0.50 × 10⁻³ mm²/s and 1.23 × 10⁻³ mm²/s, respectively. Epidermoids showed slight or marked high signal, with ADC of less than 1.03 × 10⁻³ mm²/s. The arachnoid cyst gave markedly low signal, with ADC of 3.00 × 10⁻³ mm²/s. All abscesses showed marked high signal, with ADC below 0.95 × 10⁻³ mm²/s. The cases of cysticercosis showed variable signal intensity; markedly low in five, slightly low in three and markedly high in four. Received: 17 November 1999/Accepted: 3 February 2000     

Differential diagnosis of mammographically and clinically occult breast lesions on diffusion‐weighted MRI

Purpose:

To investigate the diagnostic performance of diffusion‐weighted imaging (DWI) for mammographically and clinically occult breast lesions.

Materials and Methods:

The study included 91 women with 118 breast lesions (91 benign, 12 ductal carcinoma in situ [DCIS], 15 invasive carcinoma) initially detected on dynamic contrast‐enhanced magnetic resonance imaging (DCE‐MRI) and assigned BI‐RADS category 3, 4, or 5. DWI was acquired with b = 0 and 600 s/mm². Lesion visibility was assessed on DWI. Apparent diffusion coefficient (ADC) values were compared between malignancies, benign lesions, and normal (no abnormal enhancement on DCE‐MRI) breast tissue, and the diagnostic performance of DWI was assessed based on ADC thresholding.

Results:

Twenty‐four of 27 (89%) malignant and 74/91 (81%) benign lesions were hyperintense on the b = 600 s/mm² diffusion‐weighted images. Both DCIS (1.33 ± 0.19 × 10^?3 mm²/s) and invasive carcinomas (1.30 ± 0.27 × 10^?3mm²/s) were lower in ADC than benign lesions (1.71 ± 0.43 × 10^?3mm²/s; P < 0.001), and each lesion type was lower in ADC than normal tissue (1.90 ± 0.38 × 10^?3mm²/s, P ≤ 0.001). Receiver operating curve (ROC) analysis showed an area under the curve (AUC) of 0.77, and sensitivity = 96%, specificity = 55%, positive predictive value (PPV) = 39%, and negative predictive value (NPV) = 98% for an ADC threshold of 1.60 × 10^?3mm²/s.

Conclusion:

Many mammographically and clinically occult breast carcinomas were visibly hyperintense on diffusion‐weighted images, and ADC enabled differentiation from benign lesions. Further studies evaluating DWI while blinded to DCE‐MRI are necessary to assess the potential of DWI as a noncontrast breast screening technique. J. Magn. Reson. Imaging 2010;1:562–570. © 2010 Wiley‐Liss, Inc.

     

Quantitative diffusion-weighted MR imaging in the differential diagnosis of breast lesion

The role of diffusion-weighted magnetic resonance imaging (DWI) to differentiate breast lesions in vivo was evaluated. Sixty women (mean age, 53 years) with 81 breast lesions were enrolled. A coronal echo planar imaging (EPI) sequence sensitised to diffusion (b value=1,000 s/mm²) was added to standard MR. The mean diffusivity (MD) was calculated. Differences in MD among cysts, benign lesions and malignant lesions were evaluated, and the sensitivity and specificity of DWI to diagnose malignant and benign lesions were calculated. The diagnosis was 18 cysts, 21 benign and 42 malignant nodules. MD values (mean±SD ×10⁻³ mm²/s) were (1.48±0.37) for benign lesions, (0.95±0.18) for malignant lesions and (2.25±0.26) for cysts. Different MD values characterized different malignant breast lesion types. A MD threshold value of 1.1×10⁻³ mm²/s discriminated malignant breast lesions from benign lesions with a specificity of 81% and sensitivity of 80%. Choosing a cut-off of 1.31×10⁻³ mm²/s (MD of malignant lesions -2 SD), the specificity would be 67% with a sensitivity of 100%. Thus, MD values, related to tumor cellularity, provide reliable information to differentiate malignant breast lesions from benign ones. Quantitative DWI is not time-consuming and can be easily inserted into standard clinical breast MR imaging protocols.     

Diffusion-weighted imaging of the brain: comparison of stimulated- and spin-echo echo-planar sequences

We used a rat model of focal cerebral ischaemia to compare stimulated-echo (STE) and spin-echo (SE) echo planar (EPI) diffusion-weighted sequences as regards image quality and accuracy of calculation of apparent diffusion coefficients (ADC). Focal cerebral ischaemia was induced by endovascular occlusion of the middle cerebral artery in five rats. MRI was performed on a 2.35 tesla imager. For diffusion-weighted imaging (DWI) we used STE-EPI and SE-EPI with different diffusion times (Δ) of 15, 30, 45, 60, 75 and 90 ms using values of b of 200, 300, 400, 500, 600 and 700 s/mm². We assessed image quality, the signal-to-noise-ratio (SNR) and the accuracy of the ADC calculated from both sequences. Infarcts were delineated in all cases, independent of sequence type and Δ. The image quality and SNR of the SE-EPI images were significantly better, with a higher SNR than STE-EPI images for short and intermediate values of Δ. However, when Δ reached 75 ms STE-EPI became superior to SE-EPI. ADC calculated from STE-EPI images were smaller than those from SE-EPI images for short and intermediate diffusion times, possibly because of the lower SNR of the former. We suggest that SE-EPI sequences be used for DWI of the brain, particularly on experimental systems and whole-body imagers with enhanced gradient hardware, where it is possible to run highly diffusion-weighted sequences (b > 500 s/mm²) with Δ less than 50 ms. However, when using very long values of Δ because of hardware restrictions or for measurement of restricted diffusion, STE sequences give better results. Received: 17 August 2000 Accepted: 5 December 2000     

Combined use of T2-weighted and diffusion-weighted 3-T MR imaging for differentiating uterine sarcomas from benign leiomyomas

The objective of our study was to compare diffusion-weighted imaging (DWI) alone and DWI combined with T2-weighted MRI for the differentiation of uterine sarcomas from benign leiomyomas. T2-weighted imaging and DWI were performed in 103 patients with 103 myometrial tumours, including 8 uterine sarcomas and 95 benign leiomyomas on 3-T MR imaging. The signal intensity (SI) of the tumour on T2-weighted images was quantified as the tumour–myometrium contrast ratio (TCR) by using the following formula: (SI_tumour − SI_myometrium)/SI_myometrium. The TCR or apparent diffusion coefficient (ADC) value alone and then the ADC value combined with T2-weighted imaging were evaluated for differentiation between sarcomas and leiomyomas. The mean ADC value of sarcomas was 0.86 ± 0.11 × 10⁻³ m²/s, which was significantly lower than that of leiomyomas 1.18 ± 0.24 × 10⁻³ m²/s; however, there was a substantial overlap. The mean TCR of sarcomas was 0.66 ± 0.71, which was significantly higher than that of the leiomyomas, –0.37 ± 0.34; however, again, there was a considerable overlap. When ADC was less than 1.05 × 10⁻³ mm²/s and TCR was greater than 0 this condition was considered to confirm a sarcoma; a combination of ADC and TCR achieved a significant improvement without any overlap between sarcomas and leiomyomas (sensitivity 100%, specificity 100%). Our preliminary results indicate that combined DWI and T2-weighted MR imaging is better than DWI alone in the differentiation of uterine sarcomas from benign leiomyomas.     

Diffusion‐weighted imaging of human carotid artery using 2D single‐shot interleaved multislice inner volume diffusion‐weighted echo planar imaging (2D ss‐IMIV‐DWEPI) at 3T: Diffusion measurement in atherosclerotic plaque

Purpose:

To determine if 2D single‐shot interleaved multislice inner volume diffusion‐weighted echo planar imaging (ss‐IMIV‐DWEPI) can be used to obtain quantitative diffusion measurements that can assist in the identification of plaque components in the cervical carotid artery.

Materials and Methods:

The 2D ss‐DWEPI sequence was combined with interleaved multislice inner volume region localization to obtain diffusion weighted images with 1 mm in‐plane resolution and 2 mm slice thickness. Eleven subjects, six of whom have carotid plaque, were studied with this technique. The apparent diffusion coefficient (ADC) images were calculated using DW images with b = 10 s/mm² and b = 300 s/mm².

Results:

The mean ADC measurement in normal vessel wall of the 11 subjects was 1.28 ± 0.09 × 10^?3 mm²/s. Six of the 11 subjects had carotid plaque and ADC measurements in plaque ranged from 0.29 to 0.87 × 10^?3 mm²/s. Of the 11 common carotid artery walls studied (33 images), at least partial visualization of the wall was obtained in all ADC images, more than 50% visualization in 82% (27/33 images), and full visualization in 18% (6/33 images).

Conclusion:

2D ss‐IMIV‐DWEPI can perform diffusion‐weighted carotid magnetic resonance imaging (MRI) in vivo with reasonably high spatial resolution (1 × 1 × 2 mm³). ADC values of the carotid wall and plaque are consistent with similar values obtained from ex vivo endarterectomy specimens. The spread in ADC values obtained from plaque indicate that this technique could form a basis for plaque component identification in conjunction with other MRI/MRA techniques. J. Magn. Reson. Imaging 2009;30:1068–1077. © 2009 Wiley‐Liss, Inc.

     

Detectability and detection rate of acute cerebral hemisphere infarcts on CT and diffusion-weighted MRI

Our purpose was to compare the detectability and detection rate of acute ischaemic cerebral hemisphere infarcts on CT and diffusion-weighted MRI (DWI). We investigated 32 consecutive patients with acute hemisphere stroke with unenhanced CT and DWI within 6 h of stroke onset. The interval between CT and DWI ranged from 15 to 180 min (mean 60 min). Infarct detectability on CT and DWI was determined by comparing the initial CT, DWI and later reference images in a consensus reading of five independent examiners. The “true” detection rate was assessed by analysing all single readings. Two patients had intracerebral haematomas on DWI and CT and were excluded. There were 27 patients with ischaemic infarcts; all were visible on DWI and proven by follow-up. DWI was negative in three patients without a final diagnosis of infarct (100 % sensitivity, 100 % specificity, χ² = 30, P < 0.0001). Ischaemic infarcts were visible on 15 and not seen on 12 CT studies (55 % sensitivity, 100 %specificity, χ² = 1.48, P = 0.224). With regard to the single readings (30 examinations × 5 examiners = 150 readings), 63 CT readings were true positive and 72 false negative (sensitivity 47 %, specificity 86 %, χ² = 2.88, P = 0.089). Of the DWI readings 128 were true positive and 7 false negative (sensitivity 95 %, specificity 87 %, χ² = 70.67, P < 0.0001). Interobserver agreement was substantial for CT (ϰ = 0.72, 95 % confidence interval, 0.6–0.84) and DWI (ϰ = 0.82, 95 % confidence interval, 0.46–1). Taken together, detectability and detection rate of acute (< 6 h) hemisphere infarcts are significantly higher with DWI than with CT. Received: 14 December 1999/Accepted: 15 February 2000     

Usefulness of diffusion-weighted imaging for differentiating between desmoid tumors and malignant soft tissue tumors

Purpose

To evaluate the usefulness of diffusion‐weighted imaging (DWI) for differentiating between desmoid tumors and malignant soft tissue tumors.

Materials and Methods

Conventional MRI and DWI were performed for 8 desmoid tumors and 74 malignant soft tissue tumors. DWI was obtained with a single‐shot echo‐planar imaging sequence using a 1.5 Tesla (T) MR imager. DW images were acquired with motion‐probing gradient pulses applied along three directions (x, y, and z axes) with three b‐factors (0, 500, and 1000 s/mm²). Two observers blinded to clinical information measured three regions of interest within the solid tumor and selected a minimum apparent diffusion coefficient () in each lesion. The mean ADC of desmoid tumors was calculated and compared with that of malignant soft tissue tumors using the Mann‐Whitney U test.

Results

The mean ADC of desmoid tumors and malignant soft tissue tumors was 1.36 ± 0.48 × 10⁻³ mm²/s and 0.88 ± 0.20 × 10⁻³ mm²/s (mean ± SD), respectively. The mean ADC of the desmoid tumors was significantly higher than that of malignant soft tissue tumors (P < 0.01).

Conclusion

DWI is considered to be useful for differentiating between desmoid tumors and malignant soft tissue tumors. In the future, further investigation in a large series is necessary. J. Magn. Reson. Imaging 2011;33:189–193. © 2010 Wiley‐Liss, Inc.

     

Persistent high signal on diffusion-weighted MRI in the late stages of small cortical and lacunar ischaemic lesions

Diffusion-weighted imaging (DWI) is very sensitive to early brain infarcts. However, the late stages have been insufficiently studied. Infarcts in small vessel disease are often multiple and of different ages, and differentiation between new and old lesions might be difficult. We have therefore studied the change with time in DWI of small (< 3 ml) ischaemic lesions. We imaged 21 patients with an acute lacunar syndrome and a lesion visible on early DWI. They all had three MRI examinations 12-58 h (early), 7-16 and 54-144 days after the onset of stroke; 10 patients with high DWI signal on the third examination had a fourth examination 12-28 months after the stroke. MRI was performed at 1.5 T, using echo-planar DWI with 7 b-values from 0 to 1200 x 10(6) s/m2 and conventional T2-weighted imaging. After 7-16 days 18 of 21 lesions gave high signal on DWI, and 12/16 measurable lesions had a decreased apparent diffusion coefficient (ADC). After 54-144 days ten lesions still gave high DWI signal and two still had an ADC below normal. On the fourth examination there was no remaining high DWI signal and all ADC were higher than normal.     

Multimodal CT Provides Improved Performance for Lacunar Infarct Detection

BACKGROUND AND PURPOSE:Lacunar infarcts account for approximately 25% of acute ischemic strokes. Compared with NCCT alone, the addition of CTP improves sensitivity for detection of infarcts overall. Our aim was to systematically evaluate the diagnostic benefit and interobserver reliability of an incremental CT protocol in lacunar infarction.MATERIALS AND METHODS:Institutional review board approval and patient consent were obtained. One hundred sixty-three patients presenting with a lacunar syndrome ≤4.5 hours from symptom onset were enrolled. Images were reviewed incrementally by 2 blinded readers in 3 separate sessions (NCCT only, NCCT/CTA, and NCCT/CTA/CTP). Diagnostic confidence was recorded on a 6-point scale with DWI/ADC as a reference. Logistic regression analysis calculated differences between actual and observed diagnoses, adjusted for confidence. Predictive effects of observed diagnostic accuracy and confidence score were quantified with the entropy r² value. Sensitivity, specificity, and confidence intervals were calculated accounting for multiple readers. Receiver operating characteristic analyses were compared among diagnostic strategies. Interobserver agreement was established with Cohen κ statistic.RESULTS:The final study cohort comprised 88 patients (50% male). DWI/ADC-confirmed lacunar infarction occurred in 59/88 (67%) with 36/59 (61%) demonstrating a concordant abnormal finding on CTP. Sensitivity for definite or probable presence of lacunar infarct increased significantly from 9.3% to 42.4% with incremental protocol use, though specificity was unchanged (range, 91.9%–95.3%). The observed diagnosis was significantly related to the actual diagnosis after adjusting for CTP confidence level (P = .04) and was 5.1 and 2.4 times more likely to confirm lacunar infarct than NCCT or CTA source images. CTP area under the curve (0.77) was significantly higher than that of CTA source images (0.68, P = .006) or NCCT (0.55, P < .001).CONCLUSIONS:CTP offers an improved diagnostic benefit over NCCT and CTA for the diagnosis of lacunar infarction.

Lacunar infarcts (LIs) account for approximately 25% of all acute ischemic strokes.¹ These small subcortical infarcts are typically located in the basal ganglia, thalamus, internal capsule, corona radiata, or brain stem.² Although single perforating artery occlusion is the dominant pathophysiology, lacunar syndromes may be secondary to large-artery disease and cardioembolic causes in up to 10% of cases.³ The National Institutes of Neurological Disorders and Stroke study showed the benefit of thrombolytic use on functional outcome across all stroke subtypes, including small-vessel infarcts characterized at baseline.⁴ Although conflicting findings have been reported,^5,6 a general consensus favors thrombolytic use in lacunar infarction.⁷ Anecdotally, thrombolysis treatment of an acute LI was associated with MR imaging perfusion and DWI deficit reversal, with good clinical recovery.⁸ Inaccuracy of the LI diagnosis is present in approximately 30% of stroke presentations by using clinical and NCCT findings alone.⁹ CTP is increasingly used during acute stroke work-up due to its cost effectiveness, ease, availability, speed, and tolerability.¹⁰ CTP significantly improves sensitivity for detection of infarcts overall compared with NCCT alone.^11,12 Perfusion abnormality associated with LI is clinically important and may be associated with early clinical deterioration, infarct growth, or resolution.^8,13–15 No prior study has systematically evaluated the performance of CTP for LI, to our knowledge. The purpose of this study was to evaluate the diagnostic benefit and interobserver reliability of an incremental CT protocol in the diagnosis of LI.     

Optimization of b value in diffusion-weighted MRI for the differential diagnosis of benign and malignant vertebral fractures

Objective The objective was to explore the optimal b value in diffusion-weighted imaging (DWI) of MRI for differential diagnosis of benign and malignant vertebral fractures. Materials and Methods Thirty-four consecutive patients with vertebral compression fractures underwent sagittal diffusion-weighted imaging (DWI) with different b values. The group included 14 patients with 18 benign vertebral fractures due to osteoporosis and/or trauma and 20 patients with 27 malignant vertebral fractures due to malignancy. The quality of the images was analyzed qualitatively on a three-point scale and quantitatively by measurement of the signal-to-noise ratio (SNR). Apparent diffusion coefficient (ADC) values were also calculated. Results Smaller b values correlated with better DW image quality. We found significant differences in the qualitative points values among the DW images with different b values (F = 302.18, p < 0.001). The mean SNR of the images ranged from 21.75 ± 3.64 at a b value of 0 s/mm² to 5.31 ± 3.17 at a b value of 800 s/mm². The SNR of DWI with a b value of 300 s/mm² (18.62 ± 2.47) was significantly different from that with other b values (p < 0.01). The mean combined ADC values of malignant fractures were significantly lower than those of benign ones on DWI with a b value of 300 s/mm² (t = 9.097, p < 0.01). Four cases of benign vertebral fractures were misdiagnosed as being malignant when b values of 0 s/mm² and 100 s/mm² were used. Conclusions When DWI with multiple b values is used to differentiate benign from malignant vertebral compression fractures, b values within the range of around 300 s/mm² are recommended, taking into account both SNR and diffusion weighting of water molecules.     

In vivo DTI assessment of hepatic ischemia reperfusion injury in an experimental rat model

Purpose

To investigate hepatic ischemia reperfusion injury (IRI) using diffusion tensor imaging (DTI).

Materials and Methods

Ten Sprague‐Dawley rats were scanned at 7 Tesla (T) with DTI using b‐value of 1000 s/mm² and 6 gradient directions before, 2 h, and 1 day after 30‐min total hepatic IRI. Apparent diffusion coefficient or mean diffusivity (MD), directional diffusivities and fractional anisotropy (FA) were measured. Seven of the animals were also examined with spin‐echo echo‐planar diffusion‐weighted imaging (DWI) with seven b‐values up to 2000 s/mm² to estimate the true diffusion coefficient (D), blood pseudodiffusion coefficient (D*), and perfusion fraction (f) using a bi‐compartmental model.

Results

MD 2 h after IRI (0.77 ± 0.07 × 10^?3 mm²/s) was significantly lower (P < 0.01) than that before (1.03 ± 0.07 × 10^?3 mm²/s) and 1 day after IRI (1.01 ± 0.05 × 10^?3 mm²/s). Meanwhile, FA 2 h after IRI (0.33 ± 0.03) was significantly higher (P < 0.01) than that before (0.21 ± 0.02) and 1 day after IRI (0.20 ± 0.02). The bi‐compartmental model analysis revealed the transient decrease in D, D* and f 2 h after IRI. Liver histology showed the multifocal cell swelling 3 h after IRI and widespread cell necrosis/apoptosis 1 day after IRI. Sinusoidal narrowing and congestion of erythrocytes were also observed 3 h and 1 day after IRI.

Conclusion

DTI can characterize hepatic IRI by detecting the transient change in both MD and FA. J. Magn. Reson. Imaging 2009;30:890–895. © 2009 Wiley‐Liss, Inc.

     

Detection of axillary node metastasis using diffusion-weighted MRI in breast cancer

Breast magnetic resonance imagings (MRIs) including diffusion-weighted MRI (DWI) of 110 breast cancers (26 with pathologically proven axillary node metastasis and 84 without metastasis) were retrospectively studied. Axillary nodes were detected as high-signal-intensity areas on DWI in 71 cancers (24 with metastasis and 47 without) and not detected in 39 cancers (2 with metastasis and 37 without). The ADC of metastatic nodes was significantly greater than that of the benign ones (1.08±0.18×10^?3 mm²/s vs. 0.92±0.22×10^?3 mm²/s, P=.004). When detectability of axillary nodes on DWI and ADC over 1.05×10^?3 mm²/s was applied as a threshold, 53.8% sensitivity, 86.9% specificity, and 79.1% accuracy were provided.     

Diffusion-weighted imaging of the pancreas

Diffusion-weighted imaging (DWI) has increasingly gained in importance over the last 10 years especially in cancer imaging for differentiation of malignant and benign lesions. Through development of fast magnetic resonance imaging (MRI) sequences DWI is not only applicable in neuroradiology but also in abdominal imaging. As a diagnostic tool of the pancreas DWI enables a differentiation between normal tissue, cancer and chronic pancreatitis. The ADC values (apparent diffusion coefficient, the so-called effective diffusion coefficient) reported in the literature for healthy pancreatic tissue are in the range from 1.49 to 1.9×10^?3 mm²/s, for pancreatic cancer in the range from 1.24 to 1.46×10^?3 mm²/s and for autoimmune pancreatitis an average ADC value of 1.012×10^?3 mm²/s. There are controversial data in the literature concerning the differentiation between chronic pancreatitis and pancreatic cancer. Using DWI-derived IVIM (intravoxel incoherent motion) the parameter f (perfusion fraction) seems to be advantageous but it is important to use several b values. In the literature the mean f value in chronic pancreatitis is around 16%, in pancreatic cancer 8% and in healthy pancreatic tissue around 25%. So far, DWI has not been helpful for differentiating cystic lesions of the pancreas. There are many references with other tumor entities and in animal models which indicate that there is a possible benefit of DWI in monitoring therapy of pancreatic cancer but so far no original work has been published.     

Diffusion-weighted imaging of the healthy pancreas: apparent diffusion coefficient values of the normal head, body, and tail calculated from different sets of b-values

Purpose:

To evaluate differences in apparent diffusion coefficient (ADC) values between head, body, and tail regions and the impact of sets of b‐values used in diffusion weighted imaging (DWI) of the normal pancreas.

Materials and Methods:

In 51 healthy volunteers echo‐planar DWI of the pancreas was prospectively performed with b‐values of 50, 400, and 800 s/mm². All four possible combinations of b‐values were used to calculate ADC values in a total of 587 regions in the pancreas head, body, and tail regions. Dependency of ADC values on the anatomical regions and on the applied sets of b‐values was calculated using multivariate analysis of variance (ANOVA).

Results:

Mean ADC values differed significantly between the anatomical regions with the lowest values measured in the pancreatic tail (head 1.13 ± 0.20, body 1.05 ± 0.20, and tail 0.94 ± 0.18 × 10^?3 mm²/s; P < 0.05). ANOVA showed no dependency of ADC values on the sets of b‐values used.

Conclusion:

ADC values differed significantly between the pancreatic head, body, and tail region, with decreasing ADC values toward the tail. Cautious interpretation of DWI results with adjusted, normalized values adapted to the anatomical region seems advisable. The knowledge of such differences may enhance the method's capability to differentiate between different pancreatic pathologies. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.

     

Diffusion-weighted MR imaging (DWI) in spinal cord ischemia

Introduction Spinal cord infarction is a rare clinical diagnosis characterized by a sudden onset of paralysis, bowel and bladder dysfunction, and loss of pain and temperature perception, with preservation of proprioception and vibration sense. Magnetic resonance imaging (MRI) usually demonstrates intramedullary hyperintensity on T2-weighted MR images with cord enlargement. However, in approximately 45% of patients, MR shows no abnormality. Diffusion-weighted MR imaging (DWI) has been widely used for the evaluation of a variety of brain disorders, especially for acute stroke. Preliminary data suggest that DWI has the potential to be useful in the early detection of spinal infarction.Methods We performed DWI, using navigated, interleaved, multishot echo planar imaging (IEPI), in a series of six patients with a clinical suspicion of acute spinal cord ischemia.Results In all patients, high signal was observed on isotropic DWI images with low ADC values (0.23 and 0.86×10⁻³ cm²/s), indicative of restricted diffusion.Conclusion We analyzed the imaging findings from conventional MR sequences and diffusion-weighted MR sequences in six patients with spinal cord infarction, compared the findings with those in published series, and discuss the value of DWI in spinal cord ischemia based on current experience. Although the number of patients with described DWI findings totals only 23, the results of previously published studies and those of our study suggest that DWI has the potential to be a useful and feasible technique for the detection of spinal infarction.     

Diffusion-weighted imaging in patients with progressive multifocal leukoencephalopathy

Progressive multifocal leukoencephalopathy (PML) is a severe demyelinating disease of the central nervous system due to JC polyoma virus infection of oligodendrocytes. PML develops in patients with impaired T-cell function as occurs in HIV, malignancy or immunosuppressive drugs users. Until now no imaging methods have been reported to correlate with clinical status. Diffusion-weighted imaging (DWI) is a robust MRI tool in investigating white matter architecture and diseases. The aim of our work was to assess diffusion abnormalities in focal white matter lesions in patients with PML and to correlate the lesion load measured with conventional MRI and DWI to clinical variables. We evaluated eight patients with a biopsy or laboratory-supported diagnosis of PML. All patients underwent MRI including conventional sequences (fluid attenuated inversion recovery-FLAIR) and DWI. Mean diffusivity (MD) maps were used to quantify diffusion on white matter lesions. Global lesion load was calculated by manually tracing lesions on FLAIR images, while total, central core and peripheral lesion loads were calculated by manually tracing lesions on DWI images. Lesion load obtained with the conventional or DWI-based methods were correlated with clinical variables such as disease duration, disease severity and survival. White matter focal lesions are characterized by a central core with low signal on DWI images and high MD (1.853 × 10⁻³ mm2/s), surrounded by a rim of high signal intensity on DWI and lower MD (1.1 × 10⁻³ mm2/s). The MD value of normal-appearing white matter is higher although not statistically significant (0.783 × 10⁻³ mm2/s) with respect to control subjects (0.750 × 10⁻³ mm2/s). Inter-rater correlations of global lesion load between FLAIR (3.96%) and DWI (3.43%) was excellent (ICC =0.87). Global lesion load on FLAIR and DWI correlates with disease duration and severity (respectively, p = 0.037, p = 0.0272 with Karnofsky scale and p = 0.0338 with EDSS on FLAIR images; p = 0.043, p = 0.0296 with Karnofsky scale and p = 0.0365 with EDSS on DW images). Central core lesion load on DWI correlates with disease duration and severity (respectively p = 0.043, p = 0.0103 with Karnofsky scale and p = 0.0112 with EDSS), while peripheral lesion load does not correlate with any clinical variable. The global lesion load in PML correlates with disease duration and severity. DWI images, which can distinguish within lesions a central core from a peripheral rim, reveal that a larger central core component correlates to a worsened clinical status and longer disease duration. On the other hand the peripheral rim lesion load visualized on DWI images does not correlate with clinical variables and does not achieve obtaining further prognostic information with respect to conventional imaging.