Diffusion-weighted Magnetic Resonance Imaging Technique Research Articles

A robust multi-shot scan strategy for high-resolution diffusion weighted MRI enabled by multiplexed sensitivity-encoding (MUSE)

Diffusion weighted magnetic resonance imaging (DWI) data have been mostly acquired with single-shot echo-planar imaging (EPI) to minimize motion induced artifacts. The spatial resolution, however, is inherently limited in single-shot EPI, even when the parallel imaging (usually at an acceleration factor of 2) is incorporated. Multi-shot acquisition strategies could potentially achieve higher spatial resolution and fidelity, but they are generally susceptible to motion-induced phase errors among excitations that are exacerbated by diffusion sensitizing gradients, rendering the reconstructed images unusable. It has been shown that shot-to-shot phase variations may be corrected using navigator echoes, but at the cost of imaging throughput. To address these challenges, a novel and robust multi-shot DWI technique, termed multiplexed sensitivity-encoding (MUSE), is developed here to reliably and inherently correct nonlinear shot-to-shot phase variations without the use of navigator echoes. The performance of the MUSE technique is confirmed experimentally in healthy adult volunteers on 3Tesla MRI systems. This newly developed technique should prove highly valuable for mapping brain structures and connectivities at high spatial resolution for neuroscience studies.

The role of dynamic contrast-enhanced and diffusion weighted magnetic resonance imaging in the female pelvis

Functional imaging by means of dynamic multiphase contrast-enhanced magnetic resonance imaging (DCE-MRI) and diffusion weighted magnetic resonance imaging (DW-MRI) is now part of the standard imaging protocols for evaluation of the female pelvis. DCE-MRI and DW-MRI are important MR imaging techniques which enable the radiologist to move from morphological to functional assessment of diseases of the female pelvis. This is mainly due to the limitations of morphologic imaging, particularly in lesion characterization, accurate lymph node staging, assessment of tumour response and inability to differentiate post-treatment changes from tumour recurrence. DCE-MRI improves the accuracy of T2WI in staging of endometrial cancer. It also helps differentiate tumour recurrence from radiation fibrosis in patients with cervical cancer. DCE-MRI improves characterization of cystic adnexal lesions and detection of small peritoneal implants in patients with ovarian cancer. DW-MRI is valuable in preoperative staging of patients with endometrial and cervical cancer, especially in detection of extra-uterine disease. It does increase reader's confidence for detection of recurrent disease in gynaecological malignancies and improves detection of small peritoneal implants in patients with ovarian cancer. In this review article we give an overview of both DCE-MRI and DW-MRI techniques, concentrating on their main clinical application in the female pelvis, and present a practical approach of the added value of these techniques according to the main pathological conditions, highlighting the pearls and pitfalls of each technique.

HASTE Diffusion-Weighted 3-Tesla Magnetic Resonance Imaging in the Diagnosis of Primary and Relapsing Cholesteatoma

To evaluate the value of half-Fourier acquisition single-shot turbo-spin-echo diffusion-weighted magnetic resonance imaging (HASTE DW MRI) using a 3-Tesla (3T) unit in the diagnosis of primary and relapsing cholesteatoma. Retrospective observational investigation. Tertiary referral center. Seventeen patients suspected of having a primary cholesteatoma without clear clinical evidence of the lesion, and 13 patients who were candidates to a second-stage tympanoplasty to rule out a relapsing cholesteatoma or reconstruct the ossicular chain were investigated. All patients were scanned in a 3T scanner with a 4-channel head coil using T2 HASTE DW MRI technique sequences in axial and coronal planes covering the middle ear and mastoid regions. Images were considered positive for cholesteatoma in the presence of a hyperintense, patchy-like lesion in the petrous bone. Images showed a high signal intensity suggestive of primary cholesteatoma in 10 of 17 patients and of relapsing cholesteatoma in 7 of 13 patients. Of the 17 subjects, 15 with positive MRI findings were operated on, and the presence of cholesteatoma (ranging from 2 to 20 mm in size) was confirmed at surgery. Of the 13 subjects shown to be negative on HASTE DW MRI for cholesteatoma, 11 were operated on and were all confirmed to be cholesteatoma-free. Half-Fourier acquisition single-shot turbo-spin-echo diffusion-weighted magnetic resonance imaging technique, using a 3T unit, may be a diagnostic tool for a rapid and highly reliable discrimination between cholesteatomatous and noncholesteatomatous tissue in the middle ear, with 100% of positive and negative predictive values.

Analysis of cyclosporin A-induced reversible cortical blindness by diffusion-weighted magnetic resonance imaging techniques

Analysis of cyclosporin A-induced reversible cortical blindness by diffusion-weighted magnetic resonance imaging techniques

Early detection of periventricular leukomalacia by diffusion-weighted magnetic resonance imaging techniques

Periventricular leukomalacia (PVL), the principal form of brain injury in the premature infant, is characterized by overt focal necrotic lesions in periventricular white matter and less prominent, more diffuse cerebral white matter injury. The early detection of the latter, diffuse component of PVL is not consistently possible with conventional brain imaging techniques. We demonstrate the early detection of the diffuse component of PVL by diffusion-weighted magnetic resonance imaging (DWI). In a premature infant with no definite cerebral abnormality detectable by cranial ultrasonography or conventional magnetic resonance imaging, DWI showed a striking bilateral decrease in water diffusion in cerebral white matter. The DWI abnormality (ie, decreased apparent diffusion coefficient) was similar to that observed with acute cerebral ischemic lesions in adults. At 10 weeks of age, conventional magnetic resonance imaging and ultrasonography showed striking changes consistent with PVL, including the presence of small cysts. The observations indicate the importance of DWI in the early identification of the diffuse component of PVL and also perhaps the role of ischemia in the pathogenesis of the lesion. (J Pediatr 1999;134:631-4)

A novel fast split-echo multi-shot diffusion-weighted MRI method using navigator echoes.

Difficulties in obtaining diffusion-weighted images of acceptable quality using conventional hardware and in a reasonable time have hindered the clinical application of diffusion-weighted magnetic resonance imaging (DWI). Diffusion-weighted fast spin-echo (FSE) sequences offer the possibility of fast DWI on standard hardware without the susceptibility problems associated with echoplanar imaging. However, motion in the presence of diffusion-sensitizing gradients can prevent fulfilment of the Meiboom Gill phase condition, leading to destructive interference between echo components and consequent signal losses. A recently proposed single-shot FSE sequence employed split-echo acquisition to address this problem. However, in a segmented FSE sequence, phase errors differ between successive echo trains, causing "ghosting" in the diffusion-weighted images that are not eliminated by split-echo acquistion alone. A DWI technique is presented that combines split-echo acquisition with navigator echo phase correction in a segmented FSE sequence. It is shown to be suitable for diffusion measurements in vivo using standard hardware.

Regional differences in diffusion abnormality in cerebral white matter lesions in patients with vascular dementia of the Binswanger type and Alzheimer's disease.

We investigated changes in water diffusion in the cerebral white matter of 14 patients with vascular dementia of the Binswanger type (VDBT) and ten patients with Alzheimer's disease (AD) with periventricular hyperintensity (PVH) lesions using diffusion-weighted magnetic resonance imaging (MRI) and studied the pathophysiological differences between white matter lesions found in these two conditions. Apparent diffusion coefficients (ADCs) in the anterior and posterior white matter and the genu and splenium of the corpus callosum were significantly higher in both groups of patients than in the 12 age-matched controls, and ADC values in VDBT and AD groups were almost the same. ADC ratios, defined as diffusion restricted perpendicular to the direction of nerve fibers, were also significantly higher in the patients than in the control subjects. However, there were regional differences in ADC ratios in the two conditions, with ratios in VDBT being higher in the anterior portions of the white matter but ratios in AD were higher in the posterior portions. The diffusion-weighted MRI technique may be useful in the differential diagnosis of VDBT and AD with white matter lesions.

Imaging funzionale per diffusione (DWI) e ischemia cerebrale in fase acuta: Potenzialità diagnostiche e confronto con metodiche convenzionali

Stroke is the third leading cause of death and is a major cause of long-term disability. Neuroprotective treatment within a 4-hour «therapeutic window» has proved highly efficacious in reducing morbility and mortality in animal model. It is with this background that the need for emergent diagnosis and therapy of acute stroke in strongly suggested. Computed tomography (CT) shows the parenchymal changes of acute stroke too late to be helpful, and its role has been primarily to evaluate the possibility of intracerebral or subarachnoid hemorrhage. While conventional magnetic resonance (MR) imaging can demonstrate parenchymal abnormalities 4–6 hours after ischemia, newer techniques such as diffusion-weighted MR imaging (DWI) hold promise that a diagnosis of ischemia can be made within minutes after the acute event. In this article compares different aspects of hyperacute cerebral ischemia depicted at diffusion-weighted imaging before infarction is depicted at conventional MR or CT scans. DWI techniques may improve stroke diagnosis and may contribute to advances in treatment.

T2- and diffusion-weighted magnetic resonance imaging of a focal ischemic lesion in rat brain.

We sought to evaluate the application of T2-weighted and diffusion-weighted magnetic resonance imaging techniques in the study of a focal ischemic lesion in the rat brain. Unilateral cortical infarcts were induced using the photosensitive dye rose bengal and 560 nm light irradiation. Magnetic resonance images were recorded from a total of 11 rats at selected intervals from 1.5 hours to several days after induction of the lesion. Parallel experiments were performed in which Evans blue dye was injected into the lesioned animals either immediately after lesion induction (n = 11) or 1 hour before the animals were killed (n = 11). The second procedure was designed to show regions of blood-brain barrier permeability to plasma proteins at the time of sacrifice, whereas the first procedure showed the accumulation and subsequent dispersion of plasma protein following disruption of the blood-brain barrier. Regions of the cortex highlighted by the T2-weighted images corresponded well to the pattern of dye staining seen from the first procedure while the diffusion-weighted images showed visual correspondence with the staining pattern obtained using the second procedure. These results illustrate the complementary use of T2-weighted and diffusion-weighted magnetic resonance imaging in discerning the pathophysiology of developing lesions.