bluuebunny/crossref_metadata_2025 huggingface dataset:
MR imaging of the female pelvic floor in the supine and upright positions
Authors: Fielding Julia R. , Versi E. , Mulkern R. V. , Lerner M. H. , Griffiths D. J. , Jolesz F. A.
Published: March 2007

The goal of this study was to determine whether a .5‐T open configuration magnet system could be used to evaluate the female pelvic floor support structures and their functional changes in the upright and supine positions. We evaluated five normal volunteers with full bladders in the supine and sitting positions. Multiple measurements were obtained, including distance between symphysis and urethra, bladder neck to fixed pubococcygeal line, and posterior urethrovesical angle. The pelvic floor was evaluated for integrity of the urethra, vagina, and supporting ligaments. High quality, interpretable images were obtained for all five patients in both positions. Most of the pelvic floor structures were stable, with the exception of the posterior urethrovesical angle, which increased in the sitting position. We conclude that the vertically open configuration magnet system shows promise for evaluation of the female pelvic floor, including urinary stress incontinence and prolapse.
Artifact in SE phase images can mimic aortic dissection
Authors: Boer Jacques A. Den , Rozeboom Alfred R.
Published: March 2007

Phase images of cardiac‐triggered thoracic spin‐echo scans can present an artifactual border‐like feature across the aorta. This may be misinterpreted as a dissection. The artifact results from helical flow in the aorta; cause and appearance of the artifact are discussed.
Principles of contrast enhancement in the evaluation of brain diseases: An overview
Authors: Runge Val M. , Muroff Lawrence R. , Wells John W.
Published: March 2007

Intravenous contrast media are widely used in MR imaging of the brain. Clinical utility is high in both neoplastic and non‐neoplastic disease. The agents approved to date are all gadolinium chelates, with extracellular distribution and renal excretion. The agents differ in regard to the maximum dose that can be administered and the theoretical safety margin. When administered at the same dose, the efficacy of the different available agents is comparable. Described in the following review article are the diagnostic use of contrast media and the patterns of enhancement encountered in neoplastic disease, infection, vascular disorders, and diseases of white matter. Only in congenital brain disease, when acute abnormalities are not suspected clinically and neoplastic disease is not a question, is contrast enhancement not indicated.

The gadolinium chelates play a major role in the evaluation of patients by MR with known or suspected brain disease. These agents improve both the sensitivity and specificity of the examination. In many cases, lesions cannot be identified before contrast administration. Lesion delineation, assessment of lesion activity, and differential diagnosis are all improved, in general, with the addition of postcontrast scans. The scope of applications continues to expand as the modality and clinical experience matures.
Effects of contrast dose, delayed imaging, and magnetization transfer saturation on gadolinium‐enhanced MR imaging of brain lesions
Authors: Mathews Vincent P. , Caldemeyer Karen S. , Ulmer John L. , Nguyen Hoang , Yuh William T. C.
Published: March 2007

This paper discusses the types of paramagnetic agents available for clinical brain imaging and reviews investigations that have sought to optimize the use of these agents by varying the administered dose, delaying the imaging time after contrast administration, and altering image contrast by using magnetization transfer saturation pulses.
Use of gadolinium chelates in MR imaging of the spine
Authors: Bradley Wiliam G.
Published: March 2007

Spinal disease can be divided into intramedullary, extramedullary‐intradural, and extradural compartments. In the cord (intramedullary compartment), gadolinium chelates are useful to diagnose primary and metastatic tumors, inflammation, and demyelination, and to evaluate syringomyelia when a Chiari I malformation is not present. In the extra‐medulullary‐intradural compartment, gadolinium chelates are useful for the diagnosis of drop metastases, meningiomas, and schwannomas. In the extradural compartment, gadolinium chelates are most useful to distinguish recurrent disc herniation from epidural fibrosis in the postoperative back and may be useful to diagnosis the soft tissue component of osseous metastases.
Contrast agents for MR imaging of the liver
Authors: Low Russell N.
Published: March 2007

The evolution of contrast agents for MR imaging of the liver has proceeded along several different paths with the common goal of improving liver‐lesion contrast. These contrast agents are used to accentuate the inherent differences in liver‐lesion signal intensity through differential enhancement of proton relaxation within adjacent tissues. Contrast agents used for hepatic MR imaging can be broadly categorized into those that target the extracellular space, the hepatobiliary system, and the reticuloendothelial system. Although only a small number of liver contrast agents are currently available, others are rapidly proceeding through clinical trials and may soon be added to our clinical armamentarium. This article will briefly review the current clinical experience with these agents, discussing their mechanism of contrast enhancement, pharmacokinetics, and efficacy in the evaluation of focal liver lesions.
Iron oxide‐enhanced MR lymphography: The evaluation of cervical lymph node metastases in head and neck cancer
Authors: Anzai Yoshimi , Prince Martin R.
Published: March 2007

Accurate diagnosis of cervical lymph node metastasis is challenging, even with the latest computed tomography or MR equipment and technique. The lack of definitive criteria for distinguishing metastatic from benign nodes is a serious shortcoming of current imaging options. Dextran‐coated, ultrasmall superparamagnetic iron oxide is a new MR contrast agent, which accumulates in the reticuloendothelial system of lymph nodes. Small iron oxide particles are taken up by macrophages within normal functioning nodes, reducing their signal on postcontrast MR because of the magnetic susceptibility effects of iron oxide. Metastatic nodes, on the other hand, remain high in signal on postcontrast T2*‐weighted gradient echo images. Early clinical experience in cancer patients suggests that iron oxide‐enhanced MR lymphography is a valuable imaging technique that may improve diagnostic accuracy for nodal metastases. This article reviews development of superparamagnetic iron oxide compounds, their imaging characteristics, and clinical experience for evaluating head and neck cancer metastases.
Modeling tracer kinetics in dynamic Gd‐DTPA MR imaging
Authors: Tofts Paul S.
Published: March 2007

Three major models (from Tofts, Larsson, and Brix) for collecting and analyzing dynamic MRI gadolinium‐diethylenetriamine penta‐acetic acid (Gd‐DTPA) data are examined. All models use compartments representing the blood plasma and the abnormal extravascular extracellular space (EES), and they are intercompatible. All measure combinations of three parameters: (1) kpsρ is the influx volume transfer constant (min−1), or permeability surface area product per unit volume of tissue, between plasma and EES; (2) ve is the volume of EES space per unit volume of tissue (0 < ve < 1); and (3) kep, the efflux rate constant (min−1), is the ratio of the first two parameters (kep = kpsρ/ve). The ratio kep is the simplest to measure, requiring only signal linearity with Gd tracer concentration or, alternatively, a measurement of T1 before injection of Gd (T10). To measure the physiologic parameters kpsρ and ve separately requires knowledge of T10 and of the tissue relaxivity R1 (≈︁ in vitro value).
Performance of Gd‐EOB‐DTPA and superparamagnetic iron oxide particles in the detection of primary liver cancer: A comparative study by alternative free‐response receiver operating characteristic analysis
Authors: Tanimoto Akihiro , Satoh Yoshinori , Yuasa Yuji , Jinzaki Masahiro , Hiramatsu Kyoichi
Published: March 2007

The performance of gadolinium‐ethoxybenzyl‐dieth‐ylenetriaminepentaacetic acid (Gd‐EOB‐DTPA) and superparamagnetic iron oxide (SPIO) particles in detecting liver cancer was compared using alternative free‐response receiver operating characteristic (AFROC) analysis, which allowed observers to indicate both the confidence level and the locations of all perceived abnormalities. Axial T1‐weighted MR images (1.5 T) pre/post Gd‐EOB‐DTPA (25 μmol/kg) injection were obtained for 12 rats with chemically induced liver tumors (64 tumors). T2‐weighted images (T2WI) were obtained pre/post SPIO (10 μmol/kg) injection for the same animal. Liver signal‐to‐noise ratio (SNR), tumor‐liver contrast‐to‐noise ratio (CNR), and histopathologic sections corresponding to MR images were obtained. In AFROC, the location and the confidence level for each tumor were indicated independently on MR images by four radiologists. By plotting true‐positive fraction and probability of false‐positive per image, the area under the AFROC curve (A1) was estimated and statistically analyzed between each sequence. Either drug significantly improved tumor‐liver CNR (P < .001) and tumor detection (diameter ≤ 6 mm; P < .05). Gd‐EOB‐DTPA significantly (P < .05) improved the A1 in T1WI. There was no A1 difference between T2WI + SPIO and T1WI + Gd‐EOB‐DTPA. Gd‐EOB‐DTPA‐enhanced T1WI showed the same performance as SPIO‐enhanced T2WI in detecting liver tumors.
MR signal intensity changes in hepatic parenchyma with ductal dilation caused by intrahepatic cholangiocarcinoma
Authors: Yoshimitsu Kengo , Honda Hiroshi , Kaneko Kuniyuki , Kuroiwa Toshiro , Fukuya Tatsuro , Irie Hiroyuki , Kajiyama Kiyoshi , Takenaka Kenji , Masuda Kouji
Published: March 2007

MR images of the liver in 13 patients with surgically proven intrahepatic cholangiocarcinoma were reviewed retrospectively and correlated to the histologic analysis of surgical specimens. We paid special attention to the peripheral liver tissue with ductal dilation but without tumorous involvement. High signal intensity was observed in the hepatic parenchyma with ductal dilation on T1‐weighted spin‐echo images (8 of 12) and spoiled gradient‐recalled echo images (seven of seven), as compared with the contralateral hepatic lobe without duct dilation. The high signal intensity was not suppressed with fat saturation and showed enhancement after administration of contrast (11 of 12). Concurrent portal venous obstruction did not have significant effect on these findings (P < .05). Correlation with pathologic specimens suggested that this enhancement was associated with periportal fibrosis. The etiology of the high signal intensity on unenhanced spin echo or gradient‐recalled T1‐weighted image remains unclear. Radiologists should recognize these findings and should distinguish these from tumor involvement or the arterial buffer response caused by portal venous obstruction.
Ampullary carcinoma: Demonstration by current MR techniques
Authors: Semelka Richard C. , Kelekis Nikolaos L. , John Gesine , Ascher Susan M. , Burdeny Derek , Siegelman Evan S.
Published: March 2007

The objective of this study was to demonstrate the appearance of ampullary carcinoma using current MR techniques, including fat suppression, gadolinium enhancement, and MR cholangiography. Nine patients with ampullary carcinoma were examined by MRI at 1.5 T. MR examinations included T1‐weighted spoiled gradient echo, T1‐weighted fat‐suppressed, and immediate postgadolinium spoiled gradient echo images for all patients and MR cholangiography for three patients. The imaging features of ampullary carcinomas, including tumor size and morphology, signal intensity, and enhancement characteristics, were determined. Ampullary carcinomas shown on MR images ranged in size from 1.5 to 5.5 cm. Tumors were low in signal intensity on precontrast T1‐weighted spoiled gradient echo and T1‐weighted fat‐suppressed images relative to normal pancreatic tissue and enhanced less than normal pancreas on immediate postgadolinium spoiled gradient echo images. Tumor conspicuity was greatest on immediate postgadolinium spoiled gradient echo images. MR cholangiography demonstrated high grade obstruction of the common bile duct and mild dilatation of the pancreatic duct at the level of the ampulla with abrupt termination of the ducts in two untreated patients and moderate dilatation of the common bile duct in one patient who had a biliary stent. Ampullary carcinomas can be demonstrated on MR images as small masses arising at the ampulla. Tumors are well defined on immediate postgadolinium spoiled gradient echo images.
MR imaging of pelvic lymph nodes in primary pelvic carcinoma with ultrasmall superparamagnetic iron oxide (combidex): Preliminary observations
Authors: Harisinghani Mukesh G. , Saini Sanjay , Slater Gregory J. , Schnall Mitchell D. , Rifkin Matthew D.
Published: March 2007

The potential of ultrasmall superparamagnetic iron oxide (Combidex)‐enhanced MRI of pelvic lymph nodes in patients with primary pelvic carcinoma is evaluated. Fifteen histologically classified lymph nodes in six patients with known primary pelvic cancer (four prostate; one rectum; one uterus) were evaluated with T2‐weighted fast spin‐echo (FSE) and T2*‐weighted gradient‐echo (GRE) MRI at 1.5T 12 to 48 hours after intravenous administration of Combidex at a dose of 1.7 mg Fe/kg. Quantitative image evaluation was performed by comparing signal intensity of individual nodes on pre‐ and postcontrast images. All patients proceeded to pelvic lymph‐node biopsy or surgical dissection, where six were found to be benign and nine were malignant. Of the 15 lymph nodes, four nodes showed a decrease in signal intensity. Of these, three, in which signal loss was homogenous were benign, and one, in which the signal‐intensity decrease was heterogeneous, was malignant (micrometastases). No signal change was noted in 11 of 15 lymph nodes of which three were benign (inflammatory) and eight were malignant. Combidex is a promising MR contrast agent for evaluating pelvic lymph nodes. Our preliminary observations suggest that the agent is most useful for classifying normal lymph nodes.
Gadolinium‐enhanced MR angiography of visceral arteries in patients with suspected chronic mesenteric ischemia
Authors: Meaney James F. M. , Prince Martin R. , Nostrant Timothy T. , Stanley James C.
Published: March 2007

The purpose of this study was to evaluate accuracy of dynamic gadolinium‐enhanced MR angiography (MRA) of the celiac, superior, and inferior mesenteric arteries in patients with suspected mesenteric ischemia compared with catheter angiography or surgery. Sixty‐five patients with suspected mesenteric ischemia underwent three‐dimensional spoiled gradient‐recalled acquisition in the steady state (GRASS) gadolinium‐enhanced MRA. Correlative studies were performed on 14 patients, catheter angiography alone was performed on 12 patients, and surgery alone was performed on two patients. Six patients had mesenteric ischemia. In all patients, the celiac artery (CA) and superior mesenteric artery (SMA) were seen well enough to evaluate; however, the inferior mesenteric artery (IMA) could be evaluated in only 9 of the 14 patients. MRA showed severe stenosis (>75%) or occlusion of the celiac axis in seven patients, of the SMA in six patients, and of the IMA in four patients. The overall sensitivity and specificity were 100% and 95%, respectively, compared with catheter angiography and surgery. The two errors were caused by overgrading the severity of IMA disease. Three‐dimensional gadolinium‐enhanced MRA can accurately demonstrate the origins of the CA and SMA and is useful in evaluation of patients with suspected mesenteric ischemia.
Contrast‐enhanced magnetic resonance angiography of carotid arterial wall in pigs
Authors: Lin Weili , Abendschein Dana R. , Haacke E. Mark
Published: March 2007

This study was designed to investigate the effects of contrast agents on MR images of balloon‐injured carotid arteries containing atherosclerotic‐like lesions. We have evaluated an intravascular contrast agent, MS‐325 (METASYN INC., Cambridge, MA) and an extra‐vascular contrast agent, Optimark, (Mallinckrodt Medical Inc., St. Louis, MO) on MR angiograms obtained 4 weeks after balloon hyperinflation‐induced injury of the left common carotid artery in 12 hypercholesterolemic minipigs. High in‐plane resolution (.8 × .4 mm2), thin slice (1 mm) time‐of‐flight gradient echo sequences were used to acquire the MR angiographic images. Vascular lumen definition was compared before and after a single bolus intravenous injection of a contrast agent. Digital subtraction angiograms were obtained from all pigs after MR imaging. High grade stenosis developed in 1 of the 12 pigs and five pigs had complete occlusion of the injured vessel. The remaining pigs exhibited essentially no visible stenoses as assessed either by MR angiography or digital subtraction angiography. The vessel walls of the stenosed and occluded vessels were visible after the injection of either intravascular or extravascular contrast agent. Histologic analyses showed well developed neovascularization in the neointima or occlusive thrombosis. We conclude that the observed contrast‐enhanced vessel wall is caused by an increased vascular supply associated with thrombosis and neointimal thickening that leads to an accumulation of contrast agent in the abnormal vessel walls after the injection of the T1‐shortening paramagnetic contrast agent.
Preliminary evaluation of a polyethyleneglycol‐stabilized manganese‐substituted hydroxylapatite as an intravascular contrast agent for MR angiography
Authors: Adzamli Kofi , Dorshow Richard B. , Hynes Michael R. , Li Debiao , Nosco Dennis L. , Adams Max D.
Published: March 2007

A blood‐persistent particulate paramagnetic contrast agent has been formulated via size stabilization of manganese‐substituted hydroxylapatite by a polyethylene glycol (PEG) bearing a terminal diphosphonate. At high PEG surface densities (35–40 mol %), particles with mean diameter 8 ± 2 nm were obtained. Relaxivities of autoclaved samples (at 20 MHz proton Lamor frequency) were R1 = 18.7 ± .8 mM−1 sec−1 and R2 = 22.3 ± .7 mM−1 sec−1. The formulation persisted in rabbit blood with a biphasic clearance profile. Halflives (with amplitudes in parenthesis) were 4 ± 1 minutes (55%), and 49 ± 3 minutes (45%), respectively, for the two phases. A dose of 40 μmol Mn/kg body weight enhanced the signal from rabbit vasculature for more than 45 minutes on MR angiograms. Thus, PEG‐modified MnHA particles may find use as T1 agents for MR angiography.
MR angiography with an ultrasmall superparamagnetic iron oxide blood pool agent
Authors: Anzai Yoshimi , Prince Martin R. , Chenevert Thomas L. , Maki Jeffrey H. , London Frank Londy Manette , McLachlan Stuart J.
Published: March 2007

The purpose of the study was to investigate the use of a dextran‐coated ultrasmall superparamagnetic iron oxide (USPIO) as a blood pool contrast agent for thoracic and abdominal MR angiography. Abdominal and thoracic MR angiography was performed in six healthy volunteers using two‐dimensional and three‐dimensional spoiled gradient echo (SPGR) sequences before and after intravenous administration of USPIO. Doses ranged from 1.1 to 2.6 mg Fe/kg. Flip angle was varied from 20 to 60°. Subjective image quality, analysis of signal‐to‐noise ratio (SNR), and blood T1 relaxation times were measured. USPIO significantly lowered the T1 of blood (from 1,210 ms precontrast to 159 ms postcontrast at a dose of 2.6 mg Fe/kg) (P < .01). Image quality on coronal fast three‐dimensional breath‐hold SPGR images of the abdomen increased with increasing dose and was maximum at the highest dose, producing an aortic SNR of 9.6 compared to 1.8 precontrast. Axial two‐dimensional time‐of‐flight (TOF) aortic SNR was reduced significantly from 13 on precontrast to 6 on the postcontrast images at the highest dose (P < .05) due to T2* shortening effects. There was little flip angle dependence on image quality. Due to the T1 shortening effect and long intravascular half‐life, USPIO improved visualization of vascular anatomy using three‐dimensional fast SPGR imaging. The echo time must be minimized to minimize signal loss from T2* shortening effects. The blood pool distribution of USPIO is useful for equilibriumphase MR angiography.
Dynamic 3d‐mr mammography: Is there a benefit of sophisticated evaluation of enhancement curves for clinical routine?
Authors: Müller‐Schimpfle Markus , Ohmenhäuser Katja , Sand Jürgen , Stoll Peter , Claussen Claus D.
Published: March 2007

The purpose of the study was to compare standard analysis with pharmacokinetic analysis of time‐intensity curves in dynamic three‐dimensional (3D) MR mammography (MRM) for their capability of differentiating benign from malignant disease. Dynamic MRM of the whole breast was performed at 1.0 T using an axial fast low‐angle shot (FLASH) 3D sequence. For the standard evaluation, the enhancement of the first minute (E1) and the slope of enhancement from minute 2 to 10 (SE2–10) were calculated. For pharmacokinetic analysis, the amplitude of enhancement (A), distribution time (t21), and elimination time (tel) were computed. Sixty‐two histologically verified lesions were evaluated. The standard evaluation methods yielded a highly significant difference between benign and malignant disease for E1 (P = .0008) and SE2–10 (P = .0001). The pharmacokinetic parameters gained similarly significant P values (A, P = .0014; t21, P = .0024; tel, P = .0001). Both standard and pharmacokinetic analysis concordantly discriminated between benign and malignant lesions in discriminant analysis. Compared with standard analysis, a pharmacokinetic analysis of time‐intensity curves is not beneficial for routine clinical diagnosis.
Low molecular weight lanthanide contrast agents: In vitro studies of mechanisms of action
Authors: Fossheim Sigrid , Sæbø Karen Briley , Fahlvik Anne Kjersti , Rongved Pål , Klaveness Jo
Published: March 2007

The MR contrast properties of a series of structurally dissimilar low molecular weight (LMW) gadolinium (Gd) and dysprosium (Dy) chelates have been investigated under controlled experimental conditions in various in vitro test systems. Relaxation analysis (water, pH = 5.8, 37°C, .47 T) demonstrated the high dipolar relaxation efficacy of the tested Gd chelates. The T1 and T2 relaxivities of both metal chelate series decreased with decreasing hydration number, confirming the strong correlation between metal chelate structure and dipolar relaxivity. Susceptibility‐induced T2 relaxation, commonly known as the susceptibility effect, is modulated primarily by the magnetic susceptibility and compartmentalization of the contrast agent. The influence of these parameters on the susceptibility effect of Dy diethylenetriamine pentaacetic acid bis‐methylamide (DTPA‐BMA) and GdDTPA‐BMA was investigated in two‐compartment in vitro models. In red blood cell suspensions (45% hematocrit, 37°C, .47 T, 2 and 3 mM metal ion concentration), the T2 relaxation efficacy of DyDTPA‐BMA was markedly improved due to susceptibility effects that were shown to depend on compartmentalization. As the relaxation ability of GdDTPA‐BMA was modulated by the dipolar interactions, compartmentalization was not a prerequisite for its T2 relaxation efficacy. In a coaxial glass system with no intercompartmental water exchange, which eliminated the dipolar relaxation mechanism, DyDTPABMA was shown to be the most efficient susceptibility agent because of its higher magnetic susceptibility. The reported one‐ and two‐compartment model studies have demonstrated the different mechanism of action of LMW Gd‐ and Dy‐based contrast agents. Gd chelates are predominantly dipolar relaxation enhancers, whereas Dy chelates are efficient susceptibility agents only in compartmentalized systems.
Magnetically labeled cells can be detected by MR imaging
Authors: Weissleder Ralph , Cheng Hui‐Cheng , Bogdanova Anna , Bogdanov Alexei
Published: March 2007

To determine the feasibility of MR imaging of magnetically labeled cells, different cell lines were labeled with monocrystalline iron oxide (MION) particles. Phantoms containing MION labeled cells were then assembled and imaged by MR at 1.5 T using T1‐weighted and T2‐weighted pulse sequences. MION uptake ranged from 8.5 × 104 to 2.9 × 105 particles/cell for tumor cells (9L and LX1, respectively) to 1.5 × 106 to 4.8 × 108 particles/cell for “professional phagocytes” (J774 and peritoneal macrophages, respectively). On the T1‐weighted images, cell‐internalized MION appeared hyperintense relative to agar and similar to MION in aqueous solution. On T2‐weighted images, signal intensity varied according to concentration of MION within cells. Cell‐internalized MION caused similar MR signal changes of cells as did free MION; however, at a dose that was an order of magnitude lower, depending on the pulse sequence used. The detectability of MION within cells was approximately 2 ng Fe, which corresponded to 105 tumor cells/well or 5 × 103 macrophages/well. We conclude that a variety of cells can be efficiently labeled with MION by simple incubation. Intracellular labeling may be used for MR imaging of in vivo cell tracking.
Magnetization transfer contrast of hepatic lesions in breath‐hold gradient‐echo images of different T1 weighting
Authors: Schick Fritz , Stern Wolfgang , Forster Jürgen , Laniado Michael , Lutz Otto , Claussen Claus D.
Published: March 2007

Seventeen patients with hepatic lesions [six metastases from colon, breast, and gallbladder carcinoma; one gallbladder carcinoma; five hepatocellular carcinoma; three focal nodular hyperplasia (FNH); one adenoma; and one cyst] were examined by MR breath‐hold two‐dimensional gradient‐echo imaging to assess the potential of magnetization transfer contrast (MTC) for improved conspicuity and classification. Imaging sequences were applied with and without irradiation of off‐resonant radiofrequency (RF) prepulses, but other parameters were unchanged. Therefore, quantitative assessment of MTC could be performed. In contrast to former examinations of other researchers, no significant difference of MTC was found between malignant liver lesions and benign lesions as FNH or adenoma. MTC might provide differentiation between hemangioma and cysts versus solid tumors, but MTC is not capable of distinguishing benign and malignant types of solid liver tumors. Effects of unchanged MTC prepulses on signal intensity of normal liver tissue and most lesions were more pronounced for nearly proton density‐weighted fast low‐angle shot (FLASH) images than for T1‐weighted FLASH images, obtained by using higher excitation flip angles. Liver‐to‐lesion contrast could not be improved clearly by MTC prepulses. The contrast between liver and lesions in the gradient‐echo breath‐hold images was compared with standard T1‐ and T2‐weighted spin‐echo images. Liver‐to‐lesion contrast in the breath‐hold images was found to be inferior to T2‐weighted spin‐echo images in 14 of 17 cases. Lesion conspicuity in regions near the diaphragm was better in breath‐hold images, because problems with marked breathing motion (as in standard imaging) could be avoided.
Use of three‐dimensional segmented flash sequence with magnetization transfer contrast to improve gd‐dtpa‐enhanced intrahepatic MR portography
Authors: Suto Yuji , Kimura Toshihiko , Kamba Masayuki , Sugihara Shuji , Yoshida Kotaro , Takizawa Osamu
Published: March 2007

Twenty healthy volunteers underwent gadopentetate dimeglumine (gadolinium diethylenetriaminepentaacetic acid (Gd‐DTPA))‐enhanced MR angiography (MRA) using three‐dimensional‐segmented fast low angle shot images (FLASH) with magnetization transfer contrast (MTC) pulses. MRA was obtained at 75 seconds (early phase) and 135 seconds (late phase) after bolus injection of Gd‐DTPA (MTC+ group) during one period of breath‐holding. Within 1 week, MRA without MTC was performed under the same scanning conditions. Visualization of intrahepatic portal branches with these methods was compared in both phases. Portal vein‐liver contrast‐to‐noise ratios were significantly higher in the MTC+ group in both phases. For third‐and fourth‐order portal branches, visualization was significantly better in the MTC+ group in both phases. Use of three‐dimensional‐segmented FLASH shortened acquisition time and facilitated imaging during breath‐holding and also reduced whole‐body average specific absorption rate values. Visualization of intrahepatic portal vein branches was improved by MTC pulses, and effective imaging time was prolonged.
Mycotic aneurysm of the aorta: MRI and MRA features
Authors: Walsh Daniel W. , Ho Vincent B. , Haggerty Michael F.
Published: March 2007

Mycotic aneurysms of the abdominal aorta are potentially fatal but uncommon. We report the MRI and MRA features of an abdominal aortic mycotic aneurysm in a patient who presented with nonspecific low back pain. By delineating the saccular nature of the aneurysm and identifying the coexistence of vertebral enhancement, MRI was crucial for the final diagnosis. A potential pitfall of contrast‐enhanced MRA is also demonstrated.
Comparison of albumin‐(Gd‐DTPA)30 and Gd‐DTPA‐24‐cascade‐polymer for measurements of normal and abnormal microvascular permeability
Authors: Roberts Heidi C. , Saeed Maythem , Roberts Timothy P. L. , Mühler Andreas , Shames David M. , Mann Jeffrey S. , Stiskal Michael , Demsar Franci , Brasch Robert C.
Published: March 2007

The purpose of this study was to compare a new MR macromolecular contrast medium (MMCM), gadolinium‐diethylenetriamine pentaacetic acid (Gd‐DTPA)‐24‐cascade‐polymer, to a well‐studied prototype MMCM, for the potential of distinguishing tissues of varying endothelial permeability. Three tissue models of varying capillary permeability were studied in a total of 46 rats: normal myocardium (normal capillaries), subcutaneously implanted adenocarcinoma (mild capillary leak), and reperfused infarcted myocardium (high capillary leak). T1‐weighted MRI was performed before and dynamically after injection of either albumin‐(Gd‐DTPA)30 or the cascade polymer (each .02 mmol gadolinium [Gd] per kg). Data analysis based on a two‐compartment kinetic model yielded estimates of fractional blood volume (BV) (percentage) and fractional leak rate (FLR) (1 per hour). Permeability to the cascade polymer as reflected in FLR was considerable in normal myocardium (8.24 per hour), of similar value in tumors (8.55 per hour), but significantly greater in infarcted myocardium (39.17 per hour, P < .01) versus normal myocardium. The larger albumin‐(Gd‐DTPA)30 demonstrated minimal extravasation in normal myocardium (FLR .33 per hour); FLR in tumors was 100% higher (.66 per hour, P < .002) and FLR in reperfused capillaries was significantly greater (7.94 per hour, P < .001). Based on capillary permeability measurements, the cascade polymer may have limited utility for detection of mildly increased microvascular permeabilities. For severe tissue injury, the cascade polymer can resolve abnormal microvascular integrity.
Flow velocity of the cortical vein and its effect on functional brain MRI at 1.5t: Preliminary results by Cine‐MR venography
Authors: Yamada Kei , Naruse Shoji , Nakajima Kazuhiro , Furuya Seiichi , Morishita Hiroyuki , Kizu Osamu , Maeda Tomoho , Takeo Kazuhiro , Shimizu Khoji
Published: March 2007

The purpose of this study is to demonstrate the effect of altering flow velocity of cerebral cortical veins as the source of the signal change observed in functional magnetic resonance imaging (fMRI) of the brain. 10 healthy volunteers were examined after instructions in self‐paced hand grasping. Experiments were performed using a 1.5‐Tesla whole body MR scanner with a conventional two‐dimensional gradient echo sequence (TR/TE/flip angle 400/60/40, first order flow rephased, reduced band width 8 Hz/pixel). Flow velocity measurements were performed for the cortical veins which corresponded to the activated areas depicted on fMRI. Velocity was estimated from the cine‐MR venography (cine‐MRV) with a tagging technique. Flow phantom studies were performed to delineate the effect of flow velocity differences upon the subtraction images of fMRI. The cine‐MRV revealed increased flow velocity of the cortical veins during activation in seven volunteers, with a mean velocity difference of 15 mm/sec. Flow phantom studies suggested that the increased flow velocity may result in changes of the flow signal profile due to oblique flow displacement. Subtraction of the two images with different flow profiles produces flow signal enhancement. Increased flow velocity of the cortical veins during the activation is an important factor which contributes to the signal of fMRI.
Segmentation analysis in functional MRI: Activation sensitivity and gray‐matter specificity of RARE and FLASH
Authors: Hutchinson M. , Rusinek H. , Nenov V. I. , Feinberg D. A. , Johnson G.
Published: March 2007

Brain activation is accompanied by local decreases in vascular deoxyhemoglobin. Theoretically, gradient‐echo and spin‐echo sequences show similar sensitivity to capillary deoxyhemoglobin, but spin‐echo sequences should be less sensitive to venous deoxyhemoglobin. This is an important distinction in the context of cortical localization. We report herein a direct experimental comparison of a gradient‐echo sequence (fast low‐angle shot [FLASH]) with a spin‐echo sequence (rapid acquisition with relaxation enhancement [RARE]) for functional MRI (fMRI) in seven subjects undergoing visual stimulation. A Student t test analysis was used to locate areas of significant activation, and then computerized image segmentation was performed to determine the type of activated tissue. Contrary to previous reports, both sequences proved equally sensitive to overall activation. RARE activation, however, was more specific for gray matter, as suggested by prior theoretical models.
Field strength and angle dependence of trabecular bone marrow transverse relaxation in the calcaneus
Authors: Song H. K. , Wehrli F. W. , Ma J.
Published: March 2007

The contribution from reversible dephasing, R2, to the effective transverse relaxation rate, R2*, in trabecular bone marrow, is governed by the magnetic field inhomogeneity induced by the difference in diamagnetic susceptibility between bone and bone marrow and should, therefore, scale linearly with field strength. Measurement of R2′ in the calcaneus at 1.5 and 4 T by means of the GESFIDE (gradient‐echo sampling of free induction decay and echo) pulse sequence showed R2′ to increase by a factor of 2.73 at the higher field, which is close to the ratio of the field strengths (2.67). At both field strengths, R2′ dominates R2*, contributing more than 90% to the total relaxation rate at 4 T. The data further indicate large regional variations within the calcaneus and a notable dependence of R2′ on the angle of the foot relative to the direction of the static field. The findings have implications on the choice of the calcaneal site for assessment of trabecular density.
Useful internal standards for distinguishing infiltrative marrow pathology from hematopoietic marrow at MRI
Authors: Carroll Kevin W. , Feller John F. , Tirman Phillip F. J.
Published: March 2007

The objective of this study was to establish internal standards on MRI differentiating infiltrative marrow pathology from hematopoietic marrow. The T1‐weighted images of 74 patients (51 biopsy‐proven; 23 clinical follow‐up) were reviewed retrospectively. The relative signal intensity of bone marrow was compared to adjacent skeletal muscle (n = 65) and/or nondegenerated intervertebral disk (n = 53). Twenty foci were hyperintense compared to muscle, of which 17 (85%) cases represented normal red marrow (P < .0001); 45 were isointense or hypointense compared to muscle, of which 44 (98%) represented infiltrative marrow processes (P < .0001). Twelve were hyperintense compared to disk, of which 12 (100%) represented normal red marrow (P < .0001); 41 were isointense or hypointense compared to disk, of which 40 (98%) represented infiltrative marrow processes (P < .0001). On T1‐weighted spin‐echo MRI, skeletal muscle and intervertebral disk may serve as internal standards for differentiating infiltrative pathology from normal hematopoietic marrow. Marrow lesions that are relatively isointense or hypointense to muscle and/or disk should not be considered normal hematopoietic marrow.
Diffusion imaging with a multi‐echo MISSTEC sequence
Authors: Franconi F. , Lethimonnier F. , Sonier C. B. , Pourcelot L. , Akoka S.
Published: March 2007

An imaging method is presented to measure the water‐diffusion coefficient. The sequence (MISSTEC) uses the simultaneous acquisition of a spin echo and several stimulated echoes with the same intensity except for diffusion weighting. The optimal number of stimulated echoes was calculated to minimize the diffusion coefficient error (D). D values obtained in vitro and in vivo were in good agreement with those from the spin‐echo sequence (Intra Voxel Incoherent Motion [IVIM] method). The total acquisition time is half that of the classic IVIM method.
Correspondence of closest gradient Voxels—A robust registration algorithm
Authors: Ostuni John L. , Levin Ronald L. , Frank Joseph A. , DeCarli Charles
Published: March 2007

A robust, automatic volume registration algorithm based on intensity gradients is presented. This algorithm can successfully perform registrations under conditions of unrelated intervolume voxel intensities, significant object displacements, and/or significant amounts of missing data. It also allows the user to visualize the registration convergence, clearly illustrating any source of registration errors. This algorithm consists of a matching algorithm based on iteratively finding the correspondence of the closest voxels containing a high three‐dimensional intensity gradient magnitude. This algorithm was tested by registering T2‐weighted MR volumes that had undergone varying displacement transformations to simultaneously acquired proton‐density volumes. These transformations involved rotations of up to 25° followed by translations of up to 25 mm along the axis of rotation. For all registrations, the mean registration error was less than one‐fifth of a voxel and the mean registration time was less than 30 minutes. In conclusion, this algorithm is shown to be a powerful method of sequence‐independent MR volume registration that is simple to both use and understand.
Simulation of two‐dimensional tagged MRI
Authors: Crum William R. , Berry Elizabeth , Ridgway John P. , Sivananthan U. Mohan , Tan Lip‐Bun , Smith Michael A.
Published: March 2007

MR tagging is a recent imaging development that, in cardiac applications, makes possible the tracking of points in the myocardium during the cardiac cycle. Researchers have developed semiautomated, computer‐based methods for analyzing tagged images, but the images are complex and present a challenge to automated tracking systems. Simulation can provide an inexhaustible supply of images for testing and validation of tag tracking software and preview the effect of parameter changes in acquisition. SIMTAG is an interactive computer program that simulates two‐dimensional tagged‐MR experiments. The mathematic model used in the simulation and algorithms for simulating image noise and object deformation are described. Examples of the use of simulated images in SPAMM parameter selection, a comparison of tag contrast in signal‐averaged SPAMM and CSPAMM, and simulated images as test sets for tag‐tracking software are presented.
Database prescan: A time‐efficient alternative to brain MRI autoprescan
Authors: Medina L. Santiago , Mulkern Robert V. , Strife Katherine R. , Zurakowski David , Barnes Patrick D.
Published: March 2007

The purpose of this study was to determine the feasibility of database prescan as an alternative to conventional auto‐prescan in pediatric brain MRI. Autoprescan parameters [receiver levels and transmit gain (TG)] were analyzed prospectively in 236 pediatric brain MRI studies. Paired t test and linear regression analysis were performed to determine predictability of autoprescan parameters by database‐generated parameters. Signal‐to‐noise ratio, image quality, and potential time efficiency of database‐generated parameters were assessed. No statistical difference (P = .13) and a high correlation between the TG of the axial fast spin echo (FSE) proton density (PD) and axial FSE T2‐weighted sequences (r = .92) was seen. Strong correlations were noted between the TG of the sagittal T1‐weighted and the TG of the axial FSE PD (r = .79), axial FSE T2‐weighted (r = .81), and contrast‐enhanced T1‐weighted (r = .78) sequences. The receiver levels did not change significantly between sequences. Quantitative and qualitative analyses revealed no differences in the signal‐to‐noise ratios of the autoprescan and the database‐predicted prescan parameters. Implementation of database prescan could improve time efficiency by 28 to 33%. Autoprescan parameters can be predicted by using database‐generated information while preserving the diagnostic image quality of the study. Incorporation of database prescan into commercial MRI systems could improve MRI time efficiency and patient throughput.
Microvessel density in invasive breast cancer assessed by dynamic gd‐dtpa enhanced MRI
Authors: Buckley David L. , Drew Philip J. , Mussurakis Stavros , Monson John R. T. , Horsman Anthony
Published: March 2007

It has been postulated that the rapid enhancement demonstrated by breast carcinomas after administration of contrast media is a direct result of tumor angiogenesis. However, to date, little quantitative data have been published to support this view. A retrospective study has been undertaken to compare dynamic contrast‐enhanced data obtained from 40 patients with microvessel density (MVD) evaluated in specimens immunohistochemically stained with a factor VIII related antigen. The dynamic data were analyzed quantitatively using both simple indices of enhancement and a two‐compartment kinetic model. A moderate but significant correlation was demonstrated between initial enhancement and MVD, and this correlation strengthened when node‐positive tumors were considered in isolation (r = .77, P < .0005). However, the data showed considerable variability. The enhancement characteristics of the tumors could not be explained solely by their MVD; therefore, MRI cannot be used to predict MVD in vivo. Further work is required to address the exact relationship between contrast‐enhanced MRI and tumor angiogenesis.
Assessment of reperfusion injury by means of MR contrast agents in rat liver
Authors: Reimer Peter , Allkemper Thomas , Bremer Christoph , Rummeny Ernst J. , Spiegel Hans U. , Balzer Thomas , Peters Peter E.
Published: March 2007

The purpose of this study was to investigate whether extracellular MR contrast agents or intracellular liver‐specific MR contrast agents may enable the assessment of liver reperfusion injury. Ischemia‐related reperfusion was induced in 32 rats using Pringle's maneuver. Pringle's maneuver consisted of cross‐clamping of the complete hepatoduodenal ligament for 45 minutes followed by 90 minutes of reperfusion. Two extracellular (gadopentetate dimeglumine and gadobutrol) and two intracellular (gadoxetic acid and SH U 555 A) MR contrast agents were evaluated as model agents. Control animals and animals with liver ischemia were used to calculate changes in liver signal enhancement after Pringle's maneuver. Significant changes in liver signal after reperfusion injury were observed only with reticuloendothelial system (RES)‐specific SH U 555 A. Liver signal enhancement after Pringle's maneuver with RES‐specific SH U 555 A was decreased by 25.4% as compared with the control group. RES‐specific contrast agents such as SH U 555 A seem to be more sensitive to ischemia‐related dysfunction of the liver than hepatobiliary contrast agents such as gadoxetic acid or extracellular gadolinium chelates at different concentrations because Kupffer cells are more sensitive to liver ischemia than hepatocytes.
Oral administration of a low‐cost negative contrast agent: A three‐year experience in routine practice
Authors: Ernst Olivier , Sergent Geraldine , L'Hermine Claude
Published: March 2007

A low cost, well tolerated, and effective gastrointestinal contrast agent is needed for abdominal MRI. The authors tested, in vitro and in routine practice, a mixture of 192 g of barium sulfate (Micropaque HD oral, Guerbet, France) diluted in 500 ml of gastric antacid (Maalox, Rohrer, Fort Washington, PA). Its T1 and T2 relaxation times were 324 and 14 msec, respectively (.2 T). This contrast agent was used in routine practice in 789 patients (.5 T). It had a low signal intensity in 86% and 82% of the cases on T1‐ and T2‐weighted sequences, respectively. No side effect due to magnetic susceptibility was seen, even with gradient‐echo sequences. The dilution of barium sulfate in gastric ant‐acid, instead of water, causes a low signal intensity on all sequences for a low barium sulfate concentration (38% w/v). This product is an effective and low cost contrast agent in routine practice.
High resolution T2‐weighted imaging of the human brain using surface coils and an analytical reception profile correction
Authors: Moyher Susan E. , Wald Lawrence L. , Nelson Sarah J , Hallam Danial , Dillon William P. , Norman David , Vigneron Daniel B.
Published: March 2007

High spatial resolution T2‐weighted MR images of the human brain were obtained at 1.5 T. An optimized fast spin‐echo (FSE) sequence and 1.5 g/cm gradients were used to obtain T2‐weighted images in 4 to 9 minutes with an in‐plane resolution of .27 mm and slice thicknesses from 1.5 to 3 mm. Phased arrays of surface coils were used as receivers, providing increased sensitivity but image intensities dependent on the reception profile of the coils. This image nonuniformity was removed by analyzing the data with a theoretical intensity correction algorithm developed in this laboratory. The FSE sequences, the specialized phased arrays of surface coils, and the intensity correction algorithm allowed improved visualization of nerves within the inner auditory canals and surface anatomy of the cerebral cortex. It is expected that this technique will be useful for clinical applications that require high resolution imaging of small, superficial structures of the brain.
Evaluation of peri‐infarcted hypoperfusion with T2*‐weighted dynamic MRI
Authors: Tsuchida Chika , Yamada Hiroki , Maeda Masayuki , Sadato Norihiro , Matsuda Tsuyoshi , Kawamura Yasutaka , Hayashi Nobushige , Yamamoto Kazutaka , Yonekura Yoshiharu , Ishii Yasushi
Published: March 2007

The purpose of this study was to evaluate cerebral perfusion with T2*‐weighted dynamic MRI in the area around the infarcted core. We examined seven patients with subacute cerebral infarction. After bolus injection of gadopentetate dimeglumine, a series of gradient‐echo images were recorded in a selected slice. From these images, concentration‐time curves were created on a region‐of‐interest (ROI) basis around infarction for calculating relative regional cerebral blood volume (rrCBV). Brain perfusion single photon emission computed tomography (SPECT) study also was performed with intravenous injection of 123I‐labeled N‐isopropyl‐p‐iodoamphetamine (123I‐IMP). All patients showed prolonged signal decrease in the area around the infarcted core. ROI analysis showed significantly increased rrCBV compared to the normal side (P < .01, paired t test). The 123I‐IMP SPECT study showed that these areas had decreased cerebral blood flow. These findings suggest compensatory vascular dilatation due to decreased perfusion pressure. T2*‐weighted dynamic MRI is a useful method for detecting compensatory vasodilatation of ischemic insult in the peri‐infarcted area.