共查询到20条相似文献,搜索用时 46 毫秒
1.
Deibler AR Pollock JM Kraft RA Tan H Burdette JH Maldjian JA 《AJNR. American journal of neuroradiology》2008,29(7):1228-1234
The routine use of arterial spin-labeling (ASL) in a clinical population has led to the depiction of diverse brain pathologic features. Unique challenges in the acquisition, postprocessing, and analysis of cerebral blood flow (CBF) maps are encountered in such a population, and high-quality ASL CBF maps can be generated consistently with attention to quality control and with the use of a dedicated postprocessing pipeline. Familiarity with commonly encountered artifacts can help avoid pitfalls in the interpretation of CBF maps. The purpose of this review was to describe our experience with a heterogeneous collection of ASL perfusion cases with an emphasis on methodology and common artifacts encountered with the technique. In a period of 1 year, more than 3000 pulsed ASL cases were performed as a component of routine clinical brain MR evaluation at both 1.5 and 3T. These ASL studies were analyzed with respect to overall image quality and patterns of perfusion on final gray-scale DICOM images and color Joint Photographic Experts Group (JPEG) CBF maps, and common artifacts and their impact on final image quality were categorized. 相似文献
2.
Liau J Lee J Schroeder ME Sirlin CB Bydder M 《Journal of magnetic resonance imaging : JMRI》2012,35(2):318-327
Purpose:
To characterize cardiac motion artifacts in the liver and assess the use of a postprocessing method to mitigate these artifacts in repeat measurements.Materials and Methods:
Three subjects underwent breathhold diffusion‐weighted (DW) scans consisting of 25 repetitions for three b‐values (0, 500, 1000 sec/mm2). Statistical maps computed from these repetitions were used to assess the distribution and behavior of cardiac motion artifacts in the liver. An objective postprocessing method to reduce the artifacts was compared with radiologist‐defined gold standards.Results:
Signal dropout is pronounced in areas proximal to the heart, such as the left lobe, but also present in the right lobe and in distal liver segments. The dropout worsens with b‐value and leads to overestimation of the diffusivity. By reference to a radiologist‐defined gold standard, a postprocessing correction method is shown to reduce cardiac motion artifact.Conclusion:
Cardiac motion leads to significant artifacts in liver DW imaging; we propose a postprocessing method that may be used to mitigate the artifact and is advantageous to standard signal averaging in acquisitions with multiple repetitions. J. Magn. Reson. Imaging 2012;318‐327. © 2011 Wiley Periodicals, Inc. 相似文献3.
Juan Chen MD Daniel J. Licht MD Sabrina E. Smith MD PhD Shannon C. Agner MS Stefanie Mason BS Sumei Wang MD David W. Silvestre BA John A. Detre MD Robert A. Zimmerman MD Rebecca N. Ichord MD Jiongjiong Wang PhD 《Journal of magnetic resonance imaging : JMRI》2009,29(2):282-290
Purpose
To investigate the feasibility and utility of arterial spin labeling (ASL) perfusion MRI for characterizing alterations of cerebral blood flow (CBF) in pediatric patients with arterial ischemic stroke (AIS).Materials and Methods
Ten children with AIS were studied within 4 to 125 hours following symptom onset, using a pulsed ASL (PASL) protocol attached to clinically indicated MR examinations. The interhemisphere perfusion deficit (IHPD) was measured in predetermined vascular territories and infarct regions of restricted diffusion, which were compared with the degree of arterial stenosis and volumes of ischemic infarcts.Results
Interpretable CBF maps were obtained in all 10 patients, showing simple lesion in nine patients (five hypoperfusion, two hyperperfusion, and two normal perfusion) and complex lesions in one patient. Both acute and follow‐up infarct volumes were significantly larger in cases with hypoperfusion than in either hyper‐ or normal perfusion cases. The IHPD was found to correlate with the degree of stenosis, diffusion lesion, and follow‐up T2 infarct volumes. Mismatch between perfusion and diffusion lesions was observed. Brain regions presenting delayed arterial transit effects were tentatively associated with positive outcome.Conclusion
This study demonstrates the clinical utility of ASL in the neuroimaging diagnosis of pediatric AIS. J. Magn. Reson. Imaging 2009;29:282–290. © 2009 Wiley‐Liss, Inc. 相似文献4.
Ashley D. Harris PhD Robert K. Kosior BSc Henry S. Chen BSc Linda B. Andersen PhD Richard Frayne PhD 《Journal of magnetic resonance imaging : JMRI》2009,29(6):1262-1270
Purpose
To develop an appropriate method to evaluate the time‐course of diffusion and perfusion changes in a clinically relevant animal model of ischemic stroke and to examine lesion progression on MR images. An exploration of acute stroke infarct expansion was performed in this study by using a new methodology for developing time‐to‐infarct maps based on the time at which each voxel becomes infarcted. This enabled definition of homogeneous regions from the heterogeneous stroke infarct.Materials and Methods
Time‐to‐infarct maps were developed based on apparent diffusion coefficient (ADC) changes. These maps were validated and then applied to blood flow and time‐to‐peak maps to examine perfusion changes.Results
ADC stroke infarct showed different evolution patterns depending on the time at which that region of tissue infarcted. Applying the time‐to‐infarct maps to the perfusion maps showed localized perfusion evolution characteristics. In some regions, perfusion was immediately affected and showed little change over the experiment; however, in some regions perfusion changes were more dynamic.Conclusion
Results were consistent with the diffusion‐perfusion mismatch hypothesis. In addition, characteristics of collateral recruitment were identified, which has interesting stroke pathophysiology and treatment implications. J. Magn. Reson. Imaging 2009;29:1262–1270. © 2009 Wiley‐Liss, Inc. 相似文献5.
Ning Jin BS Robert J. Lewandowski MD Reed A. Omary MD Andrew C. Larson PhD 《Journal of magnetic resonance imaging : JMRI》2009,29(4):860-868
Purpose
To demonstrate the feasibility of using a free‐breathing (FB) respiratory self‐gated (RSG) approach for abdominal phase‐contrast (PC) blood flow measurements.Materials and Methods
PC‐magnetic resonance imaging (MRI) flow measurements were performed within the right renal artery, common hepatic artery, and main portal vein during breath‐hold (BH) and FB with both signal averaging and RSG in eight healthy volunteers. The resultant images were qualitatively scored by two independent reviewers blinded to acquisition techniques. Blood flow volume and cross‐sectional vessel size measurements were compared for three techniques.Results
The overall efficiency for the RSG‐PC sequence was 38.9% ± 4.7%. Images acquired with RSG effectively mitigated respiratory motion artifacts, which were clearly evident within FB signal‐averaged images. RSG produced similar image quality to that of BH techniques (P > 0.146) and resulted in similar vessel size measurements (P = 0.694). Flow results for both FB RSG and signal‐averaged reconstructions correlated well with BH flow measurements (r = 0.97 and 0.92, P < 0.001). However, only the RSG methods demonstrated excellent absolute agreement with BH‐PC flow measurements (P = 0.600), with signal‐averaged methods resulting in significant overestimations.Conclusion
RSG methods can limit respiratory motion artifacts to reduce flow measurement inaccuracies during free‐breathing PC measurements in the abdomen. J. Magn. Reson. Imaging 2009;29:860–868. © 2009 Wiley‐Liss, Inc. 相似文献6.
Youngkyoo Jung PhD Alexey A. Samsonov PhD Walter F. Block PhD Mariana Lazar PhD Aiming Lu PhD Jing Liu PhD Andrew L. Alexander PhD 《Journal of magnetic resonance imaging : JMRI》2009,29(5):1175-1184
Purpose
To obtain diffusion tensor images (DTI) over a large image volume rapidly with 3D isotropic spatial resolution, minimal spatial distortions, and reduced motion artifacts, a diffusion‐weighted steady‐state 3D projection (SS 3DPR) pulse sequence was developed.Materials and Methods
A diffusion gradient was inserted in a SS 3DPR pulse sequence. The acquisition was synchronized to the cardiac cycle, linear phase errors were corrected along the readout direction, and each projection was weighted by measures of consistency with other data. A new iterative parallel imaging reconstruction method was also implemented for removing off‐resonance and undersampling artifacts simultaneously.Results
The contrast and appearance of both the fractional anisotropy and eigenvector color maps were substantially improved after all correction techniques were applied. True 3D DTI datasets were obtained in vivo over the whole brain (240 mm field of view in all directions) with 1.87 mm isotropic spatial resolution, six diffusion encoding directions in under 19 minutes.Conclusion
A true 3D DTI pulse sequence with high isotropic spatial resolution was developed for whole brain imaging in under 20 minutes. To minimize the effects of brain motion, a cardiac synchronized, multiecho, DW‐SSFP pulse sequence was implemented. Motion artifacts were further reduced by a combination of linear phase correction, corrupt projection detection and rejection, sampling density reweighting, and parallel imaging reconstruction. The combination of these methods greatly improved the quality of 3D DTI in the brain. J. Magn. Reson. Imaging 2009;29:1175–1184. © 2009 Wiley‐Liss, Inc. 相似文献7.
Elan J. Grossman MS Ke Zhang MS Jing An MD Abram Voorhees PhD Matilda Inglese MD PhD Yulin Ge MD Niels Oesingmann PhD Jian Xu BS Kelly A. Mcgorty RT Qun Chen PhD 《Journal of magnetic resonance imaging : JMRI》2009,29(6):1425-1431
Purpose
To study the feasibility of using the MRI technique of segmented true–fast imaging with steady‐state precession arterial spin‐labeling (True‐FISP ASL) for the noninvasive measurement and quantification of local perfusion in cerebral deep gray matter at 3T.Materials and Methods
A flow‐sensitive alternating inversion‐recovery (FAIR) ASL perfusion preparation was used in which the echo‐planar imaging (EPI) readout was replaced with a segmented True‐FISP data acquisition strategy. The absolute perfusion for six selected regions of deep gray matter (left and right thalamus, putamen, and caudate) were calculated in 11 healthy human subjects (six male, five female; mean age = 35.5 years ± 9.9).Results
Preliminary measurements of the average absolute perfusion values at the six selected regions of deep gray matter are in agreement with published values for mean absolute cerebral blood flow (CBF) baselines acquired from healthy volunteers using positron emission tomography (PET).Conclusion
Segmented True‐FISP ASL is a practical and quantitative technique suitable to measure local tissue perfusion in cerebral deep gray matter at a high spatial resolution without the susceptibility artifacts commonly associated with EPI‐based methods of ASL. J. Magn. Reson. Imaging 2009;29:1425–1431. © 2009 Wiley‐Liss, Inc. 相似文献8.
Sean C.L. Deoni PhD 《Journal of magnetic resonance imaging : JMRI》2009,30(2):411-417
Purpose
To investigate a new approach for more completely accounting for off‐resonance affects in the DESPOT2 (driven equilibrium single pulse observation of T2) mapping technique.Materials and Methods
The DESPOT2 method derives T2 information from fully balanced steady‐state free precession (bSSFP) images acquired over multiple flip angles. Off‐resonance affects, which present as bands of altered signal intensity throughout the bSSFP images, results in erroneous T2 values in the corresponding calculated maps. Radiofrequency (RF) phase‐cycling, in which the phase of the RF pulse is incremented along the pulse train, offers a potential method for eliminating these artifacts. In this work we present a general method, referred to as DESPOT2, with full modeling (DESPOT2‐FM), for deriving T2, as well as off‐resonance frequency, from dual flip angle bSSFP data acquired with two RF phase increments.Results
The method is demonstrated in vivo through the acquisition of whole‐brain, 1 mm3 isotropic T2 maps at 3T and shown to provide near artifact‐free maps, even in areas with steep susceptibility‐induced gradients.Conclusion
DESPOT2‐FM offers an efficient method for acquiring high spatial resolution, whole‐brain T2 maps at 3T with high precision and free of artifact. J. Magn. Reson. Imaging 2009;30:411–417. © 2009 Wiley‐Liss, Inc. 相似文献9.
Todd R. Jensen PhD Kathleen M. Schmainda PhD 《Journal of magnetic resonance imaging : JMRI》2009,30(3):481-489
Purpose
To determine the potential of using a computer‐aided detection method to intelligently distinguish peritumoral edema alone from peritumor edema consisting of tumor using a combination of high‐resolution morphological and physiological magnetic resonance imaging (MRI) techniques available on most clinical MRI scanners.Materials and Methods
This retrospective study consisted of patients with two types of primary brain tumors: meningiomas (n = 7) and glioblastomas (n = 11). Meningiomas are typically benign and have a clear delineation of tumor and edema. Glioblastomas are known to invade outside the contrast‐enhancing area. Four classifiers of differing designs were trained using morphological, diffusion‐weighted, and perfusion‐weighted features derived from MRI to discriminate tumor and edema, tested on edematous regions surrounding tumors, and assessed for their ability to detect nonenhancing tumor invasion.Results
The four classifiers provided similar measures of accuracy when applied to the training and testing data. Each classifier was able to identify areas of nonenhancing tumor invasion supported with adjunct images or follow‐up studies.Conclusion
The combination of features derived from morphological and physiological imaging techniques contains the information necessary for computer‐aided detection of tumor invasion and allows for the identification of tumor invasion not previously visualized on morphological, diffusion‐weighted, and perfusion‐weighted images and maps. Further validation of this approach requires obtaining spatially coregistered tissue samples in a study with a larger sample size. J. Magn. Reson. Imaging 2009;30:481–489. © 2009 Wiley‐Liss, Inc. 相似文献10.
Miese F Kröpil P Ostendorf B Scherer A Buchbender C Quentin M Lanzman RS Blondin D Schneider M Bittersohl B Zilkens C Jellus V Ch Mamisch T Wittsack HJ 《European journal of radiology》2011,80(3):e427-e431
Purpose
To assess motion artifacts in dGEMRIC of finger joints and to evaluate the effectiveness of motion correction.Materials and methods
In 40 subjects (26 patients with finger arthritis and 14 healthy volunteers) dGEMRIC of metacarpophalangeal joint II was performed. Imaging used a dual flip angle approach (TE 3.72 ms, TR 15 ms, flip angles 5° and 26°). Two sets of T1 maps were calculated for dGEMRIC analysis from the imaging data for each subject: one with and one without motion correction. To compare image quality, visual grading analysis and precision of dGEMRIC measurement of both dGEMRIC maps for each case were evaluated.Results
Motion artifacts were present in 82% (33/40) of uncorrected dGEMRIC maps. Motion artifacts were graded as severe or as rendering evaluation impossible in 43% (17/40) of uncorrected dGEMRIC maps. Motion corrected maps showed significantly less motion artifacts (P < 0.001) and were graded as evaluable in 97% (39/40) of cases. Precision was significantly higher in motion corrected images (coefficient of variation (CV = .176 ± .077), compared to uncorrected images (CV .445 ± .347) (P < .001). Motion corrected dGERMIC was different in volunteers and patients (P = .044), whereas uncorrected dGEMRIC was not (P = .234).Conclusion
Motion correction improves image quality, dGEMRIC measurement precision and diagnostic performance in dGEMRIC of finger joints. 相似文献11.
SungDae Yun MS Sung Suk Oh MS Yeji Han PhD HyunWook Park PhD 《Journal of magnetic resonance imaging : JMRI》2009,29(4):924-936
Purpose
To develop a novel approach for high‐resolution functional MRI (fMRI) using the conventional gradient‐echo sequence.Materials and Methods
Echo‐planar imaging (EPI) techniques have generally been used for fMRI studies due to their fast imaging time. However, it is difficult for studying brain function at the submillimeter level using this sequence. In addition, EPI techniques have some drawbacks, such as Nyquist ghosts and geometric distortions in the reconstructed images, and subsequently require additional postprocessing to reduce these artifacts. One way of solving these problems is to acquire fMRI data by means of a conventional gradient‐echo imaging sequence instead of EPI. To provide a fast imaging time, the proposed method combines higher‐order generalized series (HGS) imaging with a parallel imaging technique which is called the HGS‐parallel technique.Results
The proposed HGS‐parallel technique achieves a 12.8‐fold acceleration in imaging time without the cost of spatial resolution. The proposed method was verified through the application of fMRI studies on normal subjects.Conclusion
This study suggests that the proposed method can be used for high‐resolution fMRI studies without the geometric distortion and the Nyquist ghost artifacts compared to EPI. J. Magn. Reson. Imaging 2009;29:924–936. © 2009 Wiley‐Liss, Inc. 相似文献12.
Jayme Cameron Kosior BSc Michael R. Smith PhD Robert Karl Kosior BSc Richard Frayne PhD 《Journal of magnetic resonance imaging : JMRI》2009,29(1):183-188
Purpose
To evaluate the use of bolus signals obtained from tissue as reference functions (or local reference functions [LRFs]) rather than arterial input functions (AIFs) when deriving cross‐calibrated cerebral blood flow (CBFCC) estimates via deconvolution.Materials and Methods
AIF and white matter (WM) LRF CBFCC maps (cross‐calibrated so that normal WM was 23.7 mL/minute/100 g) derived using singular value decomposition (SVD) were examined in 28 ischemic stroke patients. Median CBFCC estimates from normal gray matter (GM) and ischemic tissue were obtained.Results
AIF and LRF median CBFCC estimates resembled one another for all 28 patients (average paired CBFCC difference 0.4 ± 1.7 mL/minute/100 g and –0.4 ± 1.4 mL/minute/100 g in GM and ischemic tissue, respectively). Wilcoxon signed‐rank comparisons of patient median CBFCC measurements revealed no statistically significant differences between using AIFs and LRFs (P > 0.05).Conclusion
If CBF is quantified using a patient‐specific cross‐calibration factor, then LRF CBF estimates are at least as accurate as those from AIFs. Therefore, until AIF quantification is achievable in vivo, perfusion protocols tailored for LRFs would simplify the methodology and provide more reliable perfusion information. J. Magn. Reson. Imaging 2009;29:183–188. © 2008 Wiley‐Liss, Inc. 相似文献13.
Bart J. Emmer MD Matthias J. van Osch PhD Ona Wu PhD Gerda M. Steup‐Beekman MD Stefan C. Steens MD PhD Tom W. Huizinga MD PhD Mark A. van Buchem MD PhD Jeroen van der Grond PhD 《Journal of magnetic resonance imaging : JMRI》2010,32(2):283-288
Purpose:
To use perfusion weighted MR to quantify any perfusion abnormalities and to determine their contribution to neuropsychiatric (NP) involvement in systemic lupus erythematosus (SLE).Materials and methods:
We applied dynamic susceptibility contrast (DSC) perfusion MRI in 15 active NPSLE, 26 inactive NPSLE patients, and 11 control subjects. Cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT) maps were reconstructed and regions of interest were compared between groups. In addition, the effect of SLE criteria, NPSLE syndromes, immunological coagulation disorder, and medication on CBF, CBV, and MTT was investigated.Results:
No significant differences were found between the groups in CBF, CBV, and MTT. No significant influence of SLE criteria or NPSLE syndromes on CBF, CBV, or MTT was found. No significant influence of anti‐cardiolipin antibodies, lupus anti‐coagulant, the presence of anti‐phospholipid syndrome (APS), or medication on CBF, CBV, or MTT was found.Conclusion:
Our findings suggest CBF, CBV, and MTT in the white and the gray matter in SLE patients is not significantly different from healthy controls or between patients with and without specific symptoms or with and without immunological disorder involving coagulation. J. Magn. Reson. Imaging 2010;32:283–288. © 2010 Wiley‐Liss, Inc. 相似文献14.
Hing‐Chiu Chang MS Tzu‐Chao Chuang PhD Hsiao‐Wen Chung PhD Huey‐Shyan Lin PhD Ping‐Hong Lai MD Mei‐Jui Weng MD Jui‐Hsun Fu MD Po‐Chin Wang MD Shang‐Chieh Li MD Huay‐Ben Pan MD 《Journal of magnetic resonance imaging : JMRI》2012,36(6):1353-1361
Purpose:
To demonstrate the presence of a multilayer appearance of the capsule on contrast‐enhanced (CE) susceptibility‐weighted imaging (SWI) in patients with pyogenic brain abscesses. Possible origins for the appearance and effects of postprocessing settings are discussed.Materials and Methods:
Fourteen patients with pyogenic brain abscesses underwent post gadolinium‐enhanced SWI at 1.5 T. All SWI images were postprocessed with various filter and mask settings to compare the image appearance. Computer simulations using a paramagnetic spherical shell model were performed to verify the clinical findings.Results:
Pyogenic brain abscesses demonstrated a multilayer appearance with a darkened ring within the enhanced capsule on CE‐SWI in all patients. The multilayer appearance was slice‐orientation‐dependent, decreased with larger widths of the high‐pass filter, and increased with larger numbers of phase mask multiplication operations, consistently on both simulation results and the clinical images.Conclusion:
CE‐SWI shows the multilayer appearance of the capsule in pyogenic brain abscesses, which may arise from postprocessing procedures originally designed to enhance susceptibility contrast. Although SWI may provide additional information valuable in the diagnosis of pyogenic brain abscesses, image interpretation should be exercised with caution, particularly for CE‐SWI. J. Magn. Reson. Imaging 2012; 36:1353–1361. © 2012 Wiley Periodicals, Inc. 相似文献15.
Kathryn Richdale OD MS Peter Wassenaar MS Katharine Teal Bluestein BS Amir Abduljalil PhD John A. Christoforidis MD Titus Lanz PhD Michael V. Knopp MD PhD Petra Schmalbrock PhD 《Journal of magnetic resonance imaging : JMRI》2009,30(5):924-932
Purpose:
To develop a protocol which optimizes contrast, resolution and scan time for three‐dimensional (3D) imaging of the human eye in vivo using a 7 Tesla (T) scanner and custom radio frequency (RF) coil.Materials and Methods:
Initial testing was conducted to reduce motion and susceptibility artifacts. Three‐dimensional FFE and IR‐TFE images were obtained with variable flip angles and TI times. T1 measurements were made and numerical simulations were performed to determine the ideal contrast of certain ocular structures. Studies were performed to optimize resolution and signal‐to‐noise ratio (SNR) with scan times from 20 s to 5 min.Results:
Motion and susceptibility artifacts were reduced through careful subject preparation. T1 values of the ocular structures are in line with previous work at 1.5T. A voxel size of 0.15 × 0.25 × 1.0 mm3 was obtained with a scan time of approximately 35 s for both 3D FFE and IR‐TFE sequences. Multiple images were registered in 3D to produce final SNRs over 40.Conclusion:
Optimization of pulse sequences and avoidance of susceptibility and motion artifacts led to high quality images with spatial resolution and SNR exceeding prior work. Ocular imaging at 7T with a dedicated coil improves the ability to make measurements of the fine structures of the eye. J. Magn. Reson. Imaging 2009;30:924–932. © 2009 Wiley‐Liss, Inc. 相似文献16.
Adam Krasinski MSc Bernard Chiu PhD Aaron Fenster PhD Grace Parraga PhD 《Journal of magnetic resonance imaging : JMRI》2009,29(4):901-908
Purpose
To evaluate differences in carotid atherosclerosis measured using magnetic resonance imaging (MRI) and three‐dimensional ultrasound (3DUS).Materials and Methods
Ten subject volunteers underwent carotid 3DUS and MRI (multislice black blood fast spin echo, T1‐weighted contrast, double inversion recovery, 0.5 mm in‐plane resolution, 2 mm slice, 3.0 T) within 1 hour. 3DUS and MR images were manually segmented by two observers providing vessel wall and lumen contours for quantification of vessel wall volume (VWV) and generation of carotid thickness maps.Results
MRI VWV (1040 ± 210 mm3) and 3DUS VWV (540 ± 110 mm3) were significantly different (P < 0.0001). When normalized for the estimated adventitia volume, mean MRI VWV decreased 240 ± 50 mm3 and was significantly different from 3DUS VWV (P < 0.001). Two‐dimensional carotid maps showed qualitative evidence of regional differences in the plaque and vessel wall thickness between MR and 3DUS in all subjects. Power Doppler US confirmed that heterogeneity in the common carotid artery in all patients resulted from apparent flow disturbances, not atherosclerotic plaque.Conclusion
MRI and 3DUS VWV were significantly different and carotid maps showed homogeneous thickness differences and heterogeneity in specific regions of interest identified as MR flow artifacts in the common carotid artery. J. Magn. Reson. Imaging 2009;29:901–908. © 2009 Wiley‐Liss, Inc. 相似文献17.
Keisuke Matsubara Masanobu Ibaraki Kazuhiro Nakamura Hiroshi Yamaguchi Atsushi Umetsu Fumiko Kinoshita Toshibumi Kinoshita 《Annals of nuclear medicine》2013,27(4):335-345
Objective
Subject head motion during sequential 15O positron emission tomography (PET) scans can result in artifacts in cerebral blood flow (CBF) and oxygen metabolism maps. However, to our knowledge, there are no systematic studies examining this issue. Herein, we investigated the effect of head motion on quantification of CBF and oxygen metabolism, and proposed an image-based motion correction method dedicated to 15O PET study, correcting for transmission–emission mismatch and inter-scan mismatch of emission scans.Methods
We analyzed 15O PET data for patients with major arterial steno-occlusive disease (n = 130) to determine the occurrence frequency of head motion during 15O PET examination. Image-based motion correction without and with realignment between transmission and emission scans, termed simple and 2-step method, respectively, was applied to the cases that showed severe inter-scan motion.Results
Severe inter-scan motion (>3 mm translation or >5° rotation) was observed in 27 of 520 adjacent scan pairs (5.2 %). In these cases, unrealistic values of oxygen extraction fraction (OEF) or cerebrovascular reactivity (CVR) were observed without motion correction. Motion correction eliminated these artifacts. The volume-of-interest (VOI) analysis demonstrated that the motion correction changed the OEF on the middle cerebral artery territory by 17.3 % at maximum. The inter-scan motion also affected CBV, CMRO2 and CBF, which were improved by the motion correction. A difference of VOI values between the simple and 2-step method was also observed.Conclusions
These data suggest that image-based motion correction is useful for accurate measurement of CBF and oxygen metabolism by 15O PET. 相似文献18.
M. Filipovic P.‐A. Vuissoz A. Codreanu M. Claudon J. Felblinger 《Magnetic resonance in medicine》2011,65(3):812-822
The analysis of abdominal and thoracic dynamic contrast‐enhanced MRI is often impaired by artifacts and misregistration caused by physiological motion. Breath‐hold is too short to cover long acquisitions. A novel multipurpose reconstruction technique, entitled dynamic contrast‐enhanced generalized reconstruction by inversion of coupled systems, is presented. It performs respiratory motion compensation in terms of both motion artefact correction and registration. It comprises motion modeling and contrast‐change modeling. The method feeds on physiological signals and x‐f space properties of dynamic series to invert a coupled system of linear equations. The unknowns solved for represent the parameters for a linear nonrigid motion model and the parameters for a linear contrast‐change model based on B‐splines. Performance is demonstrated on myocardial perfusion imaging, on six simulated data sets and six clinical exams. The main purpose consists in removing motion‐induced errors from time–intensity curves, thus improving curve analysis and postprocessing in general. This method alleviates postprocessing difficulties in dynamic contrast‐enhanced MRI and opens new possibilities for dynamic contrast‐enhanced MRI analysis. Magn Reson Med, 2011. © 2010 Wiley‐Liss, Inc. 相似文献
19.
Sreenath Narayan PhD Satish C. Kalhan MD David L. Wilson PhD 《Journal of magnetic resonance imaging : JMRI》2013,37(5):1247-1253
Purpose:
To reduce swaps in fat–water separation methods, a particular issue on 7 Tesla (T) small animal scanners due to field inhomogeneity, using image postprocessing innovations that detect and correct errors in the B0 field map.Materials and Methods:
Fat–water decompositions and B0 field maps were computed for images of mice acquired on a 7T Bruker BioSpec scanner, using a computationally efficient method for solving the Markov Random Field formulation of the multi‐point Dixon model. The B0 field maps were processed with a novel hole‐filling method, based on edge strength between regions, and a novel k‐means method, based on field‐map intensities, which were iteratively applied to automatically detect and reinitialize error regions in the B0 field maps. Errors were manually assessed in the B0 field maps and chemical parameter maps both before and after error correction.Results:
Partial swaps were found in 6% of images when processed with FLAWLESS. After REFINED correction, only 0.7% of images contained partial swaps, resulting in an 88% decrease in error rate. Complete swaps were not problematic.Conclusion:
Ex post facto error correction is a viable supplement to a priori techniques for producing globally smooth B0 field maps, without partial swaps. With our processing pipeline, it is possible to process image volumes rapidly, robustly, and almost automatically. J. Magn. Reson. Imaging 2013;37:1247–1253. © 2012 Wiley Periodicals, Inc. 相似文献20.
Philip M. Robson Ananth J. Madhuranthakam Weiying Dai Ivan Pedrosa Neil M. Rofsky David C. Alsop 《Magnetic resonance in medicine》2009,61(6):1374-1387
Arterial spin labeling (ASL) perfusion measurements may have many applications outside the brain. In the abdomen, severe image artifacts can arise from motions between acquisitions of multiple signal averages in ASL, even with single‐shot image acquisition. Background suppression and respiratory motion synchronization techniques can be used to ameliorate these artifacts. Two separate in vivo studies of renal perfusion imaging using pulsed continuous ASL (pCASL) were performed. The first study assessed various combinations of background suppression and breathing strategies. The second investigated the retrospective sorting of images acquired during free breathing based on respiratory position. Quantitative assessments of the test‐retest repeatability of perfusion measurements and the image quality scored by two radiologists were made. Image quality was most significantly improved by using background suppression schemes and controlled breathing when compared to other combinations without background suppression or with free breathing, assessed by test‐retests (5% level, F‐test), and by radiologists' scores (5% level, Mann‐Whitney U‐test). Under free breathing, retrospectively sorting images based on respiratory position showed significant improvement. Both radiologists found 100% of the images had preferable image sharpness after sorting. High‐quality renal perfusion measurements with reduced respiratory motion artifacts have been demonstrated using ASL when appropriate background suppression and breathing strategies are applied. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc. 相似文献