bluuebunny/crossref_metadata_2025 huggingface dataset:
Regions of interest tracking in temporal scans based on statistical analysis of gray scale and edge properties and registration of images
Authors: Saeed Nadeem , Hajnal Joseph V. , Oatridge Angela , Young Ian R.
Published: March 2007

Precise measurement of T1 is needed for its use in temperature monitoring in vivo. Movement of tissue relative to fixed regions of interest can result in large variations in apparent T1, with consequent substantial errors in the measured temperature. This paper evaluates methods of tracking regions of interest as tissue moves during a study in an effort to minimize errors from this cause. Tracking techniques evaluated are based on maintaining constant gray scale levels, locating nearby edges and maintaining position relative to them, and global image registration.
Invited. Remember true FISP? a high SNR, near 1‐second imaging method for T2‐like contrast in interventional MRI at .2 T
Authors: Duerk Jeffrey L. , Lewin Jonathan S. , Wendt Michael , Petersilge Cheryl
Published: March 2007

Clinical requirements for interventional MRI (I‐MRI) monitoring of needle placement or thermal ablation demand rapid (near‐real‐time) image acquisition rates, high spatial resolution, and T2 weighting. Experimental analysis performed earlier (see ref. 8) suggests that many sequences used for either rapid scanning or T2 weighting at high fields fail to meet both the speed (conventional spin echo [SE], turbo SE) or contrast (ie, fast low‐angle shot [FLASH], fast imaging with steady state precession [FISP]) requirements when used at .2 T. In this work, we revisited a number of pulse sequences advocated primarily for higher field applications requiring T2 weighting and found that refocused steady state coherent pulse sequences, aka, true FISP sequences, performed superiorly in achieving both speed and T2 contrast requirements for I‐MRI at .2 T. This work focuses on our experience with this new/old technique in the I‐MRI setting and describes how one can take advantage of the low field strength and modest inhomogeneity of .2 T (and similar) systems to design pulse sequences that balance TE, TR (and hence T2 dephasing), and resonant offset frequency effects to provide images with the desired contrast and minimal artifactual field inhomogeneity “banding.” At high flip angles (∼90°), reasonably short TEs (∼5 msec) and short TRs (∼ 10 msec), we have used this method in our last 25 I‐MRI procedures (biopsies and/or radiofrequency [RF] thermal ablations) and found these sequences to be extremely useful in both needle localization phases of I‐MRI biopsy procedures, RF thermal ablation electrode guidance, and posttherapy imaging assessment. Design methods and clinical I‐MRI cases are presented that highlight these points.
Invited. Visualization of MR‐compatible catheters by electrically induced local field inhomogeneities: Evaluation in vivo
Authors: Adam Gerhard , Glowinski Arndt , Neuerburg Jörg , Bücker Arno , van Vaals Joop J. , Günther Rolf W.
Published: March 2007

The purpose of this study was to assess the feasibility of a newly developed field inhomogeneity catheter for interventional MRI in vivo. Different prototypes of a field inhomogeneity catheter (pigtail and multipurpose configuration, balloon catheters) were investigated in pigs. The catheters were introduced in Seldinger technique via the femoral vessels over a guidewire on an interventional MR system (Philips Gyroscan NT combined with a C‐arm fluoroscopy unit [Philips BV 212]). Catheters were placed in veins and arteries. The catheter position was controlled by a fast gradient‐echo sequence (turbo field echo [TFE]). Catheters were introduced over a guidewire without complications in all cases. Using the field inhomogeneity concept, catheters were easily visualized in the inferior vena cava and the aorta by the fast gradient‐echo technique on MR in all cases. Although aortic branches were successful cannulated, the catheters were not well displayed by the TFE technique due to the complex and tortuous anatomy. All animals survived the experiments without complications. MR‐guided visualization of a field inhomogeneity catheter is a simple concept that can be realized on each MR scanner and may allow intravascular MR‐guided interventions in future.
An expandable intravenous RF coil for arterial wall imaging
Authors: Martin Alastair J. , McLoughlin Raymond F. , Chu Kenneth C. , Barberi Enzo A. , Rutt Brian K.
Published: March 2007

An intravenous (iv) radiofrequency (RF) coil is proposed as a means of obtaining high resolution images of artery wall. The anatomic positioning of peripheral artery/vein pairs was investigated and a phantom mimicking the iliac artery/vein pair was constructed. Imaging results, comparing iv coils with external coils, demonstrated a potential 15‐ to 20‐fold increase in signal‐to‐noise ratio (SNR) with iv coils. The SNR benefit was measured over a cylindrical volume, adjacent to the coil, and typical of artery position. Prototype expandable iv coils were constructed of Cu‐Be loops and introduced via an 8‐Fr catheter. The effects of local and remote iv coil tuning were investigated and local tuning was found to provide significant SNR benefits. The in vivo performance of iv RF coils was demonstrated in a porcine animal model. The iv coils were found to be an excellent alternative to intraarterial coils.
Preliminary clinical experience with laser‐induced interstitial thermotherapy in patients with hepatocellular carcinoma
Authors: Bremer Christoph , Allkemper Thomas , Menzel Josef , Sulkowski Udo , Rummeny Ernst , Reimer Peter
Published: March 2007

The purpose of this preliminary study was to evaluate whether laser‐induced interstitial thermotherapy (LITT) may be used for palliative treatment of localized hepatocellular carcinomas (HCC). We applied LITT to two patients suffering from unresectable localized hepatocellular carcinomas of different sizes (2.5 and 4 cm). LITT was performed with an Nd:YAG laser (1,064 nm) at 5 W laser power (15–20 minutes). Thermometry during LITT was performed by MRI using a temperature‐sensitive T1‐weighted fast low‐angle shot (FLASH) sequence. Follow‐up for local tumor control was performed by MRI and ultrasound. LITT was well tolerated and no adverse events occurred during or after LITT; no secondary liver lesions were seen in the follow‐up (11 or 12 months, respectively). Only minimal tumor growth was observed in the larger HCC (from 4 to 5 cm), whereas the smaller HCC remained unchanged in size during 11 months of follow‐up. We conclude that LITT might be an effective minimally invasive palliative treatment option for patients with small unresectable HCC.
MR‐monitored LITT as a palliative concept in patients with high grade gliomas: Preliminary clinical experience
Authors: Reimer Peter , Bremer Christoph , Horch Christoph , Morgenroth Carlo , Allkemper Thomas , Schuierer Gerhard
Published: March 2007

The purpose of this study was to evaluate the clinical utility of laser‐induced thermotherapy (LITT) as a palliative treatment for patients with high‐grade gliomas. Four consenting patients with recurrent high grade III/IV gliomas near the primary language or motor areas were palliatively treated with LITT (2–5 W, 3–13 minutes; Neodym YAG Laser, Dornier, Friedrichshafen, Germany). Temperature monitoring was performed by T1‐weighted turbo‐fast low‐angle shot (FLASH) imaging at 1.5 T (Siemens Magnetom SP 4000, Siemens, Erlangen, Germany). MRI studies before LITT included contrast‐enhanced conventional scans and functional activation studies to localize the primary motor cortex or language areas using an echoplanar imaging (EPI) spin‐echo (SE) sequence. Follow‐up studies consisted of contrast‐enhanced conventional scans as well as diffusion studies (contrast‐enhanced Fourier‐acquired steady‐state technique and EPI‐SE) and perfusion studies (EPI‐SE with .2 mmol of gadolinium (Gd)/kg body weight) to differentiate posttherapeutic effects from residual or recurrent tumor growth. Local tumor control was achieved in areas with laser energy deposition with clinically stable conditions ⩾ 6 months. Conventional contrast‐enhanced scans demonstrated strong enhancement surrounding ablated tumor components, which showed a reduction in CBV/CBF. Perfusion studies were useful to discriminate granulomatous tissue enhancement from residual or recurrent tumor growth. Careful application of LITT may evolve as an alternative palliative concept for patients with end‐stage high‐grade cerebral gliomas reducing clinical symptoms from circumscribed areas of pathology.
MR‐guided balloon angioplasty: In vitro demonstration of the potential of MRI for guiding, monitoring, and evaluating endovascular interventions
Authors: Bakker Chris J. , Smits Henk F. , Bos Clemens , van der Weide Remko , Zuiderveld Karel J. , van Vaals Joop J. , Hurtak Wenzel F. , Viergever Max A. , Mali Willem P.
Published: March 2007

The purpose of this study was to demonstrate the potential of MRI for guiding, monitoring, and evaluating endovascular interventions. This was done by investigating the feasibility of MR‐guided balloon angioplasty in a stenosed vessel model. Catheters and guidewires were prepared for susceptibility‐based MR visualization by incorporating paramagnetic markers into their walls. Near real‐time monitoring (up to 1 image/sec) of the interventional procedure was achieved by using a dynamic two‐dimensional gradient‐echo technique. Devices were localized by on‐the‐fly subtraction of a baseline image from consecutive dynamic images and by merging the subtraction images with a previously acquired road map. All steps involved in balloon angioplasty, from the introduction and placement of a guidewire to the positioning of a catheter across the stenosis, inflation of the balloon, and dilatation of the stenosis could adequately be monitored with MR fluoroscopy. The beneficial effect of dilatation could be substantiated by a reduction of stenosis‐related hypointensities and hyperintensities in the posttreatment MR angiogram as compared to the pretreatment angiogram and by a posttreatment increase of the volumetric flow rate.
Visualization of vascular guidewires using MR tracking
Authors: Ladd Mark E. , Zimmermann Gesine G. , McKinnon Graeme C. , von Schulthess Gustav K. , Dumoulin Charles L. , Darrow Robert D. , Hofmann Eugen , Debatin Jörg F.
Published: March 2007

MR tracking of a vascular guidewire sized for a .035‐inch (.89‐mm) catheter lumen was performed. The guidewire was actively tracked by incorporation of a miniature radiofrequency (RF) receive coil built into its tip. After in vitro validation, simultaneous tracking of the guidewire and a catheter was performed in the aortic and abdominal vessels of a swine at 1.5 T. The ability to track such a small device and the ability to simultaneously track multiple devices are significant steps towards vascular interventions under MR guidance.
Invited III. New developments: 2. Virtual MR endoscopy in the central nervous system
Authors: Shigematsu Yoshinori , Korogi Yukunori , Hirai Toshinori , Okuda Tomoko , Sugahara Takeshi , Liang Luxia , Ge Yulin , Takahashi Mutsumasa
Published: March 2007

Recent advances in three‐dimensional (3D) data acquisition and postprocessing technologies have been playing a important role in widening the potential applications of 3D display. The authors described new applications of a virtual endoscopic algorithm for 3D display of high resolution MR images: (a) intracranial intravascular virtual MR endoscopy using the 3D fast imaging with steady state precession (FISP) sequence, and (b) virtual MR endoscopy of the cerebrospinal fluid (CSF) spaces using the constructive interference in steady state (CISS) three‐dimensional Fourier transform (3DFT) sequence. The virtual endoscopic images were displayed with use of a commercially available perspective volume‐rendering algorithm. Our initial experience showed that virtual MR endoscopy can be performed to observe the intracranial arteries and CSF spaces from the viewpoints within themselves. Although the clinical use of the intracranial virtual MR endoscopy has not been established yet, the images obtained are very attractive and further investigations in this field will be expected.
Invited. MRI of CNS parasitic diseases
Authors: Chang Kee‐Hyun , Han Moon Hee
Published: March 2007

This article reviews MRI findings of parasitic diseases of the central nervous system (CNS), with emphasis on neurocysticercosis, which is by far the most common CNS parasitic infection worldwide. MRI findings of neurocysticercosis are various, depending on the location (parenchymal, cisternal, ventricular, and spinal forms), and temporal evolutional stages (vesicular, colloid vesicular, granular nodular, and nodular calcified stages) of the worm. Classical findings of each location and stage are presented. Characteristic MRI findings of cerebral toxoplasmosis frequently seen in patients with acquired immunodeficiency syndrome (AIDS), paragonimiasis, and sparganosis that have most commonly been reported in East Asia are also illustrated. MRI is superior to CT scan in the evaluation of most CNS parasitic infections and is nearly diagnostic, particularly in endemic areas. Contrast‐enhanced study is essential not only for specific diagnosis of the disease, but also for assessment of the inflammatory activity.
Invited. Fukuyama congenital muscular dystrophy: A neuroradiologic review
Authors: Aida Noriko
Published: March 2007

We reviewed neuroradiologic findings of Fukuyama congenital muscular dystrophy (FCMD) and correlated them with the known neuropathology. All patients showed thick and bumpy cortices with shallow sulci corresponding to polymicrogyria, and approximately half of the patients showed pachygyric cortex with smooth surface corresponding to type II lissencephaly. The two types of cortical dysplasias presented characteristic distributions: the former demonstrated frontal lobe involvement in all and parietotemporal lobe involvement in some, whereas the latter involved the temporo‐occipital lobes. Most patients showed prolonged T1 and T2 signal in the white matter, which was indistinct in neonates and infrequently seen in adolescents. Cerebellar polymicrogyria depicted as disorganized cerebellar foliation accompanying cysts were found more than 90% of the patients. In conclusion, brain MRI demonstrates findings consistent with the known neuropathology of FCMD. The detection of the two types of cerebral cortical dysplasia with characteristic distribution and cerebellar abnormalities is helpful in the differential and early diagnosis.
Invited MRI of the liver
Authors: Laing Andrew D. P. , Gibson Robert N.
Published: March 2007

MRI of the liver is a powerful imaging modality for detection and characterization of liver pathology. MRI technology continues to evolve with developments in scanner hardware performance and refinements in imaging sequences, particularly in respect to fast imaging techniques, improving the quality of images that can be routinely achieved. Fast imaging techniques allow dynamic contrast‐enhanced scanning to assist in lesion detection and characterization. An array of tissue‐specific contrast agents are also becoming available; the clinical utility of some of these agents is yet to be fully established. An overview of scanning technique, contrast media, and the role of MRI in liver lesion detection and characterization is presented, with a review of the typical imaging characteristics of common focal and diffuse hepatic diseases. Where possible, emphasis has been placed on features that allow distinction between the various pathologic entities described.
Invited. MRI of Clonorchiasis and Cholagiocarcinoma
Authors: Choi Byung Ihn , Kin Tea Kyoung , Han Joon Koo
Published: March 2007

Intrahepatic cholangiocarcinomas are usully categorized as peripheral cholangiocarcinoma or hilar cholangiocarcinoma on the basis of the site of origin. Clonorchiasis is a trematodiasis caused by chronic infestation of liver flukes, Which are largely confined to the Orient, from Japan to Vietnam. The close relationship between clonorchiasis and cholangiocarcinoma has long been emphasized. This paper discusses the effecacy and possible roles of MRI for imaging clonorchiasis and cholangiocarcinoma of the liver. Although sonography, CT, and direct cholangiography have been used traditionally to diagnose these diseases, the role of MRI has been increasing rapidly with dramtic progress of the MRI has been increasing rapidly with dramatic progress of the MRI tecniques. We review MRU findings of clonorcjhiaiss na cholangiocarcinoma and discuss the potential usefulness of MRI.
Invited. Ossification of posterior longitudinal ligaments: Evaluation with MRI
Authors: Hirai Toshinori , Korogi Yukunori , Yamashita Yasuyuki , Takahashi Mutsumasa , Shimomura Osamu , Sakae Terumi
Published: March 2007

Ossification of the posterior longitudinal ligament is a special subcategory of degenerative disease responsible for compression of the spinal cord. On MR images, T2‐weighted sequences are the most effective to evaluate both spinal cord compression due to the ossification and abnormal signal intensity of the cord. Although ossification of the ligaments is well demonstrated on CT and plain radiographs, MRI noninvasively provides useful information about the degree and extent of spinal cord compression, as well as the character of the ossification.
Standard dose Gd‐DTPA dynamic MR of renal arteries
Authors: Tello Richard , Thomson Ken R. , Witte David , Becker Gary J. , Tress Brian M.
Published: March 2007

Renal MR contrast enhancement depends on the timing of image acquisition. Limited human trials have demonstrated efficacy of renal artery stents on salvage of renal function. This study assessed the ability of dynamic gadolinium‐diethylenetriamine pentaacetic acid (Gd‐DTPA) administration to demonstrate renal artery stenosis and renal stent patency compared to conventional angiography as the gold standard. Twenty subjects referred for renal angiography underwent 22 dynamic MR studies, including 7 with renal artery stenting (Palmaz P204 or P201, Johnson & Johnson, Sydney, Australia). All were examined with conventional angiography and after dynamic Gd‐DTPA infusion. Coronal MR images of the kidneys were acquired using a GE Signa 1.5‐T magnet (General Electric Medical Systems, Milwaukee, WI) (fast spoiled gradient echo [FSPGR]; TE = 4.2 msec, TR = 68–150 msec, flip angle = 75°) 0 to 600 seconds after iv bolus injection of 15 ml of Gd‐DTPA during sequential breath‐hold acquisitions, 13 to 32 seconds each. All 51 renal arteries (13 stenosed, 38 normal) were detected with dynamic MRI. Severity of renal artery stenosis was classified correctly with an accuracy of 98% (95% confidence interval [CI]: 85–100), yielding 98% specificity and 100% sensitivity. All nine renal stents were visualized with 100% accurate patency documentation. FSPGR MRI with bolus Gd‐DTPA administration can provide adequate time and spatial resolution to demonstrate renal artery stenosis.
The value of detection of flow voids between the uterus and the leiomyoma with MRI
Authors: Torashima Miyuki , Yamashita Yasuyuki , Matsuno Yasuhara , Takahashi Mutsumasa , Nakahara Kazuhiko , Onitsuka Yoshio , Ohtake Hideyuki , Tanaka Nobuyuki , Okamura Hitoshi
Published: March 2007

Flow voids are occasionally seen between the uterus and the leiomyoma. This study was performed to determine the prevalence of this sign and its relation to tumor size and location, internal signal intensity of the leiomyomas, and the ease of detectability using different MR sequences. Also, to understand the pathologic causes for the phenomenon of flow voids. The MR images of the pelvis in 92 females with 359 uterine leiomyomas were analyzed. Flow voids located between the uterus and the leiomyomas were seen in 32 lesions on T1‐weighted images and in 12 on T2‐weighted images. Flow void was seen exclusively in leiomyomas of 3‐cm diameter of larger. In five pedunculated subserous leiomyomas, flow voids were seen within the pedicle of the tumor. Large lieomyomas and leiomyomas with irregular signal intensity on T2‐weighted images showed significantly greater frequency of signal void than other leiomyomas (P < .01). The sign was not seen in any other pelvic tumors. On pathologic evaluation, the flow voids were found to correspond to dilated feeding arteries located outside the capsule of the leiomyoma.
Comparison of breath‐hold multishot echo‐planar and respiratory triggered fast‐spin‐echo sequences for T2‐weighted MRI of liver lesions
Authors: Yamakado Koichiro , Sakuma Hajime , Murashima Shuichi , Nakatsuka Atsuhiro , Matsumura Kaname , Takeda Kan
Published: March 2007

The purpose of this study was to evaluate the usefulness of multishot echo‐planar imaging in detecting liver tumors in comparison with respiratory triggered T2‐weighted fast‐spin‐echo (FSE) imaging. Thirty‐two patients with 70 focal liver lesions were imaged using a 1.5‐T high speed MR imager. Eight‐shot echo‐planar images covering the whole liver were acquired during a single breath‐hold period. FSE images were acquired with respiratory triggering in approximately 4 minutes. Lesion detectability and image quality of the two pulse sequences were analyzed qualitatively. Quantitative analysis was performed by means of signal‐to‐noise and tumor‐liver contrast‐to‐noise analysis. Lesion detectability was comparable in both solid (86.3% vs 90.2%: .3 < P < .5) and nonsolid lesions (89.5% vs 100%: .3 < P < .5) between echo‐planar and FSE images. Echo‐planar imaging provided significantly reduced image artifact, better lesion conspicuity, and anatomic detail compared with FSE imaging. The signal‐to‐noise and contrast‐to‐noise ratios of echo‐planar images were significantly higher than those of FSE images. Breath‐hold eight‐shot echo‐planar imaging can be an alternative to T2‐weighted FSE imaging because it can provide comparable image quality in a substantially decreased acquisition time.
Microwave coagulation therapy on hepatomas: CT and MR appearance after therapy
Authors: Hyodoh Hideki , Hyodoh Kazusa , Takahashi Koji , Furuse Makoto , Kawamoto Chiaki , Isoda Norio , Hozumi Masanori , Ido Kenichi , Hirota Norio
Published: March 2007

Laparoscopic microwave coagulation (LMC) for hepatocellular carcinomas (HCCs) was performed on 26 HCCs in 17 patients. Contrast‐enhanced CT (CECT) and MR images (T1‐weighted imaging [T1WI], T2WI, gadolinium‐diethylenetriamine pentaacetic acid [Gd‐DTPA] T1WI) were obtained to determine changes over time. The irradiated center exhibited low to moderate intensity with surrounded high intensity (HI) on T2WI and Gd‐DTPA T1WI. On T1WI, lesions showed four patterns of intensity: uniform HI (30.8%), arcuate HI (26.9%), mainly low with spot HI (30.8%), and isointensity to hypointensity (11.5%). Follow‐up imaging at more than 170 days revealed isointensity to hypointensity on T1WI (96.2%) and reduced HI on T2‐weighted imaging (T2WI) and Gd‐DTPA T1WI. All lesions became less conspicuous and were reduced in volume. HCC shows time‐related changes in signals and size after LMC. Identifying the irradiated lesion is necessary to estimate the adequacy of treatment by comparison with the pretherapeutic image.
Tissue temperature monitoring with multiple gradient‐echo imaging sequences
Authors: Mulkern Robert V. , Panych Lawrence P. , Hynynen Kullervo , Jolesz Ferenc A. , McDannold Nathan J.
Published: March 2007

The inherent sensitivity of multiple gradient‐echo sequences to the chemical shift is exploited to rapidly map muscle water frequency shifts caused by ultrasonic heating. The use of multiple echoes is shown to offer several advantages over single gradient‐echo approaches previously proposed for temperature measurement. An increase in the effective bandwidth significantly reduces aliasing problems observed with single gradient‐echo methods in high temperature applications. Of greater significance is the improved immunity to intrascan motion found for multi‐echo versus single echo gradient methods, making the former more attractive for clinical applications. Finally, a sensitivity to the presence of multiple spectral components unavailable with single gradient‐echo methods is obtained.
Biliary cystadenoma with mesenchymal stroma of the liver: Correlation between unusual MR appearance and pathologic findings
Authors: Gabata Toshifumi , Kadoya Masumi , Matsui Osamu , Yamashiro Masashi , Takashima Tsutomu , Mitchell Donald G. , Nakamura Yasutaka , Takeuchi Kazuo , Nakanuma Yasuni
Published: March 2007

We reported a case of the biliary cystadenoma of the liver. The cystic mass had labulation and septation and showed marked hyperintensity on T1‐weighted images and hypointensity on T2‐weighted images; MR findings were very unusual for cystadenoma. The content of the cystic mass was jelly‐like, thick mucinous fluid without intracystic hemorrhage. We concluded that these unusual signal intensities of the cyst were due to hyperproteinous mucinous fluid.
Dynamic MRI of transcorneal dispersion of oxygen into the anterior chamber of human eye
Authors: Obata Takayuki , Saito Kimihiko , Iwasawa Tae , Hirono Keishi , Yoshida Tetsuo , Matsubara Sho
Published: March 2007

To measure the transcorneal dispersion of oxygen into the anterior chamber, dynamic T1‐weighted fast‐spin‐echo MRI (TR = 2 seconds, TE = 15 msec, 5‐mm slice) of the human eye was performed both before and during oxygen supply to a full goggle placed on the face. During the course of the imaging, a significant increase in the signals in the anterior chamber occurred. This indicated that transcorneal dispersion of oxygen into the anterior chamber can be evaluated by this procedure, suggesting that this method may be useful for diagnosing dysfunction of the cornea or aqueous flow.
Implementation and evaluation of a new pulse sequence for rapid acquisition of double inversion recovery images for simultaneous suppression of white matter and CSF
Authors: Bedell Barry J. , Narayana Ponnada A.
Published: March 2007

We describe a fast double inversion recovery (DIR) imaging sequence that effectively attenuates signal from both white matter and cerebrospinal fluid (CSF). The pulse sequence uses a novel inversion/excitation scheme and fast spin‐echo readout to maximize scan efficiency. The white matter/CSF suppressed images can be acquired from the entire brain in ∼6 minutes. Evaluation of the fast DIR sequence on patients with multiple sclerosis (MS) demonstrates high lesion conspicuity.
Flip angle dependence of experimentally determined T1sat and apparent magnetization transfer rate constants
Authors: Finelli Daniel A. , Reed Damon R.
Published: March 2007

The purpose of this work was to develop a method for determining the T1sat and magnetization transfer (MT) rate constants by analyzing the slice‐select flip angle dependent MT behavior of normal white and gray matter. The technique uses a high MT power, three‐dimensional (3D) gradient‐recalled echo (GRE) sequence, with a well chosen MT pulse frequency offset, such that the experimental conditions closely satisfy requisite assumptions for invoking a first order rate process for MT. Integral to this method is that the T1sat and MT ratio values are obtained under explicitly identical MT saturation conditions. The T1sat of white matter was found to be approximately 300 msec, and the MT rate constant was approximately 2.0 sec−1. The T1sat of gray matter was approximately 500 msec, and the MT rate constant was 1.1 sec−1. We also found a strong dependence of the MT rate constant on the slice‐select flip angle used for the imaging sequence, independent of the MT saturation parameters. Strongly T1‐weighted imaging sequences can result in the underestimation of the MT rate constant by 50%. Practical technical suggestions for quantitative MT experiments are put forth.
Histologic confirmation of microvascular hyperpermeability to macromolecular MR contrast medium in reperfused myocardial infarction
Authors: Saeed Maythem , van Dijke Cornelis F. , Mann Jeffrey S. , Wendland Michael F. , Rosenau Werner , Higgins Charles B. , Brasch Robert C.
Published: March 2007

A macromolecular MR contrast medium (MMCM) designed to permit histochemical staining and specific tissue localization, albumin‐(biotin)10‐(Gd‐DTPA)25 (Bio‐Alb‐Gd), was used in a rat model of reperfused myocardial infarction to confirm the presence and distribution of microvascular hyperpermeability. T1‐weighted spin‐echo images were acquired before and after administration of Bio‐Alb‐Gd. An avidin‐biotin‐complex (ABC) stain, specific for the biotinylated MR contrast medium, was used to define the MMCM distribution and to detect any regional change in micro‐vascular permeability related to infarction. Immediately after Bio‐Alb‐Gd administration, the infarcted region was enhanced, with greatest signal intensity noted at the rim and less at the center. There was a gradual increase in signal intensity of the initially hypointense central region. The steady increase in signal intensity of the central region suggested convection transport of MMCM through the interstitial space and its influx into cellular compartment after leakage from the vascular compartment. Histologic findings confirmed regional microvascular hyperpermeability corresponding to the site of infarction and a predominant rim distribution of the MMCM. Bio‐Alb‐Gd was identified at high microscopic power in the intravascular, interstitial, and intracellular spaces at the periphery of reperfused infarcted myocardium. Bio‐Alb‐Gd can be used as an MR contrast medium in reperfused infarcted myocardium to confirm the existence and to localize altered microvascular permeability to macromolecules. Bio‐Alb‐Gd contrast technique removes all the ambiguity between the distribution of the MR or other imaging contrast agent and the distribution of the substrate for histochemical staining.
Quantification of mitral regurgitation with MR phase‐velocity mapping using a control volume method
Authors: Chatzimavroudis George P. , Oshinski John N. , Pettigrew Roderic I. , Walker Peter G. , Franch Robert H. , Yoganathan Ajit P.
Published: March 2007

Reliable diagnosis and quantification of mitral regurgitation are important for patient management and for optimizing the time for surgery. Previous methods have often provided suboptimal results. The aim of this in vitro study was to evaluate MR phase‐velocity mapping in quantifying the mitral regurgitant volume (MRV) using a control volume (CV) method. A number of contiguous slices were acquired with all three velocity components measured. A CV was then selected, encompassing the regurgitant orifice. Mass conservation dictates that the net inflow into the CV should be equal to the regurgitant flow. Results showed that a CV, the boundary voxels of which excluded the region of flow acceleration and aliasing at the orifice, provided accurate measurements of the regurgitant flow. A smaller CV provided erroneous results because of flow acceleration and velocity aliasing close to the orifice. A large CV generally provided inaccurate results because of reduced velocity sensitivity far from the orifice. Aortic outflow, orifice shape, and valve geometry did not affect the accuracy of the CV measurements. The CV method is a promising approach to the problem of quantification of the MRV.
Slice‐selective fat saturation in MR angiography using spatial‐spectral selective prepulses
Authors: Forster Jürgen , Schick Fritz , Breuer Johannes , Sieverding Ludger , Lutz Otto
Published: March 2007

Presaturation of fat signals by frequency‐selective radiofrequency (RF) pulses is often applied in MR angiography to improve the visualization of the blood vessels. Unfortunately, standard fat saturation methods might cause a considerable reduction of the blood signal in the measured slices. This effect is caused by an attenuation of blood magnetization in remote tissue regions with water protons showing a similar Larmor frequency as the fat protons in the recorded slice. The affected blood water protons subsequently flow into the recorded slice and provide low signal intensity. Suitable spatial‐spectral selective methods for slice‐selective fat saturation were developed to avoid this unwanted effect. A spatial‐spectral fat saturation technique was compared with a corresponding only spectrally selective approach. Both saturation techniques were included in a standard two‐dimensional (2D) cine sequence and applied in angiographic examinations of the thighs. The results indicate that spatial‐spectral saturation (acting slice selectively) leads to a clearly higher blood signal intensity in fat‐suppressed MR angiography compared with standard techniques, especially in measurements performed during the systolic phase of the cardiac cycle.
Variations in blood flow waveforms in stenotic renal arteries by 2D phase‐contrast cine MRI
Authors: Westenberg Jos J. M. , Wasser Martin N. J. M. , van der Geest Rob J. , Pattynama Peter M. T. , de Roos Albert , Vanderschoot Jan , Reiber Johan H. C.
Published: March 2007

Waveform variations in blood flow measurements through stenotic renal arteries have been reported already with echo Doppler studies. We studied these variations with MRI in 14 patients (mean age, 60 years) with suspected renal arterial stenosis (24 patent arteries, four occluded). Flow measurements were successful in 15 arteries and unsuccessful in nine, due to practical limitations. Seven healthy younger volunteers (mean age, 28 years) and five healthy older volunteers (mean age, 58 years) were recruited for comparison purposes. In patients, the severity of stenoses was also assessed by digital subtraction angiography and intraarterially measured transstenotic pressure drops. We found flow patterns to be statistically significantly (P< 0.01) age‐related. Younger healthy subjects showed shorter wave duration, higher diastolic flow, and total blood flow per minute. Also, with increasing stenosis severity, the systolic wave became more damped and the systolic wave duration became statistically significantly (P> = .03) longer.
Contrast‐enhanced 3D MRA with centric ordering in k space: A preliminary clinical experience in imaging the abdominal aorta and renal and peripheral arterial vasculature
Authors: Shetty Anil N. , Bis Kostaki G. , Vrachliotis Thomas G. , Kirsch Matthias , Shirkhoda Ali , Ellwood Robert
Published: March 2007

The objective of this study was to determine the clinical utility of a contrast‐enhanced, centric reordered, three‐dimensional (3D) MR angiography (MRA) pulse sequence in imaging the abdominal aorta and renal and peripheral lower extremity arteries. Twenty‐eight MRA studies were performed on 23 patients and four volunteers at 1.5 T using a 3D contrast‐enhanced, centric reordered pulse sequence. In 20 patients, the abdominal aorta and renal arteries were imaged, and in seven patients, the lower extremity arteries were imaged. In 19 patients, a total of 51 renal vessels were evaluated (33 renal arteries using .1 mmol/kg of gadopentetate dimeglumine and 18 renal arteries using .2 mmol/kg of gadoteridol). A total of 70 peripheral arterial segments were assessed using .2 mmol/kg of gadoteridol. Correlation with conventional angiography was made for the following 14 cases: renal artery stenosis (four cases), abdominal aortic stenosis (one case), arteriovenous fistula in a transplant kidney (one case), renal arteriovenous malformation (one case), common iliac artery aneurysms (one case), and peripheral lower extremity (six cases). Of the 70 peripheral arterial segments evaluated, in 35, there was correlation with x‐ray angiography. The mean percent of aortic signal enhancement was significantly higher in the .2 mmol/kg dose group (370.8 ± 190.3) than in the .1 mmol/kg dose group (184.5 ± 128.9) (P = .02). However, there was no apparent difference between the two doses for visualization of the renal and accessory renal arteries. There was concordance between the contrast‐enhanced 3D MRA studies and conventional angiography in all cases of renal artery and peripheral arterial stenoses and occlusions, including visualization of reconstituted peripheral arterial segments. There was no evidence of spin dephasing effects at sites of stenoses on the 3D contrast‐enhanced MRA studies. Contrast‐enhanced, centric reordered, 3D MRA can rapidly image the abdominal aorta and renal and accessory renal arteries, as well as peripheral lower extremity arteries, with high resolution. Accurate depiction of the vascular lumen at sites of stenosis is made because of the lack of spin dephasing effects, even with hemody‐namically significant stenoses. Additional larger clinical trials are required with this promising technique.
Characterization of atherosclerotic plaque components by high resolution quantitative MR and US imaging
Authors: Raynaud Jean‐Sébastien , Bridal S. Lori , Toussaint Jean‐François , Fornès Paul , Lebon Vincent , Berger Geneviève , Leroy‐Willig Anne
Published: March 2007

High resolution MRI at 3 T and US imaging at 50 MHz were used for atherosclerotic plaque characterization. For 14 excised segments of human arteries, conventional MR and US images, quantitative MR T2 maps, US integrated attenuation (IA) maps, and histologic sections were produced and compared. The MR T2 and US attenuation mean values estimated in selected regions of interest were related with tissue type as identified on histologic sections. Significant distinction between media or collagen and lipid or collagen lipidic plaque was achieved with both techniques (MR: P < .001; US: P < .01). Significant distinction was obtained between media and collagen (P < .0001) and between iliac and aortic media (P < .05) with MR T2 but not with IA. MR and US native and parametric images, with different sensitivities to tissue type, provide complementary information useful for quantitative plaque characterization.
High resolution MRI of MCF7 human breast tumors: Complemented use of iron oxide microspheres and Gd‐DTPA
Authors: Furman‐Haran Edna , Margalit Raanan , Grobgeld Dov , Degani Hadassa
Published: March 2007

The differential capacity of iron oxide microspheres and of gadolinium‐diethylenetriamine pentaacetic acid (Gd‐DTPA) to serve as contrast agents that can map the microcirculation of MCF7 human breast cancer implanted in nude mice has been examined by high resolution MRI. Modulation of signal intensity in T2*‐weighted, gradient‐echo images after iron oxide administration and the temporal signal enhancement after Gd‐DTPA administration were monitored and analyzed at a spatial resolution of 98 × 98 × 500 μm and 195 × 390 × 1,000 μm, respectively. The pathophysiologic features revealed in the contrast‐enhanced images were analyzed in reference to those obtained from the corresponding high resolution T2‐weighted, spin‐echo images and from histologic sections stained with hematoxylin and eosin and with an endothelial cell marker. The results showed that iron oxide microspheres can aid in the characterization of gross histopathologic features and in the assessment of the distribution of the microvasculature, whereas Gd‐DTPA estimates the permeability of the microvessels to this agent and determines the cellularity (cell volume fraction) in the vicinity of the vessels.
The value of respiratory triggered T2‐weighted turbo spin‐echo imaging of the liver using a phased array coil
Authors: Namimoto Tomohiro , Yamashita Yasuyuki , Mitsuzaki Katsuhiko , Takahashi Mutsumasa
Published: March 2007

The purpose of this study was to evaluate the value of the respiratory triggered turbo spin‐echo (TSE) technique for T2‐weighted MRI of liver lesions. Fifty‐nine patients (32 men, 27 women; mean age, 63.3 years) with focal hepatic lesions were prospectively studied with MRI at 1.5 T with use of a body phased array coil. In the first 15 patients, breath‐hold TSE, respiratory triggered TSE, and conventional nonrespiratory triggered TSE T2‐weighted imaging were compared. Because nonrespiratory triggered TSE imaging was significantly inferior (P < .01) to breath‐hold or respiratory triggered images, breath‐hold and respiratory triggered TSE T2‐weighted images were compared in the remaining 44 patients. Images were analyzed quantitatively by measuring the liver signal‐to‐noise ratio and the lesion‐liver and spleen‐liver contrast‐to‐noise ratios and qualitatively by evaluating the lesion conspicuity, liver parenchymal homogeneity, and sharpness of intrahepatic vessels. The imaging time was 26 seconds for breath‐hold TSE imaging, 49 to 219 seconds (mean, 149 seconds) for the respiratory triggered TSE imaging, and 79 to 379 seconds (mean, 239 seconds) for the nonrespiratory triggered TSE imaging. Quantitatively, the signal‐to‐noise ratio of the liver for breath‐hold imaging was comparable to that for respiratory triggered imaging. The lesion‐liver and liver‐spleen contrast‐to‐noise ratios for the respiratory triggered images were greater by 37% and 39%, respectively, than for the breath‐hold T2‐weighted TSE images. Qualitatively, the respiratory triggered images showed lower frequency of image artifact, better lesion conspicuity, and greatly superior depiction of intrahepatic structures compared with the breath‐hold T2‐weighted TSE images. The respiratory triggered T2‐weighted TSE technique provides better quality liver images than the breath‐hold TSE technique or nonrespiratory triggered technique within a reasonable acquisition time.
Dynamic evaluation of the hepatic uptake and clearance of manganese‐based MRI contrast agents: A 31P NMR study on the isolated and perfused rat liver
Authors: Colet Jean‐Marie , Elst Luce Vander , Muller Robert N.
Published: March 2007

This spectroscopic study compares the mechanisms of the hepatic uptake of manganese chloride (MnCl2) and manganese dipyridoxyl diphosphate (MnDPDP). Alterations of the phosphorus‐31 (31P)‐NMR spectrum of the intracellular adenosine 5′‐triphosphate (ATP) are used to monitor the internalization of manganese by the isolated and perfused rat liver. Mn2+ delivered as MnCl2 in the perfusate rapidly enters the hepatocytes, where it strongly interacts with ATP, inducing a broadening of the 31P lines. The inhibition of the process by nifedipine confirms that manganese ions cross the cellular membrane at least partly through Ca2+ channels. MnDPDP induces weaker but still significant changes of the ATP spectrum. The inability of pyridoxine to compete for the uptake of manganese confirms that the vitamin B6 carrier is not involved in the internalization process of the paramagnetic complex. Finally, preincubation of MnDPDP with blood does not increase the extent of the dissociation. The alterations of the 31P spectrum of the liver subsequent to the administration of MnDPDP are attributable to a fraction of free Mn2+ released by the chelate and delivered to the hepatocytes.
Sequential use of ferumoxide particles and gadolinium chelate for the evaluation of focal liver lesions on MRI
Authors: Semelka Richard C. , Lee Joseph K. T. , Worawattanakul Suvipapun , Noone Tara C. , Patt Richard H. , Ascher Susan M.
Published: March 2007

This study describes the sequential use of ferumoxide (superparamagnetic iron oxide) particles and nonspecific extracellular gadolinium chelate (Gd) for evaluation of focal liver lesions on MRI to evaluate order of contrast administration and imaging effect of the first contrast agent on sequences acquired after the second contrast agent. Thirteen patients underwent MR examinations that included ferumoxide and Gd. The order and timing of administration were as follows: separate sessions (three patients; Gd study 4‐19 days before ferumoxide study), same session, Gd first (seven patients; Gd study 1‐2 hours before ferumoxide study), and same session, ferumoxide first (three patients; ferumoxide administered less than 1 hour before Gd study). Postcontrast sequences were reviewed in a randomized, blinded fashion by two separate investigators. Determination was made regarding whether (a) the presence of the first agent administered could be detected on sequences obtained after the second agent and (b) the presence of the first agent interfered with the image quality of those sequences. No evidence for the presence of Gd was appreciated by either observer on postferumoxide sequences acquired in separate session studies. In same session, Gd first studies, the presence of Gd was observed in six of seven patients on T1‐weighted spoiled gradient‐echo (SGE) images obtained after ferumoxide administration. The presence of Gd was not apparent in seven of seven patients on T2‐weighted fat‐suppressed images obtained after ferumoxide. In same session, ferumoxide first studies, the presence of ferumoxide was appreciated on post‐Gd sequences in two of three patients. The presence of ferumoxide did not appreciably diminish image quality on those sequences. Exact agreement was achieved by the independent investigators. Our results suggest that Gd and ferumoxide can be administered sequentially within one study session without substantial loss of diagnostic information obtained on sequences performed after administration of the second contrast agent. Administrating Gd first resulted in less of an effect of the visualization of the first agent on sequences acquired after the second agent.
Uptake of mangafodipir trisodium in liver metastases from endocrine tumors
Authors: Wang Chen , Ahlström Håkan , Eriksson Barbro , Lönnemark Maria , McGill Steven , Hemmingsson Anders
Published: March 2007

The purpose of the study was to investigate retrospectively whether mangafodipir trisodium (MnDPDP) can enhance the liver metastases from endocrine tumors. Thirteen patients with endocrine tumors and liver metastases underwent T1‐weighted spin‐echo (SE) and turbo gradient‐echo (GRE) MRI conducted before and 20 to 60 minutes after iv infusion of MnDPDP. Additional 24‐hour‐delay scans were performed in 8 of 13 patients. MR signal intensity (SI) was measured in liver parenchyma and metastases, which was then related to that of paraspinal muscle. A total of 30 lesions on precontrast and postcontrast images and 18 lesions on 24‐hour‐delay images were measured. An enhancement by 49% in SE and 40% in GRE images (P = .0001) was observed in tumor tissues after MnDPDP infusion. In 24‐hour‐delay images, the SI of the lesions remained relatively high, but in liver parenchyma, it decreased significantly, and the tumor‐liver tissue contrast was reduced.
A three‐point dixon method for water and fat separation using 2D and 3D gradient‐echo techniques
Authors: Wang Yi , Li Debiao , Haacke E. Mark , Brown Jeffrey J.
Published: March 2007

A water and fat separation technique based on a three‐point Dixon method using two‐dimensional (2D) and three‐dimensional (3D) gradient‐echo sequences and a new phase‐unwrapping approach is presented. Using velocity‐compensated sequences, three images, with water and fat protons in phase, opposed phase, and in phase, were acquired in an interleaved fashion for each phase‐encoding line of the image. A fast 2D scan permitted acquisition of images within a single breathhold, eliminating respiratory motion artifacts. The 3D sequence allowed coverage of a large region of interest with thin, contiguous slices. To correct field inhomogeneity effects, phase unwrapping was required. This was accomplished by comparing the corresponding pixels in the two water and fat in‐phase images on a pixel‐by‐pixel basis. This phase‐unwrapping approach is faster, more reliable, and requires less user interfacing than other methods. The water and fat separation method performed well in various parts of the body.