bluuebunny/crossref_metadata_2025 huggingface dataset:
Is there a hazard to health by mercury exposure from amalgam due to MRI?
Authors: Müller‐Miny H. , Erber D. , Möller H. , Müller‐Miny B. , Bongartz G.
Published: March 2007

The local magnetic fields from computer monitors are well known. Recently a hypothesis was published that these magnetic fields may lead to a 400% increase of mercury dissolution from dental amalgam fillings. In MRI the exposure to the magnetic field exceeds by far the exposure from computer monitors. Therefore, this study examined the amalgam‐related mercury release for typical MRI conditions, separated for both the static and the variable magnetic fields in a 1.5 T MR‐unit. First, 20 dental cavities were filled with a non‐gamma‐2 amalgam, and the mercury release was measured for 14 days in a non‐magnetic environment. Second, one half of the specimens were exposed to a static magnetic field for 24 hours (group A), while the other specimens were exposed to a repetitive gradient echo sequence for 60 minutes (group B). In both experiments there was no significant increase in mercury release due to MRI. This in vitro study demonstrated no evidence of an elevated mercury dissolution from a nongamma‐2 amalgam during magnetic field exposure by MRI; therefore, there is no increased risk to health.
Magnetic resonance imaging of patients wearing a surgical traction halo
Authors: Hua Jianmin , Fox Richard A.
Published: March 2007

Magnetic resonance images of patients wearing a surgical halo may have unacceptable artifacts if the halo has a conductive loop structure. This study shows that the observed artifacts are predominantly due to eddy currents generated in the halo by switching field gradients, and that these artifacts can be substantially reduced by adjusting the phase encoding direction in MRI sequences so that it is parallel to the axis of the halo.
Contrast enhancement in experimental radiation‐induced liver injury: Comparison of hepatocellular and reticuloendothelial particulate contrast agents
Authors: Stiskal Michael , Schwickert Heidi C. , Demsar Franci , Roberts Timothy P. L. , Szolar Dieter , Weissleder Ralph , Brasch Robert C.
Published: March 2007

We compared the liver enhancement of two super‐paramagnetic agents, polycrystalline iron oxide nano‐particles (PION) and PION coated with asialofetuin (ASF), in an experimental model of focal radiation‐induced hepatitis. PION, a reticuloendothelial system‐directed agent, and PION‐ASF, a hepatocellular‐directed agent, were compared for time‐dependent liver enhancement in an experimental model of radiation‐induced liver injury. Using the reticuloendothelial system (RES)‐directed PION, the normal, nonirradiated portion of the liver decreased in signal intensity (SI) with a mean negative enhancement of –66% ± 4, whereas the irradiated portion (60 Gy, 3 days before imaging) of the liver decreased in SI by –24% ± 2, significantly less (P < .05). SI changes in irradiated liver tissue using PION were dose‐dependent, being more pronounced with lower radiation exposure. The difference in SI changes induced by PION‐ASF between irradiated and nonirradiated liver was not statistically different, but SI decreased with a mean negative enhancement of –80% ± 2. The RES‐directed PION is more sensitive for the detection of radiation‐induced hepatitis than is the hepatocyte‐directed PION‐ASF. The insensitivity of PION‐ASF enhancement for diffuse liver injury may be clinically advantageous for detecting focal lesions in the presence of diffuse hepatic injury.
MR hysterosalpingography in a rabbit model
Authors: Lee Fred T. , Grist Thomas M. , Nelson Kathleen G. , Chosy Susan G. , Rappe Alan H. , Shapiro Sander S. , Kelcz Frederick
Published: March 2007

Our objective was to evaluate the efficacy of MR imaging as compared with conventional hysterosalpingography (HSG) for the detection of fallopian tube patency after uterine injection of contrast material. Rabbit uterine horns (n = 18) were catheterized transvaginally. Five fallopian tubes were ligated and 11 were left unaltered. T1‐weighted gradient‐echo MR images were obtained before, during, and after injection of 1.0–3.0 mL of a dilute gadolinium‐containing contrast agent. Corresponding conventional studies were performed with an equivalent volume of iohexol. Images were evaluated by two blinded readers. Observers agreed in all cases on the presence (n = 11) or absence (n = 5) of peritoneal spill with conventional HSG. Interpretation of MR HSG concurred with conventional HSG in 14 of 16 cases for each observer (P > .05). Reasons for misdiagnosis included small amounts of spill (n = 2), artifact (n = 1), and subtle spill between bowel loops (n = 1). Sensitivity and specificity for MR HSG were 95.5% and 70%, respectively, for the diagnosis of tubal patency/occlusions. No statistical difference was found between MR HSG and conventional HSG for the diagnosis of fallopian tube patency/obstruction. Potential advantages of MR HSG include no ionizing radiation, potentially diminished local contrast toxicity, superior visualization of uterine fibroids and endometriosis, and visualization of ovaries. We conclude that this technique warrants further study, including the use of a primate model to better simulate human anatomy.
Dynamic contrast‐enhanced MR imaging of musculoskeletal tumors: Basic principles and clinical applications
Authors: Verstraete Koenraad L. , Woude Henk‐Jan Van der , Hogendoorn Pancras C. W. , De Deene Yves , Kunnen Marc , Bloem Johannes L.
Published: March 2007

The purpose of this article is to review the basic principles and clinical applications of dynamic contrast‐enhanced MRI in the musculoskeletal system. This method of physiologic imaging provides clinically useful information by depicting tissue vascularization and perfusion, capillary permeability, and composition of the interstitial space. Different imaging, evaluation, and postprocessing techniques are described. The most important applications in the musculoskeletal system are identification of areas of viable tumor for biopsy, tissue characterization, and monitoring of preoperative chemotherapy. Practical guidelines for performing a dynamic contrast‐enhanced MR examination are proposed.
Evaluation of frog gastric mucous secretion by 7T magnetic resonance imaging
Authors: Sbarbati Andrea , Leclercq Françoise , Zancanaro Carlo , Guerrini Uliano , Antonakis Kostas , Osculati Francesco
Published: March 2007

This work describes a new method to evaluate the action of drugs on gastric mucus secretion by 7 T MRI. A polyethylene probe was inserted into the stomach of frogs, a water washing cycle was performed, air was inflated into the stomach, and the probe was removed. Drugs were administered topically by mixing them with the water used for stomach washing, and a series of images was collected. In untreated animals, a mucous layer emitting a high intensity signal covered the gastric mucosa. Atropine administration strongly reduced the mucous layer thickness. After pilocarpine administration, MRI images showed that the mucous layer was thicker than in controls. After metacholine administration, the thickness of the mucous layer was increased in comparison with both controls and pilocarpine‐treated animals, in accord with the expected drug‐induced increase of mucous secretion. Quantitative analysis of the mucous layer thickness on MRI images confirmed the above findings. In conclusion, these results indicate that MRI at 7 T is a sensitive in vivo screening test to evaluate the effect of drugs on gastric mucus secretion in absence of surgical manipulation, thereby enabling morphofunctional studies that cannot be performed by conventional methods.
Adaptive filtering for high resolution magnetic resonance images
Authors: Ying Kui , Clymer Bradley D. , Schmalbrock Petra
Published: March 2007

We present a study of least mean square (LMS) based adaptive filters for high resolution magnetic resonance (MR) images to improve signal‐to‐noise ratio (SNR) while maintaining sharp edges. Five variations of a new technique that senses the type of noise or the presence of an edge in the filtering window, called adaptive filtering with noise estimation (AFEN) are presented and compared with the basic two‐dimensional LMS (TDLMS) algorithm, adaptive filtering with a mean estimator (AFLME), a two‐dimensional averaged LMS (TDALMS) algorithm, and a two‐dimensional median weighted LMS (TDMLMS) algorithm. Although TDLMS, TDALMS, and TDMLMS filters give better SNR improvement when applied uniformly to an image, they significantly blur edges. The AFLME and AFEN filters both show approximately a factor of 2 SNR improvement with much better retention of edges, with AFEN showing slightly better performance for both SNR and edge sharpness in phantom and in vivo inner ear images.
Enhancement efficacy of magnetic starch microspheres (MSM) in conventional spin‐echo and turbo spin‐echo sequences at 0.5 T and 1.5 T
Authors: Kreft Burkhard , Block Wolfgang , Mühlhäuser Jost , Träber Frank , Öksenda Audun , Schild Hans
Published: March 2007

The efficacy of the superparamagnetic contrast agent magnetic starch microspheres (MSM) was evaluated in vitro by NMR relaxometry and in vivo by MR imaging using T2‐weighted spin‐echo (SE) and turbo spin‐echo (TSE) sequences at 0.5 T and 1.5 T in 60 normal rats who received MSM in doses of 10–50 μmol/kg. MR imaging was performed using T2‐weighted SE and TSE sequences. The relaxation rates 1/T1 and 1/T2 for liver and spleen increased linearly with MSM concentrations up to 30 μmol/kg body weight, and approached almost constant levels for higher doses. The slopes in the linear part of the 1/T2 diagram were 0.62 Hz ± 0.03 for the liver and 0.51 Hz ± 0.06 × kg/μmol for the spleen. On all T2‐weighted sequences at 0.5 T and 1.5 T, liver signal‐to‐noise ratio (SNR) decreased by a factor of 2‐3 already at the lowest dose of 10 μmol/kg. SNR values of TSE sequences exceeded values for SE sequences by 50–80%. The SNR decrease was not significantly different between SE and TSE sequences. Our results show that MSM is well suited as a T2 contrast agent at both magnetic field strengths when using conventional SE and fast TSE sequences.
On the stationary states in gradient echo imaging
Authors: Sobol Wlad T. , Gauntt David M.
Published: March 2007

A formalism is presented that concisely describes the magnetization of a sample subjected to a periodic series of RF pulses. In this formalism, the steady state of the magnetization is shown to be a sum of magnetic substates, each with unique contrast characteristics. When more than one substate contributes to a given image, the substates interfere with each other, producing ghosts and other artifacts. Properly designed gradient protocols can image single substates, producing ghost‐free images. The contrast of the image depends largely on the choice of the imaged substate. Analytic solutions for unspoiled, RF spoiled, and gradient spoiled magnetizations are presented.
Quantification of white matter and gray matter volumes from T1 parametric images using fuzzy classifiers
Authors: Herndon R. Craig , Lancaster Jack L. , Toga Arthur W. , Fox Peter T.
Published: March 2007

White matter (WM) and gray matter (GM) were accurately measured using a technique based on a single standardized fuzzy classifier (FC) for each tissue. Fuzzy classifier development was based on experts' visual assessments of WM and GM boundaries from a set of T1 parametric MR images. The fuzzy classifier method's accuracy was validated and optimized by a set of T1 phantom images that were based on hand‐detailed human brain cryosection images. Nine sets of axial T1 images of varying thickness equally distributed throughout the brain were simulated. All T1 data sets were mapped to the standardized FCs and rapidly segmented into WM and GM voxel fraction images. Resulting volumes revealed that, in most cases, the difference between measured and actual volumes was less than 5%. This was consistent throughout most of the brain, and as expected, the accuracy improved to generally less than 2% for the 1‐mm simulated brain slices.
A model for detecting early metabolic changes in neonatal asphyxia by 1H‐MRS
Authors: Nakai Toshiharu , Rhine William D. , Enzmann Dieter R. , Stevenson David K. , Spielman Daniel M.
Published: March 2007

In newborn rabbits, the early cerebral metabolic changes caused by hypoxic‐ischemic (H‐I) insult was examined by using volume localized 1H‐MRS (STEAM). Partial ischemia was caused by unilateral carotid artery ligation, and hypoxia was induced by 10% oxygen inspiration for 150 minutes. Lactate immediately increased after hypoxia induction and almost disappeared 120 to 150 minutes after removal of hypoxia in both H‐I and hypoxia‐only experiments. Lactate production correlated well with decrease of the blood oxygen saturation. More lactate was produced on ischemic side 50 minutes post‐hypoxia induction in H‐I study. Ischemia alone did not cause any significant lactate production. Lactate caused by hypoxia can be dynamically monitored by localized 1H‐MRS. Existence of regional ischemia can induce greater anaerobic glycolysis and may affect the pattern of brain injury under hypoxia. 1H‐MRS is a sensitive tool to detect the acute metabolic changes caused by H‐I insult.
Rectal carcinoma: Prospective comparison of conventional and gadopentetate dimeglumine enhanced fat‐suppressed MR imaging
Authors: Okizuka Hiromi , Sugimura Kazuro , Yoshizako Takeshi , Kaji Yasushi , Wada Akihiko
Published: March 2007

The purpose of this study is to compare the usefulness of conventional MR imaging and gadopentetate dimeglumine enhanced fat‐suppressed MR imaging for the depiction and staging of rectal carcinoma. Thirty‐two patients were prospectively evaluated by MR imaging using a 1.5‐T unit. Based on the results of a barium study and/or digital examination, a balloon catheter was inserted to the level of the lesion before examination. Both conventional T1‐ and T2‐weighted images and gadopentetate dimeglumine enhanced fat‐suppressed T1‐weighted images were obtained for all patients. The kappa statistics were performed for the evaluation of interobserver agreement and the McNemar test was performed for the analysis of staging accuracy. When only T1‐ and T2‐weighted images were used, 5 of 32 tumors were not detected and the extent of 18 of 32 tumors were unclear. However, when gadopentetate dimeglumine enhanced fat‐suppressed imaging was added, 24 of 32 tumors were well defined and only one tumor was not detected. In determining the depth of invasion, the staging accuracy was 72% for conventional imaging and 68% for all images combined. There was no significant difference between with gadopentetate dimeglumine fat‐suppressed imaging and conventional imaging (P > .05). Use of gadopentetate dimeglumine (fat‐suppressed imaging) resulted in overestimation of muscular invasion, peri‐rectal fat invasion, and adjacent organ invasion in 12 patients, whereas nine patients were overestimated without the use of gadopentetate dimeglumine. In the detection of metastatic lymph nodes, gadopentetate dimeglumine enhanced fat‐suppressed imaging also was not useful. Tumor detection was excellent using gadopentetate dimeglumine enhanced fat‐suppressed images. However, the accuracy of staging was not improved by obtaining such images.
Intracapsular implant rupture: MR findings of incomplete shell collapse
Authors: Soo Mary Scott , Kornguth Phyllis J. , Walsh Ruth , Elenberger Charlotte , Georgiade Gregory S. , Delong David , Spritzer Charles E.
Published: March 2007

The objective of this study was to determine the frequency and significance of the MR findings of incomplete shell collapse for detecting implant rupture in a series of surgically removed breast prostheses. MR images of 86 breast implants in 44 patients were studied retrospectively and correlated with surgical findings at explanation. MR findings included (a) complete shell collapse (linguine sign), 21 implants; (b) incomplete shell collapse (subcapsular line sign, teardrop sign, and keyhole sign), 33 implants; (c) radial folds, 31 implants; and (d) normal, 1 implant. The subcapsular line sign was seen in 26 implants, the teardrop sign was seen in 27 implants, and the keyhole sign was seen in 23 implants. At surgery, 48 implants were found to be ruptured and 38 were intact. The MR findings of ruptured implants showed signs of incomplete collapse in 52% (n = 25), linguine sign in 44% (n = 21), and radial folds in 4% (n = 2). The linguine sign perfectly predicted implant rupture, but sensitivity was low. Findings of incomplete shell collapse improved sensitivity and negative predictive values, and the subcapsular line sign produced a significant incremental increase in predictive ability. MRI signs of incomplete shell collapse were more common than the linguine sign in ruptured implants and are significant contributors to the high sensitivity and negative predictive values of MRI for evaluating implant integrity.
Using cardiac phase to order reconstruction (CAPTOR): A method to improve diastolic images
Authors: Feinstein Jeffrey A. , Epstein Frederick H. , Arai Andrew E. , Foo Thomas K. F. , Hartley Michael R. , Balaban Robert S. , Wolff Steven D.
Published: March 2007

A method is proposed to reconstruct multiphase images that accurately depicts the entire cardiac cycle. A segmented, gradient‐recalled‐echo sequence (FASTCARD) was modified to acquire data continuously. Images were reconstructed retrospectively by selecting views from each heartbeat based on cardiac phase rather than the time elapsed from the QRS complex. Cardiac phase was calculated using a model that compensates for beat‐to‐beat heart rate changes. Images collected using cardiac phase to order reconstruction (CAPTOR) depict the entire cardiac cycle and lack the temporal gap that is characteristic of prospectively reconstructed sequences. Time‐volume curves of the left ventricle capture the contribution of atrial contraction to end‐diastolic volume (EDV). Transmitral phase‐contrast flow measurements show a second peak inflow (a wave) that is absent in the standard sequence. Because atrial contraction contributes to ventricular EDV, images using CAPTOR potentially may provide a more reliable measure of EDV, stroke volume, and ejection fraction than standard techniques.
Model‐free reconstruction of three‐dimensional myocardial strain from planar tagged MR images
Authors: Denney Thomas S. , McVeigh Elliot R.
Published: March 2007

A technique is presented for reconstructing a three‐dimensional myocardial strain map from a set of parallel‐tagged MR images. Radial strains were reconstructed from in vivo data from an anesthetized dog with values between .05 and .1 with a precision of ± .003 for a tag detection accuracy of .1 mm and a tag spacing of 2.5 mm. The reconstruction spatial resolution was demonstrated by reconstructing a localized displacement abnormality. In the circumferential direction, the abnormality that resulted in 50% displacement attenuation had a full width at half maximum of 5.4 ± .4 mm (mean ± SD). Graphs are presented showing the relationship between the size of an abnormality and the ability of the method to reconstruct that abnormality. The combination of high resolution parallel‐tagged MR images and the model‐free, coordinate system‐free strain reconstruction technique presented in this paper is capable of producing accurate, high resolution strain maps of the myocardium.
Effect of and correction for in‐plane myocardial motion on estimates of coronary‐volume flow rates
Authors: Frayne Richard , Polzin Jason A. , Mazaheri Yousef , Grist Thomas M. , Mistretta Charles A.
Published: March 2007

The sensitivities of phase‐difference (PD) and complex‐difference (CD) processing strategies to in‐plane motion were examined theoretically and experimentally. Errors in velocity and volume flow rate (VFR) estimates were attributed to (a) motion between different velocity encodings and, in the case of segmented k‐space acquisition strategies, (b) motion over the segment duration. PD estimates were found to be insensitive to in‐plane motion between velocity encodings, whereas CD VFR estimates were found to be sensitive to this motion. PD estimates, however, were affected by partial volume effects. A corrected CD (CD') scheme was developed that minimizes both partial‐volume and in‐plane motion effects. Segmented k‐space acquisitions with sequential offset and sequential interleaved offset (or centric) phase‐encoding schemes were studied. Images obtained using these techniques were found to include both blurring and replication artifacts. The amount of artifact generally increased with the number of views per segment (vps) and the in‐plane velocity. PD, CD, and CD' VFR estimates were found to be degraded by these artifacts. The sequential offset phase‐encoding scheme generally had acceptable VFR errors (at 4 vps, a CD' VFR error of 7.0%) when averaged over the physiologic range of myocardial motion (>12 cm second−1); however, larger errors were observed outside this range. VFR estimates obtained using the sequential interleaved phase‐encoding scheme at 4 vps were unacceptable. More accurate VFR measurements were obtained using a revised segmented PC strategy, which reversed the order in which the velocity and phase encodings were interleaved. The weighted average CD' VFR error obtained using the revised strategy was 24.5% (for 4 vps). Using displacement information obtained from the two velocity‐encoded images, an estimate of the in‐plane velocity was obtained and used to correct the acquired data. This decreased the VFR error (weighted average CD' error at 4 vps decreased from 24.5% to −6.3%); however, the implemented correction algorithm could potentially introduced other artifacts in the images.
Velocity encoding using both phase and magnitude
Authors: Madore Bruno , Henkelman R. Mark
Published: March 2007

Imaging time constitutes a major limitation of phase‐contrast (PC) angiography. It is possibly the main disadvantage of PC methods over the time‐of‐flight (TOF) methods that actually are used clinically. This relatively long imaging time comes from the fact that conventional PC methods require the acquisition of at least four images with different velocity sensitization to reconstruct a single angiogram (1, 2). However, more than one‐half of the information gathered through the acquisition of these four images is either redundant or simply discarded. We propose a faster approach to making PC angiograms in which the quantity of data acquired is diminished by as much as a factor 2. This is made possible by encoding velocity information in both the phase and magnitude of the image. Due to the use of extra radiofrequency (RF) and gradient waveforms, decreases in data requirements do not translate in a direct manner into decreases in imaging time. Nevertheless, significant reductions in imaging time are achieved with the present approach.
Multistep phase difference phase contrast imaging
Authors: Lamothe M. J. Reina , Rutt Brian K.
Published: March 2007

A new technique for multistep phase‐contrast image processing is presented. The N‐step method consists of simply forming the linear average of the N — 1 adjacent phase‐difference signals. It has similar noise reduction properties as other multistep techniques, but the simplicity of the noise variance of the N‐step technique allows intuitive insight into phase‐difference phase‐contrast processing and noise reduction, which can aid in the design of efficient and improved phase‐contrast imaging sequences. As well, the computational simplicity of the N‐step phase‐difference technique compared with any other known multistep technique is advantageous. Like other multistep techniques, it has far more efficient noise reduction properties than simple two‐step, multiple average phase‐contrast imaging, even when normalized for total scan time. A three‐step phase‐difference velocity image has 50% less variance than an image acquired with two steps and two scans averaged but is obtained in 25% less scan time. Given its advantages, it should now be the chosen technique for increasing velocity‐to‐noise and contrast‐to‐noise ratios in all phase‐difference phase‐contrast clinical applications.
Localized 31P MR spectroscopy of the transplanted human kidney in situ shows altered metabolism in rejection and acute tubular necrosis
Authors: Heindel Walter , Kugel Harald , Wenzel Folker , Stippel Dirk , Schmidt Rainer , Lackner Klaus
Published: March 2007

The purpose of this study was to investigate the function of transplant kidneys in situ, and to detect pathologic changes, using volume‐selective phosphorous NMR spectroscopy (31P MRS). Localized 31P MR spectra were obtained from 37 patients using a whole‐body MR scanner with a combination of surface coils, adiabatic excitation pulses, and a modified image‐selected in vivo spectroscopy (ISIS) sequence. Seventeen patients with pathologic changes after renal transplant were compared with a control group of 20 patients with no evidence of transplant dysfunction. The transplant kidneys with rejection reaction showed higher ratios of inorganic phosphate (Pi) to adenosine triphosphate‐α (ATP‐α) than the normal control group (.4 ± .16 compared with .22 ± .11, P = .01) and reduced pH. The spectra of transplant kidneys with tubular necrosis had lower phosphomonoester (PME)/phosphodiester (PDE) ratios than the control group (.65 ± .35 compared with .96 ± .5, P = .04). The pathologies of rejection and tubular necrosis could be differentiated from each other by pH (6.93 ± .1 in rejection versus 7.14 ± .19 in tubular necrosis, P = .04). Preliminary results indicate that localized image‐guided 31P MR spectroscopy of transplant kidneys in situ can detect rejection reactions and acute tubular necrosis noninvasively, providing an incentive for further research.
A multicenter clinical trial of gadolite oral suspension as a contrast agent for MRI
Authors: Rubin Daniel L. , Falk Karen L. , Sperling Malcolm J. , Ross Michael , Saini Sanjay , Rothman Barry , Shellock Frank , Zerhouni Elias , Stark David , Outwater Eric K. , Schmiedl Udo , Kirby Louis C. , Chezmar Judith , Coates Terry , Chang Miles , Silverman Jeffery M. , Rofsky Neil , Burnett Keith , Engel Julie , Young Stuart W.
Published: March 2007

The purpose of this study was to assess the effectiveness and safety of Gadolite Oral Suspension as a gastrointestinal (GI) contrast agent for MRI in a phase II and two phase III multicenter clinical trials. Gadolite was administered to 306 patients with known or suspected abdominal and/or pelvic disease. MRI with T1‐ and T2‐weighted sequences was performed before and after ingestion. Efficacy was evaluated by having two masked readers rate the certainty of their MR diagnosis (0 = uncertain, 1 = probable, 2 = definite) on randomly presented pre‐ and post‐Gadolite Oral Suspension enhanced images. Principal investigators also evaluated the images and established the final diagnosis. Vital signs, clinical chemistries, and adverse events were documented. Blood and urine samples were analyzed for gadolinium content to determine whether Gadolite Oral Suspension was absorbed systemically. Certainty in MR diagnosis increased significantly (P < .001) for both blinded readers between pre‐ and post‐Gadolite images (.49–1.18 for reader 1; .46–1.53 for reader 2). Sensitivity, specificity, and accuracy also increased for both masked readers. No gadolinium was detected in blood or urine samples. There were no serious adverse events and no apparent drug‐related trends in mean vital signs or laboratory values. Gadolite is a highly effective, safe, and well tolerated contrast agent for clinical use with MRI.
Origin of cartilage laminae in MRI
Authors: Xia Yang , Farquhar Tony , Burton‐Wurster Nancy , Lust George
Published: March 2007

To understand the origin of the laminated appearance of cartilage in MRI (the magic angle effect), microscopic MRI (μMRI) experiments were performed at 14‐μm pixel resolution on normal canine articular cartilage from the shoulder joints. Two‐dimensional images of the spin‐spin relaxation time (T2) of the cartilage‐bone plug at two angles (0° and 55°) were calculated quantitatively. A distinct T2 anisotropy was observed as a function of the cartilage tissue depth. The surface and the deep regions exhibit strong orientational dependence of T2, whereas the upper‐middle region exhibits little orientational dependence of T2. These three μMRI regions correspond approximately to the three histologic zones in cartilage tissue. The results from the bulk T2 measurements agreed with these μMRI results. Our studies show that the laminated appearance of cartilage in MRI is caused by T2 anisotropy of the tissue. We further suggest that the molecular origin of the T2 anisotropy is the nuclear dipolar interaction. The structure of the cartilage tissue indicates that the collagen meshwork defines this T2 anisotropy. The results show that the T2 anisotropy provides an indirect but sensitive indicator for the orientation of macromolecular structures in cartilage. The clinical implications of this anisotropy are discussed.
Understanding pulsed magnetization transfer
Authors: Graham S. J. , Henkelman R. Mark
Published: March 2007

Using a two‐pool exchange model of magnetization transfer (MT), numeric simulations were developed to predict the time dependence of longitudinal magnetization in both semisolid and liquid pools for arbitrary pulsed radiofrequency (RF) irradiation. Whereas RF excitation of the liquid pool was modeled using the time‐dependent Bloch equations, RF saturation of the semi‐solid pool was described by a time‐dependent rate proportional to both the absorption lineshape of the semisolid pool and the square of the RF pulse amplitude. Simulations show good agreement with experimental results for a 4% agar gel aqueous system in which the two‐pool kinetics have been well studied previously. These simulations provide a method for interpreting pulsed MT effects, are easily extended to biologic tissues, and provide a basis for optimizing clinical imaging applications that exploit MT contrast.
Low power method for estimating the magnetization transfer bound‐pool macromolecular fraction
Authors: Lee Roland R. , Dagher Azar P.
Published: March 2007

We present a practical method to estimate the magnetization transfer (MT) bound‐pool fraction (Mb0). The method is based on a first‐order approximation of the saturation equation and allows an in vivo estimate of Mb0, previously estimated only in vitro and requiring multiple (on the order of 102) measurements. This method requires one saturation measurement, a T1 estimate, an accurate value for input power, and uses to advantage the low power limitations of clinical scanners. The approximation is shown to be feasible in expected tissue parameter ranges using simulations. Unlike the phenomenologic magnetization transfer ratio (MTR), Mb0 is a true tissue parameter representing the semisolid proton concentration involved in saturation transfer, allowing comparability of MT effect independent of input power, off‐resonance frequency, or equipment.
Phase imaging on a .2‐T MR scanner: Application to temperature monitoring during ablation procedures
Authors: Sinha Shantanu , Oshiro Thomas , Sinha Usha , Lufkin Robert
Published: March 2007

Proton phase shift imaging methods with keyholing were developed to rapidly monitor temperature during MR‐guided radiofrequency (RF) interventional procedures on a .2‐T open configuration scanner. Temperature calibration was performed on thermally controlled gel phantom and ex vivo bovine liver samples. Keyholing methods were implemented for rapid imaging and tested both in simulation experiments and in the gel phantom. Phase drifts from extraneous sources were monitored and compensated for using reference phantoms. Sequence parameters TE, TR, and flip angle (FA) were optimized for maximum temperature sensitivity and minimum noise. Reduction of phase noise from coupling of the magnetic field to external perturbations using navigator‐echo‐based correction schemes were also investigated. The extraneous phase drifts from the magnet could be minimized by keeping the electromagnet on continuously. Navigator echo corrected keyholed FLASH sequences (TE = 30 msec, TR = 60 msec, FA = 40°, 64 × 128 matrix) were used to monitor the RF lesioning process in gel phantoms yielding images every 4 seconds with a temperature sensitivity of .015 ppm/°C. RF ablation in the bovine tissue was monitored using navigator‐echo‐corrected keyholed fast low angle shot (FLASH) sequences (TE = 30 msec, TR = 100 msec, FA = 40°, 128 × 256 matrix) with a temporal resolution of 13 seconds and a temperature sensitivity of .007 ppm/°C. The results indicate that monitoring of an RF ablation procedure by mapping temperature with sufficient temporal resolution is possible using phase images of FLASH sequences on a .2‐T open scanner.
MRI diagnosis and follow‐up of subcutaneous fat necrosis
Authors: López Jorge A. , Saez Fermín , Larena J. Alejandro , Capelastegui Ana , Martín Jose I. , Canteli Begoña
Published: March 2007

The purpose of this report is to present the MRI features of subcutaneous fat necrosis (SFN) and the natural history of this process. We have seen 12 patients with SFN, one case of which was confirmed histopathologically. In six patients, a follow‐up MRI study was performed. MRI findings were very similar in all of the cases: small, linear, and spiculated lesions with one or two components: a globular area yielding high signal intensity on T1‐weighted images, intermediate to high signal intensity on fast SE T2‐weighted images and focal signal void on short‐inversion ‐time inversion recovery (STIR) sequence, corresponding to an area of fat necrosis; and a laminar starred component, with low signal intensity on T1 and fast SE T2‐weighted images and high signal intensity on the STIR sequence, corresponding to reactive fibrous tissue. The follow‐up MRI study of six patients showed either disappearance (n = 2) or decrease in size (n = 3) of the globular component; in one patient, no change was observed. A less prominent decrease of the laminar component also was seen in five patients. One patient did not present any change in this laminar component. The most characteristic MRI findings of this lesion are the high signal intensity areas on T1‐weighted images, their small size (<3 cm), their linear spiculated shape with both laminar and globular components, and no contrast enhancement after injection of gadolinium‐diethylenetriamine pentaacetic acid (Gd‐DTPA) injection. We believe that the location, size, morphology, and MRI signal intensity of SFN may allow its differentiation from other types of soft tissue lesions.
Peripheral nerve stimulation during MRI: Effects of high gradient amplitudes and switching rates
Authors: Ham C. L. G. , Engels J. M. L. , van de Wiel G. T. , Machielsen A.
Published: March 2007

The application of high gradient amplitudes and switching rates for MRI and spectroscopy, resulting in short rise times for the gradient field and high changes of the magnetic flux density in the patient, is known to possibly evoke peripheral nerve stimulation (PNS) in patients. These effects have been studied on 20 volunteers under different experimental circumstances. The results of these measurements are partially in line with earlier findings reported in the literature. New information is found for the dependence of the PNS threshold level as a function of the rise time of the gradient waveform. The PNS threshold level, expressed in terms of dB/dt, is found to be proportional with t−05, where t is the switch time for the gradients. Indications are found that |B|, the modulus of the gradient vector field, is more closely related to the PNS threshold level than Bz, the imaging component of the gradient field. From the experiments, it is furthermore concluded that only for the imaging protocols characterized by the application of long bipolar repetitive gradient pulse trains, such as echo‐planar imaging, PNS is expected at the reported threshold levels. For the protocols based on spin echo, turbo spin echo, inversion recovery, fast field echo, etc., characterized by shorter gradient pulse trains, the threshold levels are expected to be much higher.
SPIO‐enhanced 2D‐TOF MR angiography of the portal venous system: Results of an intraindividual comparison
Authors: Reimer Peter , Marx Christian , Rummeny Ernst J. , Müller Markus , Lentschig Markus , Balzer Thomas , Dietl Karl‐Heinz , Sulkowski Udo , Berns Thomas , Shamsi Kohkan , Peters Peter E.
Published: March 2007

The purpose of this study was to investigate whether MR angiography (MRA) of the portal venous system may be improved by means of superparamagnetic iron oxides (SPIOs) during accumulation phase imaging and to study the underlying contrast mechanisms. MRA of the portal venous system was performed on 48 patients before and after intravenous injection of a new SPIO (Resovist, Schering AG, Berlin, Germany). Resovist, as a predominantly liver parenchymal darkening agent on T2‐weighted MR images with uptake into the reticuloendothelial cell system, was administered intravenously by bolus injection of 8 to 12 μmol Fe/kg body weight. Patients were scanned with breath‐hold coronal and axial two‐dimensional (2D) time of flight (TOF) MRA (TR = 31.0 msec, TE = 9.8 msec, flip angle (FA) = 50°, and 6.9‐second acquisition time per section) sequences. Signal intensity values of liver parenchyma, the portal venous system, and background were obtained for quantitative analysis. The clinical relevance of additional plain and contrast‐enhanced MRA studies for surgical planning was assessed by independent reading of three readers. Liver signal‐to‐noise ratio (SNR) significantly decreased following iv injection of Resovist; however, SNR values of the portal veins or hepatic veins did not change significantly. Visibility of the portal venous system improved significantly (tertiary branches visible: pre in 15.2% versus post in 87.0% of patients). Resovist‐enhanced 2D‐TOF MRA may improve planning of liver resections by better demonstrating the relationship of central liver lesions and vessels on source images. The decrease in liver SNR at a constant vessel SNR after iv injection of Resovist improves MRA of the liver. SPIO‐enhanced 2D‐TOF MRA scans are superior to plain 2D‐TOF MRA studies and may be added for the workup of preoperative patients.
Coronary MR angiography during peak‐systole: Work in Progress
Authors: Duerinckx André , Atkinson Dennis P.
Published: March 2007

The purpose of this study is to compare the quality of images of coronary arteries obtained with two‐dimensional breath‐hold coronary MR angiography during peak systole and mid diastole. Two‐dimensional coronary MR angiography was performed in eight normal volunteers at peak systole and in mid diastole with a commercial 1.5‐T MR imager. An ultrafast gradient‐echo sequence with incremented flip angle series and k‐space segmentation was used. The image quality grade, length, and proximal diameter of each visualized coronary artery were measured. The highest quality images in systole and diastole were compared. Coronary MR angiography provided high quality images in systole and diastole in 14 of 16 coronary vessels (87.5%). In 8 of 14 vessels (57%), there was no visible coronary MR angiogram image degradation when comparing peak systolic with mid‐diastolic images. In 4 of 14 vessels (29%), there was mild MR image degradation. There was significant MR image degradation in only one case (7%). And in one case (7%), there was mild image improvement during systole. The width and length of the visualized coronary vessels did not change significantly from diastole to systole. Existing two‐dimensional breath‐hold coronary MR angiography provides MR images during peak systole and mid‐diastole with little or no perceptible difference in quality.
Novel application of breath‐hold turbo spin‐echo T2 MRI for detection of acute myocardial infarction
Authors: Lim Tae‐Hwan , Hong Myeong‐Ki , Lee Jin Seong , Mun Chi Woong , Park Seung‐Jung , Park Seong‐Wook , Ryu Jin Sook , Lee Jung Hee , Chien Daisy , Laub Gerhard
Published: March 2007

To assess the clinical utility of the breath‐hold turbo spin‐echo T2‐weighted MRI in patients with acute myocardial infarction, the results of MRI were compared with those of electrocardiography, coronary angiography, and thallium‐201 single photon emission tomography (SPECT) in 23 patients and 5 healthy volunteers. To compare MRI and thallium‐SPECT, the left ventricle was divided into five segments, and the presence of myocardial infarction was determined in each segment. MRI demonstrated an abnormally bright signal in 49 of 140 segments (five segments each from 23 patients and 5 volunteers); thallium‐SPECT showed a fixed perfusion defect in 52 segments, for an 85% diagnostic concordance rate. The size of the myocardial infarction measured on MRI corresponded well to that measured on thallium‐SPECT (r = .70, P < .01). Breath‐hold turbo spin‐echo T2 MRI can be used for detection of acute myocardial infarction in conjunction with thallium‐SPECT, especially when accurate localization of lesion, increased spatial resolution, and anatomic landmarks are needed.
Water‐fat imaging with direct phase encoding
Authors: Xiang Qing‐San , An Li
Published: March 2007

A new method is Introduced for water‐fat imaging. With three acquisitions, a general direct phase encoding (DPE) of the chemical shift information is achieved. Pixels containing both water and fat are solved directly. Pixels with only a single component are resolved with local and global orientation filters, which use phase information from neighboring pixels. The fact that a single component is more likely to be water than fat in living tissues is also useful. A second pass solution yields water and fat images with superior signal‐to‐noise ratio. Unlike other methods, DPE does not rely on the error‐prone phase unwrapping; also, it easily handles disconnected tissues. Because the magnetization vectors of water and fat are sampled not only at parallel or antiparallel, they can be not only separated but also identified respectively, which is desirable for routine clinical work. DPE has been implemented on several imagers at various field strengths and has been demonstrated in a large number of clinical cases to be useful and robust in various parts of the body.
Multifeature analysis of Gd‐enhanced MR images of breast lesions
Authors: Sinha Shantanu , Lucas‐Quesada Flora Anne , Debruhl Nanette D. , Sayre James , Farria Dionne , Gorczyca David P. , Bassett Lawrence W.
Published: March 2007

The objective of this study was to determine whether linear discriminant analysis of different independent features of MR images of breast lesions can increase the sensitivity and specificity of this technique. For MR images of 23 benign and 20 malignant breast lesions, three independent classes of features, including characteristics of Gd‐DTPA‐uptake curve, boundary, and texture were evaluated. The three classes included five, four and eight features each, respectively. Discriminant analysis was applied both within and across the three classes, to find the best combination of features yielding the highest classification accuracy. The highest specificity and sensitivity of the different classes considered independently were as follows: Gd‐up‐take curves, 83% and 70%; boundary features, 86% and 70%; and texture, 70% and 75%, respectively. A combination of one feature each from the first two classes and age yielded a specificity of 79% and sensitivity of 90%, whereas highest figures of 93% and 95%, respectively, were obtained when a total of 10 features were combined across different classes. Statistical analysis of different independent classes of features in MR images of breast lesions can improve the classification accuracy of this technique significantly.
RARE imaging of PCr in human forearm muscles
Authors: Chao Hui , Bowers John L. , Holtzman David , Mulkern Robert V.
Published: March 2007

Rapid acquisition with relaxation enhancement (RARE) sequences have been used to map the 31P phosphocreatine (PCr) signal in human forearms at 4.7 T. Signal‐to‐noise levels of approximately 10 were achieved from the major muscle groups in 5.5‐minute scan times with a spatial resolution of 4 × 2 × 2 cm3. Exercise caused demonstrable reductions in PCr signal from activated muscles, which correlated with affected muscle groups in T2‐weighted proton images. RARE imaging of the PCr signal at 4.7 T is feasible and, with technically achievable improvements in signal‐to‐noise ratio, should prove useful in studying energy metabolism in muscle and other organs.
A segment‐interleaved motion‐compensated acquisition in the steady state (SIMCAST) technique for high resolution imaging of the inner ear
Authors: Kurucay Saban , Schmalbrock Petra , Chakeres Donald W. , Keller Paul J.
Published: March 2007

MRI, with ever‐increasing spatial resolution, recently has depicted progressively more anatomic details of the inner ear and is playing an important role in the diagnostic evaluation of patients with sensorineural hearing loss. We present a three‐dimensional (3D) segment‐interleaved, motion‐compensated acquisition in steady state (SIMCAST) sequence that allows further increase in spatial resolution in reasonable scan times minimizing artifacts due to susceptibility and motion. The sequence uses gradient moment nulling over TR and segmented interleaved acquisition of multiple data sets with different radiofrequency (RF) phase‐cycling schemes. Combination of data from multiple acquisitions by averaging and maximum intensity projection were compared. Images of phantoms and in vivo inner ears were obtained with both full and fractional echoes and compared with other high resolution techniques such as three‐dimensional gradient‐echo and two‐dimensional (2D) and three‐dimensional fast spin‐echo (FSE) sequences. The new sequence achieves improved signal‐to‐noise ratio (SNR) and spatial resolution resulting in improved depiction of inner ear structures.
Magnetization transfer fast imaging of implanted glioma in the rat brain at 4.7 T: Interpretation using a binary spin‐bath model
Authors: Quesson Bruno , Bouzier Anne‐Karine , Thiaudiere Eric , Delalande Christophe , Merle Michel , Canioni Paul
Published: March 2007

C6 glioma cells were implanted in the left caudate nucleus of the rat brain. Histologic studies confirmed the presence of neoplastic tissue surrounded by a thin edematous region. Proton magnetization transfer contrast (MTC) fast imaging, using continuous wave off‐resonance irradiation, was performed in vivo at 4.7 T with the rapid acquisition with relaxation enhancement (RARE) sequence. The observed MTC allowed very clear distinction of the tumoral region, in which magnetization transfer (MT) ratios were lower than in healthy tissues. Contrasts were analyzed as a function of the offset frequency and the amplitude of the radiofrequency (RF) irradiation. The contrast was higher between the contralateral basal ganglia and the tumor and lower between the tumor and the temporal lobe. Modeling of MT in the three brain regions was performed using a system including free water and a pool of protons with restricted motions. The rate of exchange between the two pools exhibited a decreasing hierarchy from the basal ganglia to the tumor. T2B values for the immobile protons ranged from 9.3 μsec in the basal ganglia to 7.5 μsec for the glioma. The acquisition conditions leading to the highest contrasts between the tumor and the healthy tissues correspond to 3,000 Hz offset frequency and 300 to 700 Hz RF irradiation amplitude.