bluuebunny/crossref_metadata_2025 huggingface dataset:
Normal and degenerating articular cartilage: In vitro correlation of MR imaging and histologic findings
Authors: Monson Nancy L. , Haughton Victor M. , Modi Jean M. , Sether Lowell A. , PhD Khang‐Cheng Ho
Published: March 2007

Histologic correlation of the different magnetic resonance (MR) appearances of articular cartilage has not been studied extensively. Therefore, the authors correlated thin (high‐resolution) MR sections of articular cartilage with histologic sections. Human cadaver lumbar facet joints were imaged with a 1‐mm section thickness and a 4‐cm field of view, then sectioned and stained for histologic comparison. MR imaging patterns were identified that correlated with normal cartilage and three histologically different patterns of degeneration.
Hepatic focal nodular hyperplasia: MR imaging at 1.0 and 1.5 T
Authors: Haggar Allan M. , Bree Robert L.
Published: March 2007

Ten cases of hepatic focal nodular hyperplasia (FNH) were studied with magnetic resonance (MR) imaging. Proof of diagnosis was by needle biopsy or follow‐up of as long as 5 years. Both short TR/TE and long TR/TE images were obtained. The most common finding was isointen‐sity of the lesion relative to liver parenchyma with all pulse sequences. A central scar was seen in only one patient and was hyperintense on long TR/TE images. Slight hyperintensity of the lesion on short TR/TE and long TR/TE images was seen in two cases. Textural heterogeneity was present in only one of these. The most common presentation in our series was a visually isointense lesion relative to liver on short TR/TE images and an isointense or slightly hyperintense lesion on long TR/TE images. A review of the literature and the present findings suggest that FNH has a variable appearance on MR images.
Quantitative P‐31 MR spectroscopy of the liver in alcoholic cirrhosis
Authors: Rajanayagam Vasanthan , Lee Roland R. , Ackerman Zvi , Bradley William G. , Ross Brian D.
Published: March 2007

To determine the cause of reduced urea synthesis in cirrhosis, absolute concentrations of phosphorus metabolites in the human liver have been measured in vivo with magnetic resonance (MR) spectroscopy. One‐dimensional chemical shift imaging was used to obtain phosphorus‐31 spectra from five healthy volunteers and five patients with alcoholic cirrhosis. A reference standard included in all studies enabled the calculation of absolute concentrations. In contrast to hepatic metabolite ratios, absolute concentrations reveal that in the cirrhotic patients, concentrations of adenosine triphosphate (ATP) were significantly reduced and concentrations of phosphomonoesters slightly reduced. Intracellular pH was unchanged. Histologic evidence suggests that the amount of ATP per cell was unchanged and could not account for the reduced urea production. Instead, urea synthesis depends on the functional liver cell mass, which was reduced by 31% in alcoholic cirrhosis. Quantitative in vivo P‐31 MR spectroscopy of liver has potential clinical applications and can supplement the more generally used P‐31 metabolite ratios.
Improved receiver coil for upper thoracic spine imaging in a vertical magnetic field
Authors: Malmgren Lars , Ståhlberg Freddy , Holtås Stig , Larsson Elna‐Marie , Persson Bertil R. R.
Published: March 2007

To improve image quality in the upper thoracic spine, an anatomically shaped copper wire loop coil, made to fit over the patient's shoulders, was constructed. The coil was permanently mounted on a foam‐rubber vest to facilitate attachment to the patient. Phantom and in vivo studies of the performance of the coil in healthy volunteers showed as much as a two times greater signal‐to‐noise ratio relative to that of standard coils for the upper thoracic spine. In a patient with lesions in the upper thoracic cord, the coil gave better image quality in the region of interest than did the standard coils. The coil has been integrated into the authors' routine imaging equipment and has been the coil of choice for imaging of the upper thoracic spine on their 0.3‐T vertical field system.
Tissue specificity of low‐field‐strength magnetization transfer contrast imaging
Authors: Niemi Pekka T. , Komu Markku E. S. , Koskinen Seppo K.
Published: March 2007

The time‐dependent saturation transfer technique was used to measure the transfer of magnetization in several rat tissues at 0.1 T. The length of the saturation pulse was varied from 0 to 510 msec. The magnetization transfer contrast effect was characteristic for each type of tissue. A substantial reduction of image intensity was obtained in skeletal muscle (74%), heart (71%), spleen (64%), brain (65%), pancreas (64%), liver (64%), kidneys (62%), and lungs (56%) with the longest saturation pulse available. Much smaller declines occurred in stagnant blood and peritoneal fat. The potential of this imaging technique for clinical conditions is discussed.
Change in red blood cell relaxation with hydration: Application to MR imaging of hemorrhage
Authors: Taber Katherine H. , Ford Joseph J. , Jensen Ray S. , Chin Hsiao Yang , Udden Mark M. , Plishker Gordon A. , Contant Charles F. , Hayman L. Anne
Published: March 2007

T1 and T2 were measured in unclotted blood samples with 0.24‐ and 4.7‐T spectrometers. The fraction by weight of intracellular water in the red blood cells (RBCs) was varied by either osmotic manipulation or density separation in concentrated (packed RBCs) and dilute (RBCs suspended in buffer or serum) samples. Reducing the cell water content caused a moderate decrease in T1 and a profound decrease in T2 at both 0.24 and 4.7 T. Conversely, increasing the cell water content caused an increase in both T1 and T2. The authors conclude that dehydrated RBCs in an area of hemorrhage would cause a substantial decrease in signal intensity on long TR/TE (T2‐weighted) images. Overhydration of RBCs would have the opposite effect.
MR imaging of the pelvis with an endorectal‐external multicoil array
Authors: Schnall Mitchell D. , Connick Tom , Hayes Cecil E. , Lenkinski Robert E. , Kressel Herbert Y.
Published: March 2007

Magnetic resonance (MR) images of the pelvis obtained with an endorectal coil have improved resolution relative to that of body coil images; however, they have limited spatial coverage. The sensitivity profile can be improved by using the endorectal coil combined with an external anterior coil as part of a multicoil array. If each coil is connected to a separate receiver, the individual images can be combined to provide an optimal signal‐to‐noise ratio (S/N). The authors have investigated a 5‐inch (12.7‐cm) surface coil or a two‐coil array as the anterior coil. In both of these configurations, the S/N is improved relative to that of the endorectal coil alone at distances greater than 3 cm from the endorectal coil. The anterior two‐coil array provides more lateral coverage. The improved spatial coverage available with this technique expands potential clinical applications of endorectal MR imaging.
MR microscopy of chick embryo vasculature
Authors: Smith Bradley R. , Effmann Eric L. , Allan Johnson G.
Published: March 2007

Six‐day‐old chick embryos were examined with magnetic resonance microscopy after vascular perfusion fixation and perfusion with gadolinium‐doped gelatin to highlight the developing vascular anatomy. Gadolinium gelatin, with its short T1, provided a source of signal contrast within the vessels. The entire embryo was embedded in gelatin to minimize susceptibility artifacts that are prevalent at the high field strength (7.0 T) used. A series of single‐section spin‐echo images were acquired with various TRs to determine the optimal imaging sequence for a three‐dimensional (3D) acquisition. The combination of gadolinium gelatin in the vascular spaces, gelatin embedding of the specimen, and optimal acquisition parameters yielded a 3D stack of high‐resolution images that was readily reconstructed and rendered to effectively demonstrate the developing thoracic vessels in the embryo.
Detection of zonal renal ischemia with contrast‐enhanced MR imaging with a macromolecular blood pool contrast agent
Authors: Vexler Vladimir S. , Berthèzene Yves , Clément Olivier , Mühler Andreas , Rosenau Werner , Moseley Michael E. , Brasch Robert C.
Published: March 2007

The potential of magnetic resonance (MR) imaging enhanced with albumin‐(gadolinium diethylenetri‐aminepentaacetic acid [DTPA])35, a macromolecular blood pool marker, for detection of focal changes in renal perfusion was studied in a myoglobinuric acute renal failure (ARF) model in the rat. T1‐weighted spin‐echo postcontrast images of injured kidneys at 3 hours after glycerol injection showed three distinct zones: a strongly enhanced outer cortex, a low‐intensity inner cortex, and a strongly enhanced medulla. The distinct band of low intensity in the inner cortex indicated zonal decreased blood volume, corresponding to published microsphere data showing zonal low perfusion in the inner cortex. Contrast differences between parenchymal zones were significant for at least 30 minutes. No focal ischemic changes could be delineated on nonenhanced images. Enhanced and nonenhanced images of injured kidneys obtained at 24 hours after glycerol injection revealed no zonal differentiation. Contrast‐enhanced MR imaging data in this ARF model correlated well with pathologic data and microsphere perfusion results. Contrast‐enhanced characterization of the ischemic phase of renal injury with MR imaging may improve specificity for the diagnosis of ARF and may serve as a marker for therapeutic intervention.
Selective versus nonselective preparation pulses in two‐dimensional MP‐RAGE imaging of the liver
Authors: de Lange Eduard E. , Mugler John P. , Bertolina James A. , Brookeman James R.
Published: March 2007

The use of a section‐selective preparation pulse in two‐di‐mensional (2D) T1‐weighted magnetization‐prepared rapid gradient‐echo (MP‐RAGE) imaging of the liver was investigated. The images were compared with those obtained with a nonselective pulse. The performances of the sequences were evaluated in 11 patients with 12 focal liver lesions, and lesion‐liver and lesion‐vessel signal difference‐to‐noise ratios (SD/Ns) were calculated. With the section‐selective preparation pulse, small lesions were better differentiated from vessels, and multiple, consecutive images could be obtained at shorter intervals. The mean lesion‐liver SD/N was slightly but not signiticantly greater for images obtained with a selective pulse, while the lesion‐vessel SD/N was significantly greater (P < .01). It is concluded that a section‐selective preparation pulse can improve the clinical utility of the 2D MP‐RAGE sequence in the evaluation of focal liver disease.
Optimization of three‐dimensional T1‐weighted gradient‐echo imaging of the cervical spine
Authors: Ross Jeffrey S. , Tkach Jean A. , Dillinger John , Ruggieri Paul M. , Masaryk Thomas J. , Modic Michael T.
Published: March 2007

Various parameters of the three‐dimensional (3D) T1‐weighted magnetization‐prepared rapid acquisition gradient‐echo (MP‐RAGE) sequence were evaluated to improve spatial resolution while maintaining T1 contrast and a short examination time in imaging of the cervical spine in volunteers. The most dramatic improvements in image resolution occurred by decreasing section thickness to 1.2 mm and increasing the in‐plane matrix to 192 × 256, with a 230‐mm field of view. The increase in imaging time due to the increased matrix was offset by the elimination of the preparation pulse and wait time, without dramatic changes in contrast‐tonoise ratio or overall image quality. Optimum parameters included elimination of the preparation pulse and wait time, 12° flip angle, 192 × 256 matrix, 1.2‐mm section thickness, nonselective excitation (coronal acquisition), RF spoiling, and standard k‐space ordering, for an examination time of 5 minutes 21 seconds.
Cardiac masses: Signal intensity features on spin‐echo, gradient‐echo, gadolinium‐enhanced spin‐echo, and TurboFLASH images
Authors: Semelka Richard C. , Shoenut J. Patrick , Wilson Murray E. , Pellech Andrew E. , Patton J. Norman
Published: March 2007

Fifteen patients with cardiac or paracardiac masses underwent magnetic resonance (MR) imaging with spin‐echo (n = 15), cine gradient‐echo (n = 15), gadopentetate dimeglumine‐enhanced spin‐echo (n = 15), and TurboFLASH (fast low‐angle shot) (n = 7) sequences. All masses had either histologic confirmation (n = 11) or confirmation with other imaging modalities (n = 4). Myxomas (n = 6) were characterized by an intermediate signal intensity (SI) on spin‐echo (n = 6) and low SI on cine gradient‐echo (n = 6) images and moderately high‐SI contrast enhancement (n = 5). Percent contrast enhancement for myxomas was 57% ± 11%. Thrombus (n = 4) had intermediate (n = 3) or high (n = 1) SI on spin‐echo images and low (n = 2) or intermediate (n = 2) SI on gradient‐echo images and did not show substantial contrast enhancement. Postcontrast first‐pass TurboFLASH images were useful by clearly demonstrating the nonen‐hancing mass lesion in a high‐SI blood pool. Other cardiac and paracardiac tumors (n = 5) showed variable pre‐and postcontrast spin‐echo SI; however, no other tumor showed low SI on cine gradient‐echo images.
MR angiography with adiabatic flow excitation
Authors: Lee James N. , Parker Dennis L.
Published: March 2007

A new method of magnetic resonance (MR) angiog‐raphy is presented that produces signal from flowing spins and suppresses that from stationary spins by means of a flow excitation pulse sequence consisting of adiabatic 90° and 180° radio‐frequency (RF) pulses interleaved with flow‐dephasing gradient lobes. Stationary spins are refocused along the z axis, while flowing spins are dephased by the gradient lobes and generate a transverse component that can be measured directly to produce the angio‐gram. Adiabatic RF pulses and unipolar gradient lobes give the pulse sequence a high degree of immunity to RF and magnetic field inhomogeneity. The pulse sequence can be successfully applied with a transmit/receive surface coil. The disadvantage of adiabatic RF pulses is that their long duration makes it difficult to suppress the signal of stationary spins with short T2.
MR imaging of temporomandibular joint abnormalities associated with cervical hyperextension/hyperflexion (Whiplash) injuries
Authors: Pressman Barry D. , Shellock Frank G. , Schames Joseph , Schames Mayer
Published: March 2007

Patients often have temporomandibular joint (TMJ) dysfunction‐related symptoms after cervical hyperextension/hyperflexion injuries (“whiplash”) caused by rear‐end motor‐vehicle collisions. To determine abnormalities of the TMJ associated with these injuries, 33 consecutive symptomatic patients (66 joints) with no direct trauma to the jaw, mouth, head, or face due to the accident and no prior history of TMJ dysfunction underwent magnetic resonance (MR) imaging, and the images were retrospectively analyzed. Overall, 29 (88%) patients had some type of TMJ abnormality related to whiplash injury. Displacement of the disk was seen in 37 (56%) of the TMJs as follows: 21 (32%) had anterior displacement with reduction, nine (14%) had anterior displacement without reduction, six (9%) had lateral or medial displacement, and one (2%) had posterior displacement. On T2‐weighted images, 43 (65%) TMJs had abnormal joint fluid or edema, predominantly affecting the joint capsule and/or lateral pterygoid muscles. The finding that many of the patients had joint fluid and/or soft‐tissue edema indicates that T2‐weighted images are especially useful for assessment of patients with a history of whiplash injury.
Computer‐controlled flow simulator for MR flow studies
Authors: Frayne Richard , Holdsworth David W. , Gowman Linda M. , Rickey Daniel W. , Drangova Maria , Fenster Aaron , Rutt Brian K.
Published: March 2007

A novel computer‐controlled flow simulator for use in magnetic resonance (MR) flow experiments was evaluated. The accuracy in constant‐flow mode was better than 1%. The accuracy in pulsatile‐flow mode was found to be dependent on the interconnecting tubing. The short‐term and long‐term repro‐ducibilities of pulsatile waveforms were <0.4 mL/sec (1 standard deviation). Increased response times due to the lengths of tubing required in MR flow experiments were surmounted by using a modified tubing configuration and pre‐compensated waveforms. Piston reversal was found not to cause major difficulties in MR flow experiments.
Enhancement of tumor‐liver contrast‐to‐noise ratio with gadobenate dimeglumine in MR imaging of rats
Authors: Kreft Burkhard P. , Tanimoto Akihiro , Stark David D. , Baba Yuji , Zhao Longhai , Chen John T. , Compton Carolyn C. , Paul Finn J. , Cavagna Friedrich M.
Published: March 2007

The efficacy for tumor detection of the hepatocyte‐specific contrast agent gadobenate dimeglumine (gadolinium‐BOPTA/Dimeg) was evaluated in four different experimental tumor models in rats. Histo‐logic findings were correlated with quantitative data derived from ex vivo relaxometry and in vivo magnetic resonance (MR) imaging. Noninfiltrating tumors showed maximal enhancement of liver parenchyma 5–10 minutes after contrast agent administration, with a plateau over the next 30 minutes. In contrast, infiltrating tumors, which caused hepatocellular injury and inflammatory changes, delayed maximal enhancement of tumor‐free parenchyma by 15–20 minutes. Nonspecific tumor enhancement depended on tumor vascularity and occurred in the early phase after contrast agent administration. Despite differences in specific enhancement of tumor‐free parenchyma and nonspecific tumor enhancement, tumor‐liver contrast‐to‐noise ratios increased 96%–248% in all tumor models 30 minutes after intravenous administration of 75 mmol/kg Gd‐BOPTA/Dimeg. Gd‐BOPTA/Dimeg enhanced tumor conspicuity independently of the histologic characteristics of the tumor.
Tetra‐p‐aminophenylporphyrin conjugated with Gd‐DTPA: Tumor‐specific contrast agent for MR imaging
Authors: Hindré Francois , Plouzennec Maryvonne Le , de Certaines Jacques D. , Foultier Marie Thérèse , Patrice Thierry , Simonneaux Gérard
Published: March 2007

Tetra‐P‐aminophenylporphyrin (TPP) was conjugated with gadolinium diethylenetriaminepen‐taacetic acid (DTPA) and used as a contrast agent in magnetic resonance (MR) imaging to achieve tumor selectivity in nude mice. A substantial decrease in T1 was measured in excised tissues (kidneys, tumor, and liver) from mice that received the porphy‐rin derivative Gd2(DTPA)4 TPP. Toxicity and photo‐toxicity were less than those obtained with hematoporphyrin derivative in both L1210 lym‐phoblastic leukemia cells and HT 29 human co‐lonic cancer cells, as determined with in vitro assays. MR images showed an enhancement of contrast between the tumor and adjacent tissue after injection of this agent. The results indicate that Gd2(DTPA)4TPP could be a useful prototype paramagnetic porphyrin MR imaging contrast agent with an affinity for tumors.
Preliminary evaluation of iron phytate (inositol hexaphosphate) as a gastrointestinal MR contrast agent
Authors: Unger Evan C. , Fritz Thomas A. , Palestrant David , Meakem Thomas J. , Granstrom Per , Gatenby Robert A.
Published: March 2007

A simple, effective, safe, and well‐tolerated contrast agent is needed as a bowel marker for magnetic resonance (MR) imaging. The authors tested a variety of foodstuffs admixed with ferric iron as potential gastrointestinal MR contrast agents. Phytate (inosi‐tol hexaphosphate) more than doubled the relaxiv‐ity of solutions of ferric iron. Because of the improved relaxivity of iron phytate, the concentration of iron could be reduced substantially relative to free ferric iron (eg, ferric chloride or ferric ammonium citrate). Imaging studies were performed in five volunteers to determine the optimal dose of iron phytate and in five additional volunteers to test its effectiveness. A 200 mg/L concentration of ferric iron with phytate functions as an effective gastrointestinal MR contrast agent for T1‐weighted abdominal MR imaging, significantly improving bowel contrast (P <.01). Blood studies after contrast agent administration showed no appreciable increase in serum iron. Compared with standard chelate complexcs that decrease the relaxivity of a given paramagnetic ion, phytate not only decreases the absorption of the iron but increases its relaxivity.
Safety aspects and pharmacokinetics of inhaled aerosolized gadolinium
Authors: Berthezëne Yves , Mühler Andreas , Lang Philipp , Shames David M. , Clëment Olivier , Rosenau Werner , Kuwatsuru Ryohei , Brasch Robert C.
Published: March 2007

This study evaluated the pharmacokinetics and potential toxicity of inhaled aerosolized gadopen‐tetate dimeglumine. The pharmacokinetics were evaluated with in vitro relaxometry of the lungs, blood, urine, and liver before and for up to 36 hours after a 5‐minute inhalation of aerosolized gadopen‐tetate dimeglumine (0.25 mol/L). For assessment of potential toxicity, hemodynamic variables were monitored during and for 10 minutes after inhalation. Extravascular lung water was measured before and after exposure. Finally, the potential for tissue damage was evaluated histologically. Pulmonary clearance of aerosolized gadopentetate dimeglumine was monoexponential with a half‐time of 2.16 hours. Aerosolized gadopentetate dimeglumine was excreted through the kidneys, as shown by the decrease in urinary T1. Renal elimination was completed by 30 hours. No acute hemodynamic effect, histologic change, or induction of edema was demonstrated. This study shows that inhalation of aerosolized gadopentetate dimeglumine is well tolerated in rats and favors the further evaluation of this administration route, including clinical trials.
MR imaging of the breast
Authors: Harms Steven E. , Flamig Duane P.
Published: March 2007

The current strategy for breast cancer treatment involves early detection of the neoplasm before it has metasta‐sized outside the breast, and surgical treatment of the lesion that minimizes deformity. Conventional methods of diagnostic imaging of the breast, including mammogra‐phy, sonography, and galactography, do not adequately address clinical needs with regard to lesion characterization and staging. Magnetic resonance (MR) imaging has been proposed as a modality that may address these needs. The potential clinical uses of MR imaging are defined in terms of clinical needs and technologic requirements. Applications of MR imaging in detection of breast lesions can be divided into two major approaches based on the clinical questions to be answered: (a) improved specificity and (b) improved sensitivity. These approaches are defined by specific sets of clinical needs and have substantially different technologic requirements. The specificity approach is used to reduce the number of biopsies performed to confirm false‐positive mammo‐graphic findings. The MR imaging device that is used to improve specificity must visualize only the lesions that are seen mammographically. The sensitivity approach requires the visualization of lesions not identified at mammography, so that breast disease can be more effectively staged for treatment. The technologic requirements for the sensitivity approach are considerably more rigorous, because all lesions must be identified. The advantages and disadvantages of each of these approaches and the potential clinical ramifications are described.
Preoperative local staging of rectal carcinoma with MR imaging and a rectal balloon
Authors: Okizuka Hiromi , Sugimura Kazuro , Ishida Tetsuya
Published: March 2007

Magnetic resonance (MR) imaging for the preoperative assessment of rectal carcinoma was evaluated. Thirty‐three patients underwent MR imaging with a 1.5‐T unit. On the basis of results of barium enema studies and/or digital examination, a balloon catheter was inserted to the level of the lesion before MR imaging. Both T1‐and T2‐weighted axial spin‐echo images were obtained in all patients. With the balloon catheter, the three layers of the normal bowel wall could be seen on T2‐weighted images. Muscular invasion was detected with a sensitivity of 90%, a specificity of 84%, a positive predictive value of 90%, a negative predictive value of 84%, and an overall accuracy of 88%. False‐positive results were related to chemical shift artifact and intramural lymph node metastases. Perirectal fat invasion was detected with a sensitivity of 64%, a specificity of 89%, a positive predictive value of 82%, a negative predictive value of 77%, and an overall accuracy of 79%. One of the false‐positive results was related to intramural lymph node metastases and the other to perirectal vessels. Evaluation of adjacent organ invasion was accurate in all patients. Lymph node metastasis was correctly detected in six of nine patients. Absence of lymph node metastasis was correctly predicted in 23 of 24 patients. Thus, MR imaging with a balloon catheter was useful for detection of tumor invasion into muscularis propria and adjacent organs; however, its demonstration of perirectal fat and lymph node involvement was less accurate.
Three‐dimensional MR reconstruction images of skull base tumors
Authors: Vogl Thomas J. , Assal Josef , Bergman Clifford , Grevers Gerd , Wustrow Thomas , Hamburger Christian , McMahon Christine , Lissner Josef
Published: March 2007

Forty‐eight patients with skull base tumors were evaluated prospectively with T1‐weighted spin‐echo two‐dimensional (2D) magnetic resonance (MR) sequences, a three‐dimensional (3D) MR TurboFLASH (fast low‐angle shot) sequence, and a 3D reconstruction window technique. All patients underwent surgery with histopathologic correlation, and the three MR imaging techniques were compared to assess representation of tumor margins and the topographic relationship of tumor to surrounding tissue and adjacent vasculature. The best results were obtained with standard 2D spin‐echo sequences after administration of the paramagnetic contrast agent gadopentetate dimeglumine. The 2D MR sequences gave the highest contrast‐to‐noise ratios, with decreasing values for 3D sequences and 3D reconstructions, respectively. Nevertheless, 3D MR imaging, by virtue of its good representation of adjacent structures, aided surgeons in planning surgical intervention. This study presents the technical features of 3D imaging of the skull base, the choices involved in its implementation, and its potential clinical applications.
Analysis of MR phase‐contrast measurements of pulsatile velocity waveforms
Authors: Hangiandreou Nicholas J. , Rossman Phillip J. , Riederer Stephen J.
Published: March 2007

Errors in the measurement of the mean velocity of pulsatile velocity waveforms with ungated phasecontrast techniques were studied theoretically and experimentally. Waveforms consisting of a constant and two sinusoidal components were analyzed. Variations in magnitude and phase of the vascular magnetic resonance (MR) signal resulted in errors, the severity of which increased when either factor increased. Magnitude variations always resulted in overestimation. The general shape of the waveform greatly influenced the error, with certain waveforms producing greater inherent error than others. Experimental measurements were performed, validating the predicted sensitivity of these errors to changes in imaging parameters, including TR and flow‐encoding sensitivity. Errors generally became more severe with increased flow‐encoding sensitivity. The theoretical and experimental results suggest that accurate mean velocity measurements in many vessels of the body‐with acquisition times of less than 15 seconds‐should be attainable with ungated imaging techniques and with careful selection of relevant imaging parameters.
Accuracy and precision of MR velocity mapping in measurement of stenotic cross‐sectional area, flow rate, and pressure gradient
Authors: Søndergaard Lars , Ståhlberg Freddy , Thomsen Carsten , Stensgaard Anders , Lindvig Knud , Henriksen Ole
Published: March 2007

Reliability of magnetic resonance (MR) velocity mapping to assess severity of stenosis was assessed in vitro. Steady flow at different flow rates through five stenoses with a central orifice area ranging from 17 to 176 mm2 was measured with velocity mapping performed perpendicular to the stenotic jet. Besides determination of the stenotic cross‐sectional area and flow rate, the pressure gradient was calculated with the modified Bernoulli equation and compared with manometer measurements. Cross‐sectional areas were measured with an accuracy of ⩾76%, a precision of ⩾91%, and an error of ⩽19 mm2. Flow rates had an accuracy of ⩾72%, a precision of ⩽94%, and an error of ⩽1.4 L/min. The modification of the Bernoulli equation limited its reliability to stenoses with areas of 35‐113 mm2. Pressure gradients were calculated with an accuracy of ⩾80%, a precision of ⩾88%, and an error of ⩽15 mm Hg. The method was applied in a single patient with aortic stenosis and gave estimates that agreed with those obtained by heart catheterization.
Three‐dimensional MR imaging of the coronary arteries: Preliminary clinical experience
Authors: Paschal Cynthia B. , Mark Haacke E. , Adler Lee P.
Published: March 2007

A three‐dimensional (3D) magnetization‐prepared (MP) rapid gradient‐echo (RAGE) and 3D RAGE technique was used to image the coronary arteries in healthy volunteers and patients with known disease. Each sequence produced images of volumes partitioned into 16 thin sections with differing blood‐fat‐myocardium contrast. The two types of images were subtracted to null fat signal, thus producing a third image set that showed flowing blood. Total imaging time was about 17 minutes. In the volunteers, the 3D MP‐RAGE and subtraction images consistently showed the morphology of the right coronary artery. The left main and left anterior descending arteries were also well seen. The circumflex artery was less consistently identified. Of the 17 diseased coronary artery segments identified at catheterization, 16 had altered signal intensity (narrowing, occlusion, reduced contrast‐to‐noise ratio, irregularity) on the subtraction images, while 13 had altered signal intensity on the 3D MP‐RAGE images. The results indicate that this 3D MP‐RAGE and 3D RAGE technique has potential utility as a screening method for coronary heart disease.
Sedation, anesthesia, and physiologic monitoring during MR imaging: Evaluation of procedures and equipment
Authors: Holshouser Barbara A. , Hinshaw David B. , Shellock Frank G.
Published: March 2007

The authors developed safe standard sedation and general anesthesia procedures for adults and children, including adequate physiologic monitoring, during magnetic resonance (MR) imaging. Six‐year results are reported from one institution; 75% of the 600 patients per year who require sedation or anesthesia are children who require sedation only. Testing was done to determine MR compatibility of various types of equipment essential for monitoring and supporting sedated or anesthetized patients in 1.0‐and 1.5‐T MR imagers. Use of sedation procedures that include oral chloral hydrate after sleep deprivation resulted in a failure rate of 3.8% in sedating outpatient children. Every physiologic parameter that can be monitored under normal circumstances in the critical care unit or operating room can be monitored during MR imaging. Our experience indicates that with careful consideration of the unique MR environment and with rigorous testing of monitoring equipment, MR imaging can be performed safely in sedated or anesthetized patients.
Hydrogen‐1, sodium‐23, and carbon‐13 MR spectroscopy of cartilage degradation in vitro
Authors: Jelicks Linda A. , Paul Pradip K. , O'Byrne Elizabeth , Gupta Raj K.
Published: March 2007

Viable bovine nasal cartilage was examined with magnetic resonance (MR) spectroscopy. Digestion of the proteoglycan matrix by papain or trypsin was accompanied by substantial changes in carbon‐13, sodium‐23, and hydrogen‐1 MR spectra and relaxation parameters, with C‐13 MR spectra showing the most pronounced changes. These results indicate the potential of MR spectroscopy (and imaging) for noninvasive evaluation of cartilage disease and monitoring of patients with degenerative joint diseases.
Noise reduction in three‐dimensional phase‐contrast MR velocity measurementsl
Authors: Song Samuel M. , Napel Sandy , Glover Gary H. , Pelc Norbert J.
Published: March 2007

The authors have developed a method to reduce noise in three‐dimensional (3D) phase‐contrast magnetic resonance (MR) velocity measurements by exploiting the property that blood is incompressible and, therefore, the velocity field describing its flow must be divergence‐free. The divergence‐free condition is incorporated by a projection operation in Hilbert space. The velocity field obtained with 3D phase‐contrast MR imaging is projected onto the space of divergence‐free velocity fields. The reduction of noise is achieved because the projection operation eliminates the noise component that is not divergence‐free. Signal‐to‐noise ratio (S/N) gains on the order of 15%‐25% were observed. The immediate effect of this noise reduction manifests itself in higher‐quality phase‐contrast MR angiograms. Alternatively, the S/N gain can be traded for a reduction in imaging time and/or improved spatial resolution.
Correlation of cine MR velocity measurements in the internal carotid artery with collateral flow in the circle of willis: Preliminary study
Authors: Davis Wayne L. , Turski Patrick A. , Gorbatenko Kristina G. , Weber David
Published: March 2007

The velocity‐phase relationship intrinsic to phase‐contrast magnetic resonance (MR) angiography permits the quantitative and qualitative assessment of blood flow. The ability to measure velocity and vessel cross‐sectional area allows noninvasive assessment of volume flow rate (VFR) in the internal carotid artery (ICA). Phase‐contrast techniques also demonstrate flow direction. Using two‐dimensional cine phase‐contrast angiography, the authors evaluated VFR in the ICA and collateral flow about the circle of Willis in 15 patients with ischemic neurologic symptoms. The VFR in each carotid artery was correlated with the degree of stenosis and presence or absence of abnormal circle of Willis collateral flow. There was a correlation between a decrease in VFR and abnormal circle of Willis collateral flow. In addition, a correlation between severe stenosis and a decrease in VFR was found. In patients with ischemic neurologic symptoms without severe stenosis (<70% diameter stenosis), no decrease in VFR was seen. It is hoped that flow quantification and directional flow imaging with phase‐contrast angiography will help further characterize carotid artery occlusive disease by enabling assessment of VFR changes associated with ischemic neurologic symptoms. This study also supports the hypothesis that two mechanisms‐hemodynamic and embolic‐play a role in ischemic neurologic symptoms.
Three‐dimensional MR imaging and display of intracranial disease: Improvements with the MP‐RAGE sequence and gadolinium
Authors: Brant‐Zawadzki Michael N. , Gillan Gary D. , Atkinson Dennis J. , Edalatpour Nasrola , Jensen Maureen
Published: March 2007

Three‐dimensional (3D) image rendering was performed in 14 patients who had undergone magnetic resonance (MR) imaging for focal brain lesions. The MR study included the magnetization‐prepared rapid gradient‐echo (MP‐RAGE) sequence with 64 or 128 partitions. Resultant contiguous sections 2.5 or 1.25 mm thick, respectively, were obtained. Images were acquired before and after administration of gadopen‐letate dimeglumine. Resultant 3D data sets were processed on a commercially available workstation. Correlative surgical observation was performed in four cases. All data sets were successfully processed into 3D images. The precontrast images proved superior to gadolinium‐enhanced images for brain surface rendering. Postcontrast images proved superior for reconstruction of tumors and vascular structures. The 64‐partition data set proved sufficient for all postprocessing. Coronal orientation was preferred to sagittal orientation for surface rendering because it provided optimal orthogonal orientation of sulcal and gyral brain surface features. Three‐dimensional rendition allowed easy superposition of lesion, brain, vessels, and scalp features‐all useful for surgical planning. The central sulcus was easily recognized in the mid‐line partitions and traced mediolaterally for projection on the cortical surface. MP‐RAGE provides a 3D data set that can be obtained in just over 3 minutes, from which clinically useful 3D renderings are possible. The rapidity of acquisition and capability for 3D rendering provides additional clinical utility.
MR imaging of knee hyaline cartilage: Evaluation of two‐ and three‐dimensional sequences
Authors: Tervonen Osmo , Dietz Mark J. , Carmichael Stephen W. , Ehman Richard L.
Published: March 2007

Magnetic resonance (MR) imaging of cadaveric knees was performed to determine optimal sequences for visualization of hyaline cartilage. Full‐thickness cartilage lesions ranging in diameter from 1 to 5 mm and a partial‐thickness cartilage lesion 15 mm in diameter were created in the femoral articular surfaces of three cadaveric knees. The knees were then imaged with a 1.5‐T imager with various two‐dimensional and high‐resolution three‐dimensional (3D) techniques. After imaging, the knee specimens were sectioned for evaluation. Measurements of cartilage thickness in fast spin‐echo images correlated best with those in the gross specimen. Diffuse areas of cartilage thinning were also most accurately identified with fast spinecho images. Small, focal cartilage defects were best delineated in 3D SPGR (spoiled GRASS [gradient‐recalled acquisition in the steady state]) images.
Phase‐correction method for reduction of B0 instability artifacts
Authors: Foo Thomas K. F. , Hayes Cecil E.
Published: March 2007

View‐to‐view phase shifts due to B0 instability are corrected by applying a phase correction to the low‐spatial‐frequency views. The algorithm described herein assumes that the signal intensity in the space outside of an object represents only noise. A set of phases for the low‐spatial‐frequency views are calculated by minimizing, in the image, the intensity of the induced artifacts in the space outside of the object.
Relative charaterisitics of MR angiography and competing vascular imaging modalities
Authors: Mistretta Charles A.
Published: March 2007

This article reviews the general characteristics of several vascular imaging modalities with the purpose of identifying the distinguishing features of magnetic resonance (MR) angiography. Brief discussions of conventional x‐ray film angiography, intravenous and intraarterial digital subtraction angiography (DSA), duplex and color Doppler flow ultrasound (US), computed tomographic (CT) angiography, transesophageal and intravascular US, angioscopy, and MR angiography are presented. The advantages and disadvantages of each are discussed. The general attributes and image quality features of MR angiography, intraarterial DSA, CT angiography, and US are compared. It is concluded that no single imaging modality will presently suffice for all purposes. Because of its noninvasiveness, rapidly improving image quality, and ability to directly provide velocity information, MR angiography is likely to play a role in an increasing number of clinical applications.
Flow velocity quantification in human coronary arteries with fast, breath‐hold MR angiography
Authors: Edelman Robert R. , Manning Warren J. , Gervino Ernest , Li Wei
Published: March 2007

Measurement of coronary artery flow velocities has, until now, largely required the use of invasive technologies. The authors have implemented a breath‐hold magnetic resonance (MR) angiography technique for depicting the coronary arteries and for quantifying flow velocities. The method was tested in flow phantoms and then applied to a series of subjects: 11 subjects were studied at rest, and four were studied before and during pharmacologic stress induced by intravenous adenosine. Flow velocities at rest in the midportion of the right coronary artery were 9.9 cm/sec ± 3.5 (n = 12); in the proximal left anterior descending coronary artery, they were significantly higher, measuring 20.5 cm/sec ± 5.2 (n = 6). With adenosine, flow velocities typically increased at least fourfold. The authors conclude that noninvasive measurement of coronary artery flow velocities is feasible with MR angiography; this method may prove useful for determining the physiologic significance of coronary artery stenosis.
MR imaging of silicone gel–filled breast implants in vivo with a method that visualizes silicone selectively
Authors: Mukundan Srinivasan , Thomas W. Dixon , Kruse Beth D. , Monticciolo Debra L. , Nelson Rendon C.
Published: March 2007

The lack of an adequately sensitive method for detecting silicone leakage and reported serious complications due to silicone leakage were cited as justification by the U.S. Food and Drug Administration for imposing the current restrictions on silicone gel–filled breast prostheses. The authors report a new magnetic resonance imaging method for visualizing silicone leakage: the silicone‐only sequence (SOS). The method uses the conventional STIR (short‐inversion‐time inversion‐recovery) technique combined with a 1331 radio‐frequency pulse train widely used for water suppression in spectroscopy. With the SOS, silicone can be imaged while signals from fat and water are suppressed. The authors used the SOS to image phantoms and normal and ruptured silicone gel–filled breast prostheses.
Susceptibility effects in porous media in the presence of flow
Authors: Su Min‐Ying , Nalcioglu Orhan
Published: March 2007

Magnetic resonance (MR) imaging of microvascular flow is an important topic in biomedicine because it permits access to the functional state of a biologic system. The internal heterogeneous magnetic field due to susceptibility differences within tissues is one of the factors that can affect signal intensity. A glass bead phantom simulating a porous medium was used to experimentally study the effect of the internal magnetic field on MR flow measurements. A physical model was developed to simulate the paths of the moving spins and the local magnetic field distribution in the medium to estimate the signal intensity with spin‐phase analysis. The susceptibility variation inside the glass bead phantom was estimated by comparing the simulation results with the experimental data. Experiments were also performed with a tissue‐simulating phantom, and the results indicated that the effect of the internal field inhomogeneity on in vivo microvascular flow measurements was negligible.
Acute spinal ligament disruption: MR imaging with anatomic correlation
Authors: Kliewer Mark A. , Gray Linda , Paver Jacqueline , Richardson William D. , Vogler James B. , McElhaney James H. , Myers Barry S.
Published: March 2007

Disruption of spinal ligaments can lead to instability that jeopardizes the spinal cord and nerve roots. Magnetic resonance (MR) imaging can directly image spinal ligaments; however, the sensitivity with which this modality demonstrates ligament injury has, to the authors' knowledge, not been reported. On a biomechanical testing machine, 28 cadaveric spines were subjected to controlled injury that resulted in ligament tears. The spines were then imaged with plain radiography, computed tomography, and MR imaging (1.5 T). The images were analyzed for evidence of ligament injury before dissection of the specimen. Forty‐one of 52 (79%) ligament tears of various types were correctly identified at MR imaging. Disruptions of the anterior and posterior longitudinal ligaments were most conspicuous and were detected in all seven cases in which they were present (no false‐positive or false‐negative results); disruptions of the ligamentum flavum, capsular ligaments, and interspinous ligaments could also be identified but less reliably (three false‐positive and 11 false‐negative results). That MR imaging can reliably and directly allow assessment of spinal ligament disruption in this in vitro model suggests its potential utility for this assessment in patients.
Applications of reduced‐encoding MR imaging with generalized‐series reconstruction (RIGR)
Authors: Webb Andrew G. , Liang Zhi‐Pei , Magin Richard L. , Lauterbur Paul C.
Published: March 2007

The RIGR (reduced‐encoding imaging by generalized‐series reconstruction) technique for magnetic resonance imaging uses a high‐resolution reference image as the basis set for the reconstruction of subsequent images acquired with a reduced number of phase‐encoding steps. The technique allows increased temporal resolution in applications requiring repeated acquisitions, such as the dynamic imaging of contrast agent biodistribution, and in intrinsically time‐consuming protocols such as the acquisition of a series of T2‐weighted images. Several examples are presented to demonstrate that a four‐ to eightfold improvement in spatial or temporal resolution can be achieved with this technique.
T1, T2, and concentrations of brain metabolites in neonates and adolescents estimated with H‐1 MR spectroscopy
Authors: Toft Peter B. , Christiansen Pernille , Pryds Ole , Lou Hans C. , Henriksen Ole
Published: March 2007

The protein and lipid content of the human brain increases dramatically from infancy to adolescence. The authors investigated whether this change influences the relaxation behavior of metabolites measurable with hydrogen‐1 magnetic resonance (MR) spectroscopy. H‐1 MR spectroscopy was performed in eight neonates and eight adolescents at 1.5 T with STEAM (stimulated‐echo acquisition mode) sequences. Five spectra were obtained in each volume of interest with different TE and TR values. T1 and T2 were subsequently calculated. T1 and T2 for inositols, choline‐containing compounds (Cho), phosphocreatine plus creatine (PCr + Cr), and N‐acetylaspartate (NAA) did not differ significantly between the two subject groups. Metabolite concentrations were estimated by using the fully relaxed water signal as an internal standard. Mean estimated concentrations of NAA and PCr + Cr were higher in the adolescent group, whereas the concentration of Cho was lower. The concentration of inositols was similar in the two groups.
Effect of MR imaging on the normal human pineal body: Measurement of plasma melatonin levels
Authors: Schiffman Jonathan S. , Lasch Hugh M. , Rollag Mark D. , Flanders Adam E. , Brainard George C. , Burk D. Lawrence
Published: March 2007

Production of melatonin, a hormone synthesized and secreted by the pineal body, has been suppressed by electromagnetic fields in some but not all animal studies. Magnetic resonance (MR) imaging at 1.5 T was evaluated for its ability to modulate the level of melatonin in eight male volunteers. Subjects were exposed to three conditions, respectively, between 1:00 and 2:00 AM on different nights: (a) a series of routine MR pulse sequences for brain imaging in dark conditions, (b) dark control conditions, and (c) bright‐light contro conditions. Plasma was analyzed for melatonin and cortisol levels. Hormonal changes were analyzed by one‐factor repeated measures within‐subject analysis of variance. These conditions were associated with significant differences in melatonin levels: F(2,6) = 7.95 and P =.021. Subjects exposed to darkness showed a typical increase in melatonin concentration. Subjects exposed to bright light showed a characteristic suppression of melatonin concentration. Those exposed to the MR imaging fields showed an increase in melatonin level similar to that seen in the dark control condition. Light and MR imaging had no significant effects on cortisol levels. Thus, MR imaging at field strengths known to modulate melatonin levels in rats did not suppress melatonin production in human subjects.