bluuebunny/crossref_metadata_2025 huggingface dataset:
Frequency dependence of MR relaxation times I. Paramagnetic ions
Authors: Vymazal Josef , Bulte Jeff W. M. , Frank Joseph A. , Chiro Giovanni Di , Brooks Rodney A.
Published: March 2007

T1 and T2 of paramagnetic ions in free and chelated form were measured over the range of clinical magnetic resonance imaging field strengths (0.02‐1.5 T). T1 values agreed with published data; however, to our knowledge, the field dependence of T2 has not been systematically studied before. Mn2+, Cr3+, and Fe3+ all showed T2 reduction at high field strengths, although reduction due to Fe3+ was minimal. This is believed to be due to “contact” interactions, which have been previously noted for manganese. No such T2 reduction was seen in the chelates, except that dysprosium chelate (but not free ion) showed an anomalous decrease in T2 at high field strengths, which may possibly be explained by a dephasing effect caused by the large magnetic moment of Dy3+.
Frequency dependence of MR relaxation times II. Iron oxides
Authors: Bulte Jeff W. M. , Vymazal Josef , Brooks Rodney A. , Pierpaoli Carlo , Frank Joseph A.
Published: March 2007

The frequency dependence of T1 and T2 was measured for homogeneous suspensions of magnetite and iron oxyhydroxide particles in water with various concentrations of gelatin. The transverse relaxivity showed two types of behavior: (a) For magnetite particles, there was a rapid increase in T2 relaxivity with frequency, followed by a saturation plateau, which accorded with the Langevin magnetization function. From these curves, the magnetic moment of the particle domains was estimated to range from 0.8 to 6.3 104 Bohr magnetons, (b) For iron oxyhydroxide (fer‐ritin, ferrihydrite, and akaganeite) particles, T2 relaxivity increased linearly with frequency, the slope of the increase characteristic for each particle. T2 relaxivity generally increased with increasing gelatin concentration, corresponding to the measured decrease in the water diffusion coefficient. For iron oxides, homogeneously distributed either as iatrogenic agents or endogenous biominerals, these findings may aid in the interpretation of in vivo relaxivity and the effect on MR imaging.
Implementation of wavelet‐encoded MR imaging
Authors: Panych Lawrence P. , Jakab Peter D. , Jolesz Ferenc A.
Published: March 2007

Reconstructions of images from wavelet‐encoded data are shown. The method of MR wavelet encoding in one dimension was proposed previously by Weaver and Healy. The technique relies on selective excitation with wavelet‐shaped profiles generated by special radio‐frequency waveforms. The result of the imaging sequence is a set of inner products of the image with orthogonal functions of the wavelet basis. Inversion of the wavelet data is accomplished with an efficient algorithm with processing times comparable with those of a fast Fourier transform. The experiments show that wavelet encoding by selective excitation of wavelet‐shaped profiles is feasible. Wavelet‐encoded images are compared with phase‐encoded images that have a similar signal‐to‐noise ratio, and there is no discernible degradation in image quality due to the wavelet encoding. Potential benefits of wavelet encoding are briefly discussed.
MR monitoring during cryotherapy in the liver: Predictability of histologic outcome
Authors: Matsumoto Reiko , Selig Abby M. , Colucci Vincent M. , Jolesz Ferenc A.
Published: March 2007

For well‐controlled application of cryotherapy to focal liver lesions, real‐time monitoring is necessary to limit the final necrotic effect in the treated area. In this study, near real‐time magnetic resonance (MR) monitoring images of normal rabbit liver were obtained during the freezing procedure. The MR‐monitored, freezing‐induced lesions were followed with MR images for up to 3 weeks. Corresponding histologic samples were also obtained over the same time period. Our results indicate that MR images obtained during the freezing procedure can adequately depict the area of final necrosis. Furthermore, histologic changes at each stage of lesion development correlated well with MR signal intensities on follow‐up images. With the development of an MR‐compatible cryogen probe, MR imaging may prove to be a robust method for monitoring, controlling, and following up cryotherapy in the liver.
Reduction of ringing and blurring artifacts in fast spin‐echo imaging
Authors: Zhou Xiaohong , Liang Zhi‐Pei , Cofer Gary P. , Beaulieu Chris F. , Suddarth Steve A. , Johnson G. Allan
Published: March 2007

A simple method was devised to reduce ringing and blurring artifacts caused by discontinuous T2 weighting of k‐space data in fast spin‐echo magnetic resonance (MR) imaging. The method demodulates the weighting function along the phase‐encoding direction by using multiple T2 values derived from a set of non–phase‐encoded echoes obtained from an extra excitation. The performance of this method was evaluated by computer simulations and experiments, which confirmed its capability of effectively reducing or, in some cases, even completely removing the ringing and blurring artifacts. The results also show that the proposed method produces better results than other artifact reduction methods. The method is particularly useful at high magnetic field strengths (7.1–9.4 T) and with strong gradients (>20 G/cm) used in MR microscopy, in which the apparent T2 values are short for most tissues. The authors expect that the proposed method will find useful applications in various fast spin echo pulse sequences.
Fast spin‐echo imaging of the knee: Factors influencing contrast
Authors: Piraino David W. , Hardy Peter A. , Schils Jean P. , Richmond Bradford J. , Tkach Jean A. , Belhobek George H.
Published: March 2007

Conventional T2‐weighted spin‐echo magnetic resonance imaging of the knee requires a long TR. Fast spin‐echo (FSE) imaging can improve acquisition efficiency severalfold by collecting multiple lines of k space for each TR. Compromises in resolution, section coverage, and contrast inevitably result. The authors examined the compromises encountered in FSE imaging of the knee and discuss the variations in image contrast and resolution due to choices of sequence parameters. For short TR/TE knee imaging, FSE does not appear to offer any advantages, since the increased collection efficiency for one section reduces the available number of sections, so that the total imaging time for a given number of sections remains constant relative to conventional spin‐echo imaging. For T2‐weighted images, considerable time can be saved and comparable quality images can be obtained. This saved time can be usefully spent on increasing both the resolution of the image and its signal‐to‐noise ratio, while still reducing total acquisition time by a factor of two. The preferred FSE T2‐weighted images were acquired with a TR of 4,500 msec, TE of 120 msec, and eight echoes. The available number of sections is compromised, and the sequence remains sensitive to flow artifacts; however, the FSE sequence appears to be promising for knee imaging.
Uterine contractions: Possible diagnostic pitfall at MR imaging
Authors: Togashi Kaori , Kawakami Satoshi , Kimura Isshu , Asato Reinin , Okumura Ryousuke , Fukuoka Masatsune , Mori Takahide , Konishi Junji
Published: March 2007

A total of 206 nongravid patients with various gynecologic problems underwent pelvic magnetic resonance (MR) examinations that included both sagittal T2‐weighted and contrast agent–enhanced T1‐weighted images. MR images were retrospectively reviewed to identify changes in endometrial configuration on serial images obtained during the same MR examination. In 20 MR examinations (all in women of reproductive age), endometrial distortion due to myometrial bulging was noted on T2‐weighted or contrast‐enhanced T1‐weighted images. It was absent on other MR images obtained at different times. Myometrial bulging exhibited low signal intensity in 18 examinations. The finding resembled adenomyosis or leiomyoma on T2‐weighted or contrast‐enhanced T1‐weighted images. These results evidence the presence of transient myometrial bulging and transient low‐intensity myometrium in the nongravid uterus. This phenomenon is thought to represent uterine contraction. Clinicians should be aware of the potential presence of transient low‐signal‐intensity myometrial bulging that could present diagnostic problems in the normal uterus.
MR imaging of disorders of the brachial plexus
Authors: Bilbey James H. , Lamond Rod G. , Mattrey Robert F.
Published: March 2007

The authors evaluated 64 consecutive patients with suspected brachial plexus (BP) abnormalities of diverse cause with magnetic resonance (MR) imaging, using the body coil and a standardized protocol. Of the 43 patients for whom follow‐up was available, 25 were suspected of having neoplastic involvement of the BP, nine had sustained injuries, and nine presented with BP symptoms of uncertain cause. MR imaging was 63% sensitive, 100% specific, and 77% accurate in demonstrating the abnormality in this diverse patient population. When patients with neoplastic and traumatic disorders were considered separately, sensitivity increased to 81%, accuracy to 88%, and specificity remained unchanged. In the patients with a clinical diagnosis of idiopathic or viral plexitis, the MR imaging findings were normal, serving to exclude other structural abnormalities. It is concluded that MR imaging is valuable in the assessment of a wide range of BP disorders.
MR imaging findings after transplant surgery for Parkinson disease
Authors: Rauch Ronald A. , Markham Charles H. , Rand Robert W. , Becker Donald P. , Lufkin Robert B.
Published: March 2007

The authors describe the magnetic resonance (MR) imaging appearance of the head of the right caudate nucleus in patients who have undergone adrenal medullary transplant surgery for Parkinson disease. All four patients examined showed some clinical improvement after surgery. The MR images acquired 4–6 months postoperatively showed no evidence of caudate atrophy. Three of the four patients showed some increase in size of the operated caudate head relative to preoperative studies. Neither cavitation nor high signal intensity on T2‐weighted images was evident within the caudate head. The one patient studied after administration of gadopentetate dimeglumine showed no abnormal enhancement. These images provided a description of the transplant site and also suggested that the clinical improvement seen was not due to simple ablation of caudate tissue or to postoperative inflammation. The increase in size of the caudate head also suggested that some implanted tissue may have remained in these patients at the time the MR images were acquired.
Velocity and flow quantitation in the superior sagittal sinus with ungated and cine (gated) phase‐contrast MR imaging
Authors: Jordan John E. , Pelc Norbert J. , Enzmann Dieter R.
Published: March 2007

Normal blood flow and velocity in the superior sagittal sinus were measured in 30 patients. A fast two‐dimensional ungated phase‐contrast (PC) pulse sequence was compared with a peripherally gated cine PC technique for velocity and flow quantitation. The same imaging parameters were used for both methods. Measured values for mean velocity and flow obtained with the two methods were compared by using regression analysis and t testing. For blood flow, the correlation coefficient was 0.976. For velocity measurements, r was 0.950. Mean flow was 285 mL/min ± 19 with the ungated PC method and 281 mL/min ± 19 with the cine PC method. The mean velocities measured with the two methods were 12.94 cm/sec ± 1.1 and 13.59 cm/sec ± 1.1, respectively. There was no significant difference (paired t test) between the methods for mean flow or velocity data. This was true even though flow in the superior sagittal sinus is moderately pulsatile, as shown with the cine PC technique. The ungated PC method provided these data in 13 seconds versus 3.5 minutes for the cine PC method.
Quantitative MR relaxometry study of muscle composition and function in duchenne muscular dystrophy
Authors: Huang Yanmin , Majumdar Sharmila , Genant Harry K. , Chan Wing P. , Sharma Khema R. , Yu Pearl , Mynhier Mark , Miller Robert G.
Published: March 2007

Magnetic resonance imaging and maps of T1 and T2 values were used to study muscle composition in Duchenne muscular dystrophy (DMD). The mean T2 of anterior tibial muscle was 27 msec in healthy control subjects and 43 msec with increased fatty infiltration in DMD patients. In stronger DMD patients, the distribution of muscle T2 values was narrow, centered at 27 msec as in the controls, with a nonoverlapping fat peak centered at 49 msec. In weaker DMD patients, the width of the muscle T2 peak increased and the peak shifted toward the fat peak. Mean muscle T1 decreased from 1.7 to 0.6 second with increasing fatty infiltration. These results show that quantitative T1 and T2 maps may be used to assess muscle status and monitor DMD progression.
Spin‐echo and dynamic gadoliniumenhanced flash MR imaging of hepatocellular carcinoma: Correlation with histopathologic findings
Authors: Yamashita Yasuyuki , Fan Zhan Ming , Yamamoto Hiroaki , Matsukawa Tetsuya , Yoshimatsu Shunji , Miyazaki Toshiyuki , Sumi Minako , Harada Mikihiko , Takahashi Mutsumasa
Published: March 2007

Evaluation of histologic subtype and degree of differentiation in hepatocellular carcinoma (HCC) is essential because it affects patient prognosis and treatment planning. To evaluate the histologic subtype of HCC with magnetic resonance (MR) imaging, conventional spin‐echo and dynamic studies were correlated with histopathologic and angiographic findings in 72 HCCs. Dynamic MR imaging was performed with the fast low‐angle shot (FLASH) technique after administration of gadopentetate dimeglumine. There was considerable overlap in signal intensity between various tumor grades on both T1‐ and T2‐weighted images. On dynamic MR images, the peak contrast enhancement ratio correlated with tumor grade (well‐differentiated, 29.5 ± 24.7; moderately differentiated, 63.5 ± 24.1; poorly differentiated, 86.9 ± 26.4) or degree of dilatation of the sinusoidlike vascular space between tumor cells. The maximum contrast‐to‐noise ratio in tumor (relative to surrounding liver) was achieved within 60 seconds in 45 HCCs (mostly of the trabecular or pseudoglandular type). Enhancement was slight or minimal in 17 tumors (mostly small, well‐differentiated tumors). In 10 tumors, the degree of enhancement increased with time, with maximum enhancement in the delayed phase (most frequently in scirrhous HCC). These dynamic patterns correlated with angiographic findings. These data indicate that the degree and pattern of enhancement on dynamic MR images reflect tumor differentiation and architecture of HCC.
Distribution of normal and abnormal fluid collections in the glenohumeral joint: Implications for MR arthrography
Authors: Recht Michael P. , Kramer Josef , Petersilge Cheryl A. , Yu Joseph , Pathria Mini , Trudell Debra , Sartoris David J. , Resnick Donald
Published: March 2007

Although magnetic resonance (MR) images of the glenohumeral joint frequently demonstrate intraarticular fluid, no specific criteria have, to the authors' knowledge, been published that allow accurate assessment of the amount of fluid present. Also, despite the increasing use of MR arthrography of the shoulder, the optimal amount of intra‐articular fluid that should be used with this technique has not been determined. The authors progressively distended the glenohumeral joint in six cadaveric shoulder specimens with a dilute gadopentetate dimeglumine solution and obtained MR images after injection of 2, 5, 10, 15, and 20 mL of the solution. The pattern of fluid distribution was evaluated, and these results were then used to estimate the amount of fluid that was present in the glenohumeral joint on MR images of 20 shoulders obtained in 12 asymptomatic volunteers. In 14 of these shoulders, intraarticular fluid was present; however, in none was more than 2 mL evident. Results of the cadaveric study also indicated that 15 mL of intraarticular fluid appears to be the optimal amount for MR arthrography.
Computer‐assisted identification and quantification of multiple sclerosis lesions in MR imaging volumes in the brain
Authors: Mitchell J. Ross , Karlik Stephen J. , Lee Donald H. , Fenster Aaron
Published: March 2007

Magnetic resonance (MR) imaging is the principal imaging technique for the diagnosis of multiple sclerosis (MS). However, quantifying the number and extent of lesions on MR images manually is arduous. The authors have developed a computerized three‐dimensional (3D) quantitative system to assist in the identification and analysis of MS lesions in proton‐density (PD)‐ and T2‐weighted volumes of the head. The system provides intuitive, interactive operations that allow flexible extraction of information from the data. Use of the system to analyze MR examinations of a phantom containing regular “lesions” showed that accurate (average error, <0.21 cm3) and precise (10% or better for lesions > 1 cm3) measurements of objects less than 7 cm3 is possible, and that an estimate of the quantization error predicted the uncertainty in the volume. Analysis of four MR examinations of a chronic‐progressive MS patient conducted over an 18‐month period was performed. A two‐dimensional histogram showing the frequency of voxels with particular PD‐ and T2‐weighted intensities revealed a distinct cluster only in histograms of sections that contained lesions. Measurements and 3D volume rendering of lesions clearly showed changes in lesion shape, position, and size.
Surgical sutures: MR artifacts and sequence dependence
Authors: Haramati Nogah , Penrod Brian , Staron Ronald B. , Barax Charles N.
Published: March 2007

Artifact reduction is fundamental to the daily clinical application of magnetic resonance (MR) imaging. Imaging of the postoperative patient may be difficult because of surgically introduced materials that result in artifacts. The authors tested some commonly used types of surgical suture for MR susceptibility artifact with various imaging sequences. Ten different suture types were studied. Suture was immersed in vegetable oil in separate plastic test tubes. The sutures were also studied embedded in meat. All samples were studied with T1‐weighted and T2‐weighted spin‐echo, STIR (short‐inversion‐time inversion‐recovery), and two‐dimensional and three‐dimensional gradient‐echo sequences. Silk suture produced the most artifact.
Contrast media for MR imaging of the heart
Authors: Saeed Maythem , Wendland Michael F. , Higgins Charles B.
Published: March 2007

The role of contrast media for quantitative characterization of ischemic myocardial events with magnetic resonance (MR) imaging has advanced considerably in the past few years. Contrast material‐enhanced MR imaging is useful for identifying and sizing myocardial infarcts and for distinguishing between occlusive and reperfused myocardial infarcts. Recent results suggest that contrast‐enhanced MR imaging can also be used to identify areas of cell death in regions of reperfused myocardial infarction. With the aid of MR contrast media, fast MR imaging techniques may be useful in estimating regional myocardial perfusion. Although no simple relationship between signal intensity and concentration exists, contrast‐enhanced MR perfusion imaging can demonstrate the presence and relative severity of hypoperfused myocardium. Combining myocardial perfusion imaging with the anatomic and functional information provided by other MR imaging techniques could make MR imaging a comprehensive noninvasive means of evaluating ischemic cardiac disease.
Intraluminal contrast agents for MR imaging of the abdomen and pelvis
Authors: Rijcken Tammo H. Pels , Davis Michael A. , Ros Pablo R.
Published: March 2007

Magnetic resonance (MR) imaging of the abdomen and pelvis with use of gastrointestinal (GI) contrast agents is slowly emerging as a valuable diagnostic tool. In the past few years, considerable effort has been expended on developing an oral contrast agent to serve as a bowel marker during abdominal and pelvic imaging. Four major categories of agents have been studied: compounds with positive contrast‐enhancing characteristics (ie, which increase signal intensity), which may be either miscible or immiscible with bowel contents, and compounds with negative contrast‐enhancing characteristics (ie, which decrease signal intensity), which also may be miscible or immiscible. Compared with precontrast images, MR images acquired after administration of GI contrast agents have shown increased anatomic delineation of the bowel lumen, pancreas, and paraaortic nodes, allowing increased detection of pancreatic lesions, improved assessment of bowel wall lesions, and distinction between intrahepatic and extrahepatic lesions. This review focuses on the general physics and requirements for intraluminal GI contrast media for MR imaging, the currently used intraluminal agents and their regulatory status, current and near‐future availability, and cost considerations.
Malignant lesions of the liver identified on T1‐ but not T2‐weighted MR images at 1.5 T
Authors: Semelka Richard C. , Bagley Ann S. , Brown Elizabeth D. , Kroeker Mervyn A.
Published: March 2007

The authors reviewed their 21/2‐year experience with a magnetic resonance (MR) imaging protocol for a 1.5‐T MR imager that included T2‐weighted fat‐suppressed spin‐echo, T1‐weighted breath‐hold gradient‐echo, and serial dynamic gadolinium‐enhanced T1‐weighted gradient‐echo imaging to identify histologic types of malignant liver lesions more apparent on T1‐ than on T2‐weighted images. MR images of 212 consecutive patients with malignant liver lesions were reviewed. T2‐weighted, T1‐weighted, and dynamic contrast‐enhanced T1‐weighted images were examined separately in a blinded fashion. Seven patients demonstrated liver lesions (lymphoma [two patients] and carcinoid, hepatocellular carcinoma, colon adenocarcinoma, transitional cell carcinoma, and melanoma [one patient each]) on T1‐weighted images that were inconspicuous on T2‐weighted images. In all cases, the lesions were most conspicuous on T1‐weighted images obtained immediately after administration of contrast agent. Histologic confirmation was present for all seven patients. The consistent feature among these lesions was that they were hypovascular, due either to a fibrous stroma or to dense monoclonal cellularity. These results suggest that in some patients with hypovascular primary neoplasms, the lesions may be identified only on T1‐weighted images, and that immediate postcontrast T1‐weighted images are of particular value in demonstrating lesions.
Ischemic heart disease: Assessment with gadolinium‐enhanced ultrafast MR imaging and dipyridamole stress
Authors: Eichenberger André C. , Schuiki Ernst , Köhli Victor D. , Amann F. Wolfgang , McKinnon Graeme C. , von Schulthess Gustav K.
Published: March 2007

The potential of magnetic resonance (MR) imaging for the detection of myocardial perfusion abnormalities in patients with coronary artery disease has not been fully explored. A feasibility study was conducted in 10 patients with a novel approach to determine whether myocardial ischemia can be assessed with MR imaging and dynamic first‐pass bolus tracking enhanced with gadolinium tetraazacyclododecanetetraacetic acid (DOTA). Three tomographic planes were acquired before and after pharmacologic stress with dipyridamole, with use of the bolus‐tracking series at rest as a reference. The change in myocardial rate of enhancement was compared with the results obtained by means of the established methods, exercise thallium scintigraphy and coronary angiography. Detection of ischemic regions with MR imaging showed a sensitivity, specificity, and diagnostic accuracy of 65%, 76%, and 74%, respectively. Ultrafast MR imaging can be used to detect regions of myocardial ischemia.
Comparative signal intensity measurements in dynamic gadolinium‐enhanced MR mammography
Authors: Gribbestad Ingrid S. , Nilsen Gunnar , Fjøsne Hans E. , Kvinnsland Stener , Haugen Olav A. , Rinck Peter A.
Published: March 2007

Increases in signal intensity enhancement were measured in defined regions of interest (ROIs) to allow distinction between malignant and benign tumors with dynamic gadolinium‐enhanced magnetic resonance (MR) mammography. Twenty patients with palpable breast lesions (15 malignant, five benign) underwent MR mammography. The dynamic gradient‐echo sequence was performed with intravenous bolus injection of gadopentetate dimeglumine and consisted of 25 images with a time resolution of 30 seconds. Contrast enhancement was calculated by comparing user‐defined ROIs on pre‐ and postcontrast images. An increase in signal intensity of 70% or more on the 1‐minute postcontrast image was used as the criterion of malignancy. MR mammographic results correlated with histopathologic findings in all patients when the defined ROI was in the most enhancing part of the tumor. For the ROI in areas of submaximal enhancement or when the ROI surrounded the whole lesion, only five and nine tumors, respectively, fulfilled the malignancy criterion. All malignant tumors showed large variations in signal intensity enhancement that depended on the position of the ROI in the tumor. Dynamic, gadolinium‐enhanced MR mammography allows distinction of benign from malignant breast tumors when the selected ROI is in the most enhancing part of the lesion.
Magnetoferritin: Characterization of a novel superparamagnetic MR contrast agent
Authors: Bulte Jeff W. M. , Douglas Trevor , Mann Stephen , Frankel Richard B. , Moskowitz Bruce M. , Brooks Rodney A. , Baumgarner Charles D. , Vymazal Josef , Strub Marie‐Paule , Frank Joseph A.
Published: March 2007

A protein‐encaged superparamagnetic iron oxide has been developed and characterized by using horse spleen apoferritin as a novel bioreactive environment. The roughly spherical magnetoferritin molecules, 120 Å in diameter, are composed of a monocrystalline maghemite or magnetite core 73 Å ± 14 in diameter. Except for the additional presence of iron‐rich molecules of higher molecular weight, the appearance and molecular weight (450 kd) of magnetoferritin are identical to that of natural ferritin; the molecules are externally indistinguishable from their precursor, with a pI (isoelectric point) in the range 4.3–4.6. The measured magnetic moment of the superparamagnetic cores is 13,200 Bohr magnetons per molecule, with T1 and T2 relaxivities (r1 and r2) of 8 and 175 L‐mmol−1 (Fe)‐sec−1, respectively, at body temperature and clinical field strengths. The unusually high r2/r1 ratio of 22 is thought to arise from ideal core composition, with no evidence of crystalline paramagnetic inclusions. T2 relaxation enhancement can be well correlated to the field‐dependent molecular magnetization, as given by the Langevin magnetization function, raised to a power in the range 1.4–1.6. With its nanodimensional biomimetic protein cage as a rigid, convenient matrix for complexing a plethora of bioactive substances, magnetoferritin may provide a novel template for specific targeting of selected cellular sites.
Sclerosed liver hemangioma mimicking malignant tumor at MR imaging: Pathologic correlation
Authors: Mathieu Didier , Rahmouni Alain , Vasile Norbert , Jazaerli Nedal , Duvoux Christophe , Tran Van Nhieu Jeanne , Zafrani Elie Serge
Published: March 2007

This case report illustrates atypical magnetic resonance (MR) imaging findings in a liver hemangioma mimicking a malignant lesion—lower signal intensity than cerebrospinal fluid on T2‐weighted spin‐echo images and lack of early enhancement on dynamic contrast material—enhanced gradient‐echo images. Pathologic analysis demonstrated nearly total replacement of the vascular cavities by dense fibrous tissue. In this rare, sclerosed form, this lesion could not be defined as a hemangioma with MR imaging.
Thymopharyngeal duct cyst: MR imaging of a third branchial arch anomaly in a neonate
Authors: Vade Aruna , Griffiths Allison , Hotaling Andrew , Eisenbeis John F. , Husain Aliya N.
Published: March 2007

Third branchial arch anomalies are rare. The authors present a case report of a neonate with a rapidly growing neck mass due to cystic dilation of a persistent thymopharyngeal duct, which is a derivative of the third branchial arch. The presence of thyroid and thymic tissue in the cyst wall, the communication of the cyst with the piriform sinus, and the relationship of the cyst to carotid vessels and the sternomastoid muscle were consistent with the features of a thymopharyngeal duct cyst embedded in the thyroid gland.
Tuning and matching networks for MR imaging and spectroscopy
Authors: Viohl Ingmar , Gullberg Grant T.
Published: March 2007

The authors briefly discuss four tuning and matching networks and their application range in magnetic resonance (MR) imaging and MR spectroscopy. Analytic expressions for the network elements needed to tune and match an MR imaging or spectroscopy probe for a given coil impedance are given, and the connection to the “standard” two‐element capacitive matching networks is shown. The power loss factor and the phase shift between the input current and the load current are explicitly calculated for each of the four networks. The merits of the different matching networks are then discussed in the context of a general‐purpose license plate coil commonly used in MR imaging.
Effects of spatial distribution on proton relaxation enhancement by particulate iron oxide
Authors: Tanimoto Akihiro , Pouliquen Daniel , Kreft Burkhard P. , Stark David D.
Published: March 2007

The proton relaxation effect of superparamagnetic iron oxide (SPIO) particles under varying conditions of spatial distribution was investigated with use of phantoms. Agar phantoms containing various concentrations of SPIO or gadopentetate dimeglumine, with and without Sephadex beads, were studied. Phantoms with Sephadex had a heterogeneous spatial distribution of iron oxide, comparable to liver tissue in vivo. Relaxometry at 0.47 T showed decreased T2 relaxivity of SPIO in Sephadex phantoms compared with that in agar phantoms without Sephadex. On T2‐weighted images obtained at 1.5 T, the signal intensity of Sephadex phantoms showed less SPIO relaxation effect than that of plain agar phantoms. Unlike SPIO, gadopentetate dimeglumine showed the same relaxivities and signal intensity in plain agar and Sephadex phantoms. The results show that the T2 relaxation effect of iron oxide depends on its spatial distribution. A heterogeneous spatial distribution, as in intact liver tissue, diminishes the T2 relaxivity of iron oxide particles.
Metabolite concentrations in the developing brain estimated with proton MR spectroscopy
Authors: Toft Peter B. , Leth Helle , Lou Hans C. , Pryds Ole , Henriksen Ole
Published: March 2007

The purpose of the present study was to estimate absolute concentrations and relaxation time constants of metabolites that were detectable with proton magnetic resonance (MR) spectroscopy in the healthy preterm, term, and infant brain. Five MR spectra were recorded for each infant by using STEAM (stimulated‐echo acquisition mode) sequences with different TEs and TRs. Water was used as an internal standard. The T1 of choline‐containing compounds (Cho) and the T1 of phosphocreatine plus creatine (PCr+Cr) decreased. The T2 of the N‐acetyl‐L‐aspartate (NAA) resonance increased, probably because of a relatively larger signal overlap with glutamate in the most immature brains. The concentration of NAA almost doubled, whereas the Cho concentration showed only a nonsignificant tendency to decrease; therefore, the well‐known increase in the ratio of NAA to Cho appears to be due mostly to an increase in NAA concentration. The concentration of PCr+Cr increased rapidly and reached adolescent values at approximately 4 months of age.
A novel fast T1‐mapping method
Authors: Tong Chun Y. , Prato Frank S.
Published: March 2007

The authors present a novel fast T1‐mapping technique that allows a T1 map to be reconstructed from data acquired in less than 3 seconds. Data were acquired by using two modified TurboFLASH (fast low‐angle shot) sequences and were processed with a combination of one‐dimensional Fourier transforms and a parameter‐fitting routine, instead of a standard two‐dimensional Fourier transform. Apparent T1 (T1*) maps were obtained, from which T1 maps were calculated. Comparisons of T1 values obtained in phantoms and the human brain by using this technique with those obtained with multipoint inversion‐recovery T1 mapping showed that the new method yielded accurate T1 values. Optimization of the method will further improve speed and accuracy. The general approach of this T1‐mapping technique is believed to be also applicable to other problems, such as T2 and T2* mapping.
MR imaging evaluation of knee collateral ligaments and related injuries: Comparison of T1‐weighted, T2‐weighted, and fat‐saturated T2‐weighted sequences—correlation with clinical findings
Authors: Mirowitz Scott A. , Shu Hui Hua
Published: March 2007

The objectives of this study were to compare the ability of T1‐weighted (T1W), proton density/T2‐weighted (PD/T2W), and fat saturation (FS) PD/T2W magnetic resonance (MR) sequences for depiction of the knee collateral ligaments and related injuries, and to compare MR findings with clinical findings. Ten subjects with normal knee ligaments and 64 patients with suspected collateral ligament injuries underwent coronal T1W, PD/T2W, and FS PD/T2W imaging. Abnormalities ranged from edema surrounding the collateral ligaments (grade I) to complete disruption of ligamentous fibers (grade III). FS PD/T2W images improved definition of the medial collateral ligament (MCL) and lateral collateral ligament (LCL) compared with other sequences in 78% and 81% of patients, respectively. While the apparent grade of collateral ligament injury was similar with all pulse sequences in most patients, depiction of such injury was usually most conspicuous on FS PD/T2W images (MCL, 92% of patients; LCL, 38% of patients). In no patients were clinically diagnosed collateral ligament injuries undetected or understaged with MR imaging. MR findings indicated higher‐grade MCL and LCL injuries than did clinical examination in 24 and 15 patients, respectively.
Effects of MR exposure at 1.5 T on early embryonic development of the chick
Authors: Yip Yee Ping , Capriotti Christine , Talagala S. Lalith , Yip Joseph W.
Published: March 2007

The potential teratogenicity of magnetic resonance (MR) field exposure on the early development of the chick embryo was examined. Eggs at four developmental stages within the first 42 hours of incubation were exposed 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 h. When the embryos were sacrificed shortly thereafter (at ±53 hours of incubation), the abnormality and mortality rates of exposed and unexposed (control) embryos in each of the developmental groups did not show a consistent pattern. When embryos were sacrificed on the 6th day of incubation, exposed embryos from all developmental groups showed a trend toward higher abnormality and mortality rates than their controls. More extensive studies are needed to confirm these findings.
Tracking the motion of skeletal muscle with velocity‐encoded MR imaging
Authors: Drace John E. , Pelc Norbert J.
Published: March 2007

Phase‐contrast magnetic resonance velocity‐encoding techniques were used to track two‐dimensional movement of skeletal muscle tissue. Axial and longitudinal planes in the forearms of five healthy volunteers were imaged during cyclic flexion and extension of the fingers, and the resulting data were used to plot the trajectories of the motion of pieces of muscle tissue. A phantom that produced complex two‐dimensional trajectories validated the accuracy of the imaging and analysis techniques; after adjustments for phase errors, two‐dimensional trajectories were tracked with an root‐mean‐square error of 0.1 cm. Preliminary results indicate that velocity‐encoded image data can characterize motion trajectories and that refinements in data acquisition and analysis techniques may make it possible to correlate the movements of different regions within a muscle, characterize muscle contraction, and quantify longitudinal strain. This ability to track velocity vectors may provide a foundation for quantitative analysis of muscle motion.
MR evaluation of cervical cancer in hysterectomy specimens: Correlation of quantitative T2 measurement and histology
Authors: Martin Alastair J. , Poon Colin S. , Thomas Gillian M. , Kapusta Linda R. , Shaw Patricia A. , Henkelman R. Mark
Published: March 2007

Specimens from modified radical hysterectomies performed for invasive carcinoma of the cervix were analyzed with quantitative T2 magnetic resonance (MR) imaging and histologic study to determine to what degree there was a correlation between the findings of the two modalities. The mean T2 of cervical stroma was 48 msec, while the outer zone of the cervix had a mean T2 of 62 msec and the central canal region typically had T2 values of 115 msec ± 20 (standard deviation). A total of nine cervical cancers were analyzed, and their mean T2 value was 79 msec. Separation between cervical stroma and tumor was good, with stromal T2 values ranging from 30 to 66 msec, while tumor T2s ranged from 60 to 97 msec. Statistical analysis indicated that these data were associated with a sensitivity of 89% and a specificity of 95%, with 95% confidence intervals of [50%,99.4%] and [74%,99.7%], respectively, for separating tumor from stroma on the basis of T2 value. Quantitative T2 imaging was found to provide an effective, nonsubjective means of classifying cervical anatomy and neo‐plastic disease.
MR susceptometry: an external‐phantom method for measuring bulk susceptibility from field‐echo phase reconstruction maps
Authors: Holt Randall W. , Diaz Pedro J. , Duerk Jeffrey L. , Bellon Errol M.
Published: March 2007

A novel method for estimating the susceptibility of an object by using the magnetic resonance (MR) imaging field distortions in an external‐reference water bath next to the object is described. The field measurement was obtained with a phase reconstruction from a gradient‐echo acquisition. A field model of an arbitrary object in a static magnetic field was discretely calculated from geometry determined from the magnitude reconstruction. Least‐squares estimation yields the susceptibility of the object. Required (and proven) assumptions include validity of superposition, object homogeneity, negligible higher‐order field terms, field‐model accuracy, geometric‐model accuracy, and correlation of gradient‐echo phase to field distortion. MR susceptometry estimation of phantoms yielded susceptibility estimates that correlated well with known values (r >.9975). This MR susceptometry method is a first step toward quantitation of iron levels through MR imaging phase information in patients with iron overload.
Dynamic spin‐echo imaging: Theoretical assessment and implementation
Authors: Bishop Jonathan , Henkelman R. Mark , Plewes Donald B.
Published: March 2007

A spin‐echo method for obtaining dynamic magnetic resonance (MR) images is described. The method combines the RARE (rapid acquisition with relaxation enhancement) pulse sequence with a data acquisition scheme in which only a centric fraction of the raw data is sampled to increase the time resolution of the dynamic images. The missing high‐resolution data are supplied from reference images. By these means, an effective time resolution of about 10 seconds per image is achieved, which is suitable for diagnostic assessment of contrast enhancement procedures. A promising clinical application is contrast‐enhanced MR imaging of the pituitary. Although the resolution of small objects in this size range is potentially degraded, this shortcoming is compensated for with use of variable refocusing flip angles. In the context of pituitary imaging, the centric 30%–40% of the raw data is shown to be the optimal fraction to acquire for the low‐resolution dynamic images. Ten patients with previous history of pituitary disease have been imaged with dynamic and conventional spin‐echo techniques. In six of these patients, an equivalent diagnosis was reached with dynamic and conventional images, while in two, only the dynamic images showed the lesion; in the final two patients, only the conventional images showed the lesion.
Planar‐motion correction with use of k‐space data acquired in fourier MR imaging
Authors: Wood Michael L. , Shivji Mansur J. , Stanchev Peter L.
Published: March 2007

The authors have developed a method for reducing magnetic resonance (MR) image artifacts caused by planar motion. Segments of k‐space acquired with the subject stationary are detected automatically. Each k‐space segment is Fourier transformed into an image in which rotational and translational displacements are measured manually. Before correction, k‐space is made as Hermitian as allowed by the largest symmetric range of low spatial frequencies acquired with the subject stationary. Segments of k‐space acquired with the subject in different positions are corrected separately. Although translation corrections can be applied effectively to both k‐space and the spatial domain, rotation corrections are applied in the spatial domain to avoid image artifacts. To complement the correction, data corrupted by rotation are replaced by the complex conjugate of data of the opposite kx, and ky, provided that these data have not been corrupted by rotation. The method reduced ghosts and blurring substantially on sagittal head images acquired with a standard spin‐echo pulse sequence while a volunteer subject nodded his head.
Mitral valve flow measured with cine MR velocity mapping in patients with ischemic heart disease: comparison with doppler echocardiography
Authors: Karwatowski Stefan P. , Brecker Stephen J. D. , Yang Guang Z. , Firmin David N. , Sutton Martin St John , Underwood S. Richard
Published: March 2007

Diastolic function is an important element of overall left ventricular function. The pattern of flow across the mitral valve is commonly used as a measure of diastolic ventricular function. Magnetic resonance (MR) velocity mapping of blood flow across the mitral valve was compared with Doppler echocardiography. Nineteen patients with known coronary artery disease (mean age. 62 years: 11 with previous myocardial infarction) were studied. The mean value of peak early filling velocity (± standard deviation) was 60.1 cm/sec ± 14.3 with the MR method and 59.4 cm/sec ± 13.7 with echocardiography (P = 0.732). The mean difference between the two measurements (95% confidence interval) was −0.8 cm/sec (−5.2 cm/sec. +2.2 cm/sec). The mean value of early deceleration was 4.3 mlsec2 ± 1.5 with the MR method and 4.0 m/sec2 ± 1.5 with echocardiography (P = 0.073). The mean Werence was −0.4 cm/sec2 (−0.92 cm/eec2. +0.05 cm/sec2). The mean value of peak atriosystolic velocity was 51 cm/sec ± 14.6 with the MR method and 62 cm/sec ± 17.2 with echocardiography (P = 0.002). The mean difference was −11 cm/sec (−18.1 cm/sec, −3.45 cm /sec). Peak atrial filling was consistently lower with the MR method than with echocardiography. Time‐averaged measurements of ventricular fflling with MR velocity mapping are an accurate measure of early diastolic filling but underestimate the velocity of atriosystolic fflling.
Contrast‐enhanced MR imaging of intrahepatic cholangiocarcinoma: Pathologic correlation study
Authors: Murakami Takamichi , Nakamura Hironobu , Tsuda Kyo , Ishida Takeshi , Tomoda Kaname , Hori Shinichi , Monden Morito , Kanai Toshio , Wakasa Kenichi , Sakurai Masami , Kozuka Takahiro
Published: March 2007

The authors describe the enhanced magnetic resonance (MR) imaging appearance of intrahepatic Cholangiocarcinoma. The MR Images of eight patients with intrahepatlc Cholangiocarcinoma who underwent MR examination within 3 weeks before partial hepatectomy were retrospectively studied. The MR images, including a dynamic study, were compared directly with pathologic and histologic findings. The peripheral region of the medullary subtype of Cholangiocarcinoma, with many tumor cells, showed greater enhancement relative to liver parenchyma in the early phase. The peripheral region of the scirrhous subtype, with fewer tumor cells showed less enhancement in the early phase. In one patient, the thin rim of the medullary tumor showed less enhancement in the late phase, and this rim corresponded to the peripheral region of the medullary tumor with many tumor cells. The central region of tumors with a large amount of fibrous tissue showed prolonged enhancement in the late and delayed phases. The thin rim of liver parenchyma around the tumor showed less enhancement in the early phase and greater enhancement in the late phase; this rim corresponded to congestive liver parenchyma with dilated sinusoids. Intrahepatic Cholangiocarcinoma shows various enhancement patterns, which depend on both the histologic subtype and the degree and distribution of flbrosis within the tumor.
Adrenocortical carcinoma: MR imaging appearance with current techniques
Authors: Schlund James F. , Kenney Philip J. , Brown Elizabeth D. , Ascher Susan M. , Brown Jeffrey J. , Semelka Richard C.
Published: March 2007

The purpose of the study was to define the magnetic resonance (MR) imaging appearance of adrenocortical carcinoma (ACC) with current MR techniques. Eight patients with ACC underwent high‐field‐strength MR imaging with the following sequences: axial T1‐weighted gradient echo, fat‐suppressed T1‐weighted spin echo, fat‐suppressed T2‐weighted spin echo, and gadolinium‐enhanced T1‐weighted gradient echo and fat‐suppressed T1‐weighted spin echo. Postcontrast images were also acquired in the sagittal (six patients) and coronal (three patients) planes. Out‐of‐phase gradient‐echo images were obtained in two patients. Lesion morphology, signal intensity features, and presence of metastatic disease were retrospectively evaluated. MR imaging features of ACC included internal hemorrhage (seven of eight patients), central necrosis (seven of eight), and peripheral enhancing nodules (seven of eight). Out‐of‐phase images in two of two patients demonstrated signal loss compared with in‐phase images, which may be a common feature of these tumors. Liver metastases were present in four patients. Consistent MR features of ACC are Identified.
Understanding acceleration‐induced displacement artifacts in phase‐contrast MR velocity measurements
Authors: Frayne Richard , Rutt Brian K.
Published: March 2007

A theoretical framework for understanding acceleration‐induced errors in phase‐contrast magnetic resonance velocity measurements has been developed. An important result of this framework is the interpretation of acceleration‐induced velocity errors as displacement artifacts due to the delay between velocity and spatial encoding. A rotating‐disk phantom was used to confirm the theoretically predicted displacement times (the difference between theory and experiment was 8.2%). Errors were also observed in velocity profiles measured in regions of fluid acceleration downstream from a step stenosis. The magnitude of these errors could be predicted and corrected by using the analytic framework.
Selection of K‐space samples in localized MR spectroscopy of arbitrary volumes of interest
Authors: Reeves Stanley J.
Published: March 2007

A number of Image modeling techniques have been proposed to represent magnetic resonance spectro‐scopic images. The goal of these techniques is to reduce the amount of data and thus the time required to reconstruct the image. However, little attention has been given to the choice of k‐space samples. The combination of samples acquired has a great effect on the quality of the reconstructed image. A new method for optimizing the choice of k‐space samples—in which samples from a candidate set are sequentially eliminated in a computationally efficient manner until the desired number remain—is presented and demonstrated by means of simulations.