bluuebunny/crossref_metadata_2025 huggingface dataset:
T2 and T quantification using optimal B1 image reconstruction for multicoil arrays
Authors: Graves Martin J. , Emmens Daniel , Lejay Hubert , Hariharan Hari , Polzin Jason , Lomas David J.
Published: June 2008

Purpose

To investigate the accuracy of low signal‐to‐noise ratio (SNR) T2 and T measurements using array coils and optimal B1 image reconstruction (OBR) compared to the standard root sum of squares (RSS) reconstruction.

Materials and Methods

Calibrated gels were used for the in vitro study of T2. T2 and T measurements were obtained from a volunteer's knee and liver, respectively. T2 and T measurements were performed using multiecho spin echo and multiecho gradient echo sequences, respectively. SNR was deliberately kept low. The same raw data were used for both reconstructions. For the in vivo studies the effect of signal averaging was also investigated.

Results

The optimal reconstructions demonstrated a lower mean background noise level than RSS. In vitro, the T2 measurements made with OBR images agreed better with a reference high SNR measurement than measurements made from RSS images; the RSS image results overestimated the T2. In vivo, increasing the signal averages decreased the difference between the measurements obtained using the OBR and RSS methods, with RSS resulting in longer relaxation times.

Conclusion

This work demonstrates improvements to the accuracy of T2 and T measurements obtained when OBR is used compared to RSS, particularly in the case of low SNR. J. Magn. Reson. Imaging 2008;28:278–281. © 2008 Wiley‐Liss, Inc.
MRA of intracranial aneurysms embolized with platinum coils: A vascular phantom study at 1.5T and 3T
Authors: Kakeda Shingo , Korogi Yukunori , Hiai Yasuhiro , Sato Toru , Ohnari Norihiro , Moriya Junji , Kamada Koji
Published: June 2008

Purpose

To analyze the influence of matrix and echo time (TE) of three‐dimensional time‐of‐flight (3D TOF) magnetic resonance angiography (MRA) on the depiction of residual flow in aneurysms embolized with platinum coils at 1.5T and 3T.

Materials and Methods

A simulated intracranial aneurysm of the vascular phantom was loosely packed to maintain the patency of some residual aneurysmal lumen with platinum coils and connected to an electromagnetic flow pump with pulsatile flow. MRAs were obtained altering the matrix and TE of 3D TOF sequences at 1.5T and 3T.

Results

The increased spatial resolution and the shorter TE offered better image quality at 3T. For the depiction of an aneurysm remnant, the high‐spatial‐resolution 3T MRA (matrix size of 384 × 224 and 512 × 256) with a short TE of ≤3.3 msec were superior to the 1.5T MRA obtained with any sequences.

Conclusion

3T MRA is superior to 1.5T MRA for the assessment of aneurysms embolized with platinum coils; the combination of the 512 × 256 matrix and short TE (3.3 msec or less) seems feasible at 3T. J. Magn. Reson. Imaging 2008;28:13–20. © 2008 Wiley‐Liss, Inc.
Conspicuity of zones of ablation after radiofrequency ablation in porcine livers: Comparison of an extracellular and an SPIO contrast agent
Authors: Bangard Christopher , Stippel Dirk L. , Berg Frank , Kasper Hans U. , Hellmich Martin , Fischer Jürgen H. , Hölscher Arnulf , Lackner Klaus , Gossmann Axel
Published: June 2008

Purpose

To compare conspicuity of zones of ablation on nonenhanced, gadopentetate dimeglumine‐(Gd‐DTPA) and ferucarbotran‐(SPIO)‐enhanced magnetic resonance (MR) images.

Materials and Methods

In all, 33 radiofrequency ablations (RFA) were performed in 17 healthy porcine livers at 1.5T MR imaging 1 day and 2 and 4 weeks after RFA: T2‐weighted (w) ultra turbo spin echo (UTSE), proton density (PD)‐w UTSE, T1‐w gradient echo (GRE) pre‐ and 5 minutes postcontrast administration, dynamic T1‐w GRE during Gd‐DTPA (Magnevist) or SPIO (Resovist) administration, T2‐w UTSE, and PD‐w UTSE sequences 10 minutes after SPIO administration. Regions of interest (ROIs) for contrast‐to‐noise ratio (CNR) and signal‐to‐noise ratio (SNR) were drawn in consensus by two radiologists.

Results

PD‐w SPIO‐enhanced images (23.5 ± 5.5) showed higher liver‐to‐lesion CNR than T1‐w GRE Gd‐DTPA‐enhanced images (13.5 ± 6.1) 1 day after RFA (P ≤ 0.05). At all other timepoints, liver‐to‐lesion CNR of PD‐w and T2‐w SPIO‐enhanced images did not differ significantly from T1‐w GRE Gd‐DTPA‐enhanced images (P ≥ 0.05). Nonenhanced T2‐w images revealed lower liver‐to‐lesion CNR (7.0 ± 7.5/6.5 ± 5.9/6.8 ± 5.0, 1 day/2 weeks/4 weeks, respectively) than T2‐w SPIO‐enhanced (17.4 ± 4.8/15.3 ± 4.5/14.2 ± 5.7), PD‐w SPIO‐enhanced (23.5 ± 5.5/16.9 ± 3.6, 1 day/2 weeks), and T1‐w Gd‐DTPA‐enhanced (15.3 ± 3.6/12.7 ± 3.5, 2/4 weeks) images (P ≤ 0.05). Liver‐to‐lesion CNR of SPIO‐enhanced dynamic T1‐w GRE images after 30, 80, 150, and 240 seconds did not change significantly over time (P ≥ 0.05).

Conclusion

One day after RFA lesion conspicuity on PD‐w ferucarbotran‐enhanced images is better than on T1‐w GRE Gd‐DTPA‐enhanced images. At all other timepoints, ferucarbotran is not superior to gadolinium. Ferucarbotran‐ and gadolinium‐enhanced images improve lesion conspicuity compared with nonenhanced T2‐w images at all timepoints. J. Magn. Reson. Imaging 2008;28:263–270. © 2008 Wiley‐Liss, Inc.
One‐stop measurement of iron deposition in the anterior pituitary, liver, and heart in thalassemia patients
Authors: Lam Wynnie W.M. , Au W.Y. , Chu Winnie C.W. , Tam S. , Ha S.Y. , Pennell D.J.
Published: June 2008

Purpose

To assess the feasibility of one‐stop evaluation of iron load of myocardium, liver, and anterior pituitary gland in thalassemia patients.

Materials and Methods

Fifty thalassemia major patients underwent a breath‐hold magnetic resonance imaging (MRI) sequence for assessment of T2* for liver and myocardium, a short axis cine trueFISP sequence covering base to apex to assess the ejection fraction of left ventricle, and a turbo spin echo T2‐weighted sequence for the anterior pituitary gland. The MRI parameters were correlated with serum growth hormone, insulin growth factor‐1 (IGF‐1), insulin growth factor binding protein‐3 (IGFBP‐3), and endocrine failure.

Results

Ferritin was found to be associated with T2* liver (P < 0.005), T2SI (signal intensity) pituitary (P = 0.001), and T2 pituitary/fat (P = 0.001), but not with T2* heart. There was significant correlation of T2SI pituitary with IGF‐1 and IGFBP‐3. T2* liver (P < 0.001), T2* heart (P < 0.001), pituitary SI (P < 0.001) and pituitary/fat SI (P = 0.002) were also found to be significantly correlated with a history of hypogonadism. T2* heart was also found to be significantly correlated with IGF‐1.

Conclusion

A quick MRI protocol for assessment of T2* liver, T2* heart, and T2SI pituitary is technically feasible. This might form an objective basis to monitor the response to different organs to chelation therapy. J. Magn. Reson. Imaging 2008. © 2008 Wiley‐Liss, Inc.
Production of reduced calorie structured lipid by acidolysis of tripalmitin with capric acid: optimisation by response surface methodology
Authors: Bektaş Inan , Yucel Sevil , Ustun Guldem , Aksoy H Ayse
Published: June 2008

BACKGROUND: Structured lipids (SLs) containing medium‐chain fatty acids (C8:0–C12:0) in the 1‐ and 3‐positions and long‐chain fatty acids in the 2‐position of triacylglycerols have interesting applications as reduced calorie fats. The aim of this study was to produce an SL by inserting capric acid (CA, C8:0) into tripalmitin (TP) and to optimise the reaction conditions by response surface methodology (RSM) with a three‐level, three‐factor face‐centred cubic design.

RESULTS: Lipozyme TL IM from Thermomyces lanuginosa was used for the acidolysis of TP with CA in n‐hexane. The effects of three independent parameters, namely substrate molar ratio, enzyme amount and reaction time, on CA incorporation into TP were optimised. The range of each parameter was selected as follows: substrate molar ratio (CA/TP), 4–8; enzyme amount, 9–15 wt% of total substrate; reaction time, 6–10 h. Optimal conditions were determined to be a CA/TP molar ratio of 6.5, an enzyme amount of 11.6 wt% and a reaction time of 8.9 h. Experiments conducted under these optimised conditions yielded an SL containing 35.7 wt% (44.9 mol%) CA. A second‐order polynomial model was obtained for CA incorporation.

CONCLUSION: The possibility of enriching CA in TP by enzymatic acidolysis has been established. The SL containing 44.9 mol% CA produced under optimal conditions may be considered a reduced calorie fat. Copyright © 2008 Society of Chemical Industry
Transjugular liver biopsy in patients with living donor liver transplantation: Comparison with percutaneous biopsy
Authors: Kim Kyung Rae , Ko Gi-Young , Sung Kyu-Bo , Yoon Hyun-Ki , Shin Ji Hoon , Song Ho-Young , Ryu Je-Ho , Hwang Shin , Lee Sung-Gyu , Yu Eunsil
Published: June 2008

Transjugular liver biopsy (TJLB) is an alternative method of pathological diagnosis in patients with an established contraindication to percutaneous biopsy. Between November 2005 and July 2007, 111 TJLBs were attempted in 67 patients and 95 percutaneous liver biopsies (PCLBs) were attempted in 51 patients with living donor liver transplantation suspected of having rejection. Indications of TJLB included classic contraindications to PCLB and a postoperative period of less than 30 days. TJLB was performed a mean of 111.1 ± 292.6 days after transplantation (range: 6–2478 days, median: 35 days), and PCLB was performed a mean of 534.7 ± 591.6 days after transplantation (range: 6–2555 days, median: 299 days). Technical success was 99.1% in TJLB and 100% in PCLB, and there was no significant difference between these 2 groups (P = 0.354). A clinical suspicion of rejection was confirmed by histopathology in 38 (34.2%) of 111 TJLBs and 38 (40.0%) of 95 PCLBs. The overall complication rates related to the procedure were 1.8% (2/111) in TJLB and 5.3% (5/95) in PCLB. Although there was no significant difference in complication rates between TJLB and PCLB (P = 0.172), the patients who underwent TJLB showed significantly higher incidence of ascites, coagulopathy, and thrombocytopenia, given its indication. TJLB seems to be a safe and effective procedure for pathological diagnosis of rejection in patients with living donor liver transplantation when there is a high risk of complication with PCLB. Liver Transpl 14:971–979, 2008. © 2008 AASLD.
Reliability of a new ultrasonic cardiac output monitor in recipients of living donor liver transplantation
Authors: Su Bai-Chuan , Yu Huang-Ping , Yang Ming-Wen , Lin Chih-Chung , Kao Ming-Chang , Chang Chia-Hung , Lee Wei-Chen
Published: June 2008

The ultrasonic cardiac output monitor (USCOM) is a new Doppler device for noninvasive hemodynamic monitoring. The aim of this prospective nonrandomized study was to test the feasibility, perioperative reliability, and clinical applicability of using USCOM as an alternative to pulmonary artery catheterization in recipients of living donor liver transplantation. Thirteen patients scheduled to receive living donor liver transplants were initially recruited. Three were subsequently excluded prior to the commencement of surgery because of technical difficulties in obtaining diagnostic-quality images with USCOM. Ten patients proceeded to be studied. Cardiac output measurements by thermodilution and USCOM were compared at 30-minute intervals throughout the procedure and at 10 specific procedural reference points during the surgery when hemodynamic changes were most likely to be observed. The data were analyzed with Lin's concordance coefficient and Bland-Altman analysis. Two hundred ninety paired cardiac output values were obtained from the 10 patients. The concordance between both methods was excellent in 8 patients and satisfactory in 2. Bland-Altman analysis of all data produced a mean bias of − 0.02 L/minute for USCOM, and the 95% limits of agreement were −1.06 to +1.10 L/minute. Further analysis of the 10 reference time points showed minimal bias and high levels of agreement between the methods. We conclude that USCOM provides an accurate and noninvasive method for cardiac output measurement during liver transplantation. It may therefore represent an alternative to pulmonary artery catheter placement with consequent reduction in patient's risk and morbidity associated with catheterization. Liver Transpl 14:1029–1037, 2008. © 2008 AASLD.
Prevalence and risk factors for delayed adrenal insufficiency after liver transplantation
Authors: Toniutto Pierluigi , Fabris Carlo , Fumolo Elisa , Bitetto Davide , Fornasiere Ezio , Falleti Edmondo , Rapetti Rachele , Minisini Rosalba , Pirisi Mario
Published: June 2008

Liver transplantation (LT) recipients are at risk for early and delayed adrenal insufficiency for multiple reasons. Although early adrenal insufficiency is known to occur in a high proportion of recipients maintained on steroid-free immunosuppressive regimens, the prevalence and risk factors associated with delayed functional adrenal gland atrophy (FAGA) are unknown because routine evaluation for this condition is not standard practice among LT centers. We investigated a group of 87 patients (64 males) transplanted for end-stage liver disease related to different etiologies. All underwent a standard corticotropin stimulation test (CST) when, after gradual steroid tapering, they had been maintained for at least 1 week on oral prednisone at a daily dose of 5 mg. FAGA, defined by a serum cortisol concentration that, 60 minutes after corticotropin administration, did not double the baseline level and remained <20 μg/dL, was diagnosed in 23/87 patients (26.4%). Stepwise logistic regression analysis selected as significant predictors of FAGA the cumulative dosage of corticosteroids administered (P < 0.01), the increase in the body mass index after LT (P < 0.01), a low serum cholesterol concentration (P = 0.005), and a high adrenocorticotropin hormone (ACTH) serum level (P < 0.05) at the time CST was performed. In conclusion, FAGA is a common condition among LT recipients who are maintained on prolonged corticosteroid immunosuppressive treatment. Factors associated with FAGA include the cumulative steroid dose, weight changes after LT, and ACTH and cholesterol levels at the time of steroid withdrawal. Liver Transpl 14:1014–1019, 2008. © 2008 AASLD.
Noninvasive monitoring of cerebral perfusion pressure in patients with acute liver failure using transcranial doppler ultrasonography
Authors: Aggarwal Shushma , Brooks David M. , Kang Yoogoo , Linden Peter K. , Patzer John F.
Published: June 2008

Elevated intracranial pressure (ICP) leads to loss of cerebral perfusion, cerebral herniation, and irreversible brain damage in patients with acute liver failure (ALF). Conventional techniques for monitoring ICP can be complicated by hemorrhage and infection. Transcranial doppler ultrasonography (TCD) is a noninvasive device which can continuously measure cerebral blood flow velocity, producing a velocity-time waveform that indirectly monitors changes in cerebral hemodynamics, including ICP. The primary goal of this study was to determine whether TCD waveform features could be used to differentiate ALF patients with respect to ICP or, equally important, cerebral perfusion pressure (CPP) levels. A retrospective study of 16 ALF subjects with simultaneous TCD, ICP, and CPP measurements yielded a total of 209 coupled ICP-CPP-TCD observations. The TCD waveforms were digitally scanned and seven points corresponding to a simplified linear waveform were identified. TCD waveform features including velocity, pulsatility index, resistive index, fraction of the cycle in systole, slopes, and angles associated with changes in the slope in each region, were calculated from the simplified waveform data. Paired ICP-TCD observations were divided into three groups (ICP < 20 mmHg, n = 102; 20 ≤ ICP < 30 mmHg, n = 74; and ICP ≥ 30 mmHg, n = 33). Paired CPP-TCD observations were also divided into three groups (CPP ≥ 80 mmHg, n = 42; 80 > CPP ≥ 60 mmHg, n = 111; and CPP < 60 mmHg, n = 56). Stepwise linear discriminant analysis was used to identify TCD waveform features that discriminate between ICP groups and CPP groups. Four primary features were found to discriminate between ICP groups: the blood velocity at the start of the Windkessel effect, the slope of the Windkessel upstroke, the angle between the end systolic downstroke and start diastolic upstroke, and the fraction of time spent in systole. Likewise, 4 features were found to discriminate between the CPP groups: the slope of the Windkessel upstroke, the slope of the Windkessel downstroke, the slope of the diastolic downstroke, and the angle between the end systolic downstroke and start diastolic upstroke. The TCD waveform captures the cerebral hemodynamic state and can be used to predict dynamic changes in ICP or CPP in patients with ALF. The mean TCD waveforms for corresponding, correctly classified ICP and CPP groups are remarkably similar. However, this approach to predicting intracranial hypertension and CPP needs to be further refined and developed before clinical application is feasible. Liver Transpl 14:1048–1057, 2008. © 2008 AASLD.
Sirolimus: Another Unique Use?
Authors: Perkins James D.
Published: June 2008

Abstract

The immunosuppressive agent sirolimus exerts an antiproliferative effect by inhibiting mammalian target of rapamycin (mTOR). Because excessive proliferation of the biliary epithelium is a prominent feature of the polycystic liver that accompanies autosomal dominant polycystic kidney disease (ADPKD), we hypothesized that sirolimus may benefit patients with this disorder. We retrospectively measured the volumes of polycystic livers and kidneys in ADPKD patients who had received kidney transplants and had participated in a prospective randomized trial that compared a sirolimus-containing immunosuppression regimen to a tacrolimus-containing regimen. Sixteen subjects (seven with sirolimus, nine with tacrolimus) had received abdominal imaging studies within 11 mo before and at least 7 mo after transplantation, making them suitable for our analysis. Treatment with the sirolimus regimen for an average of 19.4 mo was associated with an 11.9 ± 0.03% reduction in polycystic liver volume, whereas treatment with tacrolimus for a comparable duration was associated with a 14.1 ± 0.09% increase. A trend toward a greater reduction in native kidney volume was also noted in the sirolimus group compared with the nonsirolimus group. Regarding mechanism, the epithelium that lines hepatic cysts exhibited markedly higher levels of phospho-AKT, phospho-ERK, phospho-mTOR, and the downstream effector phospho-S6rp compared with control biliary epithelium. In summary, treatment with sirolimus was associated with decreased polycystic liver volume, perhaps by preventing aberrant activation of mTOR in epithelial cells lining the cysts.
Rivastigmine versus placebo in hyperhomocysteinemic Parkinson's disease dementia patients
Authors: Barone Paolo , Burn David J. , van Laar Teus , Hsu Chuanchieh , Poewe Werner , Lane Roger M.
Published: June 2008

The effects of rivastigmine versus placebo in Parkinson's disease dementia (PDD) patients with elevated or normal/low plasma homocysteine were determined. In this prospective analysis of a 24‐week, randomly assigned, placebo‐controlled study of rivastigmine in PDD, subpopulations comprised patients with plasma homocysteine ≥14 μmol/L (elevated) or <14 μmol/L (normal/low). Coprimary outcomes were the Alzheimer's Disease Assessment Scale–cognitive subscale (ADAS‐cog) and Alzheimer Disease Cooperative Society–Clinical Global Impression of Change (ADCS‐CGIC). Secondary outcomes included additional measures of cognition, including attention and executive function, daily function, and neuropsychiatric symptoms. Adverse events (AEs) were monitored. In total, 342 of 541 patients provided samples for analysis, from which 72% had elevated plasma homocysteine. Hyperhomocysteinemic patients showed treatment differences (rivastigmine vs. placebo) of 4.0 on ADAS‐cog and 0.7 on ADCS‐CGIC (both P < 0.01), and significant treatment differences on secondary outcomes. Rivastigmine‐ and placebo‐treated hyperhomocysteinemic patients (16.5% and 14.6%) discontinued the study because of AEs. Patients with normal/low homocysteine showed no treatment differences on primary or secondary outcomes (1.4 on the ADAS‐cog and 0.1 on ADCS‐CGIC, both P = ns); 16.7% and 10.3% rivastigmine‐ and placebo‐treated patients discontinued because of AEs. Elevated homocysteine was associated with greater rivastigmine treatment differences than normal/low homocysteine. © 2008 Movement Disorder Society
Multiresolution field map estimation using golden section search for water‐fat separation
Authors: Lu Wenmiao , Hargreaves Brian A.
Published: June 2008

Many diagnostic MRI sequences demand reliable and uniform fat suppression. Multipoint water–fat separation methods, which are based on chemical‐shift induced phase differences, have shown great success in the presence of field inhomogeneities. This work presents a computationally efficient and robust field map estimation method. The method begins with subsampling image data into a multiresolution image pyramidal structure, and then utilizes a golden section search to directly locate possible field map values at the coarsest level of the pyramidal structure. The field map estimate is refined and propagated to increasingly finer resolutions in an efficient manner until the full‐resolution field map is obtained for final water‐fat separation. The proposed method is validated with multiecho sequences where long echo‐spacings normally impose great challenges on reliable field map estimation. Magn Reson Med 60:236–244, 2008. © 2008 Wiley‐Liss, Inc.
Water–fat separation with bipolar multiecho sequences
Authors: Lu Wenmiao , Yu Huanzhou , Shimakawa Ann , Alley Marcus , Reeder Scott B. , Hargreaves Brian A.
Published: June 2008

Multiecho sequences provide an efficient means to acquire multiple echoes in a single repetition, which has found applications in spectroscopy, relaxometry, and water–fat separation. By replacing the fly‐back gradients in unipolar multiecho sequences with alternating readout gradients, bipolar multiecho sequences greatly reduce both echo‐spacing and repetition interval. This offers many attractive advantages, such as shorter scan times, higher SNR efficiency, more robust field map estimation, reduced motion‐induced artifacts, and less sensitivity to short T. However, the alternating readout gradients cause several technical problems, including delay effects and image misregistrations, which prevent direct application of existing water–fat separation methods. This work presents solutions to address these problems, including a post‐processing method that shifts k‐space data to correct k‐space echo misalignment, an image warping method that utilizes a low‐resolution field map to remove field‐inhomogeneity‐induced misregistration, and a k‐space water–fat separation method that eliminates chemical‐shift‐induced artifacts in separated water and fat images. In addition, a noise amplification factor, which characterizes the noise present in separated images, is proposed to serve as a useful guideline for choosing imaging parameters or regularization parameters in the case of ill‐conditioned separation. The proposed methods are validated both in phantoms and in vivo to enable reliable and SNR efficient water–fat separation with bipolar multiecho sequences. Magn Reson Med 60:198–209, 2008. © 2008 Wiley‐Liss, Inc.
Concomitant field terms for asymmetric gradient coils: Consequences for diffusion, flow, and echo‐planar imaging
Authors: Meier C. , Zwanger M. , Feiweier T. , Porter D.
Published: June 2008

As a consequence of the Maxwell equations, linear field gradients are accompanied by additional spatially dependent field components. A description of the Maxwell field terms is presented which explicitly takes into account the asymmetry of the gradient coil. It is shown both theoretically and experimentally that, in contrast to symmetric coils, an asymmetric coil generates concomitant field terms of zeroth and first order in space. Artifacts induced by concomitant fields can be much more pronounced for asymmetric coil designs than for symmetric ones. For the strong gradient amplitudes available on modern MR systems the effect of these concomitant magnetic fields on the evolution of magnetization has to be taken into consideration in a variety of NMR acquisition techniques. The formalism is used experimentally to compensate for artifacts observed in three different imaging methods: an image shift in standard echo planar imaging (EPI), an echo shift in diffusion‐weighted EPI, and a phase shift in a flow quantification technique based on phase contrast images. Magn Reson Med 60:128–134, 2008. © 2008 Wiley‐Liss, Inc.
Four‐dimensional MR microscopy of the mouse heart using radial acquisition and liposomal gadolinium contrast agent
Authors: Bucholz Elizabeth , Ghaghada Ketan , Qi Yi , Mukundan Srinivasan , Johnson G. Allan
Published: June 2008

Magnetic resonance microscopy (MRM) has become an important tool for small animal cardiac imaging. In relation to competing technologies (microCT and ultrasound), MR is limited by spatial resolution, temporal resolution, and acquisition time. All three of these limitations have been addressed by developing a four‐dimensional (4D) (3D plus time) radial acquisition (RA) sequence. The signal‐to‐noise ratio (SNR) has been optimized by minimizing the echo time (TE) (300 us). The temporal resolution and throughput have been improved by center‐out trajectories resulting in repetition time (TR) <2.5 ms. The contrast has been enhanced through the use of a liposomal blood pool agent that reduces the T1 of the blood to <400 ms. We have developed protocols for three specific applications: 1) high‐throughput with spatial resolution of 87 × 87 × 352 um3 (voxel volume = 2.7 nL) and acquisition time of 16 min; 2) high‐temporal resolution with spatial resolution of 87 × 87 × 352 um3 (voxel volume = 2.7 nL) and temporal resolution at 4.8 ms and acquisition time of 32 minutes; and 3) high‐resolution isotropic imaging at 87 × 87 × 87 um3 (voxel volume = 0.68 nL) and acquisition time of 31 min. The 4D image arrays allow direct measure of cardiac functional parameters dependent on chamber volumes, e.g., ejection fraction (EF), end diastolic volume (EDV), and end systolic volume (ESV). Magn Reson Med 60:111–118, 2008. © 2008 Wiley‐Liss, Inc.
In vitro investigation of poor cerebrospinal fluid suppression on fluid‐attenuated inversion recovery images in the presence of a gadolinium‐based contrast agent
Authors: Bonzano L. , Roccatagliata L. , Levrero F. , Mancardi G.L. , Sardanelli F.
Published: June 2008

Cerebrospinal fluid (CSF) enhancement on fluid‐attenuated inversion recovery (FLAIR) images obtained post‐gadolinium (Gd)‐based agent injection is described in stroke and multiple sclerosis. Blood brain barrier (BBB) disruption with contrast agent extravasation into CSF shortens T1 relaxation times, reducing fluid suppression. Reduced fluid suppression on FLAIR images was investigated in vitro in the presence of escalating gadopentetate dimeglumine (Gd‐DTPA) concentrations mixed with artificial CSF. Low Gd‐DTPA concentrations impair fluid suppression of FLAIR imaging in association with progressively reduced T1 values. At higher concentrations, the prevalent T2 shortening effect can explain signal intensity (SI) reduction. Post‐Gd FLAIR may be useful in detecting subtle BBB leakage. Magn Reson Med 60:220–223, 2008. © 2008 Wiley‐Liss, Inc.
Acquisition‐weighted stack of spirals for fast high‐resolution three‐dimensional ultra‐short echo time MR imaging
Authors: Qian Yongxian , Boada Fernando E.
Published: June 2008

Ultra‐short echo time (UTE) MRI requires both short excitation (∼0.5 ms) and short acquisition delay (<0.2 ms) to minimize T2‐induced signal decay. These requirements currently lead to low acquisition efficiency when high resolution (<1 mm) is pursued. A novel pulse sequence, acquisition‐weighted stack of spirals (AWSOS), is proposed here to acquire high‐resolution three‐dimensional (3D) UTE images with short scan time (∼72 s). The AWSOS sequence uses variable‐duration slice encoding to minimize T2 decay, separates slice thickness from in‐plane resolution to reduce the number of slice encodings, and uses spiral trajectories to accelerate in‐plane data collections. T2‐ and off‐resonance induced slice widening and image blurring were calculated from 1.5 to 7 Tesla (T) through point spread function. Computer simulations were performed to optimize spiral interleaves and readout times. Phantom scans and in vivo experiments on human heads were implemented on a clinical 1.5T scanner (Gmax = 40 mT/m, Smax = 150 T/m/s). Accounting for the limits on B1 maximum, specific absorption rate (SAR), and the lowered amplitude of slab‐select gradient, a sinc radiofrequency (RF) pulse of 0.8ms duration and 1.5 cycles was found to produce a flat slab profile. High in‐plane resolution (0.86 mm) images were obtained for the human head using echo time (TE) = 0.608 ms and total shots = 720 (30 slice‐encodings × 24 spirals). Compared with long‐TE (10 ms) images, the ultrashort‐TE AWSOS images provided clear visualization of short‐T2 tissues such as the nose cartilage, the eye optic nerve, and the brain meninges and parenchyma. Magn Reson Med 60:135–145, 2008. © 2008 Wiley‐Liss, Inc.
MR tracking of transplanted cells with “positive contrast” using manganese oxide nanoparticles
Authors: Gilad Assaf A. , Walczak Piotr , McMahon Michael T. , Na Hyon Bin , Lee Jung Hee , An Kwangjin , Hyeon Taegwhan , van Zijl Peter C.M. , Bulte Jeff W.M.
Published: June 2008

Rat glioma cells were labeled using electroporation with either manganese oxide (MnO) or superparamagnetic iron oxide (SPIO) nanoparticles. The viability and proliferation of SPIO‐labeled cells (1.9 mg Fe/ml) or cells electroporated with a low dose of MnO (100 μg Mn/ml) was not significantly different from unlabeled cells; a higher MnO dose (785 μg Mn/ml) was found to be toxic. The cellular ion content was 0.1–0.3 pg Mn/cell and 4.4 pg Fe/cell, respectively, with cellular relaxivities of 2.5–4.8 s−1 (R1) and 45–84 s−1 (R2) for MnO‐labeled cells. Labeled cells (SPIO and low‐dose MnO) were each transplanted in contralateral brain hemispheres of rats and imaged in vivo at 9.4T. While SPIO‐labeled cells produced a strong “negative contrast” due to the increase in R2, MnO‐labeled cells produced “positive contrast” with an increased R1. Simultaneous imaging of both transplants with opposite contrast offers a method for MR “double labeling” of different cell populations. Magn Reson Med 60:1–7, 2008. © 2008 Wiley‐Liss, Inc.
NMR probes for measuring magnetic fields and field dynamics in MR systems
Authors: De Zanche Nicola , Barmet Christoph , Nordmeyer‐Massner Jurek A. , Pruessmann Klaas P.
Published: June 2008

High‐resolution magnetic field probes based on pulsed liquid‐state NMR are presented. Static field measurements with an error of 10 nanotesla or less at 3 tesla are readily obtained in 100 ms. The further ability to measure dynamic magnetic fields results from using small (∼1 μL) droplets of MR‐active liquid surrounded by susceptibility‐matched materials. The consequent high field homogeneity allows free induction decay signals lasting 100 ms or more to be readily achieved. The small droplet dimensions allow the magnetic field to be measured even in the presence of large gradients. Highly sensitive detection yields sufficient SNR to follow the relevant field evolution without signal averaging and at bandwidths up to hundreds of kHz. Transient, nonreproducible effects and drifts are thus readily monitored. The typical application of k‐space trajectory mapping has been demonstrated. Potential further applications include characterization, tuning, and maintenance of gradient systems as well as the mapping of the static field distribution of MRI magnets. Connection of the probes to a standard MR spectrometer is similar to that used for imaging coils. Magn Reson Med 60:176–186, 2008. © 2008 Wiley‐Liss, Inc.
Nuclear magnetic resonance‐based metabolomics predicts exercise‐induced ischemia in patients with suspected coronary artery disease
Authors: Barba Ignasi , de León Gustavo , Martín Eva , Cuevas Antonio , Aguade Santiago , Candell‐Riera Jaume , Barrabés José A. , Garcia‐Dorado David
Published: June 2008

The purpose of this study was to develop a 1H‐nuclear magnetic resonance metabolomic approach capable of predicting the occurrence of exercise‐induced ischemia in patients with suspected coronary artery disease and to identify the metabolite patterns that contribute most importantly to the prediction. In 31 patients with suspected effort angina and without previous myocardial infarction, serum was obtained just prior to a stress single‐photon emission computed tomography. Serum NMR spectra were acquired with pulse‐and‐acquire and T2‐edited sequences. The region between 0.50 and 4.25 ppm was used for analysis. Twenty‐two patients had reversible myocardial perfusion defects and nine did not. Both groups had similar age and clinical profile, except for more smokers and diabetics in the ischemia group, and attained a similar peak heart rate. The best separation was achieved with long T2‐edited spectra, 84% of patients being correctly classified based on the partial least square discriminant analysis. The main contributors to discrimination were lactate, glucose, as well as methyl and methylene moieties of lipids and long‐chain amino acids. Metabolomic analysis of serum can predict exercise‐inducible ischemia in patients with suspected coronary artery disease. This capability could be useful in screening and risk stratification of patients with coronary risk factors. Magn Reson Med 60:27–32, 2008. © 2008 Wiley‐Liss, Inc.
Serial in vivo positive contrast MRI of iron oxide‐labeled embryonic stem cell‐derived cardiac precursor cells in a mouse model of myocardial infarction
Authors: Mani Venkatesh , Adler Eric , Briley‐Saebo Karen C. , Bystrup Anne , Fuster Valentin , Keller Gordon , Fayad Zahi A.
Published: June 2008

Myocardial regeneration with stem‐cell transplantation is a possible treatment option to reverse deleterious effects that occur after myocardial infarction. Since little is known about stem cell survival after transplantation, developing techniques for “tracking” cells would be desirable. Iron‐oxide‐labeled stem cells have been used for in vivo tracking using MRI but produce negative contrast images that are difficult to interpret. The aim of the current study was to test a positive contrast MR technique using reduced z‐gradient rephasing (GRASP) to aid in dynamically tracking stem cells in an in vivo model of mouse myocardial infraction. Ferumoxides and protamine sulfate were complexed and used to magnetically label embryonic stem cell‐derived cardiac‐precursor‐cells (ES‐CPCs). A total of 500,000 ES‐CPCs were injected in the border zone of infarcted mice and MR imaging was performed on a 9.4T scanner using T‐GRE sequences (negative contrast) and positive contrast GRASP technique before, 24 hours, and 1 week after ES‐CPC implantation. Following imaging, mice were sacrificed for histology and Perl's staining was used to confirm iron within myocardium. Good correlation was observed between signal loss seen on conventional T images, bright areas on GRASP, and the presence of iron on histology. This demonstrated the feasibility of in vivo stem cell imaging with positive contrast MRI. Magn Reson Med 60:73–81, 2008. © 2008 Wiley‐Liss, Inc.
Manganese‐enhanced MRI of the mouse auditory pathway
Authors: Watanabe Takashi , Frahm Jens , Michaelis Thomas
Published: June 2008

Functional mapping of the lateral lemniscus and the superior olivary complex as part of the auditory pathway was accomplished for the first time in mice in vivo using manganese‐enhanced MRI (2.35T, 3D FLASH, 117 μm isotropic resolution). These and other auditory centers in the brainstem presented with pronounced signal enhancements after systemic administration of manganese chloride when animals were exposed to acoustic stimuli for 48 hr, but not when kept in a quiet environment. The results indicate an activation‐dependent accumulation of manganese in the neural circuit composed of the cochlear nucleus, the superior olivary complex, the lateral lemniscus, and the inferior colliculus. The marked enhancement of the lateral lemniscus suggests that the stimulus‐related accumulation of manganese reflects not only a regional uptake from extracellular fluid but also a concurrent delivery by axonal transport within the auditory system. Magn Reson Med 60:210–212, 2008. © 2008 Wiley‐Liss, Inc.
Quantification of choline‐ and ethanolamine‐containing metabolites in human prostate tissues using 1H HR‐MAS total correlation spectroscopy
Authors: Swanson Mark G. , Keshari Kayvan R. , Tabatabai Z. Laura , Simko Jeffry P. , Shinohara Katsuto , Carroll Peter R. , Zektzer Andrew S. , Kurhanewicz John
Published: June 2008

A fast and quantitative 2D high‐resolution magic angle spinning (HR‐MAS) total correlation spectroscopy (TOCSY) experiment was developed to resolve and quantify the choline‐ and ethanolamine‐containing metabolites in human prostate tissues in ≈1 hr prior to pathologic analysis. At a 40‐ms mixing time, magnetization transfer efficiency constants were empirically determined in solution and used to calculate metabolite concentrations in tissue. Phosphocholine (PC) was observed in 11/15 (73%) cancer tissues but only 6/32 (19%) benign tissues. PC was significantly higher (0.39 ± 0.40 mmol/kg vs. 0.02 ± 0.07 mmol/kg, z = 3.5), while ethanolamine (Eth) was significantly lower in cancer versus benign prostate tissues (1.0 ± 0.8 mmol/kg vs. 2.3 ± 1.9 mmol/kg, z = 3.3). Glycerophosphocholine (GPC) (0.57 ± 0.87 mmol/kg vs. 0.29 ± 0.26 mmol/kg, z = 1.2), phosphoethanolamine (PE) (4.4 ± 2.2 mmol/kg vs. 3.4 ± 2.6 mmol/kg, z = 1.4), and glycerophosphoethanolamine (GPE) (0.54 ± 0.82 mmol/kg vs. 0.15 ± 0.15 mmol/kg, z = 1.8) were higher in cancer versus benign prostate tissues. The ratios of PC/GPC (3.5 ± 4.5 vs. 0.32 ± 1.4, z = 2.6), PC/PE (0.08 ± 0.08 vs. 0.01 ± 0.03, z = 3.5), PE/Eth (16 ± 22 vs. 2.2 ± 2.0, z = 2.4), and GPE/Eth (0.41 ± 0.51 vs. 0.06 ± 0.06, z = 2.6) were also significantly higher in cancer versus benign tissues. All samples were pathologically interpretable following HR‐MAS analysis; however, degradation experiments showed that PC, GPC, PE, and GPE decreased 7.7 ± 2.2%, while Cho+mI and Eth increased 18% in 1 hr at 1°C and a 2250 Hz spin rate. Magn Reson Med 60:33–40, 2008. © 2008 Wiley‐Liss, Inc.
Kalman filtering for real‐time navigator processing
Authors: Spincemaille Pascal , Nguyen Thanh D. , Prince Martin R. , Wang Yi
Published: June 2008

Navigator echoes are used in high‐resolution cardiac MRI for tracking physiological motion to suppress motion artifacts. Alternatives to the conventional diaphragm navigator such as the cardiac fat navigator and the k‐space center signal (self‐navigator) were developed to monitor heart motion directly. These navigator data can be noisy or may contain undesirable frequency components. Real‐time filtering of navigator data without delay, as opposed to the previously used retrospective frequency band filtering, is required for effective prospective navigator gating. One of the commonly used real‐time filtering techniques is the Kalman filter, which adaptively estimates motion and suppresses measurement noise by using Bayesian statistics and a motion model. The Kalman filter is investigated in this work to filter noise and distinguish cardiac and respiratory components in navigator data. Preliminary imaging data demonstrate the feasibility of real‐time Kalman filtering for prospective respiratory self‐gating in CINE cardiac MRI. Magn Reson Med 60:158–168, 2008. © 2008 Wiley‐Liss, Inc.
In vivo MRI using real‐time production of hyperpolarized 129Xe
Authors: Driehuys Bastiaan , Pollaro Jim , Cofer Gary P.
Published: June 2008

MR imaging of hyperpolarized (HP) nuclei is challenging because they are typically delivered in a single dose of nonrenewable magnetization, from which the entire image must be derived. This problem can be overcome with HP 129Xe, which can be produced sufficiently rapidly to deliver in dilute form (1%) continuously and on‐demand. We demonstrate a real‐time in vivo delivery of HP 129Xe mixture to rats, a capability we now routinely use for setting frequency, transmitter gain, shimming, testing pulse sequences, scout imaging, and spectroscopy. Compared to images acquired using conventional fully concentrated 129Xe, real‐time 129Xe images have 26‐fold less signal, but clearly depict ventilation abnormalities. Real‐time 129Xe MRI could be useful for time‐course studies involving acute injury or response to treatment. Ultimately, real‐time 129Xe MRI could be done with more highly concentrated 129Xe, which could increase the signal‐to‐noise ratio by 100 relative to these results to enable a new class of gas imaging applications. Magn Reson Med 60:14–20, 2008. © 2008 Wiley‐Liss, Inc.
Modeling the effects of dispersion and pulsatility of blood flow in pulsed arterial spin labeling
Authors: Gallichan Daniel , Jezzard Peter
Published: June 2008

Arterial spin labeling (ASL) is a method of using MRI to image cerebral perfusion. For the measurement to be calibrated, a model is required describing the kinetics of the flow of the inverted blood from the labeling region to the imaging region. It is common to assume plug‐flow, but alternatives such as a Gaussian distribution of arrival times have also been suggested. In this study a physiologically based model for dispersion is developed and compared to existing models when fit to experimental data. The model is based on the assumption of parabolic flow in the major arteries, and also allows inclusion of cardiac pulsatility. It was found that fitting using the proposed model leads to higher perfusion estimates, with the difference becoming more pronounced in regions where the dispersion is greater. This suggests that current models may underestimate perfusion in these areas. However, fitting using the proposed model also leads to high uncertainties in parameter estimates due to non‐orthogonality of the parameters. Effects due to pulsatility are expected to be observable, but when no cardiac‐gating is used the mean curve over several cardiac cycles is predicted to closely match the curve which assumes constant flow. Magn Reson Med 60:53–63, 2008. © 2008 Wiley‐Liss, Inc.
Influence of iron chelation on R1 and R2 calibration curves in gerbil liver and heart
Authors: Wood John C. , Aguilar Michelle , Otto‐Duessel Maya , Nick Hanspeter , Nelson Marvin D. , Moats Rex
Published: June 2008

MRI is gaining increasing importance for the noninvasive quantification of organ iron burden. Since transverse relaxation rates depend on iron distribution as well as iron concentration, physiologic and pharmacologic processes that alter iron distribution could change MRI calibration curves. This article compares the effect of three iron chelators, deferoxamine, deferiprone, and deferasirox, on R1 and R2 calibration curves according to two iron loading and chelation strategies. Thirty‐three Mongolian gerbils underwent iron loading (iron dextran 500 mg/kg/wk) for 3 weeks followed by 4 weeks of chelation. An additional 56 animals received less aggressive loading (200 mg/kg/week) for 10 weeks, followed by 12 weeks of chelation. R1 and R2 calibration curves were compared to results from 23 iron‐loaded animals that had not received chelation. Acute iron loading and chelation‐biased R1 and R2 from the unchelated reference calibration curves but chelator‐specific changes were not observed, suggesting physiologic rather than pharmacologic differences in iron distribution. Long‐term chelation deferiprone treatment increased liver R1 50% (P < 0.01), while long‐term deferasirox lowered liver R2 30.9% (P < 0.0001). The relationship between R1 and R2 and organ iron concentration may depend on the acuity of iron loading and unloading as well as the iron chelator administered. Magn Reson Med 60:82–89, 2008. © 2008 Wiley‐Liss, Inc.
Investigation of LDPE blown film instability induced by air cooling
Authors: Zhang Z. , Lafleur P.G.
Published: June 2008

This paper deals with the bubble instabilities induced by cooling airflow rate at different take‐up‐ratio (TUR) and blow‐up‐ratio (BUR) conditions in the film‐blowing process. Experimental methods to monitor the on‐site bubble instability included an in‐line scanning camera system to record the bubble oscillation and a manometer mounted on the die to measure the internal pressure corresponding to the radius variation. A good correlation between the bubble instability and the pressure inside the bubble has been obtained. Experimental results indicated that varying the cooling airflow rate at different TURs and BURs conditions produced significant differences in the dynamics of bubble instability. While a higher cooling air rate stabilized the bubble for a high BUR, the bubble was destabilized for a low BUR. The bubble with a high TUR sustained greater aerodynamics forces acting on the bubble surface, resulting in a broader operating range of stable operation. Finally, a numerical simulation using a RNG (renormalization group), k–ε model, and Fluent software was performed to analyze the effects of momentum and heat transfer from the cooling air to the polymer film on bubble instability. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers
A new application of biosurfactant for the preparation of polycaprolactone/layered silicate nanocomposites
Authors: Liao Hsin‐Tzu
Published: June 2008

In this study, by using the biosurfactant as the clay modifier, one first attempted to prepare polycaprolactone (PCL)/montmorillonite nanocomposites via a melt‐blending method. The production of biosurfactant (surfactin) and the modification of clay proceeded simultaneously by the incubation of Bacillus subtilis CWS1. The evidence for the formation of intercalated/exfoliated nanocomposites was assessed by X‐ray diffraction spectroscopy, scanning electron microscopy, and transmission electron microscopy observations. The conclusions were also supported by the result of dynamic mechanical thermal analysis, thermogravimetric analyzer, and differential scanning calorimetry. As a result, the modified clay can be well dispersed into the PCL matrix in nanoscale sizes, because the biosurfactant is partially compatible with PCL chains intercalating into clay layers. As for mechanical properties, a marked increase in tensile strength and Young's modulus can be observed when the biosurfactant‐pretreated clay was used to replace the neat clay for the preparation of nanocomposites. Based on the considerations of thermal and mechanical properties, it was also found that 10 wt% of clay content was optimal for the preparation of nanocomposite. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers