High-resolution Gradient Echo Research Articles

A study of the comparative anatomy of the brain of domestic ruminants using magnetic resonance imaging

Although magnetic resonance imaging has been used to examine the brain of domestic ruminants, detailed information relating the precise anatomical features in these species is lacking. In this study the brain structures of calves (Bos taurus domesticus), sheep (Ovis aries), goats (Capra hircus) and a mesaticephalic dog (Canis lupis familiaris) were examined using T2-weighed Turbo Spin Echo sequences; three-dimensional models based on high-resolution gradient echo scans were used to identify brain sulci and gyri in two-dimensional images. The ruminant brains examined were similar in structure and organisation to those of other mammals but particular features included the deep depression of the insula and the pronounced gyri of the cortices, the dominant position of the visual (optic nerve, optic chiasm and rostral colliculus) and olfactory (olfactory bulb, olfactory tracts and piriform lobe) systems, and the relatively large size of the diencephalon.

Gadolinium toxicity: epidermis thickness measurement by magnetic resonance imaging at 500 MHz

Regional epidermal thickening and hair follicle width measurement by delayed gadolinium contrast magnetic resonance imaging (MRI) may assess the contrast agent gadolinium toxicity on mice skin. Delayed contrast in vivo MRI was performed in mice. Six mice skin samples were removed and exposed to a gadolinium contrast agent at different times after 2, 4, 6 and 8 h. The relaxation constants of each skin structure were measured. The thickness of the epidermis and hair follicle on follow-up ex vivo delayed-contrast MRI served as an index of gadolinium toxicity on the skin. In vivo MRI by fast low-angle shot imaging technique showed distinct skin layers. High-resolution gradient echo T1-weighted and multislice multiecho proton density-weighted MRI intensities in the epidermis and hair follicle showed a positive correlation with delayed gadolinium-enhanced MRI hyperintensities (Pearson's correlation coefficient r(2)=0.81, P<0.0001) in the excised mice skin tissues. Delayed contrast-enhanced mice skin MRI after 2-4 h showed epidermis swelling and hair follicle regions with a size measurement accuracy of 65%, a sensitivity of 95%, a specificity of 25%, a positive predictive value of 65% and a negative predictive value of 65%. Areas under the receiver operating characteristic curves by MRI were 0.92-0.94 for hair and epidermis as good discriminators. MRI visualized distinct relaxation constants of the epidermis, sebaceous gland, skin papillary and reticular dermis layers and hair follicle. Gadolinium contrast-enhanced MRI may visualize the thickening of the epidermis wall and hair follicle as an index of viable mice skin. Gadolinium enhanced the MRI visibility of skin structures. Gadolinium treatment showed skin toxicity as epidermis thickening the first time due to the undesirable use of high concentrations of gadolinium in microimaging.

Cortical layer-dependent arterial blood volume changes: Improved spatial specificity relative to BOLD fMRI

The spatial specificity of functional hemodynamic responses was examined by simultaneous mapping of BOLD changes and quantitative changes in cerebral arterial blood volume (ΔCBVa) across the cortical depth in cats (n=7) during 40-s visual stimulation. Studies were performed at 9.4 T using the recently developed, non-invasive magnetization transfer (MT)-varied gradient-echo (GE) fMRI technique to separate signals from MT-independent arterial blood and MT-dependent tissue. The highest conventional BOLD signal changes occurred at the cortical surface, where large pial veins exist, whereas the highest CBVa changes occurred in the middle of the cortex, where T1-weighted images show a hyperintense layer. In the middle cortical region, the average BOLD change (echo time=20 ms) was 1.16±0.45% during stimulation and −0.59±0.31% during the post-stimulus period, while the average ΔCBVa was 0.33±0.02 ml/100 g during stimulation and −0.08±0.12 ml/100 g post-stimulus (post-stimulus ΔCBVa is not statistically significant). Time-dependencies of the ΔCBVa cortical profiles are similar to total CBV responses previously measured during visual stimulation in cats with a susceptibility contrast agent indicating, that blood volume changes mostly originate from arterial vessels. Our findings demonstrate the value of non-invasive and quantitative ΔCBVa measurement in high-resolution MT-varied GE fMRI studies, where spatial specificity is better localized to sites of neural activity as compared with conventional GE BOLD changes.

High Resolution Ultra High Field Magnetic Resonance Imaging of Glioma Microvascularity and Hypoxia Using Ultra-Small Particles of Iron Oxide

This study assessed whether ultra-small particles of iron oxide (USPIO) intravascular contrast agent could enhance visualization of tumor microvascularity in F98 glioma bearing rats by means of ultra high field (UHF) high-resolution gradient echo (GRE) magnetic resonance imaging (MRI). In an effort to explain differences in visualization of microvascularity before and after USPIO administration, hypoxia and vessel diameters were assessed on corresponding histopathologic sections. F98 glioma cells were implanted stereotactically into the brains of syngeneic Fischer rats. Based on clinical criteria, rats were imaged 1 to 2 days before their death with and without USPIO contrast on an 8 Tesla MRI. To identify hypoxic regions of the brain tumor by immunohistochemical staining, a subset of animals also received a nitroimidazole-based hypoxia marker, EF5, before euthanasia. These sections then were compared with noncontrast enhanced MR images. The relative caliber of tumor microvasculature, compared with that of normal brain, was analyzed in a third group of animals. After USPIO administration, UHF high-resolution GRE MRI consistently predicted increased microvascular density relative to normal gray matter when correlated with histopathology. The in-plane visibility of glioma microvascularity in 22 rats increased by an average of 115% and signal intensity within the tumor decreased by 13% relative to normal brain. Tumor microvascularity identified on noncontrast MR images matched hypoxic regions identified by immunohistochemical staining with a sensitivity of 83% and specificity of 89%. UHF GRE MRI was able to resolve microvessels less than 20 micro in diameter, although differences in tumor vessel size did not consistently account for differences in visualization of microvascularity. USPIO administration significantly enhanced visualization of tumor microvascularity on gradient echo 8 T MRI and significantly improved visualization of tumor microvascularity. Microvascularity identified on precontrast images is suspected to be partly associated with hypoxia.

MAGNETIC RESONANCE IMAGING ANATOMY OF THE NORMAL EQUINE LARYNX AND PHARYNX

The purpose of the present study was to describe normal magnetic resonance (MR) imaging anatomy of the equine larynx and pharynx and to present the optimal protocol, sequences, and possible limitations of this examination technique. Using a 0.3 T unit, the laryngeal and pharyngeal regions was imaged in two horses. The protocol consisted of sagittal and transverse T2-weighted (T2w) fast spin echo, transverse T1-weighted (T1w) spin echo, and dorsal high-resolution T1w gradient echo (both pre- and postcontrast enhancement) sequences. Euthanasia was performed at the end of the imaging procedure. Macroscopic anatomy of the cadaver sections were compared with the MR images in transverse, midsagittal, and parasagittal planes. There was good differentiation of anatomic structures, including soft tissues. The laryngeal cartilages, hyoid apparatus, and upper airway muscle groups with their attachments could be clearly identified. However, it was not always possible to delineate individual muscles in each plane. Most useful were both T2w and T1w transverse sequences. Intravenous application of contrast medium was helpful to identify blood vessels. The MR images corresponded with the macroscopic anatomy of cadaver sections.

Low-Field Magnetic Resonance Imaging of the Thumb Base in Severe Symptomatic Osteoarthritis: A Comparison with Radiographs and Clinical Symptoms

The objectives of this pilot study were to assess the findings of low-field MRI in symptomatic thumb base os- teoarthritis (OA), to identify suitable MRI sequences with or without Gadolinium contrast, and to compare these findings with conventional radiographs scored by the Altman atlas and patient reported pain. Twelve patients with symptomatic thumb base osteoarthritis participated. We used a 0,2T MRI system, before and after i.v. Gadolinium. The MRI images were scored on a 0-3 scale for synovitis (SYN), bone marrow edema (BME), cysts/erosions (CE) and osteophytes (OP). Interreader agreement on MRI scores was best for BME and CE but less for SYN and OP. Difficulties were in determin- ing the soft tissue involvement of the CMC1 joint, especially in demarcating the joint capsule and ligament pathology. The most informative MRI sequences were the High Resolution Gradient Echo, the STIR and the 3D volume.Gadolinium contrast provided little additional information. Cumulative MRI and radiographic scores for the 24 CMC1 joints studied were strongly correlated (Rs 0.81, p<0.001). Both BME in adjacent bones and SYN in the CMC1 joint correlated with rest pain (Rs 0.54, p<0.01 and Rs 0.45, p<0.05) respectively). BME was also associated with pain intensity on a 0-10 scale (R 0.44, p<0.05). Other radiographic and MRI variables showed no association with pain. Low-field MRI reflects CMC1 joint osteoarthritis damage and gives additional information regarding bone marrow edema and synovitis, both of which are strongly related to clinical symptoms. This study encourages further research to identify the most suitable equipment and sequences and to standardize the reading of MRI images.

Magnetic field perturbation of neural recording and stimulating microelectrodes

To improve the overall temporal and spatial resolution of brain mapping techniques, in animal models, some attempts have been reported to join electrophysiological methods with functional magnetic resonance imaging (fMRI). However, little attention has been paid to the image artefacts produced by the microelectrodes that compromise the anatomical or functional information of those studies. This work presents a group of simulations and MR images that show the limitations of wire microelectrodes and the potential advantages of silicon technology, in terms of image quality, in MRI environments. Magnetic field perturbations are calculated using a Fourier-based method for platinum (Pt) and tungsten (W) microwires as well as two different silicon technologies. We conclude that image artefacts produced by microelectrodes are highly dependent not only on the magnetic susceptibility of the materials used but also on the size, shape and orientation of the electrodes with respect to the main magnetic field. In addition silicon microelectrodes present better MRI characteristics than metallic microelectrodes. However, metallization layers added to silicon materials can adversely affect the quality of MR images. Therefore only those silicon microelectrodes that minimize the amount of metallic material can be considered MR-compatible and therefore suitable for possible simultaneous fMRI and electrophysiological studies. High resolution gradient echo images acquired at 2 T (TR/TE = 100/15 ms, voxel size = 100 × 100 × 100 µm3) of platinum–iridium (Pt–Ir, 90%–10%) and tungsten microwires show a complete signal loss that covers a volume significantly larger than the actual volume occupied by the microelectrodes: roughly 400 times larger for Pt–Ir and 180 for W, at the tip of the microelectrodes. Similar MR images of a single-shank silicon microelectrode only produce a partial volume effect on the voxels occupied by the probe with less than 50% of signal loss.

Extensive heterogeneity in white matter intensity in high-resolution T 2*-weighted MRI of the human brain at 7.0 T

MRI at high magnetic field strength potentially allows for an increase in resolution and image contrast. The gains are particularly dramatic for T 2 *-weighted imaging, which is sensitive to susceptibility effects caused by a variety of sources, including deoxyhemoglobin, iron concentration, and tissue microstructure. On the other hand, the acquisition of high quality whole brain MRI at high field is hampered by the increased inhomogeneity in B o and B 1 fields. In this report, high-resolution gradient echo MRI was performed using an 8-channel detector to obtain T 2 *-weighted images over large brain areas. The high SNR achieved with the multi-channel array enabled T 2 *-weighted images of the brain with an unprecedented spatial resolution of up to 0.2 × 0.2 × 0.5 mm 3. This high resolution greatly facilitated the detection of microscopic susceptibility effects. In addition to the expected contrast between gray, white matter, cerebral spinal fluid, and veins, a large degree of heterogeneity in contrast was observed throughout the white matter of normal brain. The measured T 2 * values in white matter varied as much as 30% with some of the variation apparently correlating with the presence of large fiber bundles.

Gradient Echo MRI Characterization of Development of Atherosclerosis in the Abdominal Aorta in Watanabe Heritable Hyperlipidemic Rabbits

The Watanabe Heritable Hyperlipidemic (WHHL) rabbit provides an important model of spontaneous atherosclerosis. With a strain of WHHL rabbits which do not develop abdominal aorta lumen stenosis even with advanced atherosclerosis, we studied the MRI-histology correlation, and the natural progression of atherosclerosis in the abdominal aorta. In addition, intra-reader segmentation repeatability and scan-rescan reproducibility were assessed. Two batches of female WHHL rabbits were used. The first batch of 6 rabbits was scanned at 20 weeks old. A second batch of 17 rabbits was scanned at 50 weeks old and then randomly divided into two subgroups: 8 were killed for histologic investigation; 9 were kept alive for follow-up, with repeat scanning a week later to assess scan-rescan reproducibility, and again at 73 weeks old to assess disease progression. MR images were acquired at 4.7 T using a chemical shift selective fat suppression gradient echo with a saturation band suppressing blood signal within the aortic lumen. Five slices per animal were acquired, centered around the renal artery region of the abdominal aorta, with in-plane resolution of 0.195 mm and slice thickness of 3 mm. The coefficient of variation for intra-reader reproducibility for aortic wall thickness measurements was 2.5% for repeat segmentations of the same scans on the same day, but segmentations of these same scans made 8 months later showed a systematic change, suggesting that intra-reader bias as well as increased variability could compromise assessments made over time. Comparative analyses were therefore performed in one postprocessing session. The coefficient of variation for scan-rescan reproducibility for aortic wall thickness was 5.5% for nine pairs of scans acquired a week apart and segmented on the same day. Good MRI-histology correlation was obtained. The MRI-measured mean aortic wall thickness of animals at 20 weeks of age was 76% that of animals at 50 weeks of age (p < 0.001). There was a small increase in aortic wall thickness between 50 and 73 weeks of age, but this was not significant (p > 0.05). The corresponding differences in lumen cross-sectional areas at 20, 50, and 73 weeks of age were not significant. These results were consistent with in-house historical histology data on this strain of rabbits. High-resolution gradient echo MRI can follow disease progression in the WHHL rabbit spontaneous atherosclerosis disease model.

Single-cell detection by gradient echo 9.4 T MRI: a parametric study

Recent studies have shown that cell migration can be monitored in vivo by magnetic resonance imaging after intracellular contrast agent incorporation. This is due to the dephasing effect on proton magnetization of the local magnetic field created by a labelled cell. Anionic iron oxide nanoparticles (AMNP) are among the most efficient and non-toxic contrast agents to be spontaneously taken up by a wide variety of cells. Here we measured the iron load and magnetization of HeLa tumour cells labelled with AMNP, as a function of the external magnetic field. High-resolution gradient echo 9.4 T MRI detected individual labelled cells, whereas spin echo sequences were poorly sensitive. We then conducted a systematic study in order to determine the gradient echo sequence parameters (echo time, cell magnetization and resolution) most suitable for in vivo identification of single cells.

Epoxy‐resin injection of the cerebral arterial microvasculature: An evaluation of the limits of spatial resolution in 8 Tesla MRI

The purpose of this study was to quantify the spatial resolution of microscopic arteries on magnetic resonance images acquired at 8 Tesla (T). Techniques similar to those used for standard MRI of the human brain in vivo at 8 T were utilized to generate high-resolution gradient echo (GE) images of a whole postmortem human brain whose common carotid arterial system had been injected with an epoxy-resin. Single slice images, along with summed images of up to 5 contiguous slices, were then compared to color digital photographs detailing the distribution of the arterial system on the surface of the same injected brain. There was excellent MR visualization of the microscopic cerebral arteries down to a spatial resolution of 200 microm. Through the use of an 8 T whole-body MRI scanner and standard GE imaging sequences, microscopic arterial structures can be clearly resolved down to a dimension of 200 microm.

Enhanced gray and white matter contrast of phase susceptibility-weighted images in ultra-high-field magnetic resonance imaging.

To evaluate if magnetic susceptibility sensitive phase postprocessed images can be used to enhance the inherent brain/gray white matter contrast in gradient echo (GE) images at 8-Tesla (T) magnetic resonance (MR). Phase and magnitude images of high-resolution GE MR 8-T images were created. Comparisons were made between the magnitude, the product of the magnitude and phase, and pure phase images. The pure phase images significantly improved the contrast between the gray and white matter structures. In general, the higher the iron content or subvoxel field inhomogeneities, the higher was the contrast, and the greater were the resultant phase shifts. The phase images best demonstrated anatomy that was not apparent on the standard magnitude images. Phase imaging can significantly improve the demonstration of the internal anatomical brain structures over standard magnitude GE imaging techniques at high field.

Invasive lobular carcinoma: spectrum of enhancement and morphology on magnetic resonance imaging.

Invasive lobular carcinoma (ILC) may be a difficult tumor to detect early by physical examination, mammography, or ultrasound. We undertook this study to describe the spectrum of gadolinium enhancement and morphologic features of ILC on magnetic resonance imaging (MRI). Nineteen patients with ILC who presented with a palpable mass, a mammographically visible abnormality, or an unknown primary underwent preoperative MRI of both breasts using a T1-weighted high-resolution gradient echo sequence (pre- and postcontrast), and an echoplanar sequence during the administration of gadolinium. Using a quantitative measure of gadolinium uptake over time, called the extraction flow (EF) product, and a normal tissue threshold EF level of 25 or less, enhancement for 15 of the 19 cancers was characterized. By consensus, three radiologists categorized the morphologic features of the lesions. For the 15 cases of ILC that had echoplanar data, analysis showed peak EFs ranging between 25 and 120, and the majority showed EFs in the 30s. A substantial portion of two tumors enhanced in a similar fashion to normal breast tissue, with EFs in the low 20s. Morphologically MRI showed a focal mass in eight cases, regional enhancement in five, segmental enhancement in one, segmental enhancement with multiple small nodules in one, a mixture of a focal mass and regional enhancement in one, diffuse enhancement in one, multiple small nodules in one, and bilateral disease in one. Of the focal masses, seven were irregular in shape and one was round; six had ill-defined margins and two had spiculated margins. All eight enhanced heterogeneously. Four cases had multifocal disease and one case had unsuspected contralateral disease discovered only on MRI. MRI using a combination of morphology and a quantitative measure of gadolinium uptake was able to detect the majority of cases of ILC. However, there was a variable morphologic appearance and contrast enhancement pattern on MRI. A few lesions were difficult to distinguish from normal tissue. This suggests that some cases of ILC may be difficult to detect on MRI.

Cerebral venous and arterial blood volumes can be estimated separately in humans using magnetic resonance imaging.

Approaches to obtain quantitative, noninvasive estimates of total cerebral blood volume (tCBV) and cerebral venous blood volume (vCBV) separately in humans are proposed. Two sequences were utilized, including a 3D high-resolution gradient-echo (GE) sequence and a 2D multi-echo GE/spin-echo (MEGESE) sequence. Images acquired by the former sequence provided an estimate of background magnetic field variations (DeltaB), while images obtained by the latter sequence were utilized to obtain separate measures of tCBV and vCBV with and without contrast agent. Prior to the calculation of vCBV and tCBV, the acquired images were corrected for signal loss induced by the presence of DeltaB. vCBV and tCBV were estimated to be 2.46% +/- 0.28% and 3.20% +/- 0.41%, respectively, after the DeltaB correction, which in turn provided a vCBV/tCBV ratio of 0.77 +/- 0.04, in excellent agreement with results reported in the literature. Our results demonstrate that quantitative estimates of vCBV and tCBV can be obtained in vivo.

Occult contralateral breast carcinoma incidentally detected by breast magnetic resonance imaging.

The incidence of synchronous bilateral breast cancers has been reported to be between 3.4% and 7.4%, as detected on mammography, physical examination, or both. We undertook a study to determine how often magnetic resonance (MR) imaging detects a contralateral abnormality in patients with known breast carcinoma. As part of an institutional review board (IRB) -approved research protocol, 17 patients with pathologically proven invasive carcinoma underwent preoperative MR imaging of both breasts using a T1-weighted, high-resolution gradient echo sequence (precontrast and postcontrast), an echo-planar sequence during administration of gadolinium, and a T2-weighted, fast-spin echo sequence. The morphology and dynamic enhancement of lesions in both breasts were assessed. Biopsy was recommended for any lesion meeting set criteria. MR imaging identified all 17 known invasive cancers in the breast of concern on mammography or physical examination. Five of 17 patients (29%) had 10 contralateral lesions identified on MR, for which biopsy was recommended. One of these lesions proved to represent a fibroadenoma. The other 9 lesions proved to represent a malignancy (6 invasive lobular, 2 infiltrating ductal, and 1 tubular). Four of the 17 patients (24%) with invasive cancer had contralateral synchronous cancers occult to physical examination, mammography, and ultrasonography. In this series, breast MR imaging of the breasts was more sensitive than mammography or physical examination in the detection of early breast cancer. Breast MR imaging of the contralateral breast may be of value as a routine screen in those patients with a known or suspected malignancy.

Cerebral oxygen extraction fraction and cerebral venous blood volume measurements using MRI: effects of magnetic field variation.

The presence of magnetic background field inhomogeneity (DeltaB) may confound quantitative measures of cerebral venous blood volume (vCBV) and cerebral oxygen extraction fraction (MR_OEF) with T2*-based methods. The goal of this study was to correct its effect and obtain more accurate estimates of vCBV and MR_OEF. A 3D high-resolution gradient echo sequence was employed to obtain DeltaB maps by two algorithms. The DeltaB maps were then used to recover the signal loss in images acquired by a 2D multiecho gradient echo / spin echo sequence. Finally, both quantitative estimates of MR_OEF and vCBV were obtained from the DeltaB- corrected 2D multiecho gradient echo / spin echo images. A total of 12 normal subjects were studied. An overestimated vCBV was observed in the brain (4.29 +/- 0.78%) prior to DeltaB correction, while the measured vCBV was substantially reduced after DeltaB correction. Whole brain vCBV of 2.97 +/- 0.44% and 2.68 +/- 0.47% were obtained by the two different DeltaB correction methods, in excellent agreement with the reported results in the literature. Furthermore, when MR_OEF was compared with and without DeltaB correction, no significant differences (P = 0.467) were observed. The ability to simultaneously obtain vCBV and MR_OEF noninvasively may have profound clinical implications for the studies of cerebrovascular disease.

Comparison of three‐dimensional fast spin echo and gradient echo sequences for high‐resolution temporal bone imaging

T2-weighted high-resolution gradient and fast spin echo sequences are widely used as an alternative or adjunct to contrast-enhanced T1-weighted temporal bone imaging. However, to date no systematic comparison has been presented. The purpose of this work is to identify optimal acquisition parameters and to compare volume gradient and fast spin echo techniques. Signal intensities and scan efficiency were computed for gradient echo segment-interleaved motion-compensated acquisition into steady state (SIMCAST), standard fast spin echo (FSE), and fast recovery fast spin echo (FR-FSE). Computations were compared with inner ear images acquired with cubic voxel sizes of 0.35–0.40 mm3in 5–8 minutes. Given otherwise identical conditions, the FR-FSE sequence produces images with improved SNR in shorter scan times than standard FSE. For FR-FSE, the scan efficiency is optimal for specific pairs of TR and echo train length, eg, 400 ms/8, 735 ms/16, and 2,050 ms/48. FR-FSE images with large TR and echo trains, while achieving better SNR, are severely compromised by blurring. Imaging with echo train lengths of 16–24 and TR of 800–1,200 ms is a good compromise, and FR-FSE signal-to-noise ratio (SNR) and scan efficiency become comparable to SIMCAST. In vivo image quality is excellent with both FR-FSE and SIMCAST, but SIMCAST images have slightly higher SNR and are significantly more crisp. J. Magn. Reson. Imaging 2000;12:814–825. © 2000 Wiley-Liss, Inc.

High-resolution segmented EPI in a motor task fMRI study

A high-resolution gradient echo, multi-slice segmented echo planar imaging method was used for functional MRI (fMRI) using a motor task at 1.5 Tesla. Functional images with an in-plane resolution of 1 mm and slice thickness of 4 mm were obtained with good white-gray matter contrast. The multi-shot approach, combined with a short total readout period of 82 ms, limits blurring effects for short T2∗ tissues (such as gray matter), assuring truly high-resolution images. In all subjects, motor functions were clearly depicted in the contralateral central sulcus over several slices and sometimes activation was detected in the supplementary motor area and/or ipsilateral central sulcus. The average signal change of 11 ± 3% was much higher than in standard low-resolution fMRI EPI experiments, as a result of larger relative blood fractions.

High resolution MRI of the deep brain vascular anatomy at 8 Tesla: susceptibility-based enhancement of the venous structures.

The purpose of this work was to describe the deep vascular anatomy of the human brain using high resolution MR gradient echo imaging at 8 T. Gradient echo images were acquired from the human head using a transverse electromagnetic resonator operating in quadrature and tuned to 340 MHz. Typical acquisition parameters were as follows: matrix = 1,024 x 1,024, flip angle = 45 degrees, TR = 750 ms, TE = 17 ms, FOV = 20 cm, slice thickness = 2 mm. This resulted in an in-plane resolution of approximately 200 microm. Images were analyzed, and vascular structures were identified on the basis of location and course. High resolution ultra high field magnetic resonance imaging (UHFMRI) enabled the visualization of many small vessels deep within the brain. These vessels were typically detected as signal voids, and the majority represented veins. The prevalence of the venous vasculature was attributed largely to the magnetic susceptibility of deoxyhemoglobin. It was possible to identify venous structures expected to measure below 100 microm in size. Perforating venous drainage within the deep gray structures was identified along with their parent vessels. The course of arterial perforators was more difficult to follow and not as readily identified as their venous counterparts. The application of high resolution gradient echo methods in UHFMRI provides a unique detailed view of particularly the deep venous vasculature of the human brain.

A keyhole echo planar hybrid imaging technique.

A hybrid keyhole imaging method is presented which demonstrates the combination of two distinctly different MR imaging techniques. In this work single shot EPI was used as a dynamic update scan for a conventional high resolution gradient echo acquisition. Problems associated with the integration of MR data from distinctly different imaging techniques are addressed. Illustration is provided by way of diffusion weighted imaging. This novel development requires further investigation which need not be limited to the hybridization of strictly Cartesian based scanning methods.