Prospective Acquisition Correction Research Articles

EFFICACY OF NAVIGATOR-TRIGGERED PACE TECHNIQUE MRCP IN CHOLEDOCHOLITHIASIS

Aim: The navigator-triggered Prospective Acquisition Correction Enhancement technique is a method used to eliminate respiratory motion artifacts caused in magnetic resonance cholangiopancreatography examinations. The purpose of this study was to compare the diagnostic accuracy of navigator-triggered Prospective Acquisition Correction Enhancement tecnique magnetic resonance cholangiopancreatography examination with endoscopic retrograde cholangiopancreatography as a gold standard reference in presence of choledocholithiasis. 
 Materıal and Method: The diagnostic rates of magnetic resonance cholangiopancreatography examination performed with Prospective Acquisition Correction Enhancement technique in the diagnosis of choledocholithiasis were compared according to the results of the endoscopic retrograde cholangiopancreatography examination, which was accepted as a gold standard reference. 
 Results: Among 107 patients included in the study, 40 patients with magnetic resonance cholangiopancreatography and 36 patients with endoscopic retrograde cholangiopancreatography were diagnosed with choledocholithiasis. endoscopic retrograde cholangiopancreatography showed the presence of choledocholithiasis in 36 patients among 40 patients diagnosed as choledocholithiasis with magnetic resonance cholangiopancreatography. The positive predictivity value of the magnetic resonance cholangiopancreatography examination performed with the Prospective Acquisition Correction Enhancement technique was 90%, the negative predictivity value was 98.5%, the sensitivity was 97.3%, the specificity was 94.3%, and the diagnostic accuracy was 95.3%. 
 Conclusıon: We think that navigator-triggered magnetic resonance cholangiopancreatography examination obtained with Prospective Acquisition Correction Enhancement technique is a reliable method with high accuracy in the diagnosis of choledocholithiasis.

Primer on Commonly Occurring MRI Artifacts and How to Overcome Them.

HomeRadioGraphicsVol. 42, No. 3 PreviousNext PhysicsRadioGraphics FundamentalsPrimer on Commonly Occurring MRI Artifacts and How to Overcome ThemChikara Noda, Bharath Ambale Venkatesh, Jennifer D. Wagner, Yoko Kato, Jason M. Ortman, João A. C. Lima Chikara Noda, Bharath Ambale Venkatesh, Jennifer D. Wagner, Yoko Kato, Jason M. Ortman, João A. C. Lima Author AffiliationsFrom the Divisions of Cardiology (C.N., Y.K., J.M.O., J.A.C.L.) and Radiology (B.A.V.), Johns Hopkins University School of Medicine, 600 N Wolfe St, Blalock 524, Baltimore, MD 21287; and Canon Medical Research USA, Cleveland, Ohio (J.D.W.).Address correspondence to J.A.C.L. (e-mail: [email protected]).Chikara NodaBharath Ambale VenkateshJennifer D. WagnerYoko KatoJason M. OrtmanJoão A. C. Lima Published Online:Apr 22 2022https://doi.org/10.1148/rg.210021MoreSectionsFull textPDF ToolsImage ViewerAdd to favoritesCiteTrack CitationsPermissionsReprints ShareShare onFacebookTwitterLinked In AbstractVarious artifacts occur at MRI, and MRI technologists and radiologists must know how to identify and avoid these artifacts so they can consistently produce high-quality images.Suggested Readings Hirokawa Y, Isoda H, Maetani YS, Arizono S, Shimada K, Togashi K. MRI artifact reduction and quality improvement in the upper abdomen with PROPELLER and prospective acquisition correction (PACE) technique. AJR Am J Roentgenol 2008;191(4):1154–1158. Crossref, Medline, Google Scholar Huang SY, Seethamraju RT, Patel P, Hahn PF, Kirsch JE, Guimaraes AR. Body MR Imaging: Artifacts, k-Space, and Solutions. RadioGraphics 2015;35(5):1439–1460. Link, Google Scholar Runge M, Ibrahim EH, Bogun F, et al. Metal Artifact Reduction in Cardiovascular MRI for Accurate Myocardial Scar Assessment in Patients With Cardiac Implantable Electronic Devices. AJR Am J Roentgenol 2019;213(3):555–561. Crossref, Medline, Google Scholar Stadler A, Schima W, Ba-Ssalamah A, Kettenbach J, Eisenhuber E. Artifacts in body MR imaging: their appearance and how to eliminate them. Eur Radiol 2007;17(5):1242–1255. Crossref, Medline, Google Scholar Tsuchihashi T. Artifact of MRI [in Japanese]. Nippon Hoshasen Gijutsu Gakkai Zasshi 2003;59(11):1370–1377. Crossref, Medline, Google ScholarArticle HistoryReceived: Feb 1 2021Revision requested: Apr 20 2021Revision received: June 29 2021Accepted: July 9 2021Published online: Apr 22 2022Published in print: May 2022 FiguresReferencesRelatedDetailsCited ByPostsurgical Evaluation of the Pediatric Foot and AnkleMaria PilarAparisi Gómez, AlbertoBazzocchi, PaoloSimoni, Emilio J.Inarejos Clemente2022 | Seminars in Musculoskeletal Radiology, Vol. 26, No. 06Accompanying This ArticlePrimer on Commonly Occurring MRI Artifacts and How to Overcome ThemApr 22 2022Default Digital Object SeriesRecommended Articles Respiratory Motion Management in Abdominal MRI: Radiology In TrainingRadiology2022Volume: 306Issue: 1pp. 47-53Invited Commentary on “Optimizing Diffusion-Tensor Imaging Acquisition for Spinal Cord Assessment,” with Response from Dr Martín Noguerol et alRadioGraphics2020Volume: 40Issue: 2pp. 428-431Impact of Data-driven Respiratory Gating in Clinical PETRadiology2016Volume: 281Issue: 1pp. 229-238Validation of Software Gating: A Practical Technology for Respiratory Motion Correction in PETRadiology2016Volume: 281Issue: 1pp. 239-248MR Neurography of Peripheral Nerve Injury in the Presence of Orthopedic Hardware: Technical ConsiderationsRadiology2021Volume: 300Issue: 2pp. 246-259See More RSNA Education Exhibits A Primer on Commonly Occurring MRI Artifacts and How to Overcome ThemDigital Posters2020Up-to-Date Technique for Improvement of CT and MRI Imaging Quality in the Head and Neck: Theory, Clinical ApplicationsDigital Posters2019Pulse Sequences Used in Musculoskeletal MRI Exams: A Review for Residents and FellowsDigital Posters2018 RSNA Case Collection Orbital blowout fractureRSNA Case Collection2020Metastatic invasive lobular breast carcinomaRSNA Case Collection2021Pulmonary SequestrationRSNA Case Collection2022 Vol. 42, No. 3 Slide PresentationMetrics Altmetric Score PDF download

Comparison of free breathing and respiratory triggered diffusion-weighted imaging sequences for liver imaging.

BACKGROUNDDiffusion-weighted imaging (DWI) has become a useful tool in the detection, characterization, and evaluation of response to treatment of many cancers, including malignant liver lesions. DWI offers higher image contrast between lesions and normal liver tissue than other sequences. DWI images acquired at two or more b-values can be used to derive an apparent diffusion coefficient (ADC). DWI in the body has several technical challenges. This include ghosting artifacts, mis-registration and susceptibility artifacts. New DWI sequences have been developed to overcome some of these challenges. Our goal is to evaluate 3 new DWI sequences for liver imaging.AIMTo qualitatively and quantitatively compare 3 DWI sequences for liver imaging: free-breathing (FB), simultaneous multislice (SMS), and prospective acquisition correction (PACE).METHODSMagnetic resonance imaging (MRI) was performed in 20 patients in this prospective study. The MR study included 3 separate DWI sequences: FB-DWI, SMS-DWI, and PACE-DWI. The image quality, mean ADC, standard deviations (SD) of ADC, and ADC histogram were compared. Wilcoxon signed-rank tests were used to compare qualitative image quality. A linear mixed model was used to compare the mean ADC and the SDs of the ADC values. All tests were 2-sided and P values of < 0.05 were considered statistically significant.RESULTSThere were 56 lesions (50 malignant) evaluated in this study. The mean qualitative image quality score of PACE-DWI was 4.48. This was significantly better than that of SMS-DWI (4.22) and FB-DWI (3.15) (P < 0.05). Quantitatively, the mean ADC values from the 3 different sequences did not significantly differ for each liver lesion. FB-DWI had a markedly higher variation in the SD of the ADC values than did SMS-DWI and PACE-DWI. We found statistically significant differences in the SDs of the ADC values for FB-DWI vs PACE-DWI (P < 0.0001) and for FB-DWI vs SMS-DWI (P = 0.03). The SD of the ADC values was not statistically significant for PACE-DWI and SMS-DWI (P = 0.18). The quality of the PACE-DWI ADC histograms were considered better than the SMS-DWI and FB-DWI.CONCLUSIONCompared to FB-DWI, both PACE-DWI and SMS-DWI provide better image quality and decreased quantitative variability in the measurement of ADC values of liver lesions.

Combining Prospective Acquisition CorrEction (PACE) with retrospective correction to reduce motion artifacts in resting state fMRI data.

BackgroundHead movement in the scanner causes spurious signal changes in the blood‐oxygen‐level‐dependent (BOLD) signal, confounding resting state functional connectivity (RSFC) estimates obtained from functional magnetic resonance imaging (fMRI). We examined the effectiveness of Prospective Acquisition CorrEction (PACE) in reducing motion artifacts in BOLD data.MethodsUsing PACE‐corrected RS‐fMRI data obtained from 44 subjects and subdividing them into low‐ and high‐motion cohorts, we investigated voxel‐wise motion‐BOLD relationships, the distance‐dependent functional connectivity artifact and the correlation between head motion and connectivity metrics such as posterior cingulate seed‐based connectivity and network degree centrality.ResultsOur results indicate that, when PACE is used in combination with standard retrospective motion correction strategies, it provides two principal advantages over conventional echo‐planar imaging (EPI) RS‐fMRI data: (a) PACE was effective in eliminating significant negative motion‐BOLD relationships, shown to be associated with signal dropouts caused by head motion, and (b) Censoring with a lower threshold (framewise displacement >0.5 mm) and a smaller window around the motion corrupted time point provided qualitatively equivalent reductions in the motion artifact with PACE when compared to a more conservative threshold of 0.2 mm required with conventional EPI data.ConclusionsPACE when used in conjunction with retrospective motion correction methods including nuisance signal and motion parameter regression, and censoring, did prove effective in almost eliminating head motion artifacts, even with a lower censoring threshold. Use of a lower censoring threshold could provide substantial savings in data that would otherwise be lost to censoring. Three‐dimensional PACE has negligible overhead in terms of scan time, sequence modifications or additional and hence presents an attractive option for head motion correction in high‐throughput resting‐state BOLD imaging.

Evaluation of incidence of acute transient dyspnea and related artifacts after administration of gadoxetate disodium: a prospective observational study.

To evaluate motion artifacts, breath-hold failure, acute transient dyspnea, and clinical parameters during hepatic arterial phase of gadoxetate disodium-enhanced magnetic resonance (MR) imaging. This was an institutional review board-approved observational prospective study (written informed consent acquired) performed in 250 consecutive patients, who underwent liver MR with a multiarterial phase technique. Oxygen saturation (SatO2) and heart rate (HR) were monitored, while patients reported subjective symptoms. Breath-holds were assessed using prospective acquisition correction technique (PACE) monitors. Three readers independently analyzed all images to establish the presence of motion artifacts. Nonparametric statistical testing and Fleiss' kappa were used. No statistical differences in SatO2 and HR values were observed during the entire length of MR examination. The PACE graphs showed an altered breath-hold in 16/250 patients (6.4%), however only 6 patients self-reported symptoms during the procedure, and among these 6 subjects, only 2 suffered from acute transient dyspnea (0.8%). Motion-related artifacts increased mostly in the third arterial phase of gadoxetate disodium acquisition (p < 0.0001): The artifacts incidence was 2.9% in the first phase; 4.0% in the second; and 19.5% in the third. This increase was mainly due to patients' inability to hold their breath for the entire duration of the examination. However, at least one gadoxetate disodium arterial phase without motion artifacts and adequate for acquisition timing, was acquired in all MR examinations. The incidence of breath-hold failure and acute transient dyspnea after gadoxetate disodium administration increased during the third arterial phase only. Our protocol allowed the acquisition of at least one arterial phase not compromised by motion artifacts and adequate for acquisition timing, in all patients.

Non-small cell lung cancer: Whole-lesion histogram analysis of the apparent diffusion coefficient for assessment of tumor grade, lymphovascular invasion and pleural invasion.

PurposeInvestigating the diagnostic accuracy of histogram analyses of apparent diffusion coefficient (ADC) values for determining non-small cell lung cancer (NSCLC) tumor grades, lymphovascular invasion, and pleural invasion.Materials and methodsWe studied 60 surgically diagnosed NSCLC patients. Diffusion-weighted imaging (DWI) was performed in the axial plane using a navigator-triggered single-shot, echo-planar imaging sequence with prospective acquisition correction. The ADC maps were generated, and we placed a volume-of-interest on the tumor to construct the whole-lesion histogram. Using the histogram, we calculated the mean, 5th, 10th, 25th, 50th, 75th, 90th, and 95th percentiles of ADC, skewness, and kurtosis. Histogram parameters were correlated with tumor grade, lymphovascular invasion, and pleural invasion. We performed a receiver operating characteristics (ROC) analysis to assess the diagnostic performance of histogram parameters for distinguishing different pathologic features.ResultsThe ADC mean, 10th, 25th, 50th, 75th, 90th, and 95th percentiles showed significant differences among the tumor grades. The ADC mean, 25th, 50th, 75th, 90th, and 95th percentiles were significant histogram parameters between high- and low-grade tumors. The ROC analysis between high- and low-grade tumors showed that the 95th percentile ADC achieved the highest area under curve (AUC) at 0.74. Lymphovascular invasion was associated with the ADC mean, 50th, 75th, 90th, and 95th percentiles, skewness, and kurtosis. Kurtosis achieved the highest AUC at 0.809. Pleural invasion was only associated with skewness, with the AUC of 0.648.ConclusionsADC histogram analyses on the basis of the entire tumor volume are able to stratify NSCLCs' tumor grade, lymphovascular invasion and pleural invasion.

A robust method for suppressing motion-induced coil sensitivity variations during prospective correction of head motion in fMRI

Prospective motion correction is a promising candidate solution to suppress the effects of head motion during fMRI, ideally allowing the imaging plane to remain fixed with respect to the moving head. Residual signal artifacts may remain, however, because head motion in relation to a fixed multi-channel receiver coil (with non-uniform sensitivity maps) can potentially introduce unwanted signal variations comparable to the weak fMRI BOLD signal (~1%–4% at 1.5–3.0T). The present work aimed to investigate the magnitude of these residual artifacts, and characterize the regime over which prospective motion correction benefits from adjusting sensitivity maps to reflect relative positional change between the head and the coil. Numerical simulations were used to inform human fMRI experiments. The simulations indicated that for axial imaging within a commonly used 12-channel head coil, 5° of head rotation in-plane produced artifact signal changes of ~3%. Subsequently, six young adults were imaged with and without overt head motions of approximately this extent, with and without prospective motion correction using the Prospective Acquisition CorrEction (PACE) method, and with and without sensitivity map adjustments. Sensitivity map adjustments combined with PACE strongly protected against the artifacts of interest, as indicated by comparing three metrics of data quality (number of activated voxels, Dice coefficient of activation overlap, temporal standard deviation of baseline fMRI timeseries data) across the different experimental conditions. It is concluded that head motion in relation to a fixed multi-channel coil can adversely affect fMRI with prospective motion correction, and that sensitivity map adjustment can mitigate this effect at 3.0T.

SimPACE: Generating simulated motion corrupted BOLD data with synthetic-navigated acquisition for the development and evaluation of SLOMOCO: A new, highly effective slicewise motion correction

Head motion in functional MRI and resting-state MRI is a major problem. Existing methods do not robustly reflect the true level of motion artifact for in vivo fMRI data. The primary issue is that current methods assume that motion is synchronized to the volume acquisition and thus ignore intra-volume motion. This manuscript covers three sections in the use of gold-standard motion-corrupted data to pursue an intra-volume motion correction. First, we present a way to get motion corrupted data with accurately known motion at the slice acquisition level. This technique simulates important data acquisition-related motion artifacts while acquiring real BOLD MRI data. It is based on a novel motion-injection pulse sequence that introduces known motion independently for every slice: Simulated Prospective Acquisition CorrEction (SimPACE). Secondly, with data acquired using SimPACE, we evaluate several motion correction and characterization techniques, including several commonly used BOLD signal- and motion parameter-based metrics. Finally, we introduce and evaluate a novel, slice-based motion correction technique. Our novel method, SLice-Oriented MOtion COrrection (SLOMOCO) performs better than the volumetric methods and, moreover, accurately detects the motion of independent slices, in this case equivalent to the known injected motion. We demonstrate that SLOMOCO can model and correct for nearly all effects of motion in BOLD data. Also, none of the commonly used motion metrics was observed to robustly identify motion corrupted events, especially in the most realistic scenario of sudden head movement. For some popular metrics, performance was poor even when using the ideal known slice motion instead of volumetric parameters. This has negative implications for methods relying on these metrics, such as recently proposed motion correction methods such as data censoring and global signal regression.

Diffusion-weighted imaging in assessing renal pathology of chronic kidney disease: A preliminary clinical study

ObjectiveTo investigate the clinical potential of diffusion-weighted imaging (DWI) in assessing renal pathology of chronic kidney disease (CKD). MethodsSeventy-one CKD patients and twelve healthy volunteers were examined using DWI with prospective acquisition correction. Renal biopsy specimens from the CKD patients were scored based on the severity of renal pathology and to confirm pathology type. CKD patients were divided into three groups according to pathology scores: mild, moderate, or severe. The association between renal apparent diffusion coefficient (ADC) values and pathology scores was investigated using Pearson's correlation and single factor analysis of variance. Multiple linear regression analysis was performed to explore associations between renal ADC values and pathology score, glomerular filtration rate, serum creatinine, and age. The Kruskal–Wallis H test was conducted to compare ADC values and pathology type. ResultsRenal ADC values correlated negatively with pathology scores (r=−0.633, P<0.001). The ADC values among the four groups (mild, moderate, severe impairment, and controls) were significantly different (F=19.512, P<0.001). However, when patients were stratified by pathology type, no significant differences were found in ADC values among these groups (χ2=9.929, P=0.270). Further multiple linear regression analysis showed that only the pathology score and ADC values were related (t=−4.586, P=0.000). ConclusionsDWI has clinical potential in assessing the severity of renal pathology in CKD and shows promise as a non-invasive and effective technique to guide therapy and follow-up.

Preoperative evaluation of the cystic duct for laparoscopic cholecystectomy: comparison of navigator-gated prospective acquisition correction- and conventional respiratory-triggered techniques at free-breathing 3D MR cholangiopancreatography

To evaluate the quality of magnetic resonance cholangiopancreatography (MRCP) images obtained with a three-dimensional navigator-gated (NG) technique and compare findings with conventional respiratory-triggered (RT) images in pre-laparoscopic cholecystectomy patients. Turbo-spin-echo (TSE) RT-MRCP (average 242 s) and balanced turbo-field-echo (bTFE) NG-MRCP (average 263 s) were acquired at 1.5-T MRI for 49 pre-laparoscopic cholecystectomy patients. Two radiologists independently assessed image quality, visibility of anatomical structures, common bile duct (CBD) stones, and signal-to-noise ratios (SNRs). Interobserver agreement was also evaluated. The anatomical details of the cystic duct were clearly demonstrated in 33 (67.3 %, reader A) and 35 (71.4 %, reader B) patients on RT-MRCP, and in 45 (91.8 %) and 44 (89.7 %) patients on NG-MRCP. On NG-MRCP, visualisation of the cystic duct (3.22/3.12), its origin (3.57/3.55), and the gallbladder(3.61/3.59) was statistically better than on RT-MRCP (2.90/2.78, 3.29/3.12, 2.98/2.88, respectively). The overall image quality was statistically better on NG-MRCP than RT-MRCP. Each technique identified the presence of CBD stones in all affected patients. The SNR was significantly higher on NG-MRCP (CHD 22.40, gallbladder 17.13) than RT-MRCP (CHD 17.05, gallbladder 9.30). Interobserver agreement was fair to perfect. Navigator-gated MRCP is more useful than respiratory-triggered MRCP for evaluating the gallbladder and cystic duct in patients scheduled for laparoscopic cholecystectomy. • Magnetic resonance cholangiopancreatography (MRCP) provides important cystic duct information before laparoscopic cholecystectomy. • Navigator-gated (NG) MRCP images were better than conventional respiratory-triggered (RT) MRCP. • The signal-to-noise ratio was significantly higher for NG-MRCP than for conventional RT-MRCP. • Balanced turbo-field-echo NG-MRCP is useful for evaluating the gallbladder and cystic duct.

Diffusion-Weighted MRI in the Assessment of Split Renal Function: Comparison of Navigator-Triggered Prospective Acquisition Correction and Breath-Hold Acquisition

The purpose of this study was to ascertain whether prospective acquisition correction (PACE) diffusion-weighted MRI (DWI) is superior to conventional breath-hold DWI in assessment of split renal function. Fifty-four subjects underwent coronal breath-hold DWI and PACE DWI with the b value set at 0 and 800 s/mm(2). Isotope renographic glomerular filtration rate (GFR) was used as the reference standard for assessing split renal function. A GFR of 40 mL/min or greater indicated normal and a GFR less than 40 mL/min indicated reduced split renal function. Reduced split renal function was further divided into a mild reduction group (GFR ≥ 20 mL/min) and a moderate-to-severe reduction group (GFR < 20 mL/min). Various comparisons between the imaging methods were conducted. The signal-to-noise and contrast-to-noise ratios of the PACE DW images were greater than those of the breath-hold DW images (p < 0.001). The correlation between the apparent diffusion coefficient (ADC) value and GFR was stronger when the ADC was measured with PACE DWI than with breath-hold DWI (p = 0.033). Area under the receiver operator curve (AUC) analysis revealed that PACE DWI (AUC, 0.790 ± 0.045; p < 0.001) but not breath-hold DWI (AUC, 0.616 ± 0.060; p = 0.053) had diagnostic value in predicting a reduction in split renal function. ADC value assessed with PACE DWI was lower in the groups with mild and moderate-to-severe reduction in split renal function than in the group with normal function (p < 0.01). Preliminary results imply that PACE DWI is superior to breath-hold DWI in the assessment of split renal function.

Resting state functional connectivity in autism spectrum disorders: an fMRI study

2. Muller RA, Shih P, Keehn B, Deyoe JR, Leyden KM, Shukla DK. Underconnected, but how? A survey of functional connectivity MRI studies in autism spectrum disorders. Cereb Cortex. 2011 Oct;21(10):2233-43. 3. Just MA, Cherkassky VL, Keller TA, Kana RK, Minshew NJ. Functional and anatomical cortical underconnectivity in autism: evidence from an FMRI study of an executive function task and corpus callosum morphometry. Cereb Cortex 2007;17:951–61. 4. Kleinhans NM, Richards T, Sterling L, Stegbauer KC, Mahurin R, Johnson LC, Greenson J, Dawson G, Aylward E. Abnormal functional connectivity in autism spectrum disorders during face processing. Brain 2008;131:1000–12. 5. Raichle ME, MacLeod AM, Snyder AZ, Powers WJ, Gusnard DA, Shulman GL. 2001. A default mode of brain function. Proc. Natl. Acad. Sci. USA 98:676–82 6. Weng SJ, Wiggins JL, Peltier SJ, Carrasco M, Risi S, Lord C, Monk CS. Alterations of resting state functional connectivity in the default network in adolescents with autism spectrum disorders. Brain Res. 2010 Feb 8;1313:202-14. 7. Monk CS, Peltier SJ, Wiggins JL, Weng SJ, Carrasco M, Risi S, Lord C. Abnormalities of intrinsic functional connectivity in autism spectrum disorders. Neuroimage 2009;47:764–772. 8. Dalton KM, BM Nacewicz, T Johnstone, HS Schaefer, MA Gernsbacher, HH Goldsmith, AL Alexander, and RJ Davidson. Gaze fixation and the neural circuitry of face processing in autism. Nat Neurosci; 2005. 8(4): p. 519-26 9. Wechsler D, Wechsler Abbreviated Scale of Intelligence (WASI). 4th ed. 1999, San Antonio, Tx: The Psychological Corporation. 10. Thesen, S., O. Heid, E. Mueller, and L.R. Schad, Prospective acquisition correction for head motion with image-based tracking for real-time fMRI. Magn Reson Med, 2000. 44(3): p. 457-65. 11. Behzadi, Y., Restom, K., Liau, J. and Liu, T.T. (2007) A component based noise correction method (CompCor) for BOLD and perfusion based fMRI. NeuroImage, 37: 90-101. Resting State Functional Connectivity in Autism Spectrum Disorders: An fMRI Study!

Volumetric navigators for real‐time motion correction in diffusion tensor imaging

Prospective motion correction methods using an optical system, diffusion-weighted prospective acquisition correction, or a free induction decay navigator have recently been applied to correct for motion in diffusion tensor imaging. These methods have some limitations and drawbacks. This article describes a novel technique using a three-dimensional-echo planar imaging navigator, of which the contrast is independent of the b-value, to perform prospective motion correction in diffusion weighted images, without having to reacquire volumes during which motion occurred, unless motion exceeded some preset thresholds. Water phantom and human brain data were acquired using the standard and navigated diffusion sequences, and the mean and whole brain histogram of the fractional anisotropy and mean diffusivity were analyzed. Our results show that adding the navigator does not influence the diffusion sequence. With head motion, the whole brain histogram-fractional anisotropy shows a shift toward lower anisotropy with a significant decrease in both the mean fractional anisotropy and the fractional anisotropy histogram peak location (P<0.01), whereas the whole brain histogram-mean diffusivity shows a shift toward higher diffusivity with a significant increase in the mean diffusivity (P<0.01), even after retrospective motion correction. These changes in the mean and the shape of the histograms are recovered substantially in the prospective motion corrected data acquired using the navigated sequence.

Clinical usefulness of free-breathing navigator-triggered 3D MRCP in non-cooperative patients: Comparison with conventional breath-hold 2D MRCP

To assess the clinical usefulness of free-breathing 3D MRCP in non-cooperative patients compared conventional breath-hold 2D MRCP. We performed FB navigator-triggered 3D MRCP using prospective acquisition correction and BH 2D MRCP in 48 consecutive, non-cooperative patients among 772 patients. Thirteen patients had malignant obstruction. Two radiologists independently graded the likelihood of a malignant obstruction, the overall image quality, and the visibility of ten, individual anatomic segments of both the biliary and pancreatic duct in each sequence. The area under the ROC curve and the repeated measures analyses of variance with multiple comparisons were used for the comparison. The κ statistics were used for interobserver agreement. The diagnostic performance for detecting malignancy was significantly higher on FB MRCP (A(z)=0.962) than on either BH SS-RARE (A(z)=0.820, P<0.0185) or MS-HASTE MRCP (A(z)=0.816, P<0.0067). Interobserver agreement was excellent for FB MRCP (κ=0.889) and fair for both BH SS-RARE (κ=0.578) and MS-HASTE MRCP (κ=0.49). FB MRCP had a significantly higher technical quality than BH MRCP (P<0.001). FB MRCP was seen to have statistically better visibility of peripheral IHD, right main IHD, CHD, cystic duct, and CBD than BH MRCP (P<0.001). FB MRCP and BH SS-RARE MRCP had statistically better visibility of both the left main IHD and pancreatic duct than did BH MS-HASTE MRCP (P<0.001). FB 3D MRCP is useful for non-cooperative patients in whom conventional BH 2D methods cannot be used successfully.

Single-camera motion measurement and monitoring for magnetic resonance applications

An optically based rigid-body six-degrees of freedom (DOF) measurement system optimized for prospective (real-time) motion correction in magnetic resonance imaging (MRI) applications is described. By optimizing system capabilities to the specific applications requirements, the six-DOF measurement is accomplished using a single camera and simple three-disc fiducial at rates of 50 Hz. The algorithm utilizes successive approximation to solve the three point pose problem for angles close to the origin. Convergence to submicroradian levels occurs within 20 iterations for angles in an approximate half-radian (29°) arc centered on the origin. The overall absolute accuracy of the instrument is 10-100 μm for translational and <100 μrad (0.005°) for rotational motions. Results for head nodding and speech tasks are presented for subjects in the MR scanner, and the instrument results are compared to standard prospective acquisition correction.

Diffusion imaging with prospective motion correction and reacquisition.

A major source of artifacts in diffusion-weighted imaging is subject motion. Slow bulk subject motion causes misalignment of data when more than one average or diffusion gradient direction is acquired. Fast bulk subject motion can cause signal dropout artifacts in diffusion-weighted images and results in erroneous derived maps, e.g., fractional anisotropy maps. To address both types of artifacts, a fully automatic method is presented that combines prospective motion correction with a reacquisition scheme. Motion correction is based on the prospective acquisition correction method modified to work with diffusion-weighted data. The images to reacquire are determined automatically during the acquisition from the imaging data, i.e., no extra reference scan, navigators, or external devices are necessary. The number of reacquired images, i.e., the additional scan duration can be adjusted freely. Diffusion-weighted prospective acquisition correction corrects slow bulk motion well and reduces misalignment artifacts like image blurring. Mean absolute residual values for translation and rotation were <0.6 mm and 0.5°. Reacquisition of images affected by signal dropout artifacts results in diffusion maps and fiber tracking free of artifacts. The presented method allows the reduction of two types of common motion related artifacts at the cost of slightly increased acquisition time.

Depiction of the thoracic duct by magnetic resonance imaging: comparison between magnetic resonance imaging and the anatomical literature

The aim of this study was to compare thoracic duct (TD) configuration depicted by magnetic resonance imaging (MRI) with TD configuration described in the anatomical literature. MRI Scans were acquired with a three-dimensional T2-weighted turbo spin echo (TSE) MRI with a two-dimensional prospective acquisition correction (PACE) technique in 63 patients. We found with MRI that TD displacement occurred more on the left side than that reported in the anatomical literature, and this tendency was more marked in elderly patients. In patients with marked leftward TD displacement, the TD configuration on MRI was compared to the descending aortic configuration on chest radiography. The degree of correspondence between the MRI findings and the anatomical literature was assessed by a χ(2) goodness-of-fit test, and P < 0.05 indicated a significant difference. The degree of similarity was determined between TD configuration and aortic configuration by Kendall's coefficient of concordance (W). On MRI scans the TD was often located to the left of the mid-vertebral line compared to the location reported in the anatomical literature (P < 0.001). Nine patients had marked leftward TD displacement, a configuration similar to that of the descending aorta (W = 1); however, no association with age was established. The TD configuration depicted by MRI differed from that described in the anatomical literature.

Improved Detection of Hepatic Metastases From Pancreatic Cancer Using Periodically Rotated Overlapping Parallel Lines With Enhanced Reconstruction (PROPELLER) Technique After SPIO Administration

The purpose of this study was to evaluate the detection of hepatic metastases from the pancreatic cancer using different MR imaging methods, including superparamagnetic iron oxide (SPIO)-enhanced fat-saturated T2-weighted imaging with periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) technique. The institutional review board approved this prospective study. Eighty-two patients (mean age, 55 years) underwent different MR imaging with a 1.5-T scanner. Diagnostic performance with receiver operating characteristics (ROC) curves and sensitivity were evaluated for the following image sets: (A) unenhanced images (T1-weighted in-phase and opposed-phase gradient-echo [GRE] images, and fat-saturated T2-weighted turbo spin-echo [TSE] images) that were included in the subsequent image sets, (B) diffusion-weighted images, (C) SPIO-enhanced fat-saturated T2-weighted TSE images with prospective acquisition correction (PACE), (D) SPIO-enhanced T2*-weighted GRE images, and (E) SPIO-enhanced fat-saturated T2-weighted TSE images acquired with PROPELLER and PACE. The areas under the ROC curves were 0.58 +/- 0.05 (mean +/- standard errors), 0.81 +/- 0.04, 0.70 +/- 0.05, 0.80 +/- 0.04, and 0.90 +/- 0.03, and sensitivity was 0.47, 0.69, 0.56, 0.66, and 0.77 for image sets (A) to (E), respectively, for all lesions. Image set (E) had significantly larger area under the ROC curve for detection of hepatic lesions and higher sensitivity than others. SPIO-enhanced fat-saturated T2-weighted MR imaging with the PROPELLER technique is more effective for detecting hepatic metastases of pancreatic cancer than diffusion-weighted MR imaging, SPIO-enhanced fat-saturated T2WI without the PROPELLER technique, or SPIO-enhanced T2*-weighted GRE imaging.

Diffusion‐weighted imaging of the liver: Comparison of navigator triggered and breathhold acquisitions

To compare a free breathing navigator triggered single shot echoplanar imaging (SS EPI) diffusion-weighted imaging (DWI) sequence with prospective acquisition correction (PACE) with a breathhold (BH) DWI sequence for liver imaging. Thirty-four patients were evaluated with PACE-DWI and BH DWI of the liver using b-values of 0, 50, and 500 s/mm(2). There were 29 focal liver lesions in 18 patients. Qualitative evaluation was performed on a 3-point scale (1-3) by two independent observers (maximum score 9). Quantitative evaluation included estimated SNR (signal to noise ratio), lesion-to-liver contrast ratio, liver and lesion apparent diffusion coefficients (ADCs), and coefficient of variation (CV) of ADC in liver parenchyma and focal liver lesions (estimate of noise contamination in ADC). PACE-DWI showed significantly better image quality, higher SNR and lesion-to-liver contrast ratio when compared with BH DWI. ADCs of liver and focal lesions with both sequences were significantly correlated (r = 0.838 for liver parenchyma, and 0.904 for lesions, P < 0.0001), but lower with the BH sequence (P < 0.02). There was higher noise contamination in ADC measurement obtained with BH DWI (with a significantly higher SD and CV of ADC). The use of a navigator echo to trigger SS EPI DWI improves image quality and liver to lesion contrast, and enables a more precise ADC quantification compared with BH DWI acquisition.

Usefulness of the application of the BLADE technique to reduce motion artifacts on navigation‐triggered prospective acquisition correction (PACE) T2‐weighted MRI (T2WI) of the liver

To evaluate the effects of the application of the BLADE (Siemens, Siemens Medical Systems, Erlangen, Germany) technique, a technique to reduce motion artifacts, on navigator-triggered prospective acquisition correction (PACE) T2-weighted MRI (T2WI) of the liver. Twenty-three consecutive patients with a total of 57 localized hepatic diseases (39 malignant, 18 benign) and 57 patients without hepatic lesion underwent MR study during eupnea. The images were assessed quantitatively by calculating the liver-lesion contrast. Two subjective analyses were also performed. Two observers independently assessed the image quality and the confidence level of the detection and characterization of hepatic nodules using a five-point scale. Statistical analysis was performed with the Wilcoxon matched-pairs test except for the diagnostic performance evaluated with jackknife alternative free-response receiver operating characteristic (JAFROC) analysis. There was no significant difference in the mean liver-lesion contrast between the PACE T2WI with BLADE (T2WI-BLADE) (mean +/- SD = 0.29 +/- 0.14) and that without BLADE (0.30 +/- 0.14) (P = 0.39). Visual assessment of PACE T2WI-BLADE (4.8 +/- 0.47) was superior to that without BLADE (4.3 +/- 0.8) (P < 0.0001), although there were no significant differences in detecting and characterizing hepatic lesions using JAFROC analysis. The BLADE technique could improve image quality by reducing motion artifacts on hepatic MRI without affecting the diagnostic performance.