bluuebunny/crossref_metadata_2025 huggingface dataset:
International epidemiology of prostate cancer: Geographical distribution and secular trends
Authors: Baade Peter D. , Youlden Danny R. , Krnjacki Lauren J.
Published: December 2008

This review outlines current international patterns in prostate cancer incidence and mortality rates and survival, including recent trends and a discussion of the possible impact of prostate‐specific antigen (PSA) testing on the observed data. Internationally, prostate cancer is the second most common cancer diagnosed among men (behind lung cancer), and is the sixth most common cause of cancer death among men. Prostate cancer is particularly prevalent in developed countries such as the United States and the Scandinavian countries, with about a six‐fold difference between high‐incidence and low‐incidence countries. Interpretation of trends in incidence and survival are complicated by the increasing impact of PSA testing, particularly in more developed countries. As Western influences become more pronounced in less developed countries, prostate cancer incidence rates in those countries are tending to increase, even though the prevalence of PSA testing is relatively low. Larger proportions of younger men are being diagnosed with prostate cancer and living longer following diagnosis of prostate cancer, which has many implications for health systems. Decreasing mortality rates are becoming widespread among more developed countries, although it is not clear whether this is due to earlier diagnosis (PSA testing), improved treatment, or some combination of these or other factors.
Traditional Japanese diet and prostate cancer
Authors: Mori Mitsuru , Masumori Naoya , Fukuta Fumimasa , Nagata Yoshie , Sonoda Tomoko , Sakauchi Fumio , Ohnishi Hirofumi , Nojima Masanori , Tsukamoto Taiji
Published: December 2008

The traditional Japanese diet has been suggested by some researchers to be associated with a decreased risk of prostate cancer (PCa). In this paper, we assumed the following three characteristics of the traditional Japanese diet high in soybean products, high in fish, and low in red meat. Isoflavones, polyunsaturated long chain (n – 3) fatty acids, and saturated fatty acids were thought to be micronutrients in biological etiology relevant to soybean products, fish, and red meat, respectively. Analytical epidemiological studies on the risk of PCa were identified using the MEDLINE database from 1998 to 2007. Some published studies showed a negative association of soybean products and isoflavones to PCa risk, an inverse association for fish or polyunsaturated long chain (n – 3) fatty acids such as eicosapentaenic acid (EPA) and docosahexaenoic acid (DHA) with PCa risk, and a positive association of red meat or saturated fatty acids with PCa risk, respectively. In conclusion, although it is possible that the traditional Japanese diet may reduce the risk of PCa through a combination of characteristics such as being high in soybean products, high in fish, and low in red meat, further well‐designed epidemiological studies such as nested case‐control studies with nutritional analyses of blood samples are needed to confirm this association.
On the steady‐state properties of actual flip angle imaging (AFI)
Authors: Nehrke Kay
Published: December 2008

AFI (actual flip angle imaging) represents an interesting approach to map the B1 transmit fields by measuring the spatial variations of the effective flip angle. However, the accuracy of the technique relies on the adequate spoiling of transverse magnetization. In the present work configuration theory was employed to develop a proper RF and gradient spoiling scheme for the AFI technique, making the sequence robust against off‐resonance without the need of large spoiling gradients. Furthermore, numerical simulations were performed to predict the steady‐state signals and, hence, the accuracy of the AFI technique as a function of the sequence and tissue parameters. It is shown that the spoiling properties of the sequence are mainly defined by the phase shift increment ϕ of the RF pulses and the diffusion sensitivity resulting from the unbalanced gradients of the sequence. Adequate spoiling may be achieved for a reasonable range of tissue parameters and flip angles for moderate spoiling gradients if a favorable value for ϕ is chosen. Phantom and in vivo head imaging experiments show an excellent agreement with the theoretical predictions, indicating that the proper operating range of the approach may be reliably predicted by the theory. Magn Reson Med 61:84–92, 2009. © 2008 Wiley‐Liss, Inc.
Rapid monitoring of oxygenation by 19F magnetic resonance imaging: Simultaneous comparison with fluorescence quenching
Authors: Jordan Bénédicte F. , Cron Greg O. , Gallez Bernard
Published: December 2008

The aim of this study was to develop an MRI fluorocarbon oximetry technique using snapshot inversion recovery and compare it with fluorescence quenching fiber‐optic probe oximetry (OxyLite) performed simultaneously in experimental mouse tumors. The oxygen reporter probe hexafluorobenzene (HFB) was injected directly into the tumors, along with the insertion of the OxyLite probe. Tumor oxygenation (pO2) was modified using carbogen or lethal doses of the anesthetic gas. MRI pO2 maps were generated in 1.5 min with an in‐plane spatial resolution of 1.88 mm. MRI and OxyLite showed consistent baseline and postmortem pO2 values. Increases in tumor pO2 during carbogen breathing showed similar kinetics for the two methods. The pO2 values observed using the OxyLite corresponded with relatively hypoxic values observed by MRI. The apparent discrepancy between mean values might be due to the difference in sampling volumes of the techniques and the observation of multiple locations using 19F MRI versus a single location using the large optical fiber. Overall, the present method provides a rapid way to map the tumor oxygenation and is particularly suitable to monitor acute changes of pO2 in tumors. Magn Reson Med, 2009. © 2008 Wiley‐Liss, Inc.
Virtual coil concept for improved parallel MRI employing conjugate symmetric signals
Authors: Blaimer Martin , Gutberlet Marcel , Kellman Peter , Breuer Felix A. , Köstler Herbert , Griswold Mark A.
Published: December 2008

A new approach for utilizing conjugate k‐space symmetry for improved parallel MRI performance is presented. By generating virtual coils containing conjugate symmetric k‐space signals from actual coils, additional image‐ and coil‐phase information can be incorporated into the reconstruction process for parallel acquisition techniques. In that way the reconstruction conditions are improved, resulting in less noise enhancement. In particular in combination with generalized autocalibrating partially parallel acquisitions (GRAPPA), the virtual coil concept represents a practical approach since no explicit spatial phase information is required. In addition, the influence of phase variations originating from the complex receiver coils as well as from the background is investigated. It is shown that there exist background phase distributions yielding an optimized pMRI reconstruction. Magn Reson Med 61:93–102, 2009. © 2008 Wiley‐Liss, Inc.
Multiecho dixon fat and water separation method for detecting fibrofatty infiltration in the myocardium
Authors: Kellman Peter , Hernando Diego , Shah Saurabh , Zuehlsdorff Sven , Jerecic Renate , Mancini Christine , Liang Zhi‐Pei , Arai Andrew E.
Published: December 2008

Conventional approaches for fat and water discrimination based on chemical‐shift fat suppression have reduced ability to characterize fatty infiltration due to poor contrast of microscopic fat. The multiecho Dixon approach to water and fat separation has advantages over chemical‐shift fat suppression: 1) water and fat images can be acquired in a single breathhold, avoiding misregistration; 2) fat has positive contrast; 3) the method is compatible with precontrast and late‐enhancement imaging, 4) less susceptible to partial‐volume effects, and 5) robust in the presence of background field variation; and 6) for the bandwidth implemented, chemical‐shift artifact is decreased. The proposed technique was applied successfully in all 28 patients studied. This included 10 studies with indication of coronary artery disease (CAD), of which four cases with chronic myocardial infarction (MI) exhibited fatty infiltration; 13 studies to rule out arrhythmogenic right ventricular cardiomyopathy (ARVC), of which there were three cases with fibrofatty infiltration and two confirmed with ARVC; and five cases of cardiac masses (two lipomas). The precontrast contrast‐to‐noise ratio (CNR) of intramyocardial fat was greatly improved, by 240% relative to conventional fat suppression. For the parameters implemented, the signal‐to‐noise ratio (SNR) was decreased by 30% relative to conventional late enhancement. The multiecho Dixon method for fat and water separation provides a sensitive means of detecting intramyocardial fat with positive signal contrast. Magn Reson Med 61:215–221, 2009. © 2008 Wiley‐Liss, Inc.
k‐t FOCUSS: A general compressed sensing framework for high resolution dynamic MRI
Authors: Jung Hong , Sung Kyunghyun , Nayak Krishna S. , Kim Eung Yeop , Ye Jong Chul
Published: December 2008

A model‐based dynamic MRI called k‐t BLAST/SENSE has drawn significant attention from the MR imaging community because of its improved spatio‐temporal resolution. Recently, we showed that the k‐t BLAST/SENSE corresponds to the special case of a new dynamic MRI algorithm called k‐t FOCUSS that is optimal from a compressed sensing perspective. The main contribution of this article is an extension of k‐t FOCUSS to a more general framework with prediction and residual encoding, where the prediction provides an initial estimate and the residual encoding takes care of the remaining residual signals. Two prediction methods, RIGR and motion estimation/compensation scheme, are proposed, which significantly sparsify the residual signals. Then, using a more sophisticated random sampling pattern and optimized temporal transform, the residual signal can be effectively estimated from a very small number of k‐t samples. Experimental results show that excellent reconstruction can be achieved even from severely limited k‐t samples without aliasing artifacts. Magn Reson Med 61:103–116, 2009. © 2008 Wiley‐Liss, Inc.
STAR and STARFIRE for flow‐dependent and flow‐independent noncontrast carotid angiography
Authors: Koktzoglou Ioannis , Edelman Robert R.
Published: December 2008

Signal Targeting with Alternating Radiofrequency (STAR) and STAR and Flow‐Independent Relaxation Enhancement (STARFIRE) are noncontrast methods for flow‐dependent and flow‐independent magnetic resonance angiography (MRA). The methods rely on the acquisition and complex subtraction of two image sets alternately labeled by spatially selective or spatially nonselective inversion radio frequency (RF) pulses. Experimental results show that the RF labeling period affects the extent of the carotid vessels seen with STAR imaging, and the conspicuity of cerebrospinal fluid (CSF) and fat in the STARFIRE images. Both methods were found to provide more detailed depiction of the carotid arteries than the alternative noncontrast MRA technique of time‐of‐flight (TOF) angiography. Magn Reson Med 61:117–124, 2009. © 2008 Wiley‐Liss, Inc.
3D blood flow characteristics in the carotid artery bifurcation assessed by flow‐sensitive 4D MRI at 3T
Authors: Harloff A. , Albrecht F. , Spreer J. , Stalder A.F. , Bock J. , Frydrychowicz A. , Schöllhorn J. , Hetzel A. , Schumacher M. , Hennig J. , Markl M.
Published: December 2008

To determine three‐dimensional (3D) blood flow patterns in the carotid bifurcation, 10 healthy volunteers and nine patients with internal carotid artery (ICA) stenosis ≥50% were examined by flow‐sensitive 4D MRI at 3T. Absolute and mean blood velocities, pulsatility index (PI), and resistance index (RI) were measured in the common carotid arteries (CCAs) by duplex sonography (DS) and compared with flow‐sensitive 4D MRI. Furthermore, 3D MRI blood flow patterns in the carotid bifurcation of volunteers and patients before and after recanalization were graded by two independent readers. Blood flow velocities measured by MRI were 31–39% lower than in DS. However, PI and RI differed by only 13–16%. Rating of 3D flow characteristics in the ICA revealed consistent patterns for filling and helical flow in volunteers. In patients with ICA stenosis, 3D blood flow visualization was successfully employed to detect markedly altered filling and helical flow patterns (forward‐moving spiral flow) in the ICA bulb and to evaluate the effect of revascularization, which restored filling and helical flow. Our results demonstrate the feasibility of flow‐sensitive 4D MRI for the quantification and 3D visualization of physiological and pathological flow patterns in the carotid artery bifurcation. Magn Reson Med 61:65–74, 2009. © 2008 Wiley‐Liss, Inc.
Imaging and analysis of lenticulostriate arteries using 7.0‐Tesla magnetic resonance angiography
Authors: Kang Chang‐Ki , Park Cheol‐Wan , Han Jae‐Yong , Kim Sang‐Hoon , Park Chan‐A , Kim Kyoung‐Nam , Hong Suk‐Min , Kim Young‐Bo , Lee Kendall H. , Cho Zang‐Hee
Published: December 2008

The purpose of this study was to analyze human lenticulostriate arteries (LSAs) obtained non‐invasively by 7.0‐T MRI. A three‐dimensional time‐of‐flight (3D TOF) magnetic resonance angiography (MRA) technique was used with an investigational 7.0‐T MRI scanner with a radio‐frequency coil that was optimized and designed for angiographic purposes. We obtained images from 16 healthy volunteers (8 males and 8 females, mean age 21 ± 2.7 years). For direct comparison of LSA images with digital subtraction angiography (DSA), we also obtained 7.0‐T MRA and DSA images from one patient, a 27‐year‐old woman with a posterior fossa arteriovenous malformation (AVM). We then analyzed the characteristics of LSAs using a custom data analysis method with MatLab for quantitative analysis. Analysis of LSA images included shape and number of branches and origins, findings that are essential and useful for quantification of LSA abnormalities in both healthy controls and patients. Ultra–high‐field MRA provided clear anatomic delineation of the LSAs, thereby suggesting that 7.0‐T MRA may be a promising technique for microvascular imaging of the LSAs. Magn Reson Med 61:136–144, 2009. © 2008 Wiley‐Liss, Inc.
Aortic vessel wall magnetic resonance imaging at 3.0 Tesla: A reproducibility study of respiratory navigator gated free‐breathing 3D black blood magnetic resonance imaging
Authors: Roes Stijntje D. , Westenberg Jos J.M. , Doornbos Joost , van der Geest Rob J. , Angelié Emmanuelle , de Roos Albert , Stuber Matthias
Published: December 2008

The purpose of this study was to evaluate a free‐breathing three‐dimensional (3D) dual inversion‐recovery (DIR) segmented k‐space gradient‐echo (turbo field echo [TFE]) imaging sequence at 3T for the quantification of aortic vessel wall dimensions. The effect of respiratory motion suppression on image quality was tested. Furthermore, the reproducibility of the aortic vessel wall measurements was investigated. Seven healthy subjects underwent 3D DIR TFE imaging of the aortic vessel wall with and without respiratory navigator. Subsequently, this sequence with respiratory navigator was performed twice in 10 healthy subjects to test its reproducibility. The signal‐to‐noise (SNR), contrast‐to‐noise ratio (CNR), vessel wall sharpness, and vessel wall volume (VWV) were assessed. Data were compared using the paired t‐test, and the reproducibility of VWV measurements was evaluated using intraclass correlation coefficients (ICCs). SNR, CNR, and vessel wall sharpness were superior in scans performed with respiratory navigator compared to scans performed without. The ICCs concerning intraobserver, interobserver, and interscan reproducibility were excellent (0.99, 0.94, and 0.95, respectively). In conclusion, respiratory motion suppression substantially improves image quality of 3D DIR TFE imaging of the aortic vessel wall at 3T. Furthermore, this optimized technique with respiratory motion suppression enables assessment of aortic vessel wall dimensions with high reproducibility. Magn Reson Med 61:35–44, 2009. © 2008 Wiley‐Liss, Inc.
Regularized sensitivity encoding (SENSE) reconstruction using bregman iterations
Authors: Liu Bo , King Kevin , Steckner Michael , Xie Jun , Sheng Jinhua , Ying Leslie
Published: December 2008

In parallel imaging, the signal‐to‐noise ratio (SNR) of sensitivity encoding (SENSE) reconstruction is usually degraded by the ill‐conditioning problem, which becomes especially serious at large acceleration factors. Existing regularization methods have been shown to alleviate the problem. However, they usually suffer from image artifacts at high acceleration factors due to the large data inconsistency resulting from heavy regularization. In this paper, we propose Bregman iteration for SENSE regularization. Unlike the existing regularization methods where the regularization function is fixed, the method adaptively updates the regularization function using the Bregman distance at different iterations, such that the iteration gradually removes the aliasing artifacts and recovers fine structures before the noise finally comes back. With a discrepancy principle as the stopping criterion, our results demonstrate that the reconstructed image using Bregman iteration preserves both sharp edges lost in Tikhonov regularization and fines structures missed in total variation (TV) regularization, while reducing more noise and aliasing artifacts. Magn Reson Med 61:145–152, 2009. © 2008 Wiley‐Liss, Inc.
3D cine displacement‐encoded MRI of pulsatile brain motion
Authors: Soellinger Michaela , Rutz Andrea K. , Kozerke Sebastian , Boesiger Peter
Published: December 2008

Pulsatile brain motion is considered to be an important mechanical link between blood and cerebrospinal fluid (CSF) dynamics. Like many severe brain diseases, different types of hydrocephalus are associated with impairment of these dynamics. In this work a cine displacement‐encoded imaging method employing stimulated echoes (DENSE) and a three‐dimensional (3D) segmented echo‐planar imaging (EPI) readout for brain motion measurements in all three spatial directions is presented. Displacement‐encoded data sets of 12 healthy volunteers were analyzed with respect to reproducibility, periodicity, and intra‐ as well as intersubject physiological consistency. In addition, displacement values were compared with data derived from phase‐contrast (PC) velocity measurements in a subset of all measured subjects. Using DENSE, displacements as low as 0.01 mm could be detected and observation of the 3D pulse pressure wave propagation was possible. Among other parameters, peak displacements in the central brain regions were measured: feet–head (FH): thalamus (0.13 ± 0.01 mm); right–left (RL): thalamus (0.06 ± 0.01 mm); and anterior–posterior (AP): caudate nucleus (0.05 ± 0.01 mm). Magn Reson Med 61:153–162, 2009. © 2008 Wiley‐Liss, Inc.
Functional brain mapping at 9.4T using a new MRI‐compatible electrode chronically implanted in rats
Authors: Dunn Jeff F. , Tuor Ursula I. , Kmech Jonn , Young Nicole A. , Henderson Amy K. , Jackson Jesse C. , Valentine Pamela A. , Teskey G. Campbell
Published: December 2008

There is a need for acute and chronic stimulation of the brain within the MRI for studies of epilepsy, as well as deep brain stimulation for movement and behavioral disorders. This work describes the production and characteristics of carbon fiber–based electrodes for acute and chronic stimulation in the brain. Increasing MRI field strengths are making it increasingly difficult to introduce foreign objects without a susceptibility artifact. We describe the production of, and the characteristics of carbon fiber–based electrodes. These are biocompatible and can be implanted for chronic studies. We show the use of these electrodes at 9.4T for studying functional activation. Data are presented showing regional connectivity. Activation not only occurs near the electrode, but at sites distant and often contralateral to the electrode. In addition, there were sites showing strong negative activation to stimulation both with direct stimulation and during a kindling‐associated seizure. Magn Reson Med 61:222–228, 2009. © 2008 Wiley‐Liss, Inc.
A Bayesian hierarchical model for the analysis of a longitudinal dynamic contrast‐enhanced MRI oncology study
Authors: Schmid Volker J. , Whitcher Brandon , Padhani Anwar R. , Taylor N. Jane , Yang Guang‐Zhong
Published: December 2008

Imaging in clinical oncology trials provides a wealth of information that contributes to the drug development process, especially in early phase studies. This article focuses on kinetic modeling in DCE‐MRI, inspired by mixed‐effects models that are frequently used in the analysis of clinical trials. Instead of summarizing each scanning session as a single kinetic parameter—such as medianktransacross all voxels in the tumor ROI–we propose to analyze all voxel time courses from all scans and across all subjects simultaneously in a single model. The kinetic parameters from the usual nonlinear regression model are decomposed into unique components associated with factors from the longitudinal study; e.g., treatment, patient, and voxel effects. A Bayesian hierarchical model provides the framework to construct a data model, a parameter model, as well as prior distributions. The posterior distribution of the kinetic parameters is estimated using Markov chain Monte Carlo (MCMC) methods. Hypothesis testing at the study level for an overall treatment effect is straightforward and the patient‐ and voxel‐level parameters capture random effects that provide additional information at various levels of resolution to allow a thorough evaluation of the clinical trial. The proposed method is validated with a breast cancer study, where the subjects were imaged before and after two cycles of chemotherapy, demonstrating the clinical potential of this method to longitudinal oncology studies. Magn Reson Med 61:163–174, 2009. © 2008 Wiley‐Liss, Inc.
Inherent fat cancellation in complementary spatial modulation of magnetization
Authors: Fahmy Ahmed S. , Basha Tamer A. , Osman Nael F.
Published: December 2008

An efficient fat suppression method is presented for MR tagging with complementary spatial modulation of magnetization (CSPAMM). In this method, the complementary modulation is applied to the water content of the tissues, while in‐phase modulation is applied to the fat content. Therefore, during image reconstruction, the subtraction of the acquired images increases the tagging contrast of the water while cancels the tagging lines of the fat. Compared with the existing fat suppression techniques, the proposed method allows imaging with higher temporal resolution and shorter echo‐time without increasing the scan time. The feasibility of applying the method on 1.5 Tesla (T) and 3.0T scanners has been tested using MR phantom and human volunteers. Magn Reson Med 61:234–238, 2009. © 2008 Wiley‐Liss, Inc.
Comparison of normal tissue R1 and R modulation by oxygen and carbogen
Authors: O'Connor James P.B. , Naish Josephine H. , Jackson Alan , Waterton John C. , Watson Yvonne , Cheung Sue , Buckley David L. , McGrath Deirdre M. , Buonaccorsi Giovanni A. , Mills Samantha J. , Roberts Caleb , Jayson Gordon C. , Parker Geoff J.M.
Published: December 2008

Magnetic resonance imaging has shown promise for evaluating tissue oxygenation. In this study differences in the tissue longitudinal relaxation rate (R1) and effective transverse relaxation rate (R), induced by inhalation of pure oxygen and carbogen, were evaluated in 10 healthy subjects. Significant reductions in R1 were demonstrated following both oxygen and carbogen inhalation in the spleen (both P < 0.001), liver (P = 0.002 air vs. oxygen; P = 0.001 air vs. carbogen), skeletal muscle (both P < 0.001), and renal cortex (P = 0.005 air vs. oxygen; P = 0.008 air vs. carbogen). No significant change in R occurred following pure oxygen in any organ. However, a significant increase in R was observed in the spleen (P < 0.001), liver (P = 0.001), skeletal muscle (P = 0.026), and renal cortex (P = 0.001) following carbogen inhalation, an opposite effect to that observed in many studies of tumor pathophysiology. Changes in R1 and R were independent of the gas administration order in the spleen and skeletal muscle. These findings suggest that the R1 and R responses to hyperoxic gases are independent biomarkers of oxygen physiology. Magn Reson Med 61:75–83, 2009. © 2008 Wiley‐Liss, Inc.
Phospholipid composition of postmortem schizophrenic brain by 31P NMR spectroscopy
Authors: Pearce John M. , Komoroski Richard A. , Mrak Robert E.
Published: December 2008

Cell membrane abnormalities due to changes in phospholipid (PL) composition and metabolism have been implicated in schizophrenia pathogenesis. That work has generally assessed membrane phospholipids from nonneural tissues such as erythrocytes and platelets. High‐resolution 31P NMR spectroscopy was used to characterize PLs of gray matter in postmortem brain for 20 schizophrenics, 20 controls, and 7 patients with other mental illnesses (psychiatric controls). Tissues from frontal, temporal, and occipital cortices were extracted with hexane–isopropanol, and 31P NMR spectra were obtained in an organic–solvent system to resolve the major PL classes (based on headgroups) and subclasses (based on linkage at the sn − 1 position). Surprisingly, repeated‐measures multivariate analysis of variance revealed no overall differences among the groups. There were no significant differences (P < .05) among the three groups for any individual PL subclass, including lysophospholipids. The sum of all phosphatidylethanolamine headgroups was significantly lower for schizophrenics than for controls or psychiatric controls in the frontal cortex. The present results are minimally correlated with previous results for aqueous PL metabolites on these same samples. The metabolite changes measured by in vivo 31P MRS in schizophrenia do not appear to reflect PL concentration changes. The present results offer very little support for the phospholipid hypothesis of schizophrenia. Magn Reson Med 61:28–34, 2009. © 2008 Wiley‐Liss, Inc.
Calibration of RF transmitter voltages for hyperpolarized gas MRI
Authors: Bashir Adil , Conradi Mark S. , Woods Jason C. , Quirk James D. , Yablonskiy Ddmitriy A.
Published: December 2008

MRI with hyperpolarized gases, 3He, 129Xe, 13C, and others, has the potential to become an important diagnostic technique for clinical imaging. Due to the nonreversible loss of magnetization in hyperpolarized gas imaging, the choice of the flip angle is a major factor that influences the signal intensity, and hence, the signal‐to‐noise ratio. Conventional automated radiofrequency (RF) calibration procedures for 1H imaging are not suitable for hyperpolarized gas imaging. Herein, we have demonstrated a simple procedure for RF calibration for magnetic resonance imaging (MRI) with hyperpolarized gases that is easily adaptable to clinical settings. We have demonstrated that there exists a linear relationship between the RF transmitter voltages required to obtain the same nutation angle for protons (V1H) and hyperpolarized gas nuclei (V3He). For our 1H and 3He coils we found that V3He = 1.937 · V1H with correlation coefficient r2 = 0.97. This calibration can be done as a one‐time procedure during the routine quality assurance (QA) protocol. The proposed procedure was found to be extremely robust in routine scanning and provided an efficient method to achieve a desired flip angle, thus allowing optimum image quality. Magn Reson Med 61:239–243, 2009. © 2008 Wiley‐Liss, Inc.
Spin‐echo MRI using π/2 and π hyperbolic secant pulses
Authors: Park Jang‐Yeon , Garwood Michael
Published: December 2008

Frequency‐modulated (FM) pulses have practical advantages for spin‐echo experiments, such as the ability to produce a broadband π rotation, with an inhomogeneous radiofrequency (RF) field. However, such use leads to a nonlinear phase of the transverse magnetization, which is why FM pulses like the hyperbolic secant (HS) pulse are not commonly used for multislice spin‐echo magnetic resonance imaging (MRI). Here, a general theory and methods are described for conventional spin‐echo imaging using a π HS pulse for refocusing. Phase profiles produced by the HS pulse are analytically described. The analysis is extended to yield the specific relationships between pulse parameters and gradients, which must be satisfied to compensate the nonlinear phase variation produced with a spin‐echo sequence composed of π/2 and π HS pulses (the π/2 HS − π HS sequence). The latter offers advantages for multislice spin‐echo MRI, including excellent slice‐selection and partial compensation for RF inhomogeneity. Furthermore, it can be implemented with a shorter echo time and lower power deposition than a previously described method using a pair of π HS pulses. Magn Reson Med 61:175–187, 2009. © 2008 Wiley‐Liss, Inc.
Quantitative magnetization transfer characteristics of the human cervical spinal cord in vivo: Application to Adrenomyeloneuropathy
Authors: Smith Seth A. , Golay Xavier , Fatemi Ali , Mahmood Asif , Raymond Gerald V. , Moser Hugo W. , van Zijl Peter C.M. , Stanisz Greg J.
Published: December 2008

Magnetization transfer (MT) imaging has assessed myelin integrity in the brain and spinal cord; however, quantitative MT (qMT) has been confined to the brain or excised tissue. We characterized spinal cord tissue with qMT in vivo, and as a first application, qMT‐derived metrics were examined in adults with the genetic disorder Adrenomyeloneuropathy (AMN). AMN is a progressive disease marked by demyelination of the white matter tracts of the cervical spinal cord, and a disease in which conventional MRI has been limited. MT data were acquired at 1.5 Tesla using 10 radiofrequency offsets at one power in the cervical cord at C2 in 6 healthy volunteers and 9 AMN patients. The data were fit to a two‐pool MT model and the macromolecular fraction (Mob), macromolecular transverse relaxation time (T2b) and the rate of MT exchange (R) for lateral and dorsal column white matter and gray matter were calculated. Mob for healthy volunteers was: WM = 13.9 ± 2.3%, GM = 7.9 ± 1.5%. In AMN, dorsal column Mob was significantly decreased (P < 0.03). T2b for volunteers was: 9 ± 2 μs and the rate of MT exchange (R) was: WM = 56 ± 11 Hz, GM = 67 ± 12 Hz. Neither T2b nor R showed significant differences between healthy and diseased cords. Comparisons are made between qMT, and conventional MT acquisitions. Magn Reson Med 61:22–27, 2009. © 2008 Wiley‐Liss, Inc.
Calculation of susceptibility through multiple orientation sampling (COSMOS): A method for conditioning the inverse problem from measured magnetic field map to susceptibility source image in MRI
Authors: Liu Tian , Spincemaille Pascal , de Rochefort Ludovic , Kressler Bryan , Wang Yi
Published: December 2008

Magnetic susceptibility differs among tissues based on their contents of iron, calcium, contrast agent, and other molecular compositions. Susceptibility modifies the magnetic field detected in the MR signal phase. The determination of an arbitrary susceptibility distribution from the induced field shifts is a challenging, ill‐posed inverse problem. A method called “calculation of susceptibility through multiple orientation sampling” (COSMOS) is proposed to stabilize this inverse problem. The field created by the susceptibility distribution is sampled at multiple orientations with respect to the polarization field, B0, and the susceptibility map is reconstructed by weighted linear least squares to account for field noise and the signal void region. Numerical simulations and phantom and in vitro imaging validations demonstrated that COSMOS is a stable and precise approach to quantify a susceptibility distribution using MRI. Magn Reson Med 61:196–204, 2009. © 2008 Wiley‐Liss, Inc.
Quantifying hepatic glycogen synthesis by direct and indirect pathways in rats under normal ad libitum feeding conditions
Authors: Soares Ana F. , Viega Francisco J. , Carvalho Rui A. , Jones John G.
Published: December 2008

Hepatic glycogen synthesis from intact hexose (direct pathway) relative to that from gluconeogenic precursors (indirect pathway) was quantified in ad libitum‐fed rats. Following 2H2O administration and overnight feeding, the livers were removed and glycogen 2H‐enrichment was measured by 2H NMR. Six controls and six rats rendered hyperglycemic by streptozotocin (STZ; fasting blood glucose = 385 ± 31 mg/dl) were studied. The indirect pathway contribution, estimated as glycogen hydrogen 5 relative to hydrogen 2 enrichment, was 54% ± 4% for control rats—similar to values from healthy, meal‐fed humans. In STZ‐treated rats, the indirect pathway contribution was significantly higher (68% ± 4%, P < 0.05 vs. controls), similar to that of Type 1 diabetic (T1D) patients. In conclusion, sources of hepatic glycogen synthesis in rats during ad libitum nocturnal feeding were quantified by analysis of glycogen enrichment from 2H2O. STZ caused alterations resembling the pathophysiology of hepatic glycogen synthesis in T1D patients. Magn Reson Med 61:1–5, 2009. © 2008 Wiley‐Liss, Inc.
Lung imaging under free‐breathing conditions
Authors: Oechsner Markus , Pracht Eberhard D. , Staeb Daniel , Arnold Johannes F.T. , Köstler Herbert , Hahn Dietbert , Beer Meinrad , Jakob Peter M.
Published: December 2008

Respiratory motion and pulsatile blood flow can generate artifacts in morphological and functional lung imaging. Total acquisition time, and thus the achievable signal to noise ratio, is limited when performing breath‐hold and/or electrocardiogram‐triggered imaging. To overcome these limitations, imaging during free respiration can be performed using respiratory gating/triggering devices or navigator echoes. However, these techniques provide only poor gating resolution and can induce saturation bands and signal fluctuations into the lung volume. In this work, acquisition schemes for nonphase encoded navigator echoes were implemented into different sequences for morphological and functional lung imaging at 1.5 Tesla (T) and 0.2T. The navigator echoes allow monitoring of respiratory motion and provide an ECG‐trigger signal for correction of the heart cycle without influencing the imaged slices. Artifact free images acquired during free respiration using a 3D GE, 2D multislice TSE or multi‐Gradient Echo sequence for oxygen‐enhanced T quantification are presented. Magn Reson Med, 2009. © 2008 Wiley‐Liss, Inc.
The tensor distribution function
Authors: Leow A. D. , Zhu S. , Zhan L. , McMahon K. , de Zubicaray G. I. , Meredith M. , Wright M. J. , Toga A. W. , Thompson P. M.
Published: December 2008

Diffusion weighted magnetic resonance imaging is a powerful tool that can be employed to study white matter microstructure by examining the 3D displacement profile of water molecules in brain tissue. By applying diffusion‐sensitized gradients along a minimum of six directions, second‐order tensors (represented by three‐by‐three positive definite matrices) can be computed to model dominant diffusion processes. However, conventional DTI is not sufficient to resolve more complicated white matter configurations, e.g., crossing fiber tracts. Recently, a number of high‐angular resolution schemes with more than six gradient directions have been employed to address this issue. In this article, we introduce the tensor distribution function (TDF), a probability function defined on the space of symmetric positive definite matrices. Using the calculus of variations, we solve the TDF that optimally describes the observed data. Here, fiber crossing is modeled as an ensemble of Gaussian diffusion processes with weights specified by the TDF. Once this optimal TDF is determined, the orientation distribution function (ODF) can easily be computed by analytic integration of the resulting displacement probability function. Moreover, a tensor orientation distribution function (TOD) may also be derived from the TDF, allowing for the estimation of principal fiber directions and their corresponding eigenvalues. Magn Reson Med 61:205–214, 2009. © 2008 Wiley‐Liss, Inc.
Single‐shot magnetic resonance spectroscopic imaging with partial parallel imaging
Authors: Posse Stefan , Otazo Ricardo , Tsai Shang‐Yueh , Yoshimoto Akio Ernesto , Lin Fa‐Hsuan
Published: December 2008

A magnetic resonance spectroscopic imaging (MRSI) pulse sequence based on proton–echo‐planar‐spectroscopic‐imaging (PEPSI) is introduced that measures two‐dimensional metabolite maps in a single excitation. Echo‐planar spatial–spectral encoding was combined with interleaved phase encoding and parallel imaging using SENSE to reconstruct absorption mode spectra. The symmetrical k‐space trajectory compensates phase errors due to convolution of spatial and spectral encoding. Single‐shot MRSI at short TE was evaluated in phantoms and in vivo on a 3‐T whole‐body scanner equipped with a 12‐channel array coil. Four‐step interleaved phase encoding and fourfold SENSE acceleration were used to encode a 16 × 16 spatial matrix with a 390‐Hz spectral width. Comparison with conventional PEPSI and PEPSI with fourfold SENSE acceleration demonstrated comparable sensitivity per unit time when taking into account g‐factor–related noise increases and differences in sampling efficiency. LCModel fitting enabled quantification of inositol, choline, creatine, and N‐acetyl‐aspartate (NAA) in vivo with concentration values in the ranges measured with conventional PEPSI and SENSE‐accelerated PEPSI. Cramer–Rao lower bounds were comparable to those obtained with conventional SENSE‐accelerated PEPSI at the same voxel size and measurement time. This single‐shot MRSI method is therefore suitable for applications that require high temporal resolution to monitor temporal dynamics or to reduce sensitivity to tissue movement. Magn Reson Med, 2009. © 2008 Wiley‐Liss, Inc.
Phase labeling using sensitivity encoding (PLUS): Data acquisition and image reconstruction for geometric distortion correction in EPI
Authors: Techavipoo Udomchai , Lackey John , Shi Jianrong , Leist Thomas , Lai Song
Published: December 2008

Geometric distortion caused by magnetic field inhomogeneity is generally an inevitable tradeoff for fast MRI acquisitions using echo‐planar imaging. Most of the existing distortion‐correction techniques require separate scans for field maps in order to correct the distortion contained in a measurement. A drawback of these current techniques is that the field map scans and the measurement can capture different patient positions, which invalidates the stationary condition. A new method was developed in this work to correct geometric distortion by using local phase shifts derived directly from the measurement itself, without the need of extra field map scans. This self‐sufficient method takes advantage of parallel imaging and k‐space trajectory modification to produce multiple images from a single acquisition. The measurement is also used to derive sensitivity maps for parallel imaging reconstruction. The derived phase shifts are retrospectively applied to the measurement for correction of geometric distortion in the measurement itself. The proposed method was successfully demonstrated using experimental data from a phantom and a human brain. Magn Reson Med, 2009. © 2008 Wiley‐Liss, Inc.
On the measurement of absolute cerebral blood volume (CBV) using vascular‐space‐occupancy (VASO) MRI
Authors: Uh Jinsoo , Lewis‐Amezcua Kelly , Varghese Rani , Lu Hanzhang
Published: December 2008

Recently, a vascular‐space‐occupancy (VASO) MRI technique was developed for quantitative assessment of cerebral blood volume (CBV). This method uses the T1‐shortening effect of gadolinium diethylenetriamine pentaacetic acid (Gd‐DTPA) with imaging parameters chosen that null the precontrast blood magnetization but allow the postcontrast blood magnetization to recover to equilibrium. A key advantage of VASO CBV estimation is that it provides a straightforward procedure for converting MR signals to absolute physiologic values. However, as with other T1‐based steady‐state approaches, several important factors need to be considered that influence the accuracy of CBV values obtained with VASO MRI. Here, the transverse relaxation (T2/T) effect in VASO MRI was investigated using multiecho spin‐echo and gradient‐echo experiments, resulting in underestimation of CBV by 14.9% ± 1.1% and 16.0% ± 2.5% for spin echo (TE = 10 ms) and gradient echo (TE = 6 ms), respectively. In addition, the influence of contrast agent clearance was studied by acquiring multiple postcontrast VASO images at 2.2‐min intervals, which showed that the concentration of Gd‐DTPA in the first 14 min (single dose) was sufficient for the blood magnetization to fully recover to equilibrium. Finally, the effect of vascular Gd‐DTPA leakage was assessed for scalp tissue, and signal extrapolation as a function of postinjection time was demonstrated to be useful in minimizing the associated errors. Specific recommendations for VASO MRI acquisition and processing strategies are provided. Magn Reson Med, 2009. © 2008 Wiley‐Liss, Inc.
High‐field diffusion MR histology: Image‐based correction of eddy‐current ghosts in diffusion‐weighted rapid acquisition with relaxation enhancement (DW‐RARE)
Authors: Tyszka J. Michael , Frank Lawrence R.
Published: December 2008

High‐resolution, diffusion‐weighted (DW) MR microscopy is gaining increasing acceptance as a nondestructive histological tool for the study of fixed tissue samples. Spin‐echo sequences are popular for high‐field diffusion imaging due to their high tolerance to B0 field inhomogeneities. Volumetric DW rapid acquisition with relaxation enhancement (DW‐RARE) currently offers the best tradeoff between imaging efficiency and image quality, but is relatively sensitive to residual eddy‐current effects on the echo train phase, resulting in encoding direction‐dependent ghosting in the DW images. We introduce two efficient, image‐based phase corrections for ghost artifact reduction in DW‐RARE of fixed tissue samples, neither of which require navigator echo acquisition. Both methods rely on the phase difference in k‐space between the unweighted reference image and a given DW image and assume a constant, per‐echo phase error arising from residual eddy‐current effects in the absence of sample motion. Significant qualitative and quantitative ghost artifact reductions are demonstrated for individual DW and calculated diffusion tensor images. Magn Reson Med, 2009. © 2008 Wiley‐Liss, Inc.
MR elastography of the human heart: Noninvasive assessment of myocardial elasticity changes by shear wave amplitude variations
Authors: Sack Ingolf , Rump Jens , Elgeti Thomas , Samani Abbas , Braun Jürgen
Published: December 2008

Many cardiovascular diseases and disorders are associated with hemodynamic dysfunction. The heart's ability to contract and pump blood through the vascular system primarily depends on the elasticity of the myocardium. This article introduces a magnetic resonance elastography (MRE) technique that allows noninvasive and time‐resolved measurement of changes in myocardial elasticity over the cardiac cycle. To this end, low‐frequency shear vibrations of 24.3 Hz were induced in the human heart via the anterior chest wall. An electrocardiograph (ECG)‐triggered, steady‐state MRE sequence was used to capture shear oscillations with a frame rate of eight images per vibration cycle. The time evolution of 2D‐shear wave fields was observed in two imaging planes through the short axis of the heart in six healthy volunteers. Correlation analysis revealed that wave amplitudes were modulated in synchrony to the heartbeat with up to 2.45 ± 0.18 higher amplitudes during diastole than during systole (interindividual mean ± SD). The reduction of wave amplitudes started at 75 ± 9 ms prior to changes in left ventricular diameter occurring at the beginning of systole. Analysis of this wave amplitude alteration using a linear elastic constitutive model revealed a maximum change in the myocardial wall stiffness of a factor of 37.7 ± 10.6 during the cardiac cycle. Magn Reson Med, 2009. © 2008 Wiley‐Liss, Inc.
Quantification of myocardial perfusion using free‐breathing MRI and prospective slice tracking
Authors: Pedersen Henrik , Kelle Sebastian , Ringgaard Steffen , Schnackenburg Bernhard , Nagel Eike , Nehrke Kay , Kim Won Yong
Published: December 2008

Quantification of myocardial perfusion using first‐pass magnetic resonance imaging (MRI) is hampered by respiratory motion of the heart. Prospective slice tracking (PST) potentially overcomes this problem, and may provide an attractive alternative or supplement to current breath‐hold techniques. This study demonstrates the feasibility of patient‐adapted 3D PST on a 3.0 Tesla MR system. Eight patients underwent free‐breathing studies of myocardial perfusion, simultaneously collecting data with and without PST. On average, PST reduced residual in‐plane motion by a factor of 2, compared to the noncorrected images, resulting in a fourfold improvement of perfusion measurements. In addition, a comparison of perfusion measurements performed with and without PST showed that through‐plane motion can contaminate measurements of myocardial perfusion. However, the quality of the navigator echoes on this field strength constituted a major source of error and needs further improvement to increase the accuracy and robustness of the method. Magn Reson Med, 2009. © 2008 Wiley‐Liss, Inc.
Rigid‐body motion correction with self‐navigation MRI
Authors: Mendes Jason , Kholmovski Eugene , Parker Dennis L.
Published: December 2008

The use of phase correlation to detect rigid‐body translational motion is reviewed and applied to individual echotrains in turbo‐spin‐echo data acquisition. It is shown that when the same echotrain is acquired twice, the subsampled correlation provides an array of delta‐functions, from which the motion that occurred between the acquisitions of the two echotrains can be measured. It is shown further that a similar correlation can be found between two sets of equally spaced measurements that are adjacent in k‐space. By measuring the motion between all adjacent pairs of k‐space subgroups, the complete motion history of a subject can be determined and the motion artifacts in the image can be corrected. Some of the limiting factors in using this technique are investigated with turbo‐spin‐echo head and hand images. Magn Reson Med, 2009. © 2008 Wiley‐Liss, Inc.
Three‐dimensional spatial and temporal temperature control with MR thermometry‐guided focused ultrasound (MRgHIFU)
Authors: Mougenot Charles , Quesson Bruno , de Senneville Baudouin Denis , de Oliveira Philippe Lourenco , Sprinkhuizen Sara , Palussière Jean , Grenier Nicolas , Moonen Chrit T.W.
Published: December 2008

High‐intensity focused ultrasound (HIFU) is an efficient noninvasive technique for local heating. Using MRI thermal maps, a proportional, integral, and derivative (PID) automatic temperature control was previously applied at the focal point, or at several points within a plane perpendicular to the beam axis using a multispiral focal point trajectory. This study presents a flexible and rapid method to extend the spatial PID temperature control to three dimensions during each MR dynamic. The temperature in the complete volume is regulated by taking into account the overlap effect of nearby sonication points, which tends to enlarge the heated area along the beam axis. Volumetric temperature control in vitro in gel and in vivo in rabbit leg muscle was shown to provide temperature control with a precision close to that of the temperature MRI measurements. The proposed temperature control ensures heating throughout the volume of interest of up to 1 ml composed of 287 voxels with 95% of the energy deposited within its boundaries and reducing the typical average temperature overshoot to 1°C. Magn Reson Med, 2009. © 2008 Wiley‐Liss, Inc.