bluuebunny/crossref_metadata_2025 huggingface dataset:
Imaging of nodal metastases in the head and neck
Authors: Anzai Yoshimi , Brunberg James A. , Lufkin Robert B.
Published: March 2007

Therapeutic outcome of head and neck cancer is influenced strongly by the presence of nodal metastases. Sensitivity and specificity of the physical examination for the diagnosis of nodal metastasis is unsatisfactory, resulting in both false negatives and false positives of 25 to 40%. Preoperative detection of nodal metastases therefore becomes one of the important goals of imaging studies of patients with head and neck cancer. Despite several advanced techniques and the wide clinical use of MR, MR has surprisingly added little to the diagnostic accuracy of contrast‐enhanced CT. Although CT and MR allow detection of abnormally enlarged nodes or necrotic nodes, neither borderline‐sized nodes without necrosis nor extracapsular spread are reliably differentiated from reactive or normal nodes in patients with head and neck cancer. Lack of definitive diagnostic methods of metastatic lymph nodes is a serious shortcoming in the preoperative workup for patients with head and neck cancer. To avoid missing small metastatic nodes, a large number of patients clinically staged as NO have undergone elective neck dissection to exclude metastases. With development of more tissue‐specific imaging techniques, patients can be better characterized according to the status of nodal disease so that an appropriate therapeutic protocol can be designed for an individual case.
Blood flow patterns in the thoracic aorta studied with three‐directional MR velocity mapping: The effects of age and coronary artery disease
Authors: Bogren Hugo G. , Mohiaddin Raad H. , Kilner Philip J. , Jimenez‐Borreguero Luis J. , Yang Guang Z. , Firmin David N.
Published: March 2007

The objective was to investigate how the blood flows in the thoracic aorta, with special emphasis on flow reversal and flow into the coronary arteries. Three‐directional MR velocity mapping was used to map multidirectional flow velocities in the aorta in 14 normal subjects and 14 patients with coronary artery disease. Dynamic flow vector maps and through‐plane velocity maps were used. The flow reversed in all subjects in the upper ascending aorta and usually also in the distal aortic arch. Retrograde flow became antegrade again at various levels in the ascending aorta and in the coronary sinuses. Seven flow characteristics were investigated that, lumped together, were significantly different (P = .0005) in normal subjects compared with patients and in normal subjects 70 years of age and older compared with those younger than 70 years of age.
Comparison of inversion recovery asymmetrical spin‐echo EPI and gradient‐echo EPI for brain motor activation study
Authors: Zheng Jie , Ehrhardt James C. , Cizadlo Ted , Yuh William T. C.
Published: March 2007

An inversion recovery asymmetric spin‐echo (IR‐ASE) echo‐planar imaging (EPI) sequence has been developed for functional studies of the brain. This technique uses an 180° inversion pulse with a long inversion time (TI) to suppress the pulsatile cerebrospinal fluid and an asymmetric spin‐echo readout to obtain activation signals from brain capillaries. Because gradient‐echo sequences are most sensitive to large vessels, motor cortex activation studies using a gradient‐echo technique also were conducted for comparison with the IR‐ASE method. The results suggest that the IR‐ASE pulse sequence may be a useful complement to the gradient‐echo technique for the study of neuronal activity of the human brain.
The pharmacokinetics of hyperpolarized xenon: Implications for cerebral MRI
Authors: Martin Charles C. , Williams Robert F. , Gao Jia‐Hong , Nickerson Lisa D. H. , Xiong Jinhu , Fox Peter T.
Published: March 2007

In this work, a compartmental model to predict the concentration of hyperpolarized xenon (Xe) in the brain is developed based on the well established kinetics of Xe and estimated T1 values for the compartments. For the gaseous compartments, T1 was set to 12 seconds. For the tissue compartments, T1 was set to 6 seconds. Three gas delivery techniques were modeled: hyperventilation followed by breath‐hold, continual breathing, and hyperventilation followed by continual breathing. Based on Xe CT, it is estimated that the maximum concentration of Xe that could be breathed is 80%. Based on this value and the estimated maximum polarization of 50%, the peak gray matter concentration of hyperpolarized Xe is calculated to be .036 mM. This leads to an estimated signal‐to‐noise ratio (SNR), at 2 T, for hyperpolarized Xe that is a factor of 50 lower than the SNR for proton MRI. The peak concentration of hyperpolarized Xe was also calculated over a wide range of gas and tissue T1 values. This model also predicts that the arterial blood will have a concentration of hyperpolarized Xe that is 10 times greater than the concentration in gray matter. An interactive version of the model can be found on the World Wide Web at http://ric.uthscsa.edu/staff/charlesmartinphd.html.
T1ρ dispersion imaging of head and neck tumors: A comparison to spin lock and magnetization transfer techniques
Authors: Markkola Antti T. , Aronen Hannu J. , Paavonen Timo , Hopsu Erkki , Sipilä Leena M. , Tanttu Jukka I. , Sepponen Raimo E.
Published: March 2007

The potential of T1ρ dispersion, spin lock (SL), and magnetization transfer (MT) techniques to differentiate benign and malignant head and neck tumors was evaluated. Twenty‐four patients with pathologically verified head and neck tumors were studied with a .1‐T MR imager. T1ρ dispersion effect was defined as 1 — (intensity with lower locking field amplitude/intensity with higher locking field amplitude). T1ρ dispersion effects were higher for malignant than benign tumors (P = .001). With T1ρ dispersion effect .14 as the threshold, sensitivity for detecting a malignant tumor was 91%, specificity was 77%, and accuracy was 83%. A strong correlation between T1ρ dispersion effects and SL effects and between T1ρ dispersion effects and MT effects in the head and neck tumors was found (r = .87, P < .001 and r = .90, P < .001, respectively). High T1ρ dispersion effects are not specific indicators of malignancy, because chronic infections, some benign tumors, and malignancies may overlap. Low T1ρ dispersion effect values are characteristic of a benign tumor.
MRI analysis of lumbar intervertebral disc height in young and older populations
Authors: Roberts Neil , Gratin Christophe , Whitehouse Graham H.
Published: March 2007

Measurements of length and section area on MR images are made conventionally by the manipulation of a tracker ball to move a cursor to define end points or delineate boundaries. This operator‐dependent method lacks the objectivity that computer‐based image analysis techniques, such as edge‐detection algorithms, can give. We describe an image analysis routine, based on earlier work by Vincent and Soille using algorithms of mathematical morphology, for automatically extracting the boundary of lumbar intervertebral discs on MR images. This is applied to the automatic measurement of the maximum disc space height and section area of non‐degenerate intervertebral discs on MR images obtained for healthy male subjects of two distinct age ranges, ie, twenty 20‐ to 30‐year‐olds and twenty 50‐ to 60‐year‐olds. Throughout the levels L1 to L4, intervertebral disc height is found to be significantly greater (P = .0003 to .0161) in the older than in the younger age group. The data support a model of the spine in which the disc adopts a more concave form as a result of microfracturing of the end plates during adult life.
Gradient‐echo perfusion imaging of musculoskeletal abnormalities with contrast‐enhanced two‐dimensional fat‐saturation FLASH
Authors: Konez Orhan , Bis Kostaki G. , Shirkhoda Ali , Shetty Anil N. , Gürgün Mehmet , Wilcox Richard , Irwin Ronald
Published: March 2007

The objective of this study was to evaluate the utility of MR perfusion imaging of various musculoskeletal lesions with a contrast‐enhanced two‐dimensional fat saturation fast low angle shot (FLASH) sequence and to assess the potential of this technique for distinguishing malignant from benign conditions. Thirty‐six musculoskeletal lesions were studied at 1.5 T. The signal intensity of the lesions, adjacent artery, muscle, bone marrow, and fat were plotted against time. The time to peak enhancement, time to maximum signal intensity, percent enhancement, rate of peak enhancement, and rate of enhancement parameters were calculated. Because of a significant overlap between malignant and benign conditions, accuracy rates were lower than reported previously. The best parameter based on these values was the rate of peak enhancement (sensitivity, 84.6%; specificity, 65.2–66.6%; positive predictive value, 57.8–68.7%). Fat saturation gradient‐echo MR perfusion imaging allows for a rapid assessment of the vascularity of musculoskeletal pathology; however, a significant overlap persists between malignant neoplasms and several benign conditions.
Prototype system for an MR simulation of intracavitary brachytherapy for cervical cancer: Preliminary results in six cases
Authors: Ebe Kazuyu , Matsunaga Naofumi
Published: March 2007

We report a newly developed MR simulation system for intracavitary brachytherapy for cervical cancer and subsequent treatment results. MR simulation was performed on six patients. The spatial relationship of the tumor to the bladder, rectum, bowel, applicators, etc. was depicted well. Doses to the tumor and surrounding normal tissues were read from isodose curves superimposed on the T2‐weighted sagittal image. This system promises to be useful in customizing the dose distribution.
Intravascular contrast agent improves magnetic resonance angiography of carotid arteries in minipigs
Authors: Lin Weili , Abendschein Dana R. , Celik Azim , Dolan Robert P. , Lauffer Randall B. , Walovitch Richard C. , Haacke E. Mark
Published: March 2007

This study was designed to optimize three‐dimensional (3D) time‐of‐flight (TOF) magnetic resonance angiography (MRA) sequences and to determine whether contrast‐enhanced MRA could improve the accuracy of lumen definition in stenosed carotid arteries of minipigs. 3D TOF MRA was acquired with use of either an intravascular (n = 13) and/or an extravascular contrast agent (n = 5) administrated at 2 to 4 weeks after balloon‐induced injury to a carotid artery in 16 minipigs. Vascular contrast, defined as signal intensity differences between blood vessels and muscle normalized to the signal intensity of muscle, was compared before and after the injection of each contrast agent and between the two agents. Different vascular patencies were observed among the animals, including completely occluded vessels (n = 5), stenotic vessels (n = 3), and vessels with no visible stenosis (n = 8). Superior vascular contrast improvement was observed for small arteries and veins and for large veins with the intravascular contrast agent when compared with the extravascular contrast agent. In addition, preliminary studies in two of the animals showed a good correlation for the extent of luminal stenosis defined by digital subtraction angiography compared with MRA obtained after administration of the intravascular contrast agent (R2 = .71, with a slope of .96 ± .04 by a linear regression analysis). We concluded that use of an intravascular contrast agent optimizes 3D TOF MRA and may improve its accuracy compared with digital subtraction angiography.
Use of k‐space segmentation in MR velocity mapping for rapid quantification of CSF flow
Authors: Ståhlberg Freddy , Nitz Wolfgang , Nilsson Christer , Holtås Stig
Published: March 2007

In this work, a k‐space segmentation technique for quantitative studies of pulsatile cerebrospinal fluid (CSF) flow is suggested. Three k‐space lines are sampled for each of two interleaved gradient‐echo sequences (velocity‐compensated and velocity‐encoded) within each repetition interval. Nine cardiac phases are obtained at a heart rate of 60 bpm with maintained nominal resolution and a factor of 3 in reduction of acquisition time relative to our conventional nonsegmented flow quantification protocol. Segmented and conventional sequences were compared in phantoms, in healthy volunteers, and in two patients with clinically suspected normal pressure hydrocephalus. Good agreement between flow curves obtained with the two sequences was demonstrated in vitro as well as in vivo. A slight underestimation of flow values in volunteers was attributed to data filtering when using the segmented sequence. Because the CSF circulation is complex and tightly connected to the vascular circulation, specific clinical applications may require flow studies at multiple positions and with different velocity encoding. In such cases, the proposed sequence can be used to gain time, but alternatively, the segmentation technique can be used to further increase spatial resolution within reasonable examination times.
MRI for the evaluation of regional myocardial perfusion in an experimental animal model
Authors: Lombardi Massimo , Jones Richard A. , Westby Jørgen , Kvaærness Jørn , Torheim Geir , Michelassi Claudio , L'Abbate Antonio , Rinck Peter A.
Published: March 2007

Myocardial perfusion was assessed in nine pigs using ultrafast gradient‐echo MRI (.5 T, 15‐mT/m gradients) at different levels of myocardial blood flow (range, .005–1.84 ml/min/g), generated either by adenosine infusion or by a mechanical occluder, and measured independently using radiolabeled microspheres. Sixty‐four consecutive, ECG‐triggered, diastolic, short axis images of the left ventricle were obtained during intravenous bolus injections (y = 30) of .05 mmol/kg of gadopentetate dimeglumine. Relative changes in peak intensity, time to peak intensity, washin slope, correlation coefficient, and cross‐correlation coefficient were computed from the time‐intensity curves obtained from four regions of interest, namely septal, anterior, lateral, and inferior walls. The values from the inferior wall acted as reference for evaluating relative changes in the other three regions. The cross‐correlation coefficient (P < .001, r = 60) and the peak intensity (P < .001, r = .72) showed the best correlation with myocardial blood flow. The washin slope showed a weak positive trend (P < .05), but the low value of r (r = .28) indicated that the use of this parameter to predict flow was invalid; the correlation coefficient and time to peak intensity were not correlated ( P = ns). In conclusion, this study shows that it is possible to evaluate relative myocardial perfusion after the first pass of a an intravenously injected bolus of gadopentetate dimeglumine, using dynamic MRI on a conventional medium field MRI system. The cross‐correlation coefficient and the peak intensity resulted in more efficient parameters to evaluate relative inhom‐ogeneity of regional myocardial perfusion.
High resolution, short echo time sodium imaging of articular cartilage
Authors: Insko E. K. , Reddy Ravinder , Leigh J. S.
Published: March 2007

The sodium present in articular cartilage interacts with the negatively charged proteoglycan aggregates in the matrix of the cartilage. Sodium images of short echo time may be useful for detecting changes that occur in the proteoglycan content of the cartilage. Such changes are indicative of early osteoarthritic damage, for example. Using an asymmetric short echo technique, sodium images of high resolution and signal‐to‐noise ratio that demonstrate anatomic features of the cartilage are presented. These images were obtained with echo times as short as 1 msec, at an inplane resolution of 39 microns by 117 microns and signal‐to‐noise ratios of up to 40:1.
Brain atrophy progression measured from registered serial MRI: Validation and application to alzheimer's disease
Authors: Fox Nick C. , Freeborough Peter A.
Published: March 2007

In this paper, we validate the brain boundary shift integral (BBSI) as a measure of brain atrophy and demonstrate its application in Alzheimer's disease (AD). Nineteen normal subjects and nine patients with AD underwent serial three‐dimensional MRI (6‐ to 30‐month scan intervals). Repeat studies were registered to the baseline studies. The accuracy of the BBSI was assessed by comparison with simulated atrophy and with segmentation; it was also tested for reproducibility, linearity, and its ability to discriminate patients with AD from healthy controls. The BBSI correlated closely with simulated volumes of atrophy (r = 1.000). The mean absolute difference between repeat measures was 1.51 ml or .13% of mean brain volume. Rates of atrophy from all 18 AD scan pairs were widely separated from those of all 31 control pairs. In matched subgroups, the mean (SD) annual rate of brain atrophy in nine controls was .24% (.32%), compared with 2.78% (.92%) in nine patients with AD. We conclude that the BBSI is a linear and highly reproducible measure of atrophy with potential uses in the early diagnosis and measurement of progression in Alzheimer's disease.
Dynamic imaging of intracranial lesions using fast spin‐echo imaging: Differentiation of brain tumors and treatment effects
Authors: Hazle John D. , Jackson Edward F. , Schomer Don F. , Leeds Norman E.
Published: March 2007

The purpose of this study was to develop a technique for differentiating between recurrent brain tumors and treatment‐related changes, such as radiation necrosis, using dynamic MRI. Ninety‐five patients with intracranial mass lesions were evaluated using T1‐weighted fast spin‐echo (FSE) MRI at 1.5 T. Pathologies included treatment‐related changes (n = 32), primary tumors (n = 41), metastatic tumors (n = 5), meningiomas (n = 4), and mixed primary/treatment related changes (n = 13). Signal enhancement‐time curves were analyzed by fitting to a sigmoidal‐exponential function. Maximal enhancement rates were calculated as the first derivative of the fitted curve. Based on the maximal enhancement rates, treatment‐related changes could be differentiated from primary tumors, metastatic tumors, and meningiomas at the P < .05 confidence level. Lesions of mixed tumor and treatment‐related change had intermediate values. Dynamic MRI can be used to differentiate treatment‐related changes from primary tumors in previously treated patient populations based on maximal enhancement rates. Individual case studies demonstrate the clinical significance of these findings.
Fuzzy clustering of gradient‐echo functional MRI in the human visual cortex. Part I: Reproducibility
Authors: Baumgartner Richard , Scarth Gordon , Teichtmeister Claudia , Somorjai Ray , Moser Ewald
Published: March 2007

Reproducibility of human functional MRI (fMRI) studies is essential for clinical and neuroresearch applications of this new human brain mapping method. Based on a recently presented study on reproducibility of gradient‐echo fMRI in the human visual cortex (Moser et al. Magn Reson Imaging 1996; 14:567–579), comparing the performance of three different threshold strategies for correlation analysis, we demonstrate that (a) fuzzy clustering is a robust, model‐independent method to extract functional information in time and space; (b) intertrial reproducibility of cortical activation is significantly improved by the capability of fuzzy clustering to separate signal contributions from larger vessels, running perpendicular to the slice orientation, from activation apparently close to the primary visual cortex; and (c) for repeated single subject studies, SDs of <20% for signal enhancement in approximately 80% of the studies and SDs of <30% for activated area size in approximately 65% of the studies are obtained. This, however, depends also on signal‐to‐noise ratio, (motion) artifacts, and subject cooperation.
Fuzzy clustering of gradient‐echo functional MRI in the human visual cortex. Part II: Quantification
Authors: Moser Ewald , Diemling Markus , Baumgartner Richard
Published: March 2007

Fuzzy cluster analysis (FCA) is a new exploratory method for analyzing fMRI data. Using simulated functional MRI (fMRI) data, the performance of FCA, as implemented in the software package Evident, was tested and a quantitative comparison with correlation analysis is presented. Furthermore, the fMRI model fit allows separation and quantification of flow and blood oxygen level dependent (BOLD) contributions in the human visual cortex. In gradient‐recalled echo fMRI at 1.5 T (TR = 60 ms, TE = 42 ms, radiofrequency excitation flip angle [ϑ] = 10°–60°) total signal enhancement in the human visual cortex, ie, flow‐enhanced BOLD plus inflow contributions, on average varies from 5% to 10% in or close to the visual cortex (average cerebral blood volume [CBV] = 4%) and from 10% to 20% in areas containing medium‐sized vessels (ie, average CBV = 12% per voxel), respectively. Inflow enhancement, however, is restricted to intravascular space (= CBV) and increases with increasing radiofrequency (RF) flip angle, whereas BOLD contributions may be obtained from a region up to three times larger and, applying an unspoiled gradient‐echo (GRE) sequence, also show a flip angle dependency with a minimum at approximately 30°. This result suggests that a localized hemodynamic response from the microvasculature at 1.5 T maybe extracted via fuzzy clustering. In summary, fuzzy clustering of fMRI data, as realized in the Evident software, is a robust and efficient method to (a) separate functional brain activation from noise or other sources resulting in time‐dependent signal changes as proven by simulated fMRI data analysis and in vivo data from the visual cortex, and (b) allows separation of different levels of activation even if the temporal pattern is indistinguishable. Combining fuzzy cluster separation of brain activation with appropriate model calculations allows quantification of flow and (flow‐enhanced) BOLD contributions in areas with different vascularization.
Discrimination of Metabolite from Lipid and Macromolecule Resonances in Cerebral Infarction in Humans Using Short Echo Proton Spectroscopy
Authors: Saunders Dawn E. , Howe Franklyn A. , Boogaart Aad Van Den , Griffiths John R. , Brown Martin M.
Published: March 2007

Short‐echo proton spectroscopy allows the noninvasive study of metabolites, lipids, and macromolecules in stroke patients, but spectra are difficult to interpret and quantify because narrow metabolite peaks are added to a broad background of lipid and macromolecule peaks. “Metabolite nulling” was used to distinguish the lactate peak from underlying lipid and macromolecule peaks. Increases in the lipid and macromolecule peaks were initially observed within the region of infarction in all patients, and further increases in lipid peaks were seen in five of the six patients during the following 6 weeks. The initial high lactate concentration decreases during the first 2 weeks after stroke, whereas lipid and macromolecule signals show a persistent elevation during the same period. Differences in the time courses of the observed changes suggest that lipid, macromolecule, and lactate signals arise from more than one source.
Centric ordering is superior to gradient moment nulling for motion artifact reduction in EPI
Authors: Jaffer Farouc A. , Wen Han , Jezzard Peter , Balaban Robert S. , Wolff Steven D.
Published: March 2007

Echo‐planar imaging (EPI) is sensitive to motion despite its rapid data acquisition rate. Compared with traditional imaging techniques, it is more sensitive to motion or flow in the phase‐encode direction, which can cause image artifacts such as ghosting, misregistration, and loss of spatial resolution. Consequently, EPI of dynamic structures (eg, the cardiovascular system) could benefit from methods that eliminate these artifacts. In this paper, two methods of artifact reduction for motion in the phase‐encode direction are evaluated. First, the k‐space trajectory is evaluated by comparing centric with top‐down ordered sequences. Next, velocity gradient moment nulling (GMN) of the phase‐encode direction is evaluated for each trajectory. Computer simulations and experiments in flow phantoms and rabbits in vivo show that uncompensated centric ordering produces the highest image quality. This is probably due to a shorter readout duration, which reduces T2* relaxation losses and off‐resonance effects, and to the linear geometry of phantoms and vessels, which can obscure centric blurring artifacts.
Volume MRI and MRSI techniques for the quantitation of treatment response in brain tumors: Presentation of a detailed case study
Authors: Nelson Sarah J. , Huhn Stephen , Vigneron Daniel B. , Day Mark R. , Wald Lawrence L. , Prados Michael , Chang Susan , Gutin Philip H. , Sneed Penny K. , Verhey Lynn , Hawkins Randall A. , Dillon William P.
Published: March 2007

Patients with primary brain tumors may be considered for several different treatments during the course of their disease. Assessments of disease progression and response to therapy are typically performed by visual interpretation of serial MRI examinations. Although such examinations provide useful morphologic information, they are unable to reliably distinguish active tumor from radiation necrosis. This poses a particular problem in the assessment of response to localized radiation therapies such as gamma knife radiosurgery. In this paper, we present methodology for evaluating changes in tissue morphology and metabolism based on serial volumetric MRI and magnetic resonance spectroscopic imaging (MRSI) examinations. Registration and quantitative analysis of these data provide measurements of the temporal and spatial distributions of gadolinium enhancement and of N‐acetylasparate, choline, creatine, and lactate/lipid. The key features of this approach and the potential clinical benefits are illustrated by a detailed analysis of six serial MRI/MRSI examinations and three serial 1‐[F‐18] fluoro‐2‐deoxy‐D‐glucose (FDG) positron emission tomography (PET) studies on a patient with a recurrent anaplastic astrocytoma.
Detection of primary breast cancer in women with known adenocarcinoma metastatic to the axilla: Use of MRI after negative clinical and mammographic examination
Authors: Brenner R. James , Rothman Barry J.
Published: March 2007

The purpose of this study was to evaluate the ability of MRI to identify a primary site of malignancy in the breast of patients who present clinically with ipsilateral lymph nodes containing metastatic carcinoma but whose physical and mammographic examination are negative. MRI of the breast was performed on four patients using a variety of imaging parameters, all with and without gadolinium contrast. All patients had biopsy‐proven adenocarcinoma of the ipsilateral axilla, with negative physical and mammographic examinations. Foci of enhancement assessed visually on precontrast and postcontrast scans (n = 1) and on substraction studies (n = 3) were considered suspicious under the clinical circumstances defined for this study. Lesions identified on MRI were re‐identified on ultrasound examination and either preoperative localization for excisional biopsy or tissue sampling was performed. Surgery was performed and histopathologic correlation was obtained in all cases. Primary sites of breast carcinoma were identified in all four patients, with multiple sites of malignancy identified in three of four patients. Breast conservation therapy was made possible for three of four patients based on the results of the MRI study showing sites of malignancy and no features of cancer elsewhere in the breast. Follow‐up data of 1, 2, and 5 years of these patients show no evidence of recurrent disease. MRI of the breast is a useful technique for identifying primary sites of malignancy in patients presenting with ipsilateral lymph nodes positive for metastatic adenocarcinoma when the physical and mammographic examinations are negative.
Elimination of nyquist ghosts in MRI by using fast linogram imaging
Authors: Gai Neville , Axel Leon
Published: March 2007

Timing inaccuracies between the even and odd echoes lead to the formation of Nyquist ghosts in conventional (blipped) echo‐planar imaging (EPI). A fast radial scanning method based on the linogram sampling geometry was designed and implemented. No ghosting effects are seen with this scheme, and correction for timing inaccuracies is performed using simple postprocessing steps before reconstruction.
The effect of mechanical deformation on magnetic properties and MRI artifacts of type 304 and type 316L stainless steel
Authors: Bendel Lee P. , Shellock Frank G. , Steckel Mark
Published: March 2007

The purpose of this study was to evaluate the influence of composition and deformation of biomedical stainless steels on mechanical properties, magnetic properties, and MRI artifacts. Type 304 and Type 316L samples were prepared using standard wire‐drawing techniques. Mechanical properties were determined using standard test methods. The amount of ferromagnetic phase present was estimated using a Severn Gage and x‐ray diffraction. Magnetic field attraction and artifacts were determined using previously described techniques. The strength of both steels increased significantly with increasing deformation. None of the type 316L wires transformed to the magnetic phase. The amount of magnetic phase in the type 304 wires increased with increasing deformation. There was no magnetic field attraction, and artifacts were minimal for all of type 316L wires and the undeformed type 304 wire. Deflection and artifacts were significant for the deformed type 304 stainless steel. These results provide guidance regarding the use of type 304 and type 316L stainless steels for bioimplants. In this regard, type 316L stainless steel seems to be a more acceptable material with respect to MR compatibility.
Invited. Compatible instrumentation for intraoperative MRI: Expanding resources
Authors: Jolesz Ferenc A. , Morrison Paul R. , Koran Susan J. , Kelley Ray J. , Hushek Steve G. , Newman Robert W. , Fried Marvin P. , Melzer Andreas , Seibel Rainer M. M. , Jalahej Heyam
Published: March 2007

Steadfast progress has been made from biopsy to surgery with interventional MRI (iMRI). Such image‐guided interventions require specialized instrumentation due to the unusual elements of the MR environment. Suppliers/manufacturers of MR‐compatible instrumentation were few in 1994, but now there are more than 50. We present fundamental issues of MR compatibility and a list of known suppliers/manufacturers.
Invited. MR systems for image‐guided therapy
Authors: Hinks R. Scott , Bronskill Michael J. , Kucharczyk Walter , Bernstein Mark , Collick Bruce D. , Henkelman R. Mark
Published: March 2007

The use of MRI to guide and monitor interventional procedures requires the merging of surgical and MRI environments. The ideal magnet shape for homogeneity and efficiency is spherical, but this design provides no access. Opening the sphere to provide both patient and surgeon access suggests cylindrical or biplanar magnets. Cylindrical magnets have poor surgical access but provide good imaging capabilities, which can be used in conjunction with a neighboring but distinct surgical environment. Biplanar magnets provide more and better approaches to the patient, but generally with lower field strength. Vertical biplanar systems allows surgical approaches from above but reduce the access of support staff to the patient. A hybrid magnet design, which combines the benefits of both cylindrical and biplanar magnets, can provide increased access with simultaneous approach from two sides of the patient. Application‐specific magnets can target a smaller region, leading to compact magnet designs that greatly expand access for both surgical intervention as well as patient support. As the field of interventional MRI matures, the suitability of each design to specific applications will be better understood, leading to more integrated system designs tailored to the needs of imageguided therapy.
Interventional MR‐guided excisional biopsy of breast lesions
Authors: Gould Stuart William Thomas , Lamb Gabrielle , Lomax David , Gedroyc Wadislaw , Darzi Ara
Published: March 2007

Interventional MR (IMR) machines have produced unique opportunities for image‐guided surgery. The open configuration design and fast pulse sequences allow intraoperative scanning to monitor procedures. This study was undertaken to assess the potential use of IMR for image‐guided surgery. Benign breast lesion excision was chosen as an uncomplicated surgical model. Ten female patients with known benign tumors underwent excision biopsy under general anesthesia in a Signa SP10 .5‐T IMR machine (General Electric Medical Systems, Milwaukee, WI). Lesions were localized with precontrast and postcontrast (intravenous gadolinium‐diethylenetriamine pentaacetic acid, .2 mmol/kg) fast multiplanar spoiled gradient‐recalled acquisition in the steady state (GRASS) sequences. Preoperative “real‐time” fast gradient‐recalled sequences were also obtained using the Flashpoint (General Electric Medical Systems, Milwaukee, WI) tracker device. The maximum dimensions of each lesion were measured from the resulting images. Excision was performed using titanium instruments and an ultrasonically activated scalpel. Intraoperative real‐time scanning demonstrated the resection margin and confirmed complete excision. The maximum dimensions of the macroscopic specimens were compared with those from the MR images. All tumors were visualized with the Signa scanner and real‐time imaging and the images were enhanced after intravenous contrast. Maximum dimensions on histologic examination were not significantly different from those measured from Signa (P > .17) or real‐time images (P > .4). There was no significant difference between lesion size from Signa and real‐time images (P > .25). All postprocedure scans demonstrated complete excision. There were six fibroadenomas, two foci of sclerosing adenosis, one area of fibrocystic disease, and one schwannoma. Intraoperative MR scanning reliably identifies palpable breast tumors and can accurately guide surgical excision. Further work using MR guidance can now be performed in other general surgical areas.
Invited. Predictability of the size of laser‐induced lesions in T1‐weighted MR images obtained during interstitial laser‐induced thermotherapy of benign prostatic hyperplasia
Authors: Mueller‐Lisse Ullrich G. , Heuck Andreas F. , Thoma Martin , Muschter Rolf , Schneede Peter , Weninger Ernst , Faber Sonja , Hofstetter Alfons , Reiser Maximilian F.
Published: March 2007

The purpose of this study was to predict diameters of lesions induced by laser‐induced thermotherapy (LITT) of benign prostatic hyperplasia (BPH) from MRI signal/tissue temperature correlations during on‐line monitoring with a temperature‐sensitive fast low‐angle shot (FLASH) sequence. Twenty LITT procedures with Nd:YAG (1,064 nm) and diode (830 nm) lasers were monitored on line with a T1‐weighted FLASH sequence at 1.5 Tesla. Interstitial prostate temperature (T) was measured on line in 10 LITT procedures and laser energy deposition in 12. Slopes of linear regression curves for signal intensity (SI) over T were applied to determine SI at 60°C to estimate diameters of intraprostatic LITT lesions. Diameters of unperfused LITT lesion cores in contrast‐enhanced T1‐weighted images served as gold standards. Linear regression curves with an average slope of −.54% SI/°C were obtained in 17 LITT procedures. Correlation coefficients were r = .92−.95 for SI/T and SI/energy deposition. Baseline variation of SI at body temperature was ±3.9%, corresponding to ±7°C. Prediction of size (13 lesions) from on‐line FLASH imaging was correct in 10 of 13, whereas 3 lesions were overestimated. Prediction of LITT lesion diameters from on‐line MRI monitoring is possible with a temperature‐sensitive FLASH sequence in the prostate. Accuracy may suffice to assign target regions of interest to tissue locations to be protected from coagulation.
Invited. MRI of laser‐induced interstitial thermal injury in an in vivo animal liver model with histologic correlation
Authors: Morrison Paul R. , Jolesz Ferenc A. , Charous Daniel , Mulkern Robert V. , Hushek Stephen G. , Margolis Randall , Fried Marvin P.
Published: March 2007

Laser‐induced interstitial thermal therapy (LITT) is a preferred method of minimally invasive therapy. MRI is a noninvasive method by which to monitor the thermal effects of LITT. To properly control such effects, changes in MRI parameters during and after LITT should be correlated with changes in the tissue. T1‐weighted fast spin echo (FSE) MRI (1 image/10 seconds) at 1.5 T monitored LITT in vivo in rabbit liver (n = 6) using an interstitial bare delivery fiber (600‐μm diameter; 3.0 W; 1,064 nm; 150 seconds). During laser irradiation, MRI signal intensity decreased around the fiber tip; after irradiation, this hypointensity proved reversible and permanent lesions were evident. The lesions had hyperintense margins that were brighter than surrounding normal tissue (P < .001); the tissue in these bright regions was mapped to tissue necrosis characterized by the presence of thermally damaged ghost red blood cells amid generally normal hepatocytes. T1‐FSE identified the spatial extent of the LITT lesions.
MR monitoring of MR‐guided radiofrequency thermal ablation of normal liver in an animal model
Authors: Boaz Travis L. , Lewin Jonathan S. , Chung Yiu‐Cho , Duerk Jeffrey L. , Clampitt Mark E. , Haaga John R.
Published: March 2007

The purpose of this study was to determine the suitability of MRI to accurately detect radiofrequency (RF) thermoablative lesions created under MR guidance. In vivo RF lesions were created in the livers of six New Zealand White rabbits using a 2‐mm‐diameter titanium alloy RF electrode with a 20‐mm exposed tip and a 50‐W RF generator. This was performed using a 0.2T clinical C‐arm MR imager for guidance and monitoring. Each animal was sacrificed and gross evaluation was performed. Histologic correlation was performed on the first two animals. The MR‐compatible RF electrode was easily identified on rapid gradient‐echo images used to guide electrode placement. A single lesion was created in each rabbit liver. Lesions ranged from approximately 10 to 17 mm in diameter (mean, 13.5 mm). T2‐weighted and short T1 inversion recovery (STIR) images demonstrated lesions ranging in diameter from 12 to 18 mm (mean, 14.6 mm). Lesion dimensions determined from images closely correlated with those determined at gross examination with the discrepancy never exceeding 2 mm, for an r2 value of .87. MRI performed at the time of MR‐guided RF ablation accurately demonstrated created lesions. This modality may provide a new option for the treatment of local and regional neoplastic disease.
Invited. MRI‐guided biopsy of bone in a hybrid system
Authors: Neuerburg Joerg‐Michael , Adam Gerhard , Buecker Arno , Zilkens Karl W. , Schmitz‐Rode Thomas , Hunter David , van Vaals Joop J. , Guenther Rolf W.
Published: March 2007

This is a report of our experience with percutaneous, MRI‐guided biopsies in 25 patients with skeletal lesions using a 1.5‐T MR hybrid system. Twenty‐five consecutive patients with skeletal lesions were referred for MRI‐guided biopsy. Biopsies were performed with a 1.5‐T Philips Gyroscan (Philips Medical Systems, Best, The Netherlands) combined with a c‐arm fluoroscopy. Specimens were obtained percutaneously either with a 14‐ or 18‐gauge “side‐slit” type of biopsy needle (n = 10 skeletal lesions that had penetrated through the cortex), or using a prototype coaxial drill system powered either by hand or an optional motor (n = 15 skeletal lesions still covered with cortical bone). All but two biopsies could be completed within the MR unit. For one patient, who required a transpedicular approach to a lumbar vertebra, and for one child, who required general anesthesia, we decided to switch to CT guidance. In 19 of the 25 cases (17 of the 23 cases performed in MR), the sample was sufficient and the histopathologic diagnosis was confirmed. Three patients had an inadequate sample, and three others had adequate samples but inaccurate results. No procedural complications occurred. Percutaneous biopsy of skeletal lesions performed under MRI‐guidance was found to be safe and reasonably accurate. There were no procedural complications in our small series. MRI may be used as an alternative to CT, but its role vis‐à‐vis CT has yet to be ascertained.
A method for simultaneous RF ablation and MRI
Authors: Zhang Qiang , Chung Yiu‐Cho , Lewin Jonathan S. , Duerk Jeffrey L.
Published: March 2007

Radiofrequency (RF) energy has many advantages in thermal tumor ablation protocols. With the recent development of open MRI systems, interventional MRI procedures, including thermal ablation, have become the focus of great research interest. However, the significant interference between RF generators and MR imagers has prevented simultaneous imaging and RF ablation and, until now, has limited the role of RF‐based thermal therapy in interventional MRI. Here, a simple switching circuit designed with consideration of patient safety provides compatibility between open MRI systems and RF thermal lesion generators. The experimental results show that the switching circuit allows imaging during RF ablation and opens new opportunity for MR‐guided thermal therapy.
Invited. Correlation of neuropathologic findings and phase‐based MRI temperature Maps in experimental laser‐induced interstitial thermotherapy
Authors: Schulze Christian P. , Kahn Thomas , Harth Thorsten , Schwurzmaier Hans‐Joachim , Schober Ralf
Published: March 2007

To investigate the correlation between the neuropathologic findings after laser‐induced interstitial thermotherapy (LITT) and MRI temperature maps during laser irradiation, a total of six pig brains from cadavers were treated with a Nd:YAG laser (λ = 1,064 nm, 3.8 W) for 15 minutes. For MRI monitoring, we used a phase‐sensitive two‐dimensional (2D) fast lowangle shot (FLASH) sequence on a 1.5‐T Magnetom SP. Temperature maps were acquired every minute (accuracy, < 1.5°C). Histopathologic methods were selected (hematoxylin and eosin stain, Masson's trichrome, Bodian silver impregnation) to demonstrate the zonal architecture of LITT lesions in ex vivo specimens. They showed extensive destruction of the nervous tissue constituents, vascular changes, and lysis of erythrocytes near the track of the laser, a transitional zone, and an 1.5‐mm broad margin with edema‐like perinuclear vacuolization. No immunoreactivity of glial fibrillary acidic protein (GFAP) could be visualized inside the lesion. In a semiquantitative evaluation, the lesion sizes were measured microscopically (mean diameter = 12.8 mm) and their margins could be defined at temperature zones of 60 to 65°C on the MRI maps.
Invited. Brain edema development after MRI‐guided focused ultrasound treatment
Authors: Mörocz István Á. , Hynynen Kullervo , Gudbjartsson HLäkon , Peled Sharon , Colucci Vincent , Jólesz Ferenc A.
Published: March 2007

The aim of this study was to investigate a potential technique for image‐guided minimally invasive neurosurgical interventions. Focused ultrasound (FUS) delivers thermal energy without an invasive probe, penetrating the dura mater, entering through the cerebrospinal fluid (CSF) space, or harming intervening brain tissue. We applied continuous on‐line monitoring by MRI to demonstrate the effect of the thermal intervention on the brain tissue. For this, seven rabbits had a part of their skull removed to create access for the FUS beam into the brain through an acoustic window of 11 mm in diameter. Dura was left intact and skin was sutured. One week later, the rabbits were sonicated for 3 seconds with 21 W acoustic power, and the FUS focus was visualized with a temperature‐sensitive T1‐weighted MRI pulse sequence. The tissue reaction was documented over 7 days with T2‐weighted images of the brain. The initial area of the central low signal intensity in the axial plane was .4 ± .3 mm2, and for the bright hyperintensity surrounding the lesion, it was 2.3 ± .6 mm2 (n = 7). In the coronal plane, the corresponding values were .4 ± .1 mm2 and 3.4 ± .9 mm2 (n = 5). The developing brain edema culminated 48 hours later and thereafter diminished during the next 5 days. Histology revealed a central necrosis in the white matter surrounded by edematous tissue with inflammatory cells. In summary, the image‐guided thermal ablation technique described here produced a relatively small lesion in the white matter at the targeted location. This was accomplished without opening the dura or the need for a stereotactical device. MRI allowed on‐line monitoring of the lesion setting and the deposition of thermal energy and demonstrated the tissue damage after the thermal injury.
Target definition and trajectory optimization for interactive MR‐guided biopsies of brain tumors in an open configuration MRI system
Authors: Kollias Spyros S. , Bernays Rene , Marugg Richard A. , Romanowski Ben , Yonekawa Yasuhiro , Valavanis Anton
Published: March 2007

We present an imaging strategy for planning and guiding brain biopsies in an open configuration MR system. Preprocedure imaging was performed in a 1.5‐T MR system and was designed to provide, in a clinically efficient manner, high resolution anatomical and functional/physiologic information for precise definition and tissue characterization of the target, aiming at optimization of the biopsy trajectory for planning a safe and accurate procedure. The interventions were performed in a .5‐T open bore magnet, and imaging was optimized to provide the imaging quality and temporal resolution necessary for performing the procedure interactively in near real time. Brain biopsies of 21 patients were performed in a 10‐month period. Segmentation and surface rendering analysis of the lesions and vascular structures and dynamic MR perfusion and cortical activation studies provided an efficient and comprehensive way to appreciate the relationship of the target to surrounding vital structures, improved tissue characterization and definition of the tumor margins, and demonstrated the location of essential cortex, allowing appropriate placement of the burr hole and choice of optimal trajectory. Interactive protocols provided good visualization of the target and the interventional devices and offered the operator real‐time feedback and control of the procedure. No complications were encountered. Advanced methods of image acquisition and processing for accurate planning of interventional brain procedures and interactive imaging with MR guidance render feasible the performance of safe and accurate neurointerventional procedures.
Invited. Calibration of water proton chemical shift with temperature for noninvasive temperature imaging during focused ultrasound surgery
Authors: Kuroda Kagayaki , Chung Andrew H. , Hynynen Kullervo , Jolesz Ferenc A.
Published: March 2007

The present work was performed to calibrate water proton chemical shift change with tissue temperature in vivo to establish a method of quantitative temperature imaging during focused ultrasound surgery. The chemical shift change measured with a phase‐mapping method using spoiled gradient‐recalled acquisition in steady state (SPGR) (TR = 26 msec, TE = 12.8 msec, matrix = 256 × 128) was calibrated with the corresponding temperature elevation (0–50°C, 32–84°C in absolute temperature) measured with a copper‐constantan thermocouple (.05‐mm‐diameter bare wires) in rabbit skeletal muscle (16 animals) under focused ultrasound exposures (10–100 W radiofrequency [RF] power, 20‐second sonication). A linear calibration with a regression coefficient of (−8.76 ± .69) × 10−3 ppm/ °C (P < .01 [P, significance level]) was obtained. Temperature distributions during a 20‐second sonication were visualized every 3.3 seconds with a 2.3‐mm3 spatial resolution and 4°C temperature uncertainty.