bluuebunny/crossref_metadata_2025 huggingface dataset:
Pulsed magnetization transfer versus continuous wave irradiation for tissue contrast enhancement
Authors: Schneider Erika , Prost Robert W. , Glover Gary H.
Published: March 2007

Pulsed magnetization transfer and continuous wave irradiation techniques are analyzed and compared for saturation efficiency and radio‐frequency (RF) power requirements at 1.5 and 0.5 T. Binomial RF pulses transmitted on resonance are a more power‐efficient method of exciting saturation transfer and are easily implemented with any pulse sequence. Binomial pulses selectively excite all short T2 species and behave as 0° pulses for on‐resonance, long T2 species.
Overlapping section coverage in multisection imaging
Authors: Hennig Jürgen
Published: March 2007

A method is proposed in which the section position for two‐dimensional Fourier transform multisection imaging is advanced from one phase‐encoding step to the next, so that information is sampled continuously over the total volume under observation. This “ramp scan”technique allows reconstruction of images from any arbitrary position within the sampled volume. The imaging properties depend strongly on the order of distribution of phase‐encoding steps to the different section positions. In practice, images are reconstructed at each nominal position of a multisection experiment, plus at each position halfway between sections. The volume under study is thus represented by overlapping sections. The gaps between sections that arise in conventional multisection imaging‐even with optimized pulse shapes‐are thus avoided. This approach is applicable not only to conventional spin‐echo imaging but to other techniques such as RARE (rapid acquisition with relaxation enhancement) and gradient‐echo and echo‐planar imaging.
Conventional and fast spin‐echo MR imaging: Minimizing echo time
Authors: Vinitski Simon , Mitchell Donald G. , Einstein Steven G. , Rao Vijay M. , Flanders Adam E. , Schweitzer Mark E. , Listerud John , Schnall Mitchell D.
Published: March 2007

Magnetic resonance imaging is frequently complicated by the presence of motion and susceptibility gradients. Also, some biologic tissues have short T2s. These problems are particularly troublesome in fast spin‐echo (FSE) imaging, in which T2 decay and motion between echoes result in image blurring and ghost artifacts. The authors reduced TE in conventional spin‐echo (SE) imaging to 5 msec and echo spacing (E‐space) in FSE imaging to 6 msec. All magnetic gradients (except readout) were kept at a maximum, with data sampling as fast as 125 kHz and only ramp waveforms used. Truncated sine radio‐frequency pulses and asymmetric echo sampling were also used in SE imaging. Short TE (5.8 msec) SE images of the upper abdomen were compared with conventional SE images (TE =11 msec). Also, FSE images with short E‐space were compared with conventional FSE images in multiple body sites. Short TE significantly improved the liver‐spleen contrast‐to‐total noise ratio (C/N) (7.9 vs 4.1, n = 9, P <.01) on T1‐weighted SE images, reduced the intensity of ghost artifacts (by 34%, P <.02), and increased the number of available imaging planes by 30%. It also improved delineation of cranial nerves and reduced susceptibility artifacts. On short E‐space FSE images, spine, lung, upper abdomen, and musculoskeletal tissues appeared crisper and measured spleen‐liver C/N increased significantly (6.9 vs 4.0, n = 12, P <.01). The delineation of tissues with short T2 (eg, cartilage) and motion artifact suppression were also improved. Short TE methods can improve image quality in both SE and FSE imaging and merit further clinical evaluation.
Pulsed magnetization transfer spin‐echo MR imaging
Authors: Bruce Pike G. , Glover Gary H. , Hu Bob S. , Enzmann Dieter R.
Published: March 2007

Cross relaxation between macromolecular protons and water protons is known to be important in biologic tissue. In magnetic resonance (MR) imaging sequences, selective saturation of the characteristically short T2 macromolecular proton pool can produce contrast called magnetization transfer contrast, based on the cross‐relaxation process. Selective saturation can be achieved with continuous wave irradiation several kilohertz off resonance or short, intense 0° pulses on resonance. The authors analyze 0° binomial pulses for T2 selective saturation, present design guidelines, and demonstrate the use of these pulses in spin‐echo imaging sequences in healthy volunteers and patients. Using the phenomenologic Bloch equations modified for two‐site exchange, the authors derive the analytic expressions for water proton relaxation under periodic pulsed saturation of the macromolecular protons. This relaxation is shown to be monoexpo‐nential, with a rate constant dependent on the saturation pulse repetition rate and the individual and cross‐relaxation rates.
Coupled‐spin fast spin‐echo MR imaging
Authors: Todd Constable R. , Smith Robert C. , Gore John C.
Published: March 2007

Distinguishing between lipid and water‐containing tissues is clinically important. Current techniques rely on the chemical shift difference between fat and water resonances or differences in relaxation times of the tissues, or a combination of both. A method is presented for separating the signals of lipid protons from those of water protons by using fast spin‐echo magnetic resonance imaging based on the principle that lipid protons behave differently from water protons in mul‐tiecho sequences. Two images are acquired with different echo train lengths and echo spacing but with identical TEs, and then subtracted to exploit differences in the behavior of lipid and water protons in mul‐tiecho sequences. The method is insensitive to B0 inhomoge‐neities or susceptibility effects and provides separate lipid and water images with a high signal‐to‐noise ratio. The advantages of the method are demonstrated with phantom studies and clinical examples.
Renal cancer staging: Comparison of contrast‐enhanced CT and gadolinium‐enhanced fat‐suppressed spin‐echo and gradient‐echo MR imaging
Authors: Semelka Richard C. , Patrick Shoenut J. , Magro Cynthia M. , Kroeker Mervyn A. , Macmahon Ross , Greenberg Howard M.
Published: March 2007

Fifty‐three consecutive patients with 61 solid or complex non‐fat‐containing renal masses compatible with renal cancer were examined with contrast‐enhanced computed tomography (CT) and magnetic resonance (MR) imaging with pre‐ and postcontrast FLASH (fast low‐angle shot) and fat‐suppressed spin‐echo sequences. CT and MR imaging were performed within a 1‐month interval. CT and MR images were prospectively interpreted. Tumor detection and staging were determined in all patients. CT and MR imaging enabled detection of 54 and 58 of 61 renal tumors, respectively. CT and MR imaging showed 34 and 35 of 38 histologically proved renal tumors, respectively, in 31 patients. Tumor size on CT and MR images demonstrated good correlation and correlated well with the size of pathologic specimens of 34 of 38 resected tumors detected with CT and MR imaging (r =.99). Of the 31 tumors in 31 patients who underwent surgical resection, 24 were correctly staged with CT and 29 with MR imaging. CT and MR imaging both enabled correct staging of four of five additional tumors with biopsy proof of tumor stage. A moderate difference in staging was observed between CT and MR imaging (P =.05). CT showed 13 and MR imaging 15 of 15 tumor thrombi. CT and MR imaging both showed 11 of 11 cases of adenopathy. The results suggest that MR imaging is moderately better than CT for the detection and staging of renal cancer.
“Keyhole” method for accelerating imaging of contrast agent uptake
Authors: Van Vaals Joop J. , Brummer Marijn E. , Thomas Dixon W. , Tuithof Hans H. , Engels Hans , Nelson Rendon C. , Gerety Brigid M. , Chezmar Judith L. , Den Boer Jacques A.
Published: March 2007

Magnetic resonance (MR) imaging methods with good spatial and contrast resolution are often too slow to follow the uptake of contrast agents with the desired temporal resolution. Imaging can be accelerated by skipping the acquisition of data normally taken with strong phase‐encoding gradients, restricting acquisition to weak‐gradient data only. If the usual procedure of substituting zeros for the missing data is followed, blurring results. Substituting instead reference data taken before or well after contrast agent injection reduces this problem. Volunteer and patient images obtained by using such reference data show that imaging can be usefully accelerated severalfold. Cortical and medullary regions of interest and whole kidney regions were studied, and both gradientand spin‐echo images are shown. The method is believed to be compatible with other acceleration methods such as half‐Fourier reconstruction and reading of more than one line of k space per excitation.
Comparison of cerebral artery blood flow measurements with gated cine and ungated phase‐contrast techniques
Authors: Enzmann Dieter R. , Marks Michael P. , Pelc Norbert J.
Published: March 2007

Cine phase‐contrast (PC) magnetic resonance (MR) pulse sequences have been used to measure blood flow in a variety of vessels. Because the cine PC sequence is time‐consuming, this prospective study was undertaken to compare it with an ungated PC technique for measuring average blood flow in individual cerebral arteries to potentially achieve substantial time savings. The following cerebral arteries were studied in 10 healthy volunteers: carotid, basilar, middle cerebral, anterior cerebral, and posterior cerebral. Imaging planes were placed perpendicular to the vessel of interest, and velocity encoding, ranging from 40 to 250 cm/sec, was matched to individual arteries. Good correlation between cine and ungated PC blood flow measurements was obtained for both high‐ and low‐flow vessels, with an overall correlation coefficient of 978. The ungated PC sequence, because of its short imaging time, allows measurement of the blood volume flow rate in the circle of Willis in approximately 20 minutes, a clinically acceptable time.
Localized proton MR spectroscopy of the brain in children
Authors: Tzika A. Aria , Vigneron Daniel B. , Ball William S. , Dunn R. Scott , Kirks Donald R.
Published: March 2007

Small‐voxel (3.0–8.0 cm3), magnetic resonance (MR) imaging–guided proton MR spectroscopy was performed in 54 patients (aged 6 days to 19 years) with intracranial masses (n = 16), neurodegenerative disorders (n = 34), and other neurologic diseases (n = 4) and in 23 age‐matched control subjects without brain disease. A combined short TE (18 msec) stimulatedecho acquisition mode (STEAM) and long TE (135 and/or 270 msec) spin‐echo point‐resolved spatially localized spectroscopy (PRESS) protocol, using designed radio‐frequency pulses, was performed at 1.5 T. STEAM spectra revealed short T2 and/or strongly coupled metabolites; prominent resonances were obtained from N‐acetyl aspartate (NAA), choline‐containing compounds (Cho), and total creatine (tCr). Lactate was well resolved with the long TE PRESS sequence. Intracranial tumors were readily differentiated from cerebrospinal fluid (CSF) collections. All tumors showed low NAA, high Cho, and reduced tCr levels. Neurodegenerative disorders showed low or absent NAA levels and enhanced mobile lipid, glutamate and glutamine, and inositol levels, consistent with neuronal loss, gliosis, demyelination, and amino acid neuro‐toxicity. Preliminary experience indicates that proton MR spectroscopy can contribute in the evaluation of central nervous system abnormalities of infants and children.
First pass of an MR susceptibility contrast agent through normal and ischemic heart: Gradient‐recalled echo‐planar imaging
Authors: Wendland Michael F. , Saeed Maythem , Masui Takayuki , Derugin Nikita , Higgins Charles B.
Published: March 2007

Gradient‐recalled echo‐planar magnetic resonance (MR) imaging was used to monitor the first pass of a magnetic susceptibility contrast agent through the heart of normal rats and rats subjected to 60‐minute occlusion of the anterior branch of the left main coronary artery. Each animal (six normal and six ischemic) received four doses (0.05, 0.1, 0.15, and 0.2 mmol/kg) of Dy‐DTPA‐BMA [diethylenetriaminepentaacetic acid–bis(methylamide)] administered as a bolus volume of 1.0 mL/kg. In both normal and ischemic rats, signal intensity in nonischemic myocardium was reduced by the contrast agent in a dose‐dependent manner. Signal intensity in the ischemic zone was reduced much less, so that at a contrast agent dose of 0.1 mmol/kg or greater the ischemic zone was clearly defined as a high‐intensity zone on echo‐planar images. Plots of the change in the apparent T2* relaxation rate (ΔR2*) during the peak bolus effect versus injected dose were well fit by straight lines for normal, nonischemic, and ischemic myocardium but not for blood in the left ventricle. No difference was seen between myocardial response in normal animals and in nonischemic regions in animals with coronary artery occlusion. These findings suggest that the contrast agent–induced changes in tissue T2* are monoexponential and support the idea that data derived from contrast transit studies may be useful for calculation of myocardial blood flow.
Discrimination between different types of white matter edema with diffusion‐weighted MR imaging
Authors: Ebisu Toshihiko , Naruse Shoji , Horikawa Yoshiharu , Ueda Satoshi , Tanaka Chuzo , Uto Mitsuhiro , Umeda Masahiro , Higuchi Toshihiro
Published: March 2007

Brain edema can be classified into three categories: vasogenic, cytotoxic, and interstitial. The mechanism of edema is thought to be different in each type. The authors studied the movement of water molecules in each type of white matter edema in a rat model by using diffusion‐weighted magnetic resonance imaging. Conventional T2‐weighted imaging did not allow distinction between the three types of white matter edema; the three types of edema were, however, distinguished by using diffusion‐weighted imaging. The apparent diffusion coefficient (ADC) of water was different in each type of edema. Water molecules in cytotoxic edema induced by triethyl‐tin intoxication showed a smaller and less anisotropic ADC than in normal white matter. In contrast, water in vasogenic edema induced by cold injury had a larger and more anisotropic ADC than in normal white matter. Water in interstitial edema due to kaolin‐induced hydrocephalus had an anisotropic and very large ADC.
Frequency response of retrospectively gated phase‐contrast MR imaging: Effect of interpolation
Authors: Frayne Richard , Rutt Brian K.
Published: March 2007

Retrospectively gated phase‐contrast (PC) magnetic resonance velocity and volume flow measurements were evaluated in both in vitro and in vivo experiments. The accuracy of these measurements was found to be affected by the interpolation window width required in the reconstruction of retrospectively gated data. Interpolation modified the frequency content of the series of temporal measurements by decreasing the response at higher frequencies. With a series of sinusoidal flow waveforms, the frequency response of one specific implementation of retrospectively gated PC velocity measurements was experimentally determined. The experimental response agreed with the theoretical response predicted from an analysis of the interpolating function (2.2% root‐mean‐square difference). In vitro experiments with a simulated carotid flow waveform demonstrated errors in the systolic measurements that were a direct result of the modified frequency response. A volunteer study was also undertaken and confirmed the in vitro findings.
Diagnosis of bronchial rupture with MR imaging
Authors: Huson Henry , Sais Gerard J. , Amendola Marco A.
Published: March 2007

Tracheobronchial rupture is a serious injury occurring in approximately 1.5% of cases of major chest trauma. This injury is associated with significant mortality and morbidity and may be difficult to recognize both clinically and radiologically. Radiologic signs are mostly nonspecific, with pneumothorax and pneumomedi‐astinum being the most common. A high level of suspicion is required to make the diagnosis. Computed tomography (CT) can be helpful; however, it provides only indirect evidence for the diagnosis. This report describes a case of complete transection of the right main bronchus, suspected at plain radiography and CT and clearly shown on magnetic resonance (MR) images. MR imaging, with its multiplanar capabilities, can be helpful in defining the location and extent of injury and in diagnosing injury not suspected or clearly demonstrated with other imaging modalities.
Measurement of stroke volume and cardiac output within a single breath hold with echo‐planar MR imaging
Authors: Hunter George J. , Hamberg Leena M. , Weisskoff Robert M. , Halpern Elkan F. , Brady Thomas J.
Published: March 2007

The measurement of cardiac output and ejection fraction is useful in the treatment of diverse cardiac and cardiopulmonary disease states. Although several techniques are available for accurate measurement of left ventricular parameters, assessment of the right ventricle is less well represented. No single method is overwhelmingly superior, each having different strengths and weaknesses. In the present study, the applicability of an echo‐planar magnetic resonance (MR) imaging method in which a complete volumetric measurement of the right and left ventricles may be obtained during 12 heartbeats is demonstrated. This rapidity permits imaging during a 15‐second breath hold. The authors show in 12 volunteers that breath‐hold echo‐planar volume measurements of both ventricles were consistent with results obtained with conventional MR imaging methods.
Asymmetric‐Echo, Short TE, Retrospectively gated MR imaging of the heart and pulmonary vessels
Authors: Richardson Donna B. , MacFall James R. , Sostman H. Dirk , Spritzer Charles E.
Published: March 2007

Although retrospectively cardiac‐gated (cine) magnetic resonance imaging has shown promise for large‐vessel pulmonary vascular imaging, it has not been able to depict the peripheral pulmonary vasculature, where signal is dephased because of susceptibility and/or motion artifacts. The authors developed a cine pulse sequence that uses asymmetric echoes and radio‐frequency envelopes to achieve reduced gradient moments and a short TE, thereby reducing signal losses due to disordered flow and susceptibility effects. The effects of TE (2.8–12 msec) and the degree of echo symmetry as measured by the echo symmetry fraction (ESF) (0.6–1.0) are considered in the pulmonary vasculature and the heart. In pulmonary vessels, the signal‐to‐noise ratio nearly doubled as TE was decreased from 12 to 2.8 msec, but there was only about a 15% difference as the ESF decreased from 1.0 to 0.6, consistent with T2* losses dominating gradient moment dephasing. At a TE of 2.8 msec, the sequence improves visualization of pulmonary vessels and may be helpful for diagnosing pulmonary emboll. In the heart, however, the contrast‐to‐noise ratio between blood and cardiac tissue decreased by 30% as TE decreased from 12 to 2.8 msec and was not affected by changes in ESF. Flow artifacts in the cardiac blood pool, including those that can aid in diagnosis (eg, signal loss due to “jet” flow), are much less pronounced when a small ESF and short TE are used, making this sequence less attractive for investigation of cardiac flow irregularities. The reduced flow artifacts in this case, however, permit excellent depiction of gross cardiac anatomy.
Comparison of T2‐weighted spin‐echo and fast spin‐echo techniques in the evaluation of myelination
Authors: Prenger Erin C. , Beckett William W. , Kollias Spyros S. , Ball William S.
Published: March 2007

To evaluate T2‐weighted fast spin‐echo (FSE) and conventional spin‐echo (CSE) magnetic resonance (MR) techniques in the assessment of brain myelination, 100 consecutive pediatric patients were imaged prospectively with both CSE and FSE sequences. All patients underwent a routine MR examination that included T2‐weighted CSE imaging (imaging time, 10 minutes 21 seconds) and T2‐weighted FSE imaging (imaging time, 2 minutes 5 seconds). The two techniques were compared for estimating the degree of myelination (using normal anatomic landmarks) by blind review. With T2‐weighted CSE images as the “gold standard” for estimation of normal myelination, FSE images were evaluated to determine if they showed the degree of myelination similarly to CSE images. There was a strong correlation (P <.01) between CSE and FSE images in the estimation of myelination over a wide range of patient ages.
Solitary hepatic metastasis: Comparison of dynamic contrast‐enhanced CT and MR imaging with fat‐suppressed T2‐weighted, Breath‐hold T1‐weighted FLASH, and dynamic gadolinium‐enhanced FLASH sequences
Authors: Semelka Richard C. , Shoenut J. Patrick , Ascher Susan M. , Kroeker Mervyn A. , Greenberg Howard M. , Yaffe Clifford S. , Micflikier Allan B.
Published: March 2007

Twenty consecutive cancer patients with a solitary hepatic metastasis detected with dynamic contrast‐material—enhanced computed tomography (CT) who were considered for hepatic resection underwent magnetic resonance (MR) imaging within 18 days after CT. Histologic confirmation was obtained in all lesions. CT depicted 20 solitary lesions. MR imaging showed a solitary lesion in 14 patients, two lesions in three patients, and more than two lesions in three patients, for a total of 37 lesions. Twenty‐three lesions less than 2 cm in diameter were missed with CT, and six lesions less than 1.3 cm in diameter were missed with MR imaging. MR imaging was superior to CT in the detection of hepatic metastases on a patient‐by‐patient basis (P <.01). The results suggest that MR imaging is superior to dynamic contrast‐enhanced CT for the detection of hepatic metastases.
Enhancement effects of a hepatocyte receptor—specific MR contrast agent in an animal model
Authors: Small William C. , Nelson Rendon C. , Sherbourne Gillian M. , Bernardino Michael E.
Published: March 2007

The enhancement characteristics of the liver and spleen produced by a hepatocyte‐specific magnetic resonance imaging agent, an arabinogalactan‐coated ultrasmall superparamagnetic iron oxide derivative, BMS 180550, were evaluated. Both heavily T1‐ and T2‐weighted sequences were used. Imaging was performed in the farm pig model, as a function of contrast agent concentration (5, 10, and 20 μmol of iron per kilogram) and delay (immediate, 0.5, 2.5, 5.0, 7.5, and 9.0 hours) after bolus injection of BMS 180550. BMS 180550 provided excellent contrast enhancement characteristics by producing marked positive enhancement with T1‐weighted sequences and marked negative enhancement with T2‐weighted sequences. The T1‐weighted enhancement immediately after contrast agent injection was of greater magnitude in the spleen (329% ± 83) than in the liver (66% ± 16). Postcontrast negative enhancement with T2‐weighted sequences was largely hepatocyte specific at 5 and 10 μmol/kg but was also seen within the spleen at 20 μmol/kg. The authors discuss the possible mechanisms that produce these changes and conclude that 10 μmol/kg BMS 180550 is near the optimum dose for maximizing the enhancement properties of this agent with all sequences in the farm pig.
Discrete signal processing of dynamic contrast‐enhanced MR imaging: Statistical validation and preliminary clinical application
Authors: Reddick Wilburn E. , Langston James W. , Meyer William H. , Gronemeyer Suzanne A. , Steen R. Grant , Chen Gang , Taylor June S.
Published: March 2007

A high‐resolution image‐based method was developed to analyze dynamic contrast agent‐enhanced magnetic resonance images quantitatively. This method determines the initial rate of contrast agent accumulation, the delayed rate of accumulation, and the maximum enhancement in each pixel. These three parameters allow characterization of the dynamic signal features. Simulated noisy test sets of dynamic enhancement curves have shown this method to yield a fast and accurate characterization of the dynamic signal. Clinical examples of both qualitative image parameter maps and quantitative statistical analysis of the parameter distributions demonstrated the quality and potential of the technique. The technique is designed to yield imaging and quantitative information on contrast agent accumulation that can be useful in detecting residual tumor and evaluating response to therapy, while requiring less than 7 minutes of imaging time and 5 minutes of processing time per study.
Dynamics of tumor imaging with Gd‐DTPA—polyethylene glycol polymers: Dependence on molecular weight
Authors: Desser Terry S. , Rubin Daniel L. , Muller Holde H. , Qing Fan , Khodor Samer , Zanazzi George , Young Stuart W. , Ladd David L. , Wellons Jennifer A. , Kellar Kenneth E. , Toner John L. , Snow Robert A.
Published: March 2007

Macromolecular contrast media offer potential advantages over freely diffusible agents in magnetic resonance (MR) imaging outside the central nervous system. To identify an optimum molecular weight for macromolecular contrast media, the authors studied a novel macromolecular contrast agent, gadolinium diethylenetriaminepentaacetic acid polyethylene glycol (DTPA‐PEG), synthesized in seven polymer (average) molecular weights ranging from 10 to 83 kd. Twenty‐eight rabbits bearing V2 carcinoma in thighs underwent T1‐weighted spin‐echo imaging before injection and 5–60 minutes and 24 hours after injection of the Gd‐DTPA‐PEG polymers or Gd‐DTPA at a gadolinium dose of 0.1 mmol/kg. Tumor region‐of‐interest measurements were obtained at each time point to determine contrast enhancement dynamics. Blood‐pool enhancement dynamics were observed for the Gd‐DTPA‐PEG polymers larger than 20 kd. Polymers smaller than 20 kd displayed dynamics similar to those of the freely diffusible agent Gd‐DTPA. Above the 20 kd threshold, tumor enhancement was more rapid for smaller polymers. The authors conclude that the 21.9‐kd Gd‐DTPA‐PEG polymer is best suited for clinical MR imaging.
Effect of a patellar realignment brace on patellofemoral relationships: Evaluation with kinematic MR imaging
Authors: Shellock Frank G. , Mink Jerrold H. , Deutsch Andrew L. , Fox James , Molnar Todd , Kvitne Ronald , Ferkel Richard
Published: March 2007

The effect of a newly developed patellar realignment brace was evaluated in 21 patellofemoral joints (19 patients) with patellar subluxation (13 joints with lateral subluxation and eight with medial subluxation) by using active‐movement, loaded kinematic magnetic resonance (MR) imaging. Sixteen patellofemoral joints (76%) demonstrated a qualitative correction of or improvement in patellar subluxation (ie, centralization of the patella or a decrease in the displacement of the patella) after application of the brace. Four of the five “failures” occurred in patellofemoral joints that had patella alta and/or dysplastic bone anatomy. These results indicate that the patellar realignment brace was able to counteract patellar subluxation in the majority of patellofemoral joints studied, as shown by active‐movement, loaded kinematic MR imaging. This brace appears to be useful for conservative treatment of patients with patellofemoral joint pain secondary to patellar malalignment and maltracking.
Oxygen tension mapping with F‐19 echo‐planar MR imaging of sequestered perfluorocarbon
Authors: Barker Bruce R. , Mason Ralph P. , Bansal Navin , Peshock Ronald M.
Published: March 2007

The authors used fluorine‐19 inversion‐recovery (IR) echo‐planar imaging (EPI) to map oxygen tension on the basis of the spin‐lattice relaxation rate (R1) of sequestered perfluorocarbon. R1 measured with IR‐EPI varied as a linear function of oxygen tension and temperature, and the relationship agreed well with earlier spectroscopic findings. Oxygen tension maps of a mouse that had received a dose of perflubron emulsion were acquired before, during, and after the mouse breathed pure oxygen. Results showed low liver oxygen tension during air breathing, which increased during breathing of pure oxygen, with distinct regional heterogeneity, to 8–17%atm (60–130 torr [8.0–17.3 kPa]).
Precise and accurate measurement of proton T1 in human brain in vivo: Validation and preliminary clinical application
Authors: Steen R. Grant , Gronemeyer Suzanne A. , Kingsley Peter B. , Reddick Wilbum E. , Langston James S. , Taylor June S.
Published: March 2007

Precise and accurate inversion‐recovery (PAIR) magnetic resonance (MR) measurements of T1 were obtained in eight brain regions and cerebrospinal fluid of 26 healthy volunteers. Accuracy of the technique was assessed by measuring T1 in small fluid volumes with the PAIR technique and with two independent spectroscopic techniques. The mean difference between T1 measured with PAIR and with the two spectroscopic techniques was 3.1% ± 1.3. The precision (reproducibility) of measurements with the PAIR technique was excellent. The coefficient of variation (CV) across 16 measurements in a head phantom was 2.0%, compared with a CV of 2.7% across 45 separate measurements in a single subject. The within‐subject CV was 1.8% ± 0.6 in white matter and 1.4% ± 1.0 in basal ganglia. The between‐subject CV in 26 healthy volunteers was 3.6% ± 0.6 in white matter and 4.1% ± 1.9 in basal ganglia. Comparison between a patient with an active recurrent brain tumor and an agematched patient with an inactive brain tumor showed that T1 was significantly elevated throughout the brain of the active‐tumor patient, especially in white matter tracts, even though no tumor or edema was detected in the white matter on standard MR images. Comparisons between five brain tumor patients and four healthy volunteers of similar age showed that T1 was significantly and substantially elevated throughout the white matter tracts and in the caudate nucleus, putamen, and thalamus. These results are consistent with the hypothesis that white matter tracts are selectively vulnerable to edema and that T1 increases in white matter are a sensitive indicator of patient status or tumor aggressiveness.
Pulsation artifact in short TR MR imaging and angiography: Exacerbation with signal averaging
Authors: Mitchell Donald G. , Tasciyan Talin , Ortega Hector V. , Outwater Eric , Vinitski Simon
Published: March 2007

Averaging the signals from more than one excitation per phase‐encoding view increases the signal‐to‐noise ratio and, in conventional spin‐echo magnetic resonance imaging, reduces most motion artifacts. To determine the effects of signal averaging on two‐dimensional gradient‐echo images, acquisitions with different TRs and with no averaging versus multiple‐signal averaging were compared in a pulsatile flow phantom and the human abdominal aorta. Intraview (each view repeated before changing the phase‐encoding value) and interview (obtaining all views sequentially and then repeating the entire set) averaging methods were used. Pulsation artifacts were present on all images of the flow phantom and the aorta. Intraview signal averaging, the method most commonly used, exacerbated rather than ameliorated pulsation artifacts with short TR sequences. Pulsation artifacts on two‐dimensional images obtained with a short TR can be minimized by completing the acquisition as rapidly as possible, avoiding signal averaging. If signal averaging is used for short TR images, it should be interview averaging.
Ex vivo evaluation of ferromagnetism, heating, and artifacts produced by heart valve prostheses exposed to a 1.5‐T MR system
Authors: Shellock Frank G. , Morisoli Stacy M.
Published: March 2007

Ex vivo testing techniques were used to determine the ferromagnetic qualities of, presence of heating in, and artifacts produced by 13 different heart valve prostheses exposed to a 1.5‐T (64‐MHz) magnetic resonance (MR) system. None of the heart valve prostheses showed a measurable deflection in the 1.5‐T static magnetic field. Only minimal artifacts were produced during MR imaging with a fast spoiled GRASS (gradient‐recalled acquisition in the steady state) pulse sequence. The largest temperature changes measured during a “worst case” MR imaging sequence (estimated average specific absorption rate, 2.5 W/kg; estimated spatial peak specific absorption rate, 7.6 W/kg) were +0.2°C with the implant imaged “in air” and +0.3°C with the implant imaged in normal saline. Therefore, MR procedures performed with a 1.5‐T (64‐MHz) MR system may be performed safely in patients with any of the 13 different heart valve prostheses evaluated in this study.
Comparison of breath‐hold T1‐weighted MR sequences for imaging of the liver
Authors: Semelka Richard C. , Willms Ann Bagley , Brown Mark A. , Brown Elizabeth D. , Finn J. Paul
Published: March 2007

Three rapid T1‐weighted gradient‐echo techniques for imaging of the liver were compared: fast low‐angle shot (FLASH) and section‐selective (SSTF) and non‐section‐selective (NSTF) inversion‐recovery TurboFLASH. Ten healthy volunteers were imaged at 1.5 T, with breath‐hold images acquired in the transaxial and coronal planes and non‐breath‐hold images in the transaxial plane. Breath‐hold images were evaluated quantitatively and qualitatively, and non–breath‐hold images were evaluated qualitatively. FLASH images had significantly higher (P <.001) spleenliver signal difference–to‐noise ratios (SD/Ns) than NSTF and SSTF images. Liver signal‐to‐noise ratios (S/Ns) were significantly higher (P <.001) on FLASH images than on NSTF and SSTF images. With breath hold. FLASH images were rated as having the highest quality in the axial plane, followed by NSTF and SSTF images. In the coronal plane, NSTF images were rated as having the highest quality. For images acquired during patient respiration, NSTF images had the highest quality and showed the least degradation. The results suggest that FLASH images have the highest SD/N and S/N for liver imaging and have the highest quality in the axial plane. In patients who cannot suspend respiration, NSTF images may be least affected by breathing artifact and provide reasonable image quality.
Determination of Background Gradients with Diffusion MR Imaging
Authors: Jara Hernán , Wehrli Felix W.
Published: March 2007

A new magnetic resonance (MR) imaging technique, opposite‐polarity pulsed‐field‐gradient technique, with which the effects of background magnetic field gradients can be separated from the effects of diffusion, is described. It is based on the processing of two sets of diffusion‐weighted images, the acquisition parameters of which differ only in the polarity of the applied diffusion pulses. The two effects can be separated because the cross term (bc) of the gradient factor function is antisymmetric with respect to reversal of the sign of the applied diffusion pulses. The technique permits simultaneous measurement of the spatial distribution of both the diffusion constants and background magnetic field gradients, with the same spatial resolution as the parent images from which they were derived. The technique has been validated with a phantom in which the spatial distribution of susceptibility‐induced background gradients is known, the results showing excellent agreement with theory. The technique was applied to two systems in which the spatial distribution of the background gradient is unknown. Sources of error in the measurement of background gradients and (unrestricted) diffusion constants are analyzed, including the effects of voxel size, partial volumes, and interactions between background and imaging gradients.
Effects of MR exposure on cell proliferation and migration of chick motoneurons
Authors: Yip Yee Ping , Capriotti Christine , Norbash Sepideh Gilani , Talagala S. Lalith , Yip Joseph W.
Published: March 2007

The effect of magnetic resonance (MR) exposure on the proliferation and migration of motoneurons was examined in chick embryos. Embryos were exposed in ovo to a static magnetic field of 1.5 T for 6 hours and to 64‐MHz radio‐frequency field pulses and a switched magnetic field gradient with an amplitude of 0.6 G/cm for 4 hours. For cell proliferation studies, embryos were exposed to MR fields during the developmental stage at which motoneuron proliferation is most active. For cell migration studies, embryos were exposed to MR fields at the developmental stage just before lateral motoneuron migration. The results show that the birth dates, migration, and proliferation of lateral motoneurons were unaffected by the MR exposure conditions in this study.
Effect of joint position and ligament tension on the MR signal intensity of the cruciate ligaments of the knee
Authors: Smith Kevin L. , Daniels John L. , Arnoczky Steven P. , Dodds Julie A. , Cooper Thomas G. , Gottschalk Alexander , Shaw Daniel A.
Published: March 2007

Six cadaveric lower extremities were imaged with T1‐weighted spin‐echo pulse sequences with the knees extended and flexed to 90°. Magnetic resonance signal intensities of the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) were compared. Changing from extension to flexion resulted in decreased signal intensity in six of six ACLs and five of six PCLs. Two of the knees were then imaged with and without tension applied to the ACL. Both specimens showed a decrease in signal intensity with tension, followed by an increase in signal intensity with release of the tension. Finally, in three of the limbs the ACL was surgically reconstructed and then imaged with and without tension applied to the tension graft. Signal intensity decreased with tension and increased with release of the tension in all three specimens. Thus, joint position and changes in ligament tension affect the signal intensity of the ACL and PCL, generally resulting in a signal intensity decrease with tension.
MR measurement of pulsatile pressure gradients
Authors: Urchuk Steven N. , Plewes Donald B.
Published: March 2007

A magnetic resonance (MR) imaging method for evaluating pulsatile pressure gradients in laminar blood flow is presented. The technique is based on an evaluation of fluid shear and inertial forces from cardiac‐gated phase‐contrast velocity measurements. The technique was experimentally validated by comparing MR and manometer pressure gradient measurements performed in a pulsatile flow phantom. Analyses of random noise propagation and sampling error were performed to determine the precision and accuracy of the method. The results indicate that a precision of 0.01–0.03 mmHg/cm and an accuracy of better than 8% can be achieved by using standard clinical pulse sequences in tubes exceeding 6 mm in diameter. The authors conclude that MR measurement of pressure gradients is feasible and that additional hemodynamic information may be derived from conventional phase‐contrast imaging studies.
Effects of physiologic waveform variability in triggered MR imaging: Theoretical analysis
Authors: Lauzon M. Louis , Holdsworth David W. , Frayne Richard , Rutt Brian K.
Published: March 2007

One of the assumptions inherent in most forms of triggered magnetic resonance (MR) imaging is that the pulsatile waveform (be it cardiac, respiratory, or some other) is purely periodic. In reality, the periodicity condition is rarely met. Physiologic waveform variability may lead to image artifacts and errors in velocity or volume flow rate estimates. The authors analyze the effects of physiologic waveform variability in triggered MR imaging. They propose that this variability be treated as a modulation of the underlying motion waveform. This report concentrates on amplitude modulation of the velocity waveform, which results in amplitude and phase modulation of the transverse magnetization. Established Fourier and modulation theory and the recently described principles of (k, t)‐space were used to derive the appearance of physiologic waveform variability artifacts in triggered MR images and to predict errors in time‐averaged and instantaneous velocity estimates that may result from such motion effects, including effects such as ghost overlap. Simulations and experimental results are provided to confirm the theory.
Characterization of a gadolinium‐labeled cholesterol derivative as an organ‐specific contrast agent for adrenal MR imaging
Authors: Muhler Andreas , Platzek Johannes , Radüchel Bernd , Frenzel Thomas , Weinmann Hanns‐Joachim
Published: March 2007

The purpose of the study was to determine if derivatization of cholesterol with a paramagnetic label could result in an organ‐specific contrast agent for magnetic resonance imaging of the adrenal glands. Gadolinium‐DO3A‐labeled cholesterol was synthesized and the relaxivities in water and blood plasma determined at 0.47 T and 40°C. Organ distribution was measured at 2 (n = 2) and 24 (n = 2) hours after intravenous injection of a 50 μmol/kg dose of Gd‐DO3A‐cholesterol in rats weighing 220–240 g. T1‐weighted spin‐echo images were acquired at 2 T before and after injection of 50 μmol/kg Gd‐DO3A‐cholesterol (n = 2) and Gd‐DTPA (diethylenetriaminepentaacetic acid)‐albumin (n = 2). More than 99% of the Gd‐DO3A‐cholesterol was found to be protein bound in bovine serum. High T1 and T2 relaxivities were found in water and plasma. High tissue concentrations of Gd‐DO3A‐cholesterol were found only in adrenal glands and liver. At 24 hours, adrenal gadolinium concentrations were about 10 times higher than in blood. At 2 hours after injection of Gd‐DO3A‐cholesterol. enhancement was 162% in adrenal glands and 146% in liver. With Gd‐DTPA‐albumin, enhancement values were 57% and 56%. respectively.
Quantitative mr imaging data in the evaluation of hepatic metastases during systemic chemotherapy
Authors: Giovagnoni Andrea , Paci Enrico , Terilli Filippo , Cellerino Riccardo , Piga Andrea
Published: March 2007

To identify changes induced by chemotherapy in hepatic metastases, 34 patients with metastases underwent magnetic resonance (MR) imaging before the start of systemic chemotherapy and monthly thereafter. The number, size, and morphologic patterns of the lesions and changes in quantitative parameters (signal‐to‐noise ratio [S/N], contrast‐to‐noise ratio, and signal intensity ratio) were evaluated and correlated with response to treatment and prognosis. After treatment, seven patients showed a partial response, 18 had stable disease, and nine had progressive disease. No relevant changes in the patterns of the lesions were observed. Quantitative data showed that patients with a good prognosis had an increase in S/N on T1‐weighted images and a relative decrease on T2‐weighted images; patients with a poor prognosis showed a decrease in S/N on T1‐weighted images and an increase on T2‐weighted images. The differences between patient groups were significant for both T1‐ and T2‐ weighted images. This study demonstrates the value of MR imaging in follow‐up of liver metastases and suggests the usefulness of quantitative MR imaging data.
Hybrid dante and phase‐contrast imaging technique for measurement of three‐ dimensional myocardial wall motion
Authors: Perman William H. , Creswell Lawrence L. , Wyers Stephan G. , Moulton Michael J. , Pasque Michael K.
Published: March 2007

Characterization of myocardial stress and strain is necessary for a complete understanding of myocardial function. The precise quantification of regional myocardial strain is complicated by its time‐varying pattern and regional variation resulting from the anisotropy of the myocardium and by complex torsional and shortening motions of the heart during the cardiac cycle. The authors have developed a technique for point‐specific tracking of myocardial motion along all three axes in a constant selected section of myocardium by combining prospective section selection with in‐plane DANTE (delays alternating with nutations for tailored excitation) tissue tagging and phase‐contrast detection of motion perpendicular to the image plane. With this technique, it is possible to determine point‐specific myocardial strain values in vivo.
Analysis of on‐ and off‐resonance magnetization transfer techniques
Authors: Hua Jianmin , Hurst Gregory C.
Published: March 2007

Three methods of performing magnetization transfer (MT) MR imaging ere emlyzed: (a) off‐resonance continuous wave, (b) off‐rceonance shaped pulses, end (c) on‐resonance binomial pulses. With two‐pool Bloch‐model simulations., signal levels from “MT active” spin systems were calculated. with reference to direct saturation of “MT inactive” systems. allowing calculation of contrast due to MT. Simulations demonstrate several trends with variation of excitation amplitude and Offret fiequency for the off‐resoname methods and with variation of excitation emplitude end pulse shape „order”︁ for binomial pulses. The simulations show that nominally optimized versions of each of these approaches provide essentially equivalent contrast at a given level of applied MT power, contrary to previous claims. Experiments with an MT‐inactive phentom, with a whole‐body syetem, show results with off‐ rewnence pulses to be in good agreement with simulations. whereas binomiel‐ pulse experiments show anomalously large direct saturation.
A complex‐difference phase‐contrast technique for measurement of volume flow rates
Authors: Polzin Jason A. , Alley Marcus T. , Korosec Frank R. , Gristn Thomas M , Wang Yi , Mistretta Charles A.
Published: March 2007

Magnetic resonance (MR) phase‐difference methods work well for measuring volumetric flow rates when the vessel diameter is large compared with the in‐plane voxel dimensions. For small vessels (eg, coronary arteries), partial‐volume effects introduce substantial errors in the measured volume flow rate. To correctly measure flow rates through a voxel, both the fraction of the voxel containing moving spins and the phase shift imparted to those spins must be known. The authors propose a flow measurement method that combines information obtained with both the complex‐difference and phase‐difference processing techniques and thereby provides the fractional volume occupied by the moving spins and the phase of those spins. The complex‐difference flow map method proposed results in improved accuracy of MR phase‐contrast flow measurements in the presence of partial‐volume effects.
Correction of partial‐volume effects in phase‐contrast flow measurements
Authors: Tang Chao , Blatter Duane D. , Parker Dennis L.
Published: March 2007

Because of the relatively small size of vessels and limited magnetic resonance (MR) imaging resolution, the accuracy of volume flow rate measurements is limited. A technique that corrects the partial‐volume effect in volume flow rate measurements is presented. The technique uses small‐phase‐shift approximation, with the assumption that blood flow in the voxels at the boundary of the vessel is slow. With the proposed correction technique, the volume flow rate in partially occupied voxels is corrected on a voxel‐by‐voxel basis and the accuracy of flow measurements increases. Results are shown analytically and for MR phantom data.
Separation of fat and water in fast spin‐echo MR imaging with the three‐point dixon technique
Authors: Hardy Peter A. , Hinks R. Scott , Tkach Jean A.
Published: March 2007

A method for suppressing fat in fast spin‐echo imaging with the three‐point Dixon technique is described. The method differs from the three‐point Dixon method used in conventional spin‐echo imaging in that the readout gradient instead of a radio‐frequency pulse is shifted. This method preserves the Carr‐Purcell‐Meiboom‐Gill nature of the fast spin‐echo sequence and hence is less sensitive to magnetic field inhomogeneities and resonance frequency mistiming. As in the original three‐point Dixon technique used in conventional spin‐echo imaging, three acquisitions are required to estimate the field inhomogeneity and completely separate fat and water. The extra time required is not excessive considering that the fast spin‐echo method is frequently applied with multiple signal acquisition. Also, this technique achieves an expected signal‐to‐noise ratio comparable to 2.67 signal acquisitions, which is approximately 94% of the signal‐to‐noise ratio obtained with three signal acquisitions. The method is demonstrated with applications to phantoms and a human volunteer.