bluuebunny/crossref_metadata_2025 huggingface dataset:
Dual effects of gadodiamide injection in depiction of the region of myocardial ischemia
Authors: Saeed Maythem , Wendland Michael F. , Yu Kyle K. , Li Hong‐Tai , Higgins Charles B.
Published: March 2007

The high safety index of the nonionic magnetic resonance (MR) contrast agent gadodiamide injection permits a wide dose range without induction of he‐modynamic effects. The wide dose range might confer a diagnostic advantage by providing both T1 enhancing and magnetic susceptibility effects for demarcating pathologic regions. The dual utility of this contrast agent for T1 and T2 enhancement in creating differential contrast between normal and acutely ischemic myocardium was explored. MR imaging was initiated 20–40 minutes after occlusion of the left coronary artery in two groups of rats: Group 1 (n = 8) received 0.3 mmol/kg gadodiamide injection before and after acquisition of T1‐weighted images; group 2 (n = 10) received 0.5 mmol/kg before and after acquisition of T2‐weighted images. Postcontrast T1‐weighted images showed clear delineation of the ischemic region as a relatively low‐signal‐intensity area for 15 minutes. On postcontrast T2‐weighted images, the ischemic region appeared as a relatively high‐signal‐intensity area for 60 minutes. These effects were obtained with doses of gadodiamide injection that have safety indexes greater than those of gado‐pentetate dimeglumine.
Comparison of Gd‐EOB‐DTPA and Gd‐DTPA for contrast‐enhanced MR imaging of liver tumors
Authors: Clemént Olivier , Mühler Andreas , Vexler Vladimir S. , Kuwatsuru Ryohei , Berthezéne Yves , Rosenau Werner , Brasch Robert C.
Published: March 2007

A new hepatobiliary contrast agent for magnetic resonance (MR) imaging, gadolinium‐ethoxybenzy1 (EOB)‐diethylemetriaminepentaacetic acid (DTPA), was compared with Gd‐DTPA to define the potential for improving tumor‐liver contrast in a rodent liver adenocarcinoma model. With a T1‐weighted spin‐echo sequence, the contrast‐to‐noise ratio (C/N) for tumor before contrast agent administration was 5 (arbitrary units), the tumor appearing slightly hypo‐intense with respect to liver parenchyma. After Gd‐DTPA injection (0.1 mmol/kg), tumor enhanced more strongly than liver, resulting in an equalization of tumor and liver signal intensities and a decline in C/N to zero at 3 minutes after injection. After Gd‐EOB‐DTPA injection (0.1 mmol/kg), liver enhanced more strongly than tumor. Five minutes after injection, C/N increased from 5 to 25 and remained above 17 for 50 minutes. The data indicate that Gd‐EOB‐DTPA yields higher and more prolonged tumor‐liver contrast than Gd‐DTPA on T1‐weighted spin‐echo images. The high liver‐tumor contrast after Gd‐EOB‐DTPA administration should prove clinically advantageous for MR imaging detection of focal hepatic masses.
Polymeric contrast agents for MR imaging of adrenal glands
Authors: Weissleder Ralph , Wang Yun Ming , Papisov Mikhail , Bogdanov Alex , Schaffer Brad , Brady Thomas J. , Wittenberg Jack
Published: March 2007

A variety of adrenal imaging agents have been used in nuclear medicine, but no agent has been developed for magnetic resonance (MR) imaging. The authors have previously observed accumulation of aminated macromolecules in adrenal glands. They now report the synthesis of a model polymeric aminated contrast agent for enhanced MR imaging of the adrenal glands. The model agent consisted of a poly‐L‐lysine conjugate (molecular weight, 245kd) that had 70% free epsilon amino groups and 30% diethylenetriaminepentaacetic acid (DTPA)‐deriv‐atized amino groups to bind indium‐111 or gadolinium. One hour after intravenous administration of this compound, adrenal uptake was 10.1% ± 0.7 of injected dose per gram of tissue. When all free epsilon amino groups of the polylysine were completely substituted with DTPA, adrenal uptake was 3.4 times lower, indicating the importance of free amino groups for adrenal uptake. MR imaging in rats showed that a dose of 0.08 mmol of gadolinium per kilogram of the agent was sufficient to enhance the signal intensity of adrenal glands. Three hours after intravenous administration of the agent, signal intensity of the adrenal glands was 186% of precon‐trast values (liver, 165%; kidney, 91%). Fluorescence microscopy showed that the agent accumulated primarily in the cortical zona glomerulosa and in the adrenal medulla. These initial studies demonstrate the feasibility of designing contrast agents for MR imaging of the adrenal glands.
Primary ovarian cancer: Prospective comparison of contrast‐enhanced CT and pre‐and postcontrast, fat‐ suppressed MR imaging, with histologic correlation
Authors: Semelka Richard C. , Lawrence Patrick H. , Patrick Shoenut J. , Heywood Mark , Kroeker Mervyn A. , Lotocki Robert
Published: March 2007

Sixteen patients with clinically suspected malignant ovarian disease underwent contrast agent‐enhanced computed tomography (CT) and magnetic resonance (MR) imaging in a prospective comparative study. MR imaging included fat‐suppressed spin‐echo and breath‐hold FLASH (fast low‐angle shot) before and after intravenous injection of gadopentetate dimeglumine. Histologic confirmation was obtained at laparotomy (n = 13) and biopsy (n = 3). Thirteen patients had histologically proven primary ovarian cancer. MR images showed the internal architecture of ovarian tumors better than CT in nine patients and equivalently in seven. MR images showed the relationship between ovarian tumors and adjacent pelvic structures (uterus [n = 9], sigmoid colon [n = 7], bladder [n = 7], and rectum [n = 3]) better than CT in nine patients and equivalently in seven. Intraabdominal extent of disease was better defined on MR than on CT images in nine patients, equivalently in six, and worse in one. Peritoneal metastases 1–2 cm in diameter were detected on MR images and missed on CT scans in six patients. In only one case did this result in a staging error with CT. The results suggest that MR imaging is at least equivalent and may be superior to CT in the evaluation of ovarian malignancy.
Basic physics of MR contrast agents and maximization of image contrast
Authors: Hendrick R. Edward , Mark Haacke E.
Published: March 2007

This review summarizes the physical basis of magnetic resonance (MR) imaging contrast agents, including both T1 agents, such as gadolinium‐DTPA (diethylenetri‐aminepentaacetic acid), and T2 or T2* agents, such as superparamagnetic iron oxides. The maximization of image contrast and lesion visibility with contrast agents is described, and the use of contrast agents in MR angiogra‐phy and perfusion imaging is discussed.
Evaluation of adrenal masses with gadolinium enhancement and fat‐suppressed MR imaging
Authors: Semelka Richard C. , Patrick Shoenut J. , Lawrence Patrick H. , Greenberg Howard M. , Maycher Bruce , Madden Terrance P. , Kroeker Mervyn A.
Published: March 2007

A study was undertaken to determine the ability to characterize benign and malignant masses with unenhanced and contrast material‐enhanced fast lowangle shot and fat‐suppressed spin‐echo magnetic resonance (MR) imaging. Thirty patients with adrenal masses detected at computed tomography (CT) underwent MR imaging within 14 days after CT. CT and MR images were interpreted in a prospective, blinded fashion. Sixteen patients had 20 benign adrenal masses, and 14 patients had 18 malignant masses. Quantitative measurements included percentage of contrast enhancement on immediate postcontrast dynamic images and periphery ‐ center signal‐to‐noise ratio (S/N) on gadolinium‐enhanced fat‐suppressed images. Qualitative evaluation included determination of the regularity of lesion margins, homogeneity of signal intensity, and local extension. MR imaging depicted all adrenal masses discovered at CT examinations. Lesions ranged in diameter from 1 to 15 (mean, 4.4) cm. No significant difference was observed in percentage of contrast enhancement between benign (90.5% ± 59.0 [standard deviation]) and malignant (110.5% ± 116.4) masses. A difference was observed between periphery ‐ center S/N for benign (−.05 ± 1.5) and malignant (7.7 ± 9.8) masses; overlap between the two, however, occurred. Qualitative evaluation allowed correct characterization of 32 of 38 masses, comparing favorably with CT, which allowed characterization of 30 lesions.
Characterization of atherosclerosis with a 1.5‐T imaging system
Authors: Gold Garry E. , Pauly John M. , Glover Gary H. , Moretto John C. , Macovski Albert , Herfkens Robert J.
Published: March 2007

It is shown that a conventional 1.5‐T magnetic resonance (MR) imaging system can help characterize some of the key components of atherosclerotic plaque ex vivo. Fresh human aorta with atheromata was suspended in solutions of agarose and manganese chloride and heated to body temperature. The specimens were imaged with modified Dixon and projection‐reconstruction imaging sequences. The specimens were then examined histologically to obtain direct correlation between images, spectra, and histologic characteristics. The results show that vessel wall and plaque components can be identified by means of their MR characteristics and correlated with their histologic appearance. The authors were able to identify normal vessel wall components, such as adventitial lipids and smooth muscle. They were also able to identify and localize plaque components such as fibrous tissue, calcification, lipids, and possible areas of hemorrhage and hemosiderin deposition.
Multicenter trial of automated border detection in cardiac MR imaging
Authors: Fleagle Steven R. , Thedens Daniel R. , Stanford William , Pettigrew Roderic I. , Reichek Nathaniel , Skorton David J.
Published: March 2007

The purpose of the present study was to evaluate the robustness of a method of automated border detection in cardiac magnetic resonance (MR) imaging. Thirty‐seven short‐axis spin‐echo cardiac images were acquired from three medical centers, each with its own image‐acquisition protocol. Endo‐ and epicardial borders and areas were derived from these images with a graph‐searching‐based method of edge detection. Computer results were compared with observer‐traced borders. The method accurately defined myocardial borders in 36 of 37 images (97%), with excellent agreement between computer‐ and observer‐derived endocardial and epicardial areas (correlation coefficients,.94‐.99). The algorithm worked equally well for data from all three centers, despite differences in image‐acquisition protocols, MR systems, and field strengths. These data suggest that a method of computer‐assisted edge detection based on graphsearching principles yields endocardial and epicardial areas that correlate well with those derived by an independent observer.
On‐line monitoring of ultrasonic surgery with MR imaging
Authors: Darkazanli Ammar , Hynynen Kullervo , Unger Evan C. , Schenck John F.
Published: March 2007

Ultrasonic surgery was performed in rabbits and dogs under the guidance of magnetic resonance (MR) imaging. Two different MR techniques were used to guide the ultrasound beam. T2‐weighted images showed lesion formation within a few minutes after sonication. T1‐weighted GRASS (gradient‐recalled acquisition in the steady state) images were sensitive to temperature elevations, permitting monitoring of lesion creation with MR imaging. Short TR T1‐weighted GRASS images were not as helpful in detecting temperature elevation because of a reduction in signal‐to‐noise ratio. T2‐weighted fast spin‐echo images were compared with conventional T2‐weighted spin‐echo images. The former produced high‐quality images in a fraction of the imaging time. This study shows that it is possible to monitor and guide ultrasonic surgery with MR imaging.
Hemorrhagic lymphangioma mimicking hemoperitoneum: MR imaging diagnosis
Authors: Stoupis Christophoros , Ros Pablo R. , Williams Jonathan L.
Published: March 2007

Omental cystic lymphangioma is an uncommon malformation that occurs in children. The authors report the magnetic resonance (MR) imaging findings in a case of hemorrhagic cystic abdominal lymphangioma, which clinically mimicked a recurrent hemoperitoneum. They demonstrate the superiority of MR imaging relative to computed tomography and ultrasound in diagnosing large hemorrhagic cystic masses and differentiating them from free intraperitoneal fluid with multi‐planar imaging and fluid characterization. This enables precise tumor localization and extension, aiding surgical resection.
Variation in MR signal intensity across normal human knee cartilage
Authors: Paul Pradip K. , Kris Jasani M. , Sebok David , Rakhit Ashok , Dunton Alan W. , Douglas Frank L.
Published: March 2007

Signal intensity(SI) of individual pixels on sagittal magnetic resonance (MR)images of normal human knee cartilage was quantified to investigate whether it was related to cartilage proteoglycan content. In five subjects, images were acquired with spin‐echo sequences with a TR msec/TE msec ofl,OOO or 7OO/2O and a three‐dimensional gradient‐echo(GRE)sequence (60/15). In a sixth subject, the GRE sequence alone was used with 15°,30°,and 50° flip angles. In all subjects, SI was maximal in pixel layers of the medial zone and minimal at both cartilage edges, resulting in the presence of a bell‐shaped curve of interpixel(zonal) SI variation across the cartilage thickness. The magnitude of SI was dependent on the pulse sequence and flip angle, but the bell shape of the SI variation curve was independent of them. For example, in the medial tibial cartilage, the peak SI was highest with the 1,000/20 spin‐echo sequence, intermediate with the 7OO/2O sequence, and lowest with the GRE sequence. The differences were statistically significant. The bell‐shaped SI variation curve resembled the curve for zonal variation in cartilage proteoglycan content but not the curves for collagen or free water content. The physiologic basis for this resemblance and the potential usefulness of the findings for early diagnosis of diseases such as osteoarthritis are discussed.
Fatty replacement of bone marrow after radiation therapy for Hodgkin disease: Quantification with chemical shift imaging
Authors: Kauczor Hans‐Ulrich , Dietl Barbara , Brix Gunnar , Jarosch Klaus , Knopp Michael V. , Van Kaick Gerhard
Published: March 2007

The authors studied the long‐term fatty replacement of bone marrow in 23 patients who had received radiation therapy for Hodgkin disease, with T1‐weighted magnetic resonance imaging and quantitative chemical shift imaging. T1‐weighted images revealed a mostly homogeneous high‐signal‐intensity pattern, in contrast to the hypointense pattern of nonirradiated marrow. The degree of fatty replacement was objectively assessed with chemical shift imaging, comparing patients to age‐matched healthy volunteers. The authors found an increase in relative fat signal of 37% in the thoracic spine and 34% in the lumbar spine. The relative fat signal of nonirradiated pelvic and femoral marrow was decreased by 8%, indicating marrow reconversion. No radiation dose dependence was found in the range from 25 to 50 Gy. No signs of marrow regeneration were observed 15‐126 months after radiation therapy. With chemical shift imaging, the degree of long‐term radiogenic fatty replacement of the bone marrow can be quantified, confirming the lack of regeneration after radiation therapy for Hodgkin disease.
Flow pattern analysis in the abdominal aorta with velocity‐encoded cine MR imaging
Authors: Mostbeck Gerhard H. , Dulce Matthias C. , Caputo Gary R. , Proctor Evelyn , Higgins Charles B.
Published: March 2007

The sites of deposition of atherosclerotic plaque on the aortic wall are considered to be influenced by secondary and retrograde flow patterns that cause regions of altered shear stress. To detect secondary flow patterns and areas of retrograde flow in the abdominal aorta, velocity‐encoded cine (VEC) magnetic resonance (MR) imaging was performed at five different levels of the abdominal aorta in nine healthy volunteers. Net retrograde flow (expressed as a percentage of antegrade flow) increased from proximal to distal levels and was maximal (13.8% ± 11.8) just distal to the origin of the renal arteries. An increase in the duration of retrograde flow over the cardiac cycle was observed from proximal to distal levels. Whereas retrograde flow was present at end systole and early diastole in each volunteer at every level, the duration and amount of retrograde flow during diastole showed high interindividual variation. Such differences suggest the possibility of variable vascular geometric risk factors in the population for the development of atherosclerotic plaque. The location of retrograde flow in the abdominal aorta demonstrated in vivo with VEC MR imaging was close to that obtained with in vitro flow visualization studies in models of the abdominal aorta.
Pulsatile flow artifacts in two‐dimensional time‐of‐flight MR angiography: Initial studies in elastic models of human carotid arteries
Authors: Buxton Richard B. , Kerber Charles W. , Frank Lawrence R.
Published: March 2007

Initial experimental and numerical analysis of artifacts due to pulsatile flow in two‐dimensional time‐of‐flight (2D‐TOF) magnetic resonance (MR) angiography are presented. The experimental studies used elastic models of the carotid artery bifurcation cast from fresh cadavers and accurately reproducing the twisting and tapering of the human blood vessels, allowing direct comparison of images with and without flow. Prominent image artifacts, including periodic ghosts and signal loss, were produced by pulsatile flow even though flow‐compensated gradient waveforms were used. The dependence of artifacts due to partial saturation on pulse sequence parameters (TR and flip angle) was investigated theoretically for a simple pulsatile velocity profile and compared with experimental results from a model of a normal carotid artery. Signal reduction was observed proximal and distal to the stenosis in a model with a 70% internal carotid artery (ICA) stenosis and a model with 90% stenoses in both the ICA and the external carotid artery. Although this study deals exclusively with 2D‐TOF imaging, the methods can also be applied to evaluate other MR angiography techniques.
Mn‐DPDP–enhanced MR imaging of malignant liver lesions: Efficacy and safety in 20 patients
Authors: Aicher Klaus P. , Laniado Michael , Kopp Andreas F. , Grönewäller Eckart , Duda Stephan H. , Claussen Claus D.
Published: March 2007

Twenty patients with malignant liver lesions underwent magnetic resonance (MR) imaging with manganese (II) DPDP [N,N′‐dipyridoxylethylenediamine‐N,N′‐diacetate 5,5′‐bis(phosphate)] to evaluate the safety and efficacy of the contrast agent. In two groups of 10 patients each, 5 μmol/kg Mn‐DPDP was administered intravenously (3 mL/min) at a concentration of either 50 or 10 μmol/mL. T1‐ and T2‐weighted images were obtained with a 1.5‐T imager. Six patients reported a total of eight instances of side effects (flush, feeling of warmth, metallic taste) of which seven occured at the 50 μmol/mL concentration. A significant decrease in alkaline phosphatase levels 2 hours after injection was recorded. On T1‐weighted images, the 10 μmol/mL formulation yielded significantly greater increases in contrast‐to‐noise ratio (79.8%–137.5%) than the 50 μmol/mL formulation (46.2%–86.6%). In a blinded reader study of 10 patients with one to five lesions each, no lesion was missed on Mn‐DPDP–enhanced T1‐weighted images; however, four false‐positive foci were identified. The authors conclude that slow administration of 5 μmol/kg Mn‐DPDP at a concentration of 10 μmol/mL is safe and efficient enough to proceed to further clinical trials.
Adrenal tissue characterization with 0.5‐T MR imaging: Value of T2*‐weighted images
Authors: Ichikawa Tomoaki , Fujimoto Hajime , Murakami Koji , Tauchi Mikio , Mochizuki Shigeru , Ohtomo Kuni , Uchiyama Guio
Published: March 2007

The authors investigated the value of magnetic resonance (MR) imaging at 0.5 T for distinguishing adrenal adenomas from adrenal metastases. The series included 23 adrenal adenomas (18 nonhyperfunctioning, five hyperfunctioning) and 23 adrenal metastases from various organs. Adrenal tumor–liver signal intensity ratios on T1‐, T2‐, and T2*‐weighted images were calculated for adrenal tissue characterization. Adrenal adenomas were more precisely distinguished from adrenal metastases on T2*‐weighted images (21 of 23, 91%) than on T2‐weighted images (15 of 23, 65%). T1‐weighted images were not useful for this distinction. In conclusion, T2*‐weighted images were better than routine T2‐weighted images for distinguishing adrenal adenomas from adrenal metastases. It can be postulated that the total signal intensity of adrenal adenomas, which contain some fat components, decreased on T2*‐weighted images because of an out‐of‐phase effect.
Perfusion and diffusion MR imaging of thromboembolic stroke
Authors: de Crespigny Alexander J. , Tsuura Mitsuharu , Moseley Michael E. , Kucharczyk John
Published: March 2007

A carotid embolic stroke model in rats was studied with a combination of diffusion‐ and perfusion‐sensitive magnetic resonance (MR) imaging at 4.7 T. Capillary blood deoxygenation changes were monitored during formation of focal ischemia by acquiring multisection magnetic susceptibility‐weighted echo‐planar images. A signal intensity decrease of 7% ± 3 in ischemic brain (1% ± 2 in normal brain) was attributable to a T2* decrease due to increased blood deoxygenation, which correlated well with subsequently measured decreases in the apparent diffusion coefficient. The same multisection methods were used to track the first‐pass transit of a bolus of dysprosium‐DTPA‐BMA [diethylenetriaminepentaacetic acid‐bis(methylam‐ide)] to assess relative tissue perfusion before and after stroke and after treatment with a thrombolytic agent. Analysis of contrast agent transit profiles suggested a total perfusion deficit in ischemic tissue and essentially unchanged perfusion in normal brain tissue after stroke.
Theoretical analysis of gadopentetate dimeglumine enhancement in T1‐weighted imaging of the brain: Comparison of two‐dimensional spin‐echo and three‐dimensional gradient‐echo sequences
Authors: Mugler John P. , Brookeman James R.
Published: March 2007

By using a theoretical model, the signal difference‐to noise ratios between simulated lesions and normal white matter and gray matter were calculated as a function of lesion concentration of gadopentetate dimeglumine (GD) for two‐dimensional (2D) T1‐weighted spin‐echo (SE), three‐dimensional (3D) steady‐state spoiled gradient‐echo (GRE) (FLASH [fast low‐angle shot]), and 3D magnetization‐prepared rapid gradient echo (MP‐RAGE) pulse sequences. The 3D GRE sequences provided greater contrast enhancement at relatively high [GD], and the 2D SE sequence demonstrated greater enhancement and a higher rate of enhancement at low [GD]. The results predict that at low [GD], certain lesions could probably be detected with the 2D SE sequence but possibly not with one or both of the 3D GRE sequences. At high [GD], certain lesions could probably be detected with one or both of the 3D GRE sequences but possibly not with the 2D SE sequence. This provides a potential explanation for the clinical observation that certain contrast agent enhanced lesions appear less conspicuous on 3D GRE images than on 2D SE images and vice versa. Modified parameter values were derived for the 3D FLASH and 3D MP‐RAGE sequences that are predicted to produce contrast enhancement behavior equivalent or superior to that of a conventional 2D SE sequence.
Ghost phase cancellation with phase‐encoding gradient modulation
Authors: Hinks R. Scott , Xiang Qing‐San , Henkelman R. Mark
Published: March 2007

Motion artifacts are a dominant cause of magnetic resonance image quality degradation. Periodic or nearly periodic motion results in image replicates of the moving structures in spin‐warp Fourier imaging. The replicates, or ghosts, propagate in the image in the phase encoding, or y, direction. These ghosted images can be considered to consist of the time‐averaged spin density I0and a ghost mask g. A set of J ghosted images Ij may be acquired in which the ghost mask is intentionally phase shifted by varying amounts relative to I0 with interleaved acquisitions that have shifted phaseencoding orders or by acquiring multiple images during a single readout period in the presence of an oscillating phase‐encoding gradient. The resulting complex images Ij have the same time‐averaged spin density I0 but have ghost contributions gj that, on a pixel‐by‐pixel basis, trace part of a circle around I0. The source images Ij can then be used to estimate I0. Simulations and experiments with the phase‐encoding gradient modulation method show good general ghost suppression for a variety of quasi‐periodic motion sources including both respiratory‐type artifacts and flow artifacts. The primary limitation of the method is the need for rapid gradient switching.
Evaluation of hepatocyte‐specific paramagnetic contrast media for MR imaging of hepatitis
Authors: Tanimoto Akihiro , Kreft Burkhard P. , Baba Yuji , Zhao Longhai , Finn J. Paul , Compton Carolyn C. , Stark David D.
Published: March 2007

The hepatocyte‐specific paramagnetic magnetic resonance (MR) contrast agents manganese‐DPDP [N,N′‐dipyridoxylethylenediamine‐N,N′‐diacetate 5,5′ bis‐(phosphate)] and gadobenate dimeglumine were used for diagnosing chemically induced hepatitis in rats. Ex vivo liver tissue relaxation times and in vivo MR image signal‐to‐noise ratios were compared before and after contrast agent administration. Ex vivo relaxometry and in vivo MR imaging showed that Mn‐DPDP enhanced normal and diseased livers to the same degree at all time points from 5 to 120 minutes. Gadobenate dimeglumine showed reduced T1 and T2 enhancements in hepatitis relative to those of normal liver, in the early phase (5–30 minutes). However, these effects are offsetting, and as a result, MR imaging failed to allow distinction of diseased from normal livers. This surprising result observed in vivo was in fact predicted by applying the Bloch equation to our ex vivo data. Our results show that detection and quantitation of hepatitis with MR imaging enhanced with paramagnetic cellspecific contrast agents will be more difficult than anticipated.
Pulse sequence strategies for vascular contrast in time‐of‐flight carotid MR angiography
Authors: Tkach Jean A. , Ruggieri Paul M. , Ross Jeffrey S. , Modic Michael T. , Dillinger John J. , Masaryk Thomas J.
Published: March 2007

A systematic evaluation in healthy volunteers of the relative efficacy of various techniques for background suppression to improve two‐dimensional (2D) and three‐dimensional (3D) time‐of‐flight magnetic resonance angiography of the cervical carotid arteries was performed. Conventional 2D and 3D FISP (fast imaging with steady‐state precession) sequences with flow compensation were compared with modifications of these sequences, including a tracking saturation pulse (2D), prolonged absolute TEs for fat suppression based on T2* decay (2D and 3D), frequency‐selective saturation of fat (2D and 3D), in‐plane spatial saturation (2D), and magnetization transfer contrast (2D and 3D). The tracking saturation pulse and slight overlap of the excitation sections provided uniform background suppression without impairing depiction of the morphology of the cervical carotid arteries. Frequency‐selective fat saturation was the most effective background suppression scheme among the 2D and 3D techniques but was occasionally compromised by local field inhomo‐geneities. Magnetization transfer contrast provided little suppression of stationary tissues in the neck because of the intrinsic limitations of the coil. In‐plane spatial saturation yielded the highest background suppression but reduced apparent arterial diameters and could not be implemented in a 3D version. The T2* decay method not only reduced the apparent size of the vessels but also their signal intensity.
MR imaging of patellar retinacular ligament injuries
Authors: Quinn Stephen F. , Brown Thomas R. , Demlow Thomas A.
Published: March 2007

Seventeen patients with patellar retinacular ligament injuries were evaluated with magnetic resonance (MR) imaging. MR findings were correlated with clinical, surgical, and arthroscopic findings. The injuries involved the medial retinacular ligament in 16 of 17 patients and the medial and lateral retinacular ligament in one patient. Nine of 17 patients showed MR evidence of a patellar dislocation. In these patients, a triad of findings that included focal impaction injuries involving the lateral femoral condyle, osteochondral injuries of the medial patellar facet, and injuries of the medial retinacular ligament were seen. Seven of the nine patients with patellar dislocation injuries had frank osteochondral injuries. The injured retinaculum had an indistinct, irregular appearance associated with edema and hemorrhage. The patellar dislocations were clinically unsuspected in the initial evaluation of eight of these nine patients. In eight of 17 patients, the mechanism of injury was a patellar tendon tear (n = 1) or valgus hyperextension (n = 7). In the seven patients with hyperextension injuries, three had associated meniscal and cruciate ligament tears. MR imaging can help define patellar retinacular and associated osteochondral injuries, which may be clinically useful information.
Automated pixel‐by‐pixel mapping of dynamic contrast‐enhanced MR images for evaluation of osteosarcoma response to chemotherapy: Preliminary results
Authors: Hanna Soheil L. , Reddick Wilburn E. , Parham David M. , Gronemeyer Suzanne A. , Taylor June S. , Fletcher Barry D.
Published: March 2007

An automated technique for pixel‐by‐pixel computer mapping of tumor necrosis was developed to improve the accuracy and applicability of dynamic contrast agent–enhanced magnetic resonance (MR) imaging in assessing the response of osteosarcoma to preoperative chemotherapy. The technique was evaluated in nine osteosarcoma patients who underwent MR imaging at diagnosis (n = 7) and after preoperative chemotherapy (n = 9). Sequential FLASH (fast low‐angle shot) images of the tumor were obtained in one plane every 15 seconds before and for 3 minutes after gadopentetate dimeglumine injection. A region of interest was selected that included the entire tumor area. Slopes representing percent increase in signal intensity over baseline values per minute were calculated automatically for each pixel and displayed as grayscale maps of the tumor. Matching histologic maps of each tumor were obtained. Visual region‐by‐region comparison of the pixel and histologic maps showed a high degree of correlation and the ability of the MR imaging technique to help identify small foci of residual viable tumor.
Functional mapping of human motor cortical activation with conventional MR imaging at 1.5 T
Authors: Cao Yue , Towle Vernon L. , Levin David N. , Balter James M.
Published: March 2007

A conventional 1.5‐T magnetic resonance (MR) imager was used to detect signal intensity changes on T2*‐weighted images of human motor and sensory cortices during performance of hand and tongue movements. Narrow receiver bandwidths were used to improve the signal‐to‐noise ratio. Protocols consisting of baseline, motor task, rest, and second motor task periods were performed by nine volunteers. Two‐dimensional cross correlation was applied to correct in‐plane translation and rotation of the head during the imaging session before the control images were subtracted from the task images. Measurements obtained during finger movement tasks indicated a 3%–8% increase in signal intensity near the contralateral central sulcus and smaller ipsilateral signal intensity increases. Bilateral signal intensity increases were also observed during tongue movement studies. A retrospective image registration technique was used to map the signal changes onto conventional anatomic images, which were used to create integrated three‐dimensional models of brain structure and function. These integrated images showed that the highest signal intensity due to hand movement was near the putative central sulcus.
Three‐dimensional fast spin‐echo imaging: Pulse sequence and in vivo image evaluation
Authors: Yuan Chun , Schmiedl Udo P. , Weinberger Edward , Krueck Wolfgang R. , Rand Scott D.
Published: March 2007

Three‐dimensional (3D) magnetic resonance imaging allows thin‐section acquisition and therefore more accurate multiplanar reconstruction than conventional two‐dimensional spin‐echo imaging. Unfortunately, addition of a third acquisition plane extends imaging time greatly. With gradient‐echo techniques, 3D acquisitions have become clinically useful. These techniques are limited, however, by susceptibility and other field inhomogeneity artifacts and decreased signal‐to‐noise ratios compared with spin‐echo techniques. The authors describe implementation of a true spin‐echo 3D technique that, by using fast spin‐echo parameters, reduces acquisition time to a clinically useful level. Potential applications of the technique are demonstrated.
MR imaging and proton spectroscopy of the brain in posttraumatic cortical blindness
Authors: Felber Stephan R. , Ettl Armin R. , Birbamer Günther G. , Luz Gaby , Aichner Franz T.
Published: March 2007

Magnetic resonance (MR) imaging and localized proton MR spectroscopy of the occipital lobes were performed in a patient with cortical blindness following brain trauma. Computed tomography (CT) scans and MR images of the visual cortex were normal in the acute stage. Six weeks after the trauma, MR images showed cortical lesions in both occipital lobes, while the spectra showed elevated lactate and decreased N‐acetyl aspartate levels relative to those of healthy volunteers. One year later, visual acuity had improved and follow‐up studies revealed an increase in the ratios of N‐acetyl aspartate to choline and creatine. These results demonstrate that parenchymal lesions may develop in brain regions that appear normal at CT and MR imaging during the acute stage after trauma. Metabolic changes can be observed in these areas by means of localized proton MR spectroscopy.
Techniques for high‐resolution MR imaging of atherosclerotic plaque
Authors: Yuan Chun , Tsuruda Jay S. , Beach Kirk N. , Hayes Cecil E. , Ferguson Marina S. , Alpers Charles E. , Foo Thomas K. , Strandness D. Eugene
Published: March 2007

Atherosclerotic cardiovascular disease is the most common cause of death in the United States. Investigation of atherosclerotic plaque morphology and composition is important because the findings may be useful in predicting prognosis or response to therapy. This study presents high‐resolution magnetic resonance (MR) imaging techniques developed on a 1.5‐T whole‐body imager with a custom‐built surface coil, for characterizing the composition and morphology of plaque removed at carotid endarterectomy. The initial comparison of MR imaging and histologic results showed good correlation. In conjunction with MR angiography, these techniques could be used in in vivo imaging to define the size, location, and contents of atherosclerotic plaque at the carotid bifurcation.
Hybrid RARE: Implementations for abdominal MR imaging
Authors: Mitchell Donald G. , Outwater Eric K. , Vinitski Simon
Published: March 2007

Hybrid RARE (rapid acquisition with relaxation enhancement) is a family of magnetic resonance (MR) imaging techniques whereby a set of images is phase encoded with more than one spin echo per excitation pulse. This increases the efficiency of obtaining T2‐weighted images, allowing greater flexibility regarding acquisition time, resolution, signal‐to‐noise ratio, and tissue contrast. Hybrid RARE techniques involve several important new user‐selectable parameters such as effective TE, echo train length, and echo spacing. Choices of other parameters, such as TR, sampling bandwidth, and acquisition matrix, may be different from those of comparable conventional T2‐weighted spin‐echo images. Different hybrid RARE implementations can be used for abdominal screening, with T2‐weighted or T2‐weighted and inversion‐recovery contrast, or for characterizing liver lesions or imaging the biliary system with an extremely long TE. High‐resolution images may be obtained by averaging multiple signals during quiet breathing, or images may be acquired more rapidly during suspended respiration. In this review, the authors discuss the basic principles of hybrid RARE techniques and how various imaging parameters can be manipulated to increase the quality and flexibility of abdominal T2‐weighted MR imaging.
Blood flow measurements in the aorta and major arteries with MR velocity mapping
Authors: Bogren Hugo G. , Buonocore Michael H.
Published: March 2007

The purpose of this study was to measure antegrade and retrograde flow in the aorta and the major arterial pathways in the body noninvasively with cine magnetic resonance (MR) velocity mapping, to determine the hemodynamic significance of retrograde flow in arteries. Two hundred forty cine velocity maps for blood flow measurements were obtained at 29 sites in the aorta and the major arteries in 31 healthy human subjects of varying age at rest. Synchronous or isolated antegrade and retrograde flow was found in the entire aorta and in arteries supplying muscles. No retrograde flow was found in arteries supplying internal organs, such as the internal carotid or splanchnic arteries. The retrograde flow in the aorta and the extremity arteries contributes substantially to supplying diastolic perfusion of internal organs such as the heart, brain, and kidneys. Antegrade flow tends to be helical in the thoracic aorta.
Retrospective registration of X‐ray angiograms with MR images by using vessels as intrinsic landmarks
Authors: Alperin Noam , Levin David N. , Pelizzari Charles A.
Published: March 2007

Conventional x‐ray angiography (XRA) images are projections of the vasculature with high spatial and temporal resolution, while magnetic resonance (MR) angiography (MRA) and MR imaging data show the three‐dimensional locations of vessels relative to brain parenchyma. The authors have developed a retrospective method of registering these studies, which makes it practical to produce multimodality displays of this complementary information. Registration was performed by matching vessels seen on both XRA and MRA images. First, the authors determined the coordinates of the center lines of a few “landmark” vessels on the XRA image and the three‐dimensional locations of the corresponding intraluminal voxels in the MRA volume. Registration was performed by rotating and translating the MRA–MR imaging volume until the perspective projection of the MRA landmark vessels matched the corresponding vessel center lines on the XRA image. Experiments with phantoms and patients indicated that the two studies were registered with an average error of less than 2 mm. A linked‐cursor display was developed to show correspondence between points on the registered XRA and MRA‐MR images.
Evaluation of loose bodies in the elbow with MR imaging
Authors: Quinn Stephen F. , Haberman Joseph J. , Fitzgerald Steven W. , Traughber Paul D. , Belkin Rod I. , Murray William T.
Published: March 2007

The evaluation of loose bodies in the elbow is usually done by means of clinical examination, radiography, and postarthrographic computed tomography (CT). The authors review their experience with magnetic resonance (MR) imaging in place of postarthrographic CT for the evaluation of loose bodies in the elbow. The prospective interpretation of MR studies of the elbow in 20 patients was compared with arthroscopic findings. All elbows were imaged in multiple planes with thin sections, surface coils, and combinations of T1, T2, and proton‐density weighting. The sensitivity for showing loose bodies with MR imaging was 100%, and the specificity was 67%. Because this was a nonblinded study, the results are biased and caution must be used when extrapolating these results to the general population. In this limited experience, MR imaging has reliably shown loose bodies in the elbow, and in the authors' institutions has replaced postarthrographic CT for that purpose.
Increased self‐diffusion of brain water in normal aging
Authors: Gideon Peter , Thomsen Carsten , Henriksen Ole
Published: March 2007

With magnetic resonance (MR) imaging, brain water self‐diffusion was measured in 17 healthy volunteers 22–76 (mean, 44.6) years old. The calculated values for the apparent diffusion coefficients (ADCs) ranged from 0.58 × 10−9 to 1.23 × 10−9 m2/sec in cerebral white matter. A significant correlation was found between the ADC in white matter and age (r =.7069, P <.01). The calculated values for ADC in cortical gray matter ranged from 1.06 × 10−9 to 1.72 × 10−9 m2/sec no correlation was found between ADCs in gray matter and age. The increased ADC in white matter may be caused by an increase in the extracellular volume due to age‐dependent neuronal degeneration or to changes in myelination. These findings have implications for future clinical investigations with diffusion MR imaging techniques in patients with neurologic diseases, and stress the importance of having an agematched group of healthy volunteers for comparison.
Ex vivo evaluation of ferromagnetism and artifacts of cardiac occluders exposed to a 1.5‐T MR system
Authors: Shellock Frank G. , Morisoli Stacy M.
Published: March 2007

Magnetic resonance (MR) procedures are contraindicated for patients with certain ferromagnetic biomedical implants, primarily owing to the risk of movement or dislodgment of the implants by the static magnetic field. An additional concern is the amount of artifact that the implant produces, which can affect image quality and interpretation of the examination. Therefore, an ex vivo assessment of ferromagnetism and artifact was conducted for 12 different occluders used to treat patients with patent ductus arteriosus, atrial septal defects, and ventricular septal defects, in a 1.5‐T MR system. Seven of the occluders, made of 304 stainless steel, were ferromagnetic and displayed deflection forces of 248–299 dynes. Five of the implants, made of MP35n, were nonferromagnetic. Artifacts were variable and depended primarily on the type and amount of metal used to construct the implant. The authors conclude that patients with ferromagnetic cardiac occluders may undergo MR procedures approximately 6 weeks after placement of these devices, to allow tissue growth to provide additional retentive force. After this time, it is highly unlikely that the magnetic fields associated with a 1.5‐T MR system are capable of moving or dislodging any of these cardiac occluders.
Three‐dimensional steady‐state MR angiography of the lower extremities
Authors: Schmalbrock Petra , Hacker Vicky A. , Rao Anita
Published: March 2007

Volume steady‐state black‐blood magnetic resonance imaging was evaluated as a method for depicting lower extremity vasculature. In steady‐state imaging, flow has low signal intensity because motion destroys the coherence of transverse magnetization. To optimize image contrast, computations and measurements were obtained for the three‐dimensional (3D) GRASS (gradient‐recalled acquisition in the steady state) and 3D SSFP (steady‐state free precession) sequences and a range of TRs and flip angles to determine optimal vessel‐muscle contrast. The best results were achieved with a 3D GRASS sequence with a TR msec/TE msec of 25/5 and a flip angle of 30°. Coronal images of the femoral and popliteal vessels were obtained in healthy volunteers with various fields of view and voxel sizes. Inflow of unsaturated spins from outside the image region, yielding high signal intensity, could be a potential drawback in steady‐state black‐blood imaging; however, problems can be avoided by using coronal acquisitions and large fields of view. Steady‐state black‐blood imaging depicts vessels with high accuracy and is faster and free of flow artifacts.
Prolonged positive contrast enhancement with Gd‐EOB‐DTPA in experimental liver tumors: Potential value in tissue characterization
Authors: Ni Yicheng , Marchal Guy , Yu Jie , Mühler Andreas , Lukito Gregorius , Baert Albert L.
Published: March 2007

To evaluate the potential of the hepatobiliary magnetic resonance (MR) imaging contrast agent gadolinium EOB‐DTPA (ethoxybenzyl diethylenetria‐minepentaacetic acid) for the characterization of hepatic tumors, 79 primary and six implanted hepatomas in 38 rats were studied. MR imaging findings after administration of Gd‐DTPA (0.3 mmol/kg) and Gd‐EOB‐DTPA (30 μmol/kg) were correlated with microangiographic and histologic findings. Gd‐EOB‐DTPA produced a strong liver enhancement, which caused prompt negative contrast enhancement (CE) in all implanted hepatomas and in 77 of 79 primary hepatomas. A positive CE that lasted up to 2 hours was found in two of 79 primary hepatomas, both of which were highly differentiated (grade I) hepatocellular carcinomas (HCCs). The rest were moderately differentiated to undifferentiated HCCs (grades II‐IV). Rim enhancement, which corresponded histologically to peritumoral malignant infiltration sequestering normal hepatocytes, was seen around all implanted and some primary hepatomas. Positive tumor CE after administration of Gd‐EOB‐DTPA in this study is much less frequent but much more specific in comparison with the results of previous studies with manganese‐DPDP (N, N′‐dipyridoxylethylenediamine‐N,N′‐diacetate 5,5′‐bis[phosphate]). These findings may help further discriminate hepatic tumors.
Measurement of renal transit of gadopentetate dimeglumine with echo‐planar MR imaging
Authors: Wolf Gerald L. , Hoop Bernard , Cannillo John A. , Rogowska Jadwiga A. , Halpern Elkan F.
Published: March 2007

Times of peak gadolinium concentration ([Gd]) after intravenous (IV) and left ventricular (LV) bolus injection of gadopentetate dimeglumine were determined in renal cortex and medulla in normal rabbits and in rabbits after saline load (overhydration) or hemorrhage (dehydration). Magnetic resonance images were obtained with echo‐planar inversion‐recovery sequences, and signal intensity‐versus‐time curves in cortical and medullary regions of interest were converted to [Gd]‐versus‐time curves. Cortical perfusion measured with microspheres demonstrated that the three physiologic states were significantly different. There were three separate [Gd] peaks in both the cortex and medulla as the bolus moved from one anatomic compartment to the next. The first cortical peak occurred sooner after LV than after IV bolus injection (P <.05) and later in dehydrated than in normal and overhydrated rabbits (P <.05). The first medullary peak always followed the first cortical peak by about 6–10 seconds and mirrored the cortical patterns. The second and third cortical peaks were consistent with proximal and distal tubular transit. These peaks similarly showed faster response to LV than IV injection and were delayed by hemorrhage. The authors conclude that quantitative physiologic information can be obtained with dynamic contrast‐enhanced MR imaging of the kidney.