共查询到20条相似文献,搜索用时 31 毫秒
1.
Purpose
To develop a method for estimating metabolite concentrations using phased-array coils and sensitivity-encoded (SENSE) magnetic resonance spectroscopic images (MRSI) of the human brain.Materials and Methods
The method is based on the phantom replacement technique and uses receive coil sensitivity maps and body-coil loading factors to account for receive B1 inhomogeneity and variable coil loading, respectively. Corrections for cerebrospinal fluid content from the MRSI voxel were also applied, and the total protocol scan time was less than 15 min. The method was applied to 10 normal human volunteers using a multislice 2D-MRSI sequence at 3 T, and seven different brain regions were quantified.Results
N-Acetyl aspartate (NAA) concentrations varied from 9.7 to 14.7 mM, creatine (Cr) varied from 6.6 to 10.6 mM and choline (Cho) varied from 1.6 to 3.0 mM, in good general agreement with prior literature values.Conclusions
Quantitative SENSE-MRSI of the human brain is routinely possible using an adapted phantom-replacement technique. The method may also be applied to other MRSI techniques, including conventional phase encoding, with phased-array receiver coils, provided that coil sensitivity profiles can be measured. 相似文献2.
Morita S Saito N Suzuki K Ohnishi T Imura C Mitsuhashi N 《Magnetic resonance imaging》2008,26(9):1244-1249
Purpose
To compare the degree of visualization of the bile duct and portal vein in terms of the difference in k-space ordering on a three-dimensional (3D) segmented true fast imaging with steady-state precession (trueFISP) sequence.Materials and Methods
A breath-hold coronal 3D segmented trueFISP sequence was prospectively performed on 14 healthy volunteers. Images obtained with centric and linear k-space ordering in the k(x)–k(y) plane were compared by two independent radiologists qualitatively with depiction scores on a five-point scale (1=not seen to 5=excellent depiction) using the Wilcoxon signed-rank test. Images were also compared quantitatively using relative contrast values for the bile duct and portal vein against the hepatic parenchyma using a paired t-test.Results
With centric ordering, both the mean depiction scores and relative contrast values for the portal vein were significantly lower than those with linear ordering (1.5 vs. 3.5, P<.01; and 0.08±0.19 vs. 0.51±0.10, P<.01, respectively). However, in the bile duct, there were no significant differences, only slight differences were found among the results obtained with centric and linear ordering (3.9 vs. 3.8, P=.72; and 0.59±0.06 vs. 0.68±0.06, P<.01, respectively).Conclusion
For visualizing the bile duct, centric k-space ordering on 3D segmented trueFISP sequence is recommended, while linear ordering is recommended for portal vein visualization. 相似文献3.
QingShi Zeng HePeng LiuKai Zhang ChuanFu LiGengYin Zhou 《Magnetic resonance imaging》2011,29(1):25-31
Objective
To determine whether metabolite ratios in multivoxel 3D proton MR spectroscopy (1H MRS) is different between low-grade and high-grade gliomas and may be useful for glioma grading.Materials and Methods
Thirty-nine patients (23 male and 16 female; 22-75 years old; mean age, 44.92±12.65 years) suspected of having gliomas underwent 3D 1H MRS examinations. Metabolite ratios [choline (Cho)/creatine (Cr), N-acetylaspartate (NAA)/Cr and Cho/NAA] were measured. Tumor grade was determined by using the histopathologic grading. Receiver operating characteristic analysis of metabolite ratios was performed, and optimum thresholds for tumor grading were determined. The resulting sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) for identifying high-grade gliomas were calculated.Results
Diagnostic-quality 3D 1H MRS with readily quantifiable Cho, Cr and NAA peaks was obtained in 94.87% of the cases. The Cho/Cr and Cho/NAA ratios were significantly higher in high-grade than in low-grade glioma (P<.001), whereas the NAA/Cr ratios were significantly lower in high-grade than in low-grade glioma (P<.001). Receiver operating characteristic analysis demonstrated a threshold value of 2.04 for Cho/Cr ratio to provide sensitivity, specificity, PPV and NPV of 84.00%, 83.33%, 91.30% and 71.43%, respectively. Threshold value of 2.20 for Cho/NAA ratio resulted in sensitivity, specificity, PPV and NPV of 88.00%, 66.67%, 84.62% and 72.73%, respectively. Overall diagnostic accuracy was not statistically significantly different between Cho/Cr and Cho/NAA ratios (χ2=0.093, P=.76).Conclusion
Metabolite ratios of low-grade gliomas were significantly different from high-grade gliomas. Cho/Cr and Cho/NAA ratios could have the superior diagnostic performance in predicting the glioma grade. 相似文献4.
von Morze C Purcell DD Banerjee S Xu D Mukherjee P Kelley DA Majumdar S Vigneron DB 《Magnetic resonance imaging》2008,26(10):1329-1333
Purpose
Greater spatial resolution in intracranial three-dimensional time-of-flight (TOF) magnetic resonance angiography (MRA) is possible at higher field strengths, due to the increased contrast-to-noise ratio (CNR) from the higher signal-to-noise ratio and the improved background suppression. However, at very high fields, spatial resolution is limited in practice by the acquisition time required for sequential phase encoding. In this study, we applied parallel imaging to 7T TOF MRA studies of normal volunteers and patients with vascular disease, in order to obtain very high resolution (0.12 mm3) images within a reasonable scan time.Materials and Methods
Custom parallel imaging acquisition and reconstruction methods were developed for 7T MRA, based on generalized autocalibrating partially parallel acquisition (GRAPPA). The techniques were compared and applied to studies of seven normal volunteers and three patients with cerebrovascular disease.Results
The technique produced high resolution studies free from discernible reconstruction artifacts in all subjects and provided excellent depiction of vascular pathology in patients.Conclusions
7T TOF MRA with parallel imaging is a valuable noninvasive angiographic technique that can attain very high spatial resolution. 相似文献5.
Weis J Ahlström H Hlavcak P Häggman M Ortiz-Nieto F Bergman A 《Magnetic resonance imaging》2009,27(1):87-93
Purpose
To minimize user and vendor dependence of the spectrum processing of prostate spectra, to measure the ratio of choline (Cho) plus creatine (Cr) to citrate (Cit) in the prostate tissue of normal volunteers and cancer patients, and to compare the results with pathologic findings after radical prostatectomy.Materials and methods
Four healthy volunteers and 13 patients with prostate cancer were measured. Measurements were performed using two-dimensional magnetic resonance spectroscopic imaging (MRSI) and endorectal coil. A standard vendor's spectrum processing approach has been modified. An original feature of this methodology was the combination of vendor-optimized and user-independent spectrum preprocessing in the scanner and user-independent quantitation in the environment of an MRUI software package. (Cho+Cr)/Cit ratio was used for the classification of prostate tissue. Results were compared with histopathology after radical prostatectomy.Results
Eight of 13 cancer patients were classified as suspicious or very suspicious for cancer at spectroscopy, three were ambiguous for cancer and two patients were evaluated as false negative. A considerable overlap of metabolite ratios at various Gleason score was found.Conclusion
The proposed spectrum processing has the potential to improve the accuracy and user independency of the (Cho+Cr)/Cit quantitation. This study confirmed the previous results that a considerable overlap of (Cho+Cr)/Cit ratios exists at various Gleason score levels. 相似文献6.
Chengcheng Zhu Umar Sadat Andrew J. Patterson Zhongzhao Teng Jonathan H. Gillard Martin J. Graves 《Magnetic resonance imaging》2014
Objective
Development of a fast 3D high-resolution magnetic resonance imaging (MRI) protocol for improved carotid artery plaque imaging.Methods
Two patients with carotid atherosclerosis disease underwent 3D high-resolution MRI which included time-of-flight and T1-weighted variable flip angle, fast-spin-echo (FSE) imaging, pre- and post-intravenous gadolinium-based contrast agent administration.Results
Good quality images with intrinsic blood suppression were obtained pre- and post-contrast administration using a 3D FSE sequence. The plaque burden, lipid core volume, hemorrhage volume and fibrous cap thickness were well determined.Conclusions
3D high-resolution MR imaging of carotid plaque using TOF and 3D FSE can achieve high isotropic resolution, large coverage, and excellent image quality within a short acquisition time. 相似文献7.
William H. Perman Pratip Bhattacharya Jochen Leupold Alexander P. Lin Kent C. Harris Valerie A. Norton Jan-Bernd Hövener Brian D. Ross 《Magnetic resonance imaging》2010
Purpose
The goal of this work was to develop a fast 3D chemical shift imaging technique for the noninvasive measurement of hyperpolarized 13C-labeled substrates and metabolic products at low concentration.Materials and Methods
Multiple echo 3D balanced steady state magnetic resonance imaging (ME-3DbSSFP) was performed in vitro on a syringe containing hyperpolarized [1,3,3-2H3; 1-13C]2-hydroxyethylpropionate (HEP) adjacent to a 13C-enriched acetate phantom, and in vivo on a rat before and after intravenous injection of hyperpolarized HEP at 1.5 T. Chemical shift images of the hyperpolarized HEP were derived from the multiple echo data by Fourier transformation along the echoes on a voxel by voxel basis for each slice of the 3D data set.Results
ME-3DbSSFP imaging was able to provide chemical shift images of hyperpolarized HEP in vitro, and in a rat with isotropic 7-mm spatial resolution, 93 Hz spectral resolution and 16-s temporal resolution for a period greater than 45 s.Conclusion
Multiple echo 3D bSSFP imaging can provide chemical shift images of hyperpolarized 13C-labeled compounds in vivo with relatively high spatial resolution and moderate spectral resolution. The increased signal-to-noise ratio of this 3D technique will enable the detection of hyperpolarized 13C-labeled metabolites at lower concentrations as compared to a 2D technique. 相似文献8.
Purpose
To determine whether a greatly reduced spatial resolution of fully reconstructed projection MR images can be used for the simultaneous 3D localization of multiple MR-visible markers and to assess the feasibility of a subsecond position tracking for clinical purposes.Materials and Methods
Miniature, inductively coupled RF coils were imaged in three orthogonal planes with a balanced steady-state free precession (SSFP) sequence and automatically localized using a two-dimensional template fitting and a subsequent three-dimensional (3D) matching of the coordinates. Precision, accuracy, speed and robustness of 3D localization were assessed for decreasing in-plane resolutions (0.6–4.7 mm). The feasibility of marker tracking was evaluated at the lowest resolution by following a robotically driven needle on a complex 3D trajectory.Results
Average 3D precision and accuracy, sensitivity and specificity of localization ranged between 0.1 and 0.4 mm, 0.5 and 1.0 mm, 100% and 95%, and 100% and 96%, respectively. At the lowest resolution, imaging and localization took ≈350 ms and provided an accuracy of ≈1.0 mm. In the tracking experiment, the needle was clearly depicted on the oblique scan planes defined by the markers.Conclusion
Image-based marker localization at a greatly reduced spatial resolution is considered a feasible approach to monitor reference points or rigid instruments at subsecond update rates. 相似文献9.
Breyer T Echternach M Arndt S Richter B Speck O Schumacher M Markl M 《Magnetic resonance imaging》2009,27(1):48-54
Object
To evaluate the feasibility of an optimized MRI protocol based on high field imaging at 3 T in combination with accelerated data acquisition by parallel imaging for the analysis of oropharyngeal and laryngeal function.Materials and Methods
Fast 2D gradient echo (GRE) MRI with different spatial resolutions (1.7×2.7 and 1.1×1.5 mm2) and image update rates (4 and 10 frames per second) was employed to assess pharyngeal movements and visualize swallowing via tracking of an oral contrast bolus (blueberry juice). In a study with 10 normal volunteers, image quality was semi-quantitatively graded by three independent observers with respect to the delineation of anatomical detail and depiction of oropharynx and larynx function. Additionally, the feasibility of the technique for the visualization of pathological pre- and post-surgical oropharynx and larynx function was evaluated in a patient with inspiratory stridor.Results
Image grading demonstrated the feasibility of dynamic MRI for the assessment of normal oropharynx and larynx anatomy and function. Superior image quality (P<.05) was found for data acquisition with four frames per second and higher spatial resolution. In the patient, dynamic MRI detected pathological hypermobility of the epiglottis resulting in airway obstruction. Additional post-surgical MRI for one clinical case revealed morphological changes of the epiglottis and improved function, i.e., absence of airway obstruction and normal swallowing.Conclusion
Results of the volunteer study demonstrated the feasibility of dynamic MRI at 3 T for the visualization of the oropharynx and larynx function during breathing, movements of the tongue and swallowing. Future studies are necessary to evaluate its clinical value compared to existing modalities based on endoscopy or radiographic techniques. 相似文献10.
Purpose
The purpose of the study was to evaluate the value of high-resolution three-dimensional fast imaging employing steady-state acquisition (3D FIESTA) imaging in the visualization of neurovascular relationship in patients with trigeminal neuralgia (TN).Methods
Thirty-seven patients with unilateral typical TN underwent 3D FIESTA imaging. Neurovascular relationship at the trigeminal root entry zone was reviewed by an experienced neuroradiologist, who was blinded to the clinical details. The imaging results were compared with the operative findings in all patients.Results
In 37 patients with TN, 3D FIESTA imaging identified surgically verified neurovascular contact in 35 of 36 symptomatic nerves. Based on surgical findings, the sensitivity and specificity of magnetic resonance (MR) imaging were 97.2% and 100%, respectively. Agreement between the position (medial, lateral, superior and inferior) of the compressing vessel relative to the trigeminal nerve identified by MR imaging and surgery was excellent (K=0.81; 95% confidence interval, 0.56–1.00). A statistically significant difference was found between the site of neurovascular contact and the clinical symptom related to the trigeminal branch (Fisher's Exact Test, P<.001).Conclusions
Use of 3D FIESTA sequence enables accurate visualization of neurovascular contact in patients with TN. Anatomic relationships defined by this method can be useful in surgical planning and predicting surgical findings. 相似文献11.
Santiago Aja-Fernández Gonzalo Vegas-Sánchez-Ferrero Antonio Tristán-Vega 《Magnetic resonance imaging》2014
Parallel imaging methods allow to increase the acquisition rate via subsampled acquisitions of the k-space. SENSE and GRAPPA are the most popular reconstruction methods proposed in order to suppress the artifacts created by this subsampling. The reconstruction process carried out by both methods yields to a variance of noise value which is dependent on the position within the final image. Hence, the traditional noise estimation methods – based on a single noise level for the whole image – fail. In this paper we propose a novel methodology to estimate the spatial dependent pattern of the variance of noise in SENSE and GRAPPA reconstructed images. In both cases, some additional information must be known beforehand: the sensitivity maps of each receiver coil in the SENSE case and the reconstruction coefficients for GRAPPA. 相似文献
12.
Masaaki Hori Harushi Mori Shigeki Aoki Osamu Abe Tomohiko Masumoto Satoshi Kunimatsu Kuni Ohtomo Hiroyuki Kabasawa Nobuyuki Shiraga Tsutomu Araki 《Magnetic resonance imaging》2010
Object
Although three-dimensional (3D), high-spatial resolution susceptibility-weighted imaging (SWI) appears to be valuable in the evaluation of central nervous system gliomas, several evaluation methods are proposed in the literature. The purpose of this study was to evaluate the use of 3D SWI for grading intracranial gliomas with various analysis methods.Materials and Methods
Twenty-three patients suspected of having gliomas participated in this study. SWI was performed in addition to conventional MR sequences. In 15 cases, post-gadolinium enhanced SWI was also obtained. Imaging evaluation criteria were conventional grade, hypointensity ratio in the tumor-dominant structure of hypointensity on SWI (hemorrhage or vascular structure) and presence of abnormal enhancement surrounding the tumor.Results
Mean grading scores of conventional grade showed no statistically significant difference among WHO grades. Mean grading scores of hypointensity ratios in the tumor were higher for WHO Grades 3 and 4 than for lower grade tumors (P=.05, Mann–Whitney U test). Hemorrhagic foci were more frequently seen in the higher grade tumor. Post-contrast susceptibility-weighted images of five of 11 WHO Grade 3 and 4 cases showed bright enhancement surrounding the tumor, suggesting a breakdown of the blood–brain barrier.Conclusions
SWI at 3 T may be a useful method to analyze the structural characteristics of gliomas and to evaluate pathology in vivo. Assessment of hypointensity ratios in the glioma was the most preferable method in grading glioma. However, more studies, specifically concerning a suitable method for image analysis, are needed to establish SWI at 3 T as a useful tool in clinical routine. 相似文献13.
One of the drawbacks of scanning patients using multiple-voxel spectroscopic imaging is the long acquisition time. This is
especially true when one is interested in obtaining absolute metabolite concentrations which requires acquisition of unsuppressed
water spectra in addition to the suppressed spectra. In our experiment, turbo spectroscopic imaging (TSI) method with acquisition
of three echoes per excitation was applied to reduce scanning time without lowering the spatial resolution. In 15 relapsing-remitting
multiple sclerosis patients (mean age 37.07 years, mean disease duration 7.67 years), an MRSI scan at the level of centrum
semiovale was obtained. The scan time was approximately 7 min including the unsuppressed spectra. Tissue water was used as
an internal concentration reference to obtain absolute metabolite concentrations of N-acetyl-aspartate (NAA), creatine (Cr),
and choline (Cho). The peak areas were corrected for differences in transversal and longitudinal relaxation times and a water
concentration of 55.5 M was assumed. A three-dimensional high-resolution T
1 scan was acquired and used to segment tissue in gray matter (GM), white matter (WM), and cerebrospinal fluid using FSL’S
FAST segmentation method (a software library of the automated segmentation tool by the Center of Functional MRI of the Brain,
Oxford, UK). Finally, a regression analysis was employed to address the metabolite concentrations and ratios in GM and WM,
respectively. Our study shows that the metabolite concentrations (NAA, Cho, Cr) and metabolite ratios (NAA/Cr and Cho/Cr)
in GM and WM obtained using the methods discussed earlier are comparable to the results found in other studies of similar
patient groups. It also shows that TSI method can be used to obtain the absolute metabolite ratios in a reasonable scan time. 相似文献
14.
Matthias Rief Moritz Wagner Tobias Franiel Viola Bresan Matthias Taupitz Christian Klessen Bernd Hamm Patrick Asbach 《Magnetic resonance imaging》2009,27(9):1223-1229
Purpose
To investigate the image quality and detection rate of focal liver lesions by comparing a T2-weighted breath-hold single-shot sequence and a T2-weighted high spatial resolution fast spin-echo sequence with respiratory triggering via unenhanced and superparamagnetic iron oxide (SPIO)-enhanced liver imaging.Materials and Methods
The study was approved by the local ethical review board; informed consent was waived. Liver-lesion contrast was measured and a qualitative consensus evaluation of image quality and lesion detection was performed in 42 consecutive patients using a 1.5-T MR system.Results
The liver-lesion contrast was significantly higher (P<.05) for the respiratory-triggered sequence compared to the breath-hold sequence regarding unenhanced and SPIO-enhanced imaging. The respiratory-triggered sequences revealed significantly higher image quality scores as well as higher numbers of detected liver lesions compared to the breath-hold sequence on unenhanced and SPIO-enhanced imaging. The SPIO contrast did not significantly improve the number of detected lesions on the respective sequences (P>.05).Conclusion
We find that respiratory-triggered fast spin-echo sequences produce a higher image quality and a more precise liver-lesion detection rate thereby justifying the increased acquisition time necessary for this method. 相似文献15.
Lucia Manganaro Giorgio Vittori Valeria Vinci Francesca Fierro Alessandra Tomei Pietro Lodise Paolo Sollazzo Maria E. Sergi Silvia Bernardo Laura Ballesio Mario Marini Maria G. Porpora 《Magnetic resonance imaging》2012
Objectives
Endometriosis is the ectopic localization of endometrial glands. Symptoms include a wide variety of chronic pelvic pain. Ovarian endometriosis represents the most frequent site of implantation followed by the Douglas pouch which is undepicted unless peritoneal fluid is present. Pelvic exams may be reported as normal in 40% of evaluations, although multiple nodularities are located in this region. Nowadays, laparoscopy represents the standard technique for endometriosis evaluation. However, magnetic resonance imaging (MRI) remains the best noninvasive technique for the evaluation of pelvic lesions. According to the importance of a precise preoperative diagnosis of deep infiltrative endometriosis involving the Douglas pouch, we evaluated feasibility of a 3-T system in the evaluation of this particular region.Methods
We enrolled 19 women coming with either ultrasound or anamnestic suspicion of endometriosis. Pelvic MRI examination was performed on the 3-T system. We applied a standard exam protocol including pulse sequences [single-shot fast spin echo (FSE)] and high-resolution T2W and T1W FSE sequences with and without FS.Results
MRI diagnosed posterior cul-de-sac obliteration in 15/19 patients. MRI findings were compared with laparoscopy, thus obtaining the following statistical values: mean sensitivity, specificity, positive predictive value and negative predictive value, respectively, of 93%, 75%, 93% and 75%. Moreover, we calculated an interobserver agreement k value of 0.72 with a substantial degree of agreement between two radiologists of a sensitivity value of 93% and specificity value of 75%.Conclusions
Precise preoperative mapping of posterior cul-de-sac region is essential for a preoperative planning. In our work, the 3-T MRI was shown to be excellent in the evaluation of posterior cul-de-sac obliteration associated to an optimal evaluation of the uterosacral ligaments due to the higher contrast spatial resolution. 相似文献16.
Christopher K. Macgowan Garry K.C. Liu Joshua F.P. van Amerom Marshall S. Sussman Graham A. Wright 《Magnetic resonance imaging》2010
Self-gating is investigated to improve the velocity resolution of real-time Fourier velocity encoding measurements in the absence of a reliable electrocardiogram waveform (e.g., fetal magnetic resonance or severe arrhythmia). Real-time flow data are acquired using interleaved k-space trajectories which share a common path near the origin of k-space. These common data provide a rapid self-gating signal that can be used to combine the interleaved data. The combined interleaves cover a greater area of k-space than a single real-time acquisition, thereby providing higher velocity resolution for a given aliasing velocity and temporal resolution. For example, this approach provided velocity spectra with a temporal resolution of 19 ms and velocity resolution of 22 cm/s over an 818 cm/s field-of-view. The method was validated experimentally using a computer-controlled pulsatile flow apparatus and applied in vivo to measure aortic-valve flow in a healthy volunteer. 相似文献
17.
Objective
Magnetic resonance spectroscopy (MRS) allows to monitor brain metabolites noninvasively in amyotrophic lateral sclerosis (ALS). The objective of this study was to use MRS to monitor the effect of minocycline treatment (200 mg/day) over a short period (6 weeks) on the brain metabolites in the precentral gyrus and brainstem in newly diagnosed ALS patients.Methods
Ten ALS patients (not on riluzole treatment) were recruited and submitted to single-voxel proton MRS longitudinal examinations (1) before minocycline treatment, (2) 3 weeks and (3) 6 weeks after initiation of treatment.Results
Results did not show the expected decrease of N-acetylaspartate/creatine (NAA/Cr) in the precentral gyrus, and an increased NAA/Cr ratio in the brainstem suggested neuronal recovery. The myo-inositol (mI)/Cr ratio was unchanged in the precentral gyrus, but increased in the brainstem, indicating a glial reaction.Conclusions
MRS results suggest that minocycline treatment could be beneficial in the early stages of ALS. 相似文献18.
Yusuke Inoue Hirofumi Hata Ai Nakajima Yuji Iwadate Gou Ogasawara Keiji Matsunaga 《Magnetic resonance imaging》2014
Purpose
To optimize the navigator-gating technique for the acquisition of high-quality three-dimensional spoiled gradient-recalled echo (3D SPGR) images of the liver during free breathing.Materials and methods
Ten healthy volunteers underwent 3D SPGR magnetic resonance imaging of the liver using a conventional navigator-gated 3D SPGR (cNAV-3D-SPGR) sequence or an enhanced navigator-gated 3D SPGR (eNAV-3D-SPGR) sequence. No exogenous contrast agent was used. A 20-ms wait period was inserted between the 3D SPGR acquisition component and navigator component of the eNAV-3D-SPGR sequence to allow T1 recovery. Visual evaluation and calculation of the signal-to-noise ratio were performed to compare image quality between the imaging techniques.Result
The eNAV-3D-SPGR sequence provided better noise properties than the cNAV-3D-SPGR sequence visually and quantitatively. Navigator gating with an acceptance window of 2 mm effectively inhibited respiratory motion artifacts. The widening of the window to 6 mm shortened the acquisition time but increased motion artifacts, resulting in degradation of overall image quality. Neither slice tracking nor incorporation of short breath holding successfully compensated for the widening of the window.Conclusion
The eNAV-3D-SPGR sequence with an acceptance window of 2 mm provides high-quality 3D SPGR images of the liver. 相似文献19.
Matthew Ethan MacDonald Randall B. Stafford Jérôme Yerly Linda B. Andersen Cheryl R. McCreary Richard Frayne 《Magnetic resonance imaging》2013
Background
Using magnetic resonance (MR) imaging for navigating catheters has several advantages when compared with the current “gold standard” modality of X-ray imaging. A significant drawback to interventional MR is inferior temporal and spatial resolutions, as high spatial resolution images cannot be collected and displayed at rates equal to X-ray imaging. In particular, passive MR catheter tracking experiments that use positive contrast mechanisms have poor temporal imaging rates and signal-to-noise ratio. As a result, with passive methods, it is often difficult to reconstruct motion artifact-free tracking images from areas with motion, such as the thoracic cavity.Methods
In this study, several accelerated MR acquisition strategies, including parallel imaging and compressed sensing (CS), were evaluated to determine which method is most effective at improving the frame rate and passive detection of catheters in regions of physiological motion. Device navigation was performed both in vitro, through the aortic arch of an anthropomorphic chest phantom, and in vivo from the femoral artery, up the descending aorta into the supra-aortic branching vessels in canines.Results and Discussion
The different parallel imaging methods produced images of low quality. CS with a two-fold acceleration was found to be the most effective method for generating tracking images, improving the image frame rate to 5.2 Hz, while maintaining a relatively high in-plane resolution. Using CS, motion artifact was decreased and the catheters were visualized with good conspicuity near the heart.Conclusions
The improvement in the imaging frame rate by image acceleration was sufficient to overcome motion artifacts and to better visualize catheters in the thoracic cavity with passive tracking. CS preformed best at tracking. Navigation with passive MR catheter tracking was demonstrated from the femoral artery to the carotid artery in canines. 相似文献20.
Three-dimensional (3D) twisted projection imaging (TPI) trajectory has a unique advantage in sodium (23Na) imaging on clinical MRI scanners at 1.5 or 3 T, generating a high signal-to-noise ratio (SNR) with a short acquisition time (∼10 min). Parallel imaging with an array of coil elements transits SNR benefits from small coil elements to acquisition efficiency by sampling partial k-space. This study investigates the feasibility of parallel sodium imaging with emphases on SNR and acceleration benefits provided by the 3D TPI trajectory. Computer simulations were used to find available acceleration factors and noise amplification. Human head studies were performed on clinical 1.5/3-T scanners with four-element coil arrays to verify simulation outcomes. In in vivo studies, proton (1H) data, however, were acquired for concept–proof purpose. The sensitivity encoding (SENSE) method with the conjugate gradient algorithm was used to reconstruct images from accelerated TPI-SENSE data sets. Self-calibration was employed to estimate coil sensitivities. Noise amplification in TPI-SENSE was evaluated using multiple noise trials. It was found that the acceleration factor was as high as 5.53 (corresponding to acceleration number 2×3, ring-by-rotation), with a small image error of 6.9% when TPI projections were reduced in both polar (ring) and azimuthal (rotation) directions. The average noise amplification was as low as 98.7%, or 27% lower than Cartesian SENSE at that acceleration factor. The 3D nature of both TPI trajectory and coil sensitivities might be responsible for the high acceleration and low noise amplification. Consequently, TPI-SENSE may have potential advantages for parallel sodium imaging. 相似文献