bluuebunny/crossref_metadata_2025 huggingface dataset:
Perfusion‐weighted MRI using gadobutrol as a contrast agent in a rat stroke model
Authors: Heiland Sabine , Benner Thomas , Reith Wolfgang , Forsting Michael , Sartor Klaus
Published: March 2007

The purpose of this study was to examine the new nonionic contrast agent gadobutrol in MR perfusion‐weighted imaging, including the influence of different concentrations and dosages of the agent on the sensitivity to perfusion alterations. Sixteen rats were examined within 35 to 105 minutes after endovascular occlusion of the middle cerebral artery. A fast T2*‐weighted fast low‐angle shot (FLASH) sequence was used to acquire four images before and 16 images after bolus injection of .1, .2, .3, and .4 mmol/kg gadobutrol as .5 molar and 1.0 molar formulation. From user‐defined regions, we obtained the maximum signal decrease, the relative regional cerebral blood volume, and the bolus delay. Contrast between ischemic and nonischemic regions during bolus passage increased with dose and concentration of the contrast agent. For low doses (.1 and .2 mmol/kg), the ischemic lesion could not or could barely be discerned. For higher doses (.3 and .4 mmol/kg), administration of the 1 molar contrast agent yielded a better contrast between ischemic and nonischemic tissue. Our results suggest that administration of gadobutrol at higher dosage and higher concentration increases sensitivity to perfusion alterations. These results are potentially useful for perfusion‐weighted imaging of the human brain, because the volume of contrast agent will be reduced if a solution with higher concentration is used. When using contrast agents in higher concentrations for human examinations, a significant signal decrease may be achieved also with the low doses (.1–.15 mmol/kg).
First pass MRA of the Abdomen: Ultrafast, non‐breath‐hold time‐of‐flight imaging using Gd‐DTPA bolus
Authors: Atkinson Dennis J. , Vu Bach , Chen Dar‐Yeong , Duerinckx Andre , Bradley William G.
Published: March 2007

The authors describe a new fast imaging sequence that can produce projection angiograms of the abdominal vessels at a rate of 2 to 3 frames per second. The result is a versatile imaging technique that can track the arrival of a bolus of contrast in major vessels. With very fast data acquisition, gross patient motion is not a problem, and routine vascular projection studies may be performed without the need for breath‐holding. This method is compatible with later high‐resolution three‐dimensional gradient echo studies using contrast agents and may, in fact, be used as an accurate timing protocol to gauge the arrival time of contrast in various segments of the abdominal vessels. Compared with echo planar imaging, this method has the advantages of avoiding susceptibility artifacts and depicting retroperitoneum and other abdominal fat‐containing landmarks and does not require extensive hardware modifications for a clinical system.
Breath‐hold R2* mapping with a multiple gradient‐recalled echo sequence: Application to the evaluation of intrarenal oxygenation
Authors: Prasad Pottumarthi V. , Chen Qun , Goldfarb James W. , Epstein Franklin H. , Edelman Robert R.
Published: March 2007

Blood oxygenation level dependent (BOLD) MRI is sensitive to changes in regional oxygen supply versus demand and is therefore potentially useful in evaluating susceptibility to ischemic injury. Recently, we have demonstrated the use of BOLD MRI to evaluate intrarenal oxygenation using single shot echo‐planar imaging (EPI). Here, we present an alternate implementation of BOLD MRI sequence, using multiple gradient echoes, that does not require any specialized hardware.
Accessory equipment considerations with respect to MRI compatibility
Authors: Keeler Elaine K. , Casey Francis X. , Engels Hans , Lauder Elizabeth , Pirto Catherine Anne , Reisker Theodore , Rogers James , Schaefer Daniel J. , Tynes Thomas
Published: March 2007

The MR Section of The National Electrical Manufacturers Association (NEMA), in response to a request from the Food & Drug Administration (FDA), recently issued a position paper to address generic issues related to the compatibility of accessory equipment produced by third party equipment manufacturers or MR equipment users and intended to be used in conjunction with MR equipment or within the MR scanning room. The recommendations concern scanning accessories, such as radiofrequency (RF) coils, patient monitoring equipment and injectors, as well as patient comfort accessories and positioning devices. The following issues related to safety performance are discussed: (a) the interaction of the equipment with the MR scanner, (b) interactions of the MR scanner with the equipment, and (c) potential safety hazards for patients and staff that can be posed by accessory equipment in the MR scan environment. The recommendations are based on combined input from NEMA member companies who manufacture MR systems and MR accessories and are presented for consideration in the design of MR accessory products and incorporation of these concepts into testing plans to ensure MR compatibility of third party devices.
Malignant hepatic tumors: Changes on MRI after hepatic arterial chemoembolization – preliminary findings
Authors: Semelka Richard C. , Worawattanakul Suvipapun , Mauro Matthew A. , Bernard Stephen A. , Cance William G.
Published: March 2007

This study describes the MR appearances of malignant hypervascular liver lesions pre‐ and post‐hepatic‐arterial chemoembolization, with correlation to serial imaging and clinical responses. Eight patients with malignant hypervascular liver lesions underwent pretreatment and posttreatment MR examination on a 1.5‐T MR imager. MR sequences included T1‐weighted spoiled gradient echo (SGE), T2‐weighted fat‐suppressed spin echo or turbo spin echo, and dynamic gadolinium‐enhanced SGE images. All patients underwent pretreatment, initial posttreatment, and subsequent posttreatment MR studies. The histology of primary tumors included various types of hepatocellular carcinoma (HCC) (four patients: fibrolamellar HCC [one patient], HCC [two patients], mixed HCC/cholangiocarcinoma [one patient]) and liver metastases (four patients: untyped islet cell tumor [two patients], gastrinoma [one patient], carcinoid [one patient]). Response to chemoembolization was determined by three assessments: MR response, serial imaging response, and clinical response. The appearance of MR response to chemoembolization was determined based on the correlation with clinical and serial imaging response. The MR response of lesions that showed good clinical response included: increase in signal intensity on T1‐weighted images (three patients), decrease in signal intensity on T2‐weighted images (three patients), and negligible or minimal enhancement on immediate postgadolinium images (four patients) after chemoembolization. The most marked change in lesion appearance was observed in lesions < 1 cm, which had intense homogeneous enhancement on pretreatment MR studies and negligible enhancement on initial posttreatment MR examinations. MR response of lesions that showed moderate clinical response demonstrated a variety of lesion appearances from substantial change to minimal change. MR response of lesions that showed poor clinical response demonstrated no change in lesion appearances compared with the pretreatment MR study. Our results demonstrated change in appearance of liver lesions between pre‐ and post‐hepatic‐arterial chemoembolization MR studies. MR response correlated with response determined by serial imaging studies and clinical findings.
Calculated RF electric field and temperature distributions in RF thermal ablation: Comparison with gel experiments and liver imaging
Authors: Cheng Yu‐Chung N. , Brown Robert W. , Chung Yiu‐Cho , Duerk Jeffrey L. , Fujita Hiroyuki , Lewin Jonathan S. , Schuele Donald E. , Shvartsman Shmaryu
Published: March 2007

The present paper is a study of theoretic modeling and experimental tests of that modeling for the local heating due to radiofrequency thermal ablation. A model is developed for the current and the associated electric field produced by a radiofrequency ablation probe. The temperature distributions resulting from the induced ohmic currents in the surrounding material are considered. A comparison is made between the theoretic temperature profiles and the shapes of thermal ablation ‘lesions’ produced in a controlled gelatin sample experiment. Comparison with the contours of human thermally induced liver lesions found in MRI studies also provides a validation of the success of the modeling. Successful modeling should lead to methods for optimization of the ablation procedure, especially as it is used in interventional MRI.
Evaluation of 3D image registration as applied to MR‐guided thermal treatment of liver cancer
Authors: Wilson David L. , Carrillo Andres , Zheng Lan , Genc Ahmet , Duerk Jeffrey L. , Lewin Jonathan S.
Published: March 2007

There are many potential applications of three‐dimensional (3D) image registration in MR‐guided radiofrequency (RF) thermal ablation of tumors. For example, after registration of image volumes obtained before and after thermal ablation, a variety of quantitative and visual assessments of therapy were performed. For liver tumors, the accuracy of rigid body, manual registration on 19 pairs of image volumes was evaluated, almost all of which were obtained during thermal treatment sessions. Registration error was estimated as a distance between anatomical landmarks, including both internal vascular structures as well as the surface of the liver. Over all image pairs and throughout a large portion of the liver, the registration error was 3.1 mm (mean + 1 SD). From the bottom to the top of the liver, error increased on the order of 13%, probably because of liver motion and deformation resulting from respiration. Although probably insufficient for blind guidance of therapy, registration accuracy was undoubtedly sufficient for interesting applications in the planning, assessment, and optimization of interventional MR‐guided thermal treatment of liver tumors.
MRI evaluation of thermal ablation of tumors with focused ultrasound
Authors: McDannold Nathan , Hynynen Kullervo , Wolf Delia , Wolf Gerald , Jolesz Ferenc
Published: March 2007

MRI was used to target and evaluate the tissue effects of focused ultrasound ablation on tumors implanted in the skeletal muscle of rabbits in vivo. First, MRI was used to localize the tumors and plan the ultrasound therapy. Second, temperature‐sensitive phase‐difference images were acquired to monitor the location of the ultrasound focus and to estimate the effects of temperature rise. After the treatment, the spatial and temporal temperature profiles for defining boundaries of tissue coagulation were calculated. Finally, these boundaries were compared to T2‐weighted and contrast‐enhanced T1‐weighted images obtained immediately after therapy. The results indicate that using MRI for planning and evaluating focused ultrasound surgery is feasible. We showed a linear relationship between applied power and shifts in the proton resonant frequency. Fluctuations in the location of the focus about the target location were on the order of the resolution of the MR images. The temperature rise and lesion size varied significantly. Regions of tissue coagulation calculated from MR data correlated well with post‐therapy imaging.
Invited. On the feasibility of MRI‐guided focused ultrasound for local induction of gene expression
Authors: Madio David P. , van Gelderen Peter , DesPres Daryl , Olson Alan W. , de Zwart Jacco A. , Fawcett Timothy W. , Holbrook Nikki J. , Mandel Myrna , Moonen Chrit T. W.
Published: March 2007

Gene therapy is a promising approach to the treatment of many forms of disease, including cancer. Of critical concern in its implementation is the ability to control the location, duration, and level of expression of the therapeutic gene. Here, we propose the use of local heat in combination with a heat‐sensitive promoter to help accomplish this. Certain members of the family of heat shock protein (hsp) promoters display a regulation that depends strongly on temperature. We present a study of natural hsp70 induction in rat leg by MRI‐guided focused ultrasound to investigate the hsp70 promoter as a possible candidate for use in control of gene expression with local heat. A temperature increase of 5–8°C in the focal region for 45 minutes led to a differential expression of the hsp70 mRNA between the focal region and the surrounding tissue ranging from a factor of 3 to 67.
MR‐guided placement of a temporary vena cava filter: Technique and feasibility
Authors: Frahm Christian , Gehl Hans‐Björn , Lorch Heike , Zwaan Martin , Drobnitzky Matthias , Laub Gerhard A. , Weiss Hans‐Dieter
Published: March 2007

The purpose of this paper was to investigate the feasibility of MR‐guided insertion of a temporary vena cava filter on an open low‐field imager. In vivo procedures were performed on four anesthetized pigs using a common nonferromagnetic temporary vena cava filter and a special prototype guidewire developed for vascular interventions guided by low‐field MRI. Breath‐hold spoiled gradient‐echo sequences (fast low‐angle shot [FLASH]) with flow compensation were used for position monitoring of the passively visualized intravascular devices. Using the described technique and equipment, all steps of the procedure were feasible in the MR unit. Practicability of the procedure seems to be sufficient for clinical purposes but was inferior compared to the conventional technique of filter placement.
Invited. Temperature monitoring of interstitial thermal tissue coagulation using MR phase images
Authors: Stollberger Rudolf , Ascher Peter W. , Huber Dietrich , Renhart Werner , Radner Herbert , Ebner Franz
Published: March 2007

The temperature‐dependent water proton frequency shift was investigated for temperature monitoring of interstitial thermal coagulation. A procedure for online temperature calculation was developed, and errors due to temperature‐dependent susceptibility were investigated by finite element analysis and reference measurements. The temperature coefficient of magnetic susceptibility and proton chemical shift were determined for brain tissue and other substances. With the proposed procedure, the location of isotherms could be well visualized during laser‐induced interstitial coagulation in vitro and in vivo. Systematic errors caused by magnetic susceptibility changes with temperature depend strongly on the characteristics of the heat source and can exceed susceptibility effects caused by physiologic tissue changes. For the laser applicators discussed here, however, a first order compensation for this effect was found to be satisfactory, because it reduces the absolute error to the range of ± 1°C. The proposed method represents a very promising approach for monitoring of the interstitial thermal coagulation.
Active MR visualization of a vascular guidewire in vivo
Authors: Ladd Mark E. , Zimmermann Gesine G. , Quick Harald H. , Debatin Jörg F. , Boesiger Peter , von Schulthess Gustav K. , McKinnon Graeme C.
Published: March 2007

The purpose of this study was development of an actively visualized .035‐inch vascular guidewire for use in MR‐guided interventions. The guidewire was actively visualized by inclusion of a 6‐cm‐long radiofrequency coil in its tip. A high contrast outline of the distal tip of the guidewire was obtained by acquiring an image with the radiofrequency coil as the receiving antenna. The position of the guidewire relative to the surrounding anatomy was determined by overlaying the guidewire image on a previously acquired road map. The guidewire was evaluated in vivo in the abdominal vessels of a rabbit and swine at 1.5 T. The built‐in radiofrequency coil delivered a high contrast signal over its full length, enabling visualization of the position and curvature of the tip of the guidewire. The ability to see the curvature of the guidewire over several centimeters significantly eased manipulation into targeted vessels and represents an important advance toward MR‐guided vascular interventions.
Intraoperative, real‐time, functional MRI
Authors: Gering David T. , Weber David M.
Published: March 2007

Functional MRI (fMRI) methods have been demonstrated to noninvasively identify motor‐sensory, visual, and other areas of eloquent cortex for guiding surgical intervention. Typically, fMRI data are acquired preoperatively during a conventional surgical planning MRI examination. Unlike direct cortical stimulation at the time of surgery, however, preoperative fMRI methods do not account for the potential movement of tissues (relative to the time of functional imaging) that may occur in the surgical suite as a direct result of the intervention. Recently, an MRI device has been demonstrated for use in the surgical suite that has the potential to reduce the extent of cortical exposure required for the intervention. However, the invasive requirements of cortical mapping may supersede the invasive requirements of the surgical intervention itself. Consequently, we demonstrate here a modification to the intraoperative MRI device that facilitates a noninvasive, real‐time, functional MR examination in the surgical suite.
Shifted rotated keyhole imaging and active tip‐tracking for interventional procedure guidance
Authors: Wendt Michael , Busch Martin , Wetzler Rainer , Zhang Qiang , Melzer Andreas , Wacker Frank , Duerk Jeffrey L. , Lewin Jonathan S.
Published: March 2007

The tools and devices used for patient treatment during interventional procedures must be accurately and safely localized. Recently, procedure guidance has been performed increasingly with MRI, but tool localization has been performed primarily by analyzing the lack of signal caused by displaced excited tissue and/or susceptibility artifacts. In this investigation, a new technique was developed to actively detect and visualize interventional tools using receive coils mounted on the tip of the interventional devices. Unlike earlier methods, in which images from small devicemounted coils are superimposed on a previously acquired image data set, our localization method uses similar tip‐mounted tools in combination with a radiofrequency (RF) switching circuit, standard imaging coils, and specially modified sequences to toggle between the standard and tipmounted receive coil within a single fluoroscopic mode sequence. With this technique, the misregistration between the reported anatomic location and true location of interventional devices is minimized.
Rapid tip tracking with MRI by a limited projection reconstruction technique
Authors: Shimizu Kenji , Mulkern Robert V. , Oshio Koichi , Panych Lawrence P. , Yoo Seung‐Schik , Jolesz Ferenc A. , Kikinis Ron
Published: March 2007

To rapidly track invasive devices within MRI systems, a novel approach using a limited projection reconstruction technique is presented. Our method exploits the difference between images reconstructed from a limited number of projections and serves to depict the tip of a needle during its advancement. This method was implemented on a standard MRI system with a radial fast‐spin‐echo sequence and examined in phantom studies. We demonstrated that the proposed method could track the tip every 300 msec and the tip depicted by the present technique was consistently displaced along the needle by a small distance (5 mm).
Invited. MR findings of Minamata disease — Organic mercury poisoning
Authors: Korogi Yukunori , Takahashi Mutsumasa , Okajima Toru , Eto Komyo
Published: March 2007

We describe MR findings in patients with Minamata disease who have been followed for a long time. All patients examined were affected after daily eating of a large quantity of methylmercury‐contaminated seafood, from 1955 to 1958, and showed typical neurological findings. On MR images, the visual cortex, the cerebellar vermis and hemispheres, and the postcentral cortex are significantly atrophic in Minamata disease. The visual cortex is slightly hypointense on T1‐weighted images and hyperintense on T2‐weighted images, probably representing the pathologic changes of status spongiosus. MRI can demonstrate the lesions located in the calcarine area, cerebellum, and postcentral gyri, which are probably related to three of the characteristic manifestations of this disease: the constriction of the visual fields, ataxia, and sensory disturbance, respectively.
Invited. Hepatitis, cirrhosis, and hepatoma
Authors: Murakami Takamichi , Kim Tonsok , Nakamura Hironobu
Published: March 2007

Virus hepatitis and liver cirrhosis are found at high incidence in Asia, and they require not only biochemical examination of blood but also subsequent imaging, because they are often complicated by hepatocellular carcinoma (HCC). It is, therefore, very important to know the specific appearances of hepatitis, liver cirrhosis, and HCC when we diagnose these diffuse liver diseases. Liver necrosis due to severe hepatitis is seen as high intensity on T2‐weighted spin echo images. Regeneration is seen as low intensity on T2‐weighted images. Morphologic and pathologic changes of cirrhotic liver are well demonstrated by MR imaging techniques. Fibrotic septum with inflammatory cell infiltration or rich pseudo bile duct show high intensity on T2‐weighted images, and regenerating nodules shows low intensity. Gradient echo images show regenerating nodules with iron deposition as low‐intensity nodules due to susceptibility artifact. MRI also has the potential to evaluate function of diffuse liver disease, cirrhosis, and hepatitis. MRI can visualize and diagnose HCC objectively. Dynamic MRI is very useful for diagnosing HCC. It is also applied for evaluation of effect after transcatheter arterial chemoembolization, because it shows enhancement only in the viable region at an arterial phase. MRI is less invasive and is thus an extremely important form of liver imaging.
Invited. Ultrafast MR imaging of the abdomen: Echo planar imaging and diffusion‐weighted imaging
Authors: Yamashita Yasuyuki , Tang Yi , Takahashi Mutsumasa
Published: March 2007

Ultrafast MRI technique has become available with the introduction of new generation MR scanners for abdominal imaging. However, there is no consensus about the optimal imaging acquisition at the present time. Because single shot echo planar imaging (EPI) technique is based on high technology and had just applied in clinical imaging, further clinical investigation will be needed. Currently, the hypersensitivity to magnetic inhomogeneity and local magnetic susceptibility and the low spatial resolution may limit the widespread application of EPI technique. In addition to providing information for morphologic diagnosis, EPI will be more widely used for functional and qualitative diagnosis. Diffusion‐weighted imaging can be used for differentiation of solid tumors according to their different cellular construction, evaluation of cystic lesions based on the different viscosity of their contents, and assessment of diffused pathologic changes in the parenchyma of solid organs. In addition to the previous parameters such as proton density and T1 and T2 values, diffusion factors may provide important information for the qualitative and dynamic evaluation of abdominal pathologic changes. Even though there are many difficulties that must be solved for diffusion‐weighted imaging, a more wide application of this technique is expected through technologic improvement.
Invited. Application of MRI for Small Intestinal Diseases
Authors: Ha Hyun Kwon , Lee Eun Hye , Lim Cheong Hwan , Shin Yong Moon , Jeong Yoong Ki , Yoon Kwon Ha , Lee Moon‐Gyu , Min Young Ii , Auh Yong Ho
Published: March 2007

Until recently, MRI has not been considered to be suitable for the evaluation of the small intestine due to artifacts associated with bowel peristalsis or respiration. However, recent advances of MR techniques enable the acquisition of clear images of the small intestine. Therefore, the purpose of this article is to review the details for the application of MRI in patients with small intestinal diseases. This article discusses bowel preparation and oral contrast agents as well as MR techniques and pulse sequences. Thereafter, the usefulness of MRI for the lesions in the peritoneal cavity or in the gastrointestinal tract are discussed. Small intestinal lesions are categorized into inflammatory, neoplastic, ischemic, and obstructive bowel diseases. In conclusion, MRI can be used as an alternate modality of choice for imaging various diseases of the small intestine.
Invited. Ultrafast T2‐weighted imaging of the abdomen and pelvis: Use of single shot fast spin‐echo imaging
Authors: Tang Yi , Yamashita Yasuyuki , Takahashi Mutsumasa
Published: March 2007

Single shot (SS) rapid acquisition with relaxation enhancement (RARE) and half Fourier SS‐RARE (HFSS‐RARE, HASTE, or SS‐FSE) sequences allow ultrafast imaging acquisition and generate high imaging quality. Images can be acquired within a very short time, without artifacts from physiologic motion. They are widely applied in the abdominal MRI. Clinical application of the ultrafast SS‐RARE imaging techniques provide not only improved temporal resolution but better spatial resolution, higher SNR, and higher tissue contrast. Imaging parameters must be optimized for different MR scanners to obtain diagnostic images.
Invited. Cervical cancer
Authors: Togashi Kaori , Morikawa Kenji , Kataoka Milliam Lika , Konishi Junji
Published: March 2007

The stage estimated by clinical FIGO staging is the main determinant in guiding the treatment decisions. However, clinical FIGO staging does have inherent inaccuracies, because it does not include significant prognostic factors. Presently, MRI is not officially incorporated in the staging workup system; however, it is widely accepted as the most reliable imaging modality in evaluating cervical cancer and in treatment planning. MRI offers direct tumor visualization, accurate assessment of the depth of stromal invasion and tumor volume, lymph node evaluation, and reliable staging accuracy. Published reports show the superiority of MRI over clinical staging, and several recent works on dynamic MRI suggest further improvement of MRI in evaluating cervical cancer.
Invited. Takayasu arteritis: MR manifestations and diagnosis of acute and chronic phase
Authors: Matsunaga Naofumi , Hayashi Kuniaki , Sakamoto Ichiro , Matsuoka Yojiro , Ogawa Yoji , Honjo Kazumitsu , Takano Katsuyuki
Published: March 2007

Diagnosis of Takayasu arteritis is difficult because the clinical features are similar to those of other diseases. In the late occlusive or pulseless phase Takayasu arteritis, angiography usually demonstrates luminal changes such as such as stenosis, occlusion, or aneurysmal dilatation of the aorta and pulmonary artery and of their branches. However, absence of such luminal changes does not exclude the possibility of early or systemic phase Takayasu arteritis. Cross‐sectional scanning such as CT scan and MRI plays an important role in demonstrating arterial wall changes in the early diagnosis of Takayasu arteritis. Improvement in the clinical findings and subsidence of the active inflammatory process can be expected with early steroid treatment. The common and uncommon MR appearances of the late occlusive phase and the recently described radiographic features of the early systemic phase are illustrated.
Invited. Application of MR in stereotactic radiosurgery
Authors: Guo Wan‐Yuo
Published: March 2007

Radiosurgery, a bladeless brain surgery without opening skull, requires higher imaging accuracy as compared to microsurgery. Accordingly, we must refine the ways we use the MR scanner and interpret the obtained images. A well tuned and regularly calibrated MR scanner provides excellent images, which allow us to define detailed intracranial structures without distortion. This enables us to obtain a reliable imaging diagnosis despite the fact that pathologic diagnosis is not available in many radiosurgical patients. Due to its three‐dimensional imaging and excellence in tissue and spatial contrast, MR is important in exploring new radiosurgical indications. Large arteriovenous malformations (AVM), dural AVM of cavernous sinus and trigeminal neuralgia are some of the successful examples. By using MR, longitudinal investigation of radiosurgical effects becomes feasible. For tumors, the longitudinal studies are important in optimization of dose selection. For AVM, MR is reliable in verification of radiosurgical result. The reliability is comparable to conventional x‐ray angiography. Application of MR enhances the essence of noninvasiveness of radiosurgery.
Characterization of focal liver lesions with half‐Fourier acquisition single‐shot turbo‐spin‐echo (HASTE) and inversion recovery (IR)‐HASTE sequences
Authors: Tang Yi , Yamashita Yasuyuki , Namimoto Tomohiro , Takahashi Mutsumasa
Published: March 2007

The half‐Fourier acquisition single‐shot turbo‐spinecho (HASTE) sequence allows for heavily T2‐weighted images, and the inversion recovery (IR)‐HASTE sequence represents the T1 value of the tissue in a very short time. This study was undertaken to determine whether characterizing focal liver lesions can be made by combination with these very fast sequences. Seventy‐four patients (33 cysts, 28 hemangiomas, and 33 malignant solid liver masses [15 metastatic tumors, 14 hepatocellular carcinomas, and 4 cholangiocarcinomasl]) underwent dynamic CT and breath‐hold abdominal MRI using turbo‐spin‐echo (TSE), HASTE, and IR‐HASTE sequences with variable TI values on a 1.5‐T MR unit. The imaging time for each slice was 2 seconds for HASTE imaging and 2 to 4 seconds for IR‐HASTE imaging. Lesion detection and qualitative characterization were evaluated. Quantitative analysis was performed by measuring the contrast‐to‐noise ratios (CNRs) as well as visual analysis. The inversion time (TI) nulling values were also statistically analyzed. All cystic lesions were detected on both TSE and HASTE imagings. For solid lesions, TSE failed to detect one small solid lesion and HASTE sequence failed to detect three lesions. With HASTE sequences, all cysts and hemangiomas were markedly hyperintense in comparison with malignant solid masses. CNRs of hemangiomas or cysts were significantly higher than those of malignant solid masses (P < .01), and there was no overlap. The TI nulling value was 1,100 ± 100 msec for hemangiomas, 1,900 ± 110 msec for cysts, and 740 ± 140 msec for malignant solid masses. There was no overlap between the TI nulling values of hemangiomas and cysts (P < .01). By combining the CNR from the HASTE sequence and the TI nulling value from the IR‐HASTE sequence, complete discrimination among malignant solid masses, hemangiomas, and cysts of the liver could be made. Application of HASTE (representing T2 values) and IR‐HASTE (representing T1 values) sequences provided a rapid and reliable imaging method for characterizing focal liver lesions without the use of contrast medium.
Enhancement of phase‐contrast MR angiography with superparamagnetic iron oxide
Authors: Tanimoto Akihiro , Yuasa Yuji , Hiramatsu Kyoichi
Published: March 2007

The effect of superparamagnetic iron oxide particles (AMI‐227) was assessed in three‐dimensional (3D) phase‐contrast (PC) MR angiography (MRA), with various scanning parameters for rats at 1.5 T. The blood T1 and T2 before and after 20 μmol Fe/kg of AMI‐227 injection were measured sequentially at .47 T. The visualization of abdominal aorta, renal artery, inferior vena cava, and portal vein was respectively evaluated before and after AMI‐227 injection qualitatively by the four confidence levels and quantitatively by analysis of signal‐to‐noise ratio (SNR) of vessels. The blood T1 and T2 were sufficiently shortened for at least 1 hour after AMI‐227 injection. The visualization of each vessel was improved by AMI‐227 at various velocity encoding (VENC) value, suggesting the extended application of PC‐MRA in various conditions. The optimal flip angle was increased from 20° to 30° in higher VENC after AMI‐227 injection, resulting in higher signal from blood flow. Quantitative analyses showed that the optimal flip angle to achieve the maximum SNR seemed to be 20° in unenhanced images, but the optimal flip angle of the high speed flow was increased by contrast enhancement. The postcontrast PC‐MRA provides the increased sensitivity of slow flow components, even with a high VENC gradient. AMI‐227 can significantly improve SNR to blood vessels during 3D‐PC‐MRA with various scanning parameters.
Improvement of MR cholangiopancreatography at .5 T: Three‐dimensional half‐averaged single‐shot fast spin echo with multi‐breath‐hold technique
Authors: Ichikawa Tomoaki , Haradome Hiroki , Hanaoka Hideto , Kassai Yosimori , Nitatori Toshiaki , Hachiya Junichi , Araki Tsutomu
Published: March 2007

The purpose of this study was to determine the advantage of a three‐dimensional (3D) single‐shot fast‐spin‐echo (SSFSE) sequence to obtain MR cholangiopancreatography (MRCP) with a .5‐T MR unit by comparison with a two‐dimensional (2D) SSFSE sequence. MRCP with 2D‐SSFSE and with 3D‐SSFSE with 128 echo train lengths was performed on 15 volunteers and 38 patients with pancreatobiliary disease using a .5‐T MR unit. For maximum intensity projection (MIP) reconstruction, the section thickness of source images was 4 mm in the 2D‐SSFSE and 3 mm in the 3D‐SSFSE. 3D volume data in 3D‐SSFSE were obtained using repeated short breath‐hold of 2 seconds for every repetition time throughout the examination. The image quality, duct conspicuity, signal‐intensity ratio (SIR), and contrast‐to‐noise ratio (CNR) were evaluated. In 23 of the patients who underwent both MRCP and direct cholangiopancreatography (endoscopic retrograde cholangiopancreatography [ERCP]/percutaneous transhepatic cholangiography [PTC]), a comparison between these two modalities was also conducted. The image quality of the MIP image with 3D‐SSFSE (49 of 53, 92.5% graded excellent or good) was superior to that with 2D‐SSFSE (31 of 53, 58.4%). Duct conspicuity, SIR, and CNR were significantly higher with 3D‐SSFSE than with 2D‐SSFSE. 3D‐SSFSE also showed a stronger relationship with the ERCP/PTC findings compared to 2D‐SSFSE. 3D‐SSFSE provided satisfactory quality, SIR, and CNR of MRCP images, even when a .5‐T MR unit was used, because the breath‐hold technique used during 3D data sampling minimized all types of motion effects.
Measurement of magnetization transfer in different stages of neurocysticercosis
Authors: Kathuria Manoj K. , Gupta Rakesh K. , Roy R. , Gaur Vandana , Husain N. , Pradhan Sunil
Published: March 2007

The purpose of this study was to establish magnetization transfer ratio (MTR) in different stages of neurocysticercosis. A total 2,532 cysticerci were studied prospectively in 15 cases. MTR from different regions of the lesions (ie, the cyst, the protoscolex or mural nodule, the granuloma wall) were calculated in different stages of evolution/degeneration in all cases. Of a total 2,532 lesions studied, 2,261 (89.29%) were seen on routine spin‐echo (SE) imaging. The rest of the lesions were only seen on magnetization transfer (MT) SE imaging. Maximum MTR was calculated from healing lesions (mean + SD = 31.0 ± 2.8) and from the core of SE invisible lesions (30.0 ± 5.1). Innocuous cystic lesions, which were hyperintense on T2‐weighted images, did not show any MT (MTR = 5.10 ± 1.2), whereas degenerating T2 hyperintense lesions showed MTR of 26.40 ± 2.7. Nondegenerating and degenerating scolices showed an intermediate MTR of 21.7 ± 3.3 and 15.0 ± 4.5, respectively. MT varies between different parts of the lesion and also from the same part in different stages of evolution/degeneration of the lesion. The visibility of a lesion on MT‐SE sequence was dependent on its MTR and its location at a particular site (cortical gray matter, white matter, or deep gray matter). The difference in MTR of the lesion and the surrounding brain parenchyma decides the resulting contrast and visibility of the lesion.
A reproducible method for automated extraction of brain volumes from 3D human head mr images
Authors: Wang Deming , Galloway Graham J. , de Zubicaray Greig I. , Rose Stephen E. , Chalk Jonathan B. , Doddrell David M. , Semple James
Published: March 2007

An automated method for extracting brain volumes from three commonly acquired three‐dimensional (3D) MR images (proton density, T1 weighted, and T2‐weighted) of the human head is described. The procedure is divided into four levels: preprocessing, segmentation, scalp removal, and postprocessing. A user‐provided reference point is the sole operator‐dependent input required. The method's parameters were first optimized and then fixed and applied to 30 repeat data sets from 15 normal older adult subjects to investigate its reproducibility. Percent differences between total brain volumes (TBVs) for the subjects' repeated data sets ranged from .5% to 2.2%. We conclude that the method is both robust and reproducible and has the potential for wide application.
Throwing injury of the elbow: Assessment with gradient three‐dimensional, Fourier transform gradient‐echo and short tau inversion recovery images
Authors: Sugimoto Hideharu , Hyodoh Kazusa , Shinozaki Takeshi
Published: March 2007

We assessed MR findings of throwing injuries occurring in the elbow joint using three‐dimensional Fourier transform (3DFT) and short tau inversion recovery (STIR) images. MR images of 63 elbows in 63 male patients aged from 10 to 32 years (mean age, 15 years 11 months) suffering from throwing injury were visually analyzed. The sequences used for the study were axial 3DFT and coronal STIR. Full‐thickness tears were demonstrated in 34 elbows and undersurface tears of the ulnar collateral ligament (UCL) were demonstrated in five elbows. Thirty loose bodies were detected in 14 elbows. Cartilaginous damage due to osteochondral injury was depicted in 21 elbows. Multiplanar reformatted images using the 3DFT data set were useful for assessing torn UCLs, intraarticular loose bodies, and capitellar fragments. Full‐thickness tears and undersurface tears of the UCL could be differentiated with STIR images. 3DFT and STIR sequences depict various aspects of throwing injuries occurring in the elbow.
Can MRCP replace ERCP?
Authors: Takehara Yasuo
Published: March 2007

Magnetic resonance cholangiopancreatography (MRCP) has replaced direct cholangiography and pancreatography in many instances. Its complete noninvasiveness and flexibility are less onerous for patients. For the use of screening as well as scrutiny, MRCP has played an important role in diagnosing various pathologies in this field. The usefulness of MRCP is not limited to anatomical evaluations; it can also yield physiologic and functional information. From a cost‐performance basis, MRCP is undoubtedly superior to direct methods. Coupled with a cutting‐edge MR system, MRCP has the potential to limit the use of invasive transpapillary and percutaneous methods merely to interventional purposes. In the near future, the emergence of interventional MR scanners will make MRCP even more competitive, and the replacement will be accelerated.
Quantitative MRI of the brain in children with sickle cell disease reveals abnormalities unseen by conventional MRI
Authors: Steen R. Grant , Reddick Wilburn E. , Mulhern Raymond K. , Langston James W. , Ogg Robert J. , Bieberich Andrea A. , Kingsley Peter B. , Wang Winfred C.
Published: March 2007

Conventional MRI (cMRI) has shown that brain abnormalities without clinical stroke can manifest in patients with sickle cell disease (SCD). We used quantitative MRI (qMRI) and psychometric testing to determine whether brain abnormalities can also be present in patients with SCD who appear normal on cMRI. Patients 4 years of age and older with no clinical evidence of stroke were stratified by cMRI as normal (n= 17) or abnormal (n= 13). Spin‐lattice relaxation time (T1) of gray and white matter structures was measured by the precise and accurate inversion recovery (PAIR) qMRI method. Patient cognitive ability was assessed with a standard psychometric instrument (WISC‐III or WISC‐R). In all 30 patients with SCD, qMRI T1 was lower than in 24 age‐ and race‐matched controls, in cortical gray matter (P< .0006) and caudate (P< .0009), as well as in the ratio of gray‐to‐white matter T1 (P< .008). In the 17 patients who were shown to be normal by cMRI, qMRI T1 was still lower than in controls, in both cortical gray matter (P< .02) and caudate (P< .004). Histograms of voxel T1 show that the proportion of voxels with T1 values intermediate between gray and white matter (ie, consistent with encephalomalacia) was 9% higher than controls in patients shown to be normal by cMRI (P< .05) and 15% higher than controls in patients shown to be abnormal by cMRI (P< .0005). The full scale intelligence quotient (FSIQ) of all patients with SCD was 75, compared to the FSIQ of 88 in a historical control group of patient siblings (P< .001). The FSIQ of patients shown to be normal by cMRI was 79, significantly lower than the FSIQ of patient siblings (P< .04). The FSIQ of 71 in patients shown to be abnormal by cMRI was significantly lower than both the patient siblings (P< .005) and the patients shown to be normal by cMRI (P< .04). Patients shown to be abnormal by cMRI scored lower than patients shown to be normal by cMRI, specifically on the subtests of vocabulary (P= .003) and information (P= .03). Cognitive impairment is thus significant, even in patients with SCD who were shown to be normal by cMRI, suggesting that cMRI may be insensitive to subtle neurologic damage that can be detected by qMRI. Because cognitive impairment can occur in children normal by cMRI, our findings imply that prophylactic therapy may be needed earlier in the course of SCD to mitigate neurologic damage.
Quantification of in‐plane motion of the coronary arteries during the cardiac cycle: Implications for acquisition window duration for MR flow quantification
Authors: Hofman Mark B. M. , Wickline Samuel A. , Lorenz Christine H.
Published: March 2007

Motion of the coronary arteries during the heart cycle can result in image blurring and inaccurate flow quantification by MR. This condition applies particularly for longer acquisition windows that are typical of breath‐hold coronary flow measurements. To determine the sensitivity of the technique to in‐plane motion of different coronary arteries, the temporal variation in coronary position was measured in a plane perpendicular to the proximal portion of the vessel. The results indicated the presence of substantial displacement of the coronary arteries within the cardiac cycle, with a magnitude of motion approximately twice as large for the right as for the left coronary arteries. An estimation of the resulting vessel blurring was calculated, showing that the duration of the acquisition window for high spatial resolution coronary flow acquisitions should be less than 25 to 120 msec, depending on the specific coronary artery studied. In addition, these data specify optimal acquisition window placement for high resolution coronary angiography.
Value of image subtraction in 3D gadolinium‐enhanced MR angiography of the renal arteries
Authors: Leung Daniel A. , Pelkonen Pia , Hany Thomas F. , Zimmermann Gesine , Pfammatter Thomas , Debatin Jörg F.
Published: March 2007

The objective of this study was to evaluate quantitatively and qualitatively the effect of image subtraction on the image quality of three‐dimensional (3D) gadolinium‐enhanced MR angiograms of the renal arteries. Breath‐hold 3D gadolinium MR angiography (MRA) as well as conventional contrast angiography of the renal arteries was performed on 20 patients with suspected renovascular hypertension. MR angiograms were acquired before and during dynamic infusion of gadolinium‐diethylenetriamine pentaacetic acid (Gd‐DTPA). Contrast‐enhanced images were compared with images that had undergone voxel‐by‐voxel signal intensity subtraction of contrast‐enhanced data from precontrast data. One false positive finding for significant renal artery stenosis was recorded with MRA using conventional angiography as the gold standard. Image subtraction did not alter the diagnosis at MRA in any case. The mean contrast‐to‐noise ratio (CNR) was significantly higher (P < .05) on the subtraction MR angiograms compared to the nonsubtracted MR angiograms. There was no significant difference in the signal‐to‐noise ratio (SNR). Qualitative analysis revealed a significant improvement in image quality after image subtraction with respect to visualization of the distal renal arteries. In conclusion, image subtraction improves the quality of renal MRA in terms of both CNR and visualization of the distal renal arteries.
Contrast‐enhanced 3D‐TOF MRA of peripheral vessels: Intravascular versus extracellular MR contrast media
Authors: Engelbrecht Marc R. , Saeed Maythem , Wendland Michael F. , Canet Emmanuelle , Øksendal Audun N. , Higgins Charles B.
Published: March 2007

MR contrast media have been used to improve MR angiography (MRA). Their effect has been particularly beneficial for extracranial MRA. This study evaluated the efficacy of a new formulation of ultrasmall super‐paramagnetic iron oxide particles (USPIO) on three‐dimensional (3D) time of flight (TOF) MRA in the pelvis and lower limb circulation. Each of six dogs received 3 mg/kg of USPIO and .2 mmol/kg of gadolinium‐dieth‐ylenetriamine pentaacetic acid (Gd‐DTPA) bis‐meth‐ylamide (BMA) by intravenous infusion on separate examinations. Precontrast and postcontrast 3D‐TOF MRA images of the lower extremities were acquired over the course of 45 minutes postinjection. Signal intensity (SI) was measured on axial views along the external iliac, femoral, and popliteal arteries. USPIO provided clear demarcation of the major primary, secondary, and tertiary vessels and the improved contrast‐to‐noise ratio (CNR) was maintained for 45 minutes. Gd‐DTPA‐BMA provided less signal enhancement than USPIO. The increase in CNR with this agent had significantly declined by 15 minutes after injection. The major vessels could no longer be visualized at 30 and 45 minutes after injection of Gd‐DTPA‐BMA. This study demonstrates the efficacy of USPIO as a contrast medium for 3D‐TOF MRA. It was concluded that USPIO provided effective and persistent enhancement of the peripheral vessels.
Three‐dimensional low dose gadolinium‐enhanced peripheral MR venography
Authors: Li Wei , David Vivek , Kaplan Richard , Edelman Robert R.
Published: March 2007

Our initial experience with low dose contrast‐enhanced (LCE) peripheral MR venography (MRV) is presented. Five subjects were studied using three‐dimensional (3D) fast imaging with a steady‐state precession (FISP) sequence. A dose of 60 ml of gadopentetate dimeglumine diluted 1:20 was used. A tourniquet was applied during lower extremity MR venography. The venous anatomy was well depicted with the 3D LCE technique in all subjects. Compared to the two‐dimensional (2D) time‐of‐flight (TOF) technique, acquisition time of 3D LCE MRV was much shorter, images looked sharper, and more veins could be seen. It is not affected by in‐plane saturation and can be performed repeatedly because of the low dose of contrast. This technique holds promise for the detection of venous thrombosis and other disorders.
Determination of sample time for T1 measurement
Authors: Zhang Yantian , Yeung Hong N. , O'Donnell Matthew , Carson Paul L.
Published: March 2007

In spin‐lattice relaxation time measurements, the relaxation time T1 is estimated from measuring the longitudinal magnetization during its return to thermal equilibrium from an initial (nonequilibrium) state. T1 estimation error depends on a number of factors, including the sample spacing, number of sample points, target T1 range, etc. We describe here a sample‐time determination method based on the principles of optimal experimental design. A two‐parameter model and a more general three‐parameter model of the general T1 measurement experiment are used in this study. Both linear and power‐law sample spacing strategies are evaluated. The proposed method formulates the sample‐time determination problem in closed form expressions that allow for easy calculation of optimum sample times, if a prior T1 estimate or a probable T1 distribution over the target range is given. Valuable insights can be gained from evaluation of these expressions concerning the relationship of T1 estimation error and the sample spacing, number of sample points, target T1 range, etc.