Scan-rescan Reproducibility Research Articles

Abdominal Aortic Aneurysms with High Thrombus Signal Intensity on Magnetic Resonance Imaging are Associated with High Growth Rate

A layer of intraluminal thrombus is commonly observed in abdominal aortic aneurysms (AAAs). The purpose of this study was to investigate whether AAAs with high thrombus signal intensity (SI) at T1-weighted (T1w) magnetic resonance imaging (MRI) exhibit a faster aneurysm growth rate. This was a prospective follow-up study. Patients with a small AAA underwent MRI examinations at 6 month intervals. Aneurysm thrombus and psoas muscle SI at the point of maximal diameter on T1w images were measured and expressed as a ratio (thrombus SI/muscle SI). Based on these measurements, patients were categorized into three groups: AAA with relative thrombus SI above (group A) and below (group B) the mean relative thrombus SI of 1.20. Patients with AAA without thrombus constituted group C. Eight patients were scanned twice within 2 weeks to investigate scan-rescan reproducibility. Aneurysm growth rates were expressed as the change in maximal cross sectional area (cm(2)). A total of 35 patients (m/f: 26/9; age 72 ± 7 years; AAA maximal diameter 4.9 ± 0.5 cm) were included. Mean aneurysm growth rate for patients in group A (n = 11, 1.87 cm(2)/0.5 year) was two-fold higher than group B (n = 17, 0.78 cm(2)/0.5 year, p = .005) and eight-fold higher than group C (n = 7, 0.23 cm(2)/0.5 years, p = .004) at 6 months' follow-up. At 12 months' follow-up, the mean aneurysm growth rate remained significantly higher in group A (n = 7, 3.03 cm(2)/year) than groups B (n = 10, 1.63 cm(2)/year, p = .03) and C (n = 7, 0.73 cm(2)/year, p = .004). The reproducibility for thrombus SI measurements was found to be high with a coefficient of variation of 6.2%. Aneurysm maximal cross-sectional area at baseline was not significantly different for the three groups. Abdominal aortic aneurysms with high thrombus SI on T1w MR images are associated with higher aneurysm growth rates.

Multi-contrast multi-atlas parcellation of diffusion tensor imaging of the human brain.

In this paper, we propose a novel method for parcellating the human brain into 193 anatomical structures based on diffusion tensor images (DTIs). This was accomplished in the setting of multi-contrast diffeomorphic likelihood fusion using multiple DTI atlases. DTI images are modeled as high dimensional fields, with each voxel exhibiting a vector valued feature comprising of mean diffusivity (MD), fractional anisotropy (FA), and fiber angle. For each structure, the probability distribution of each element in the feature vector is modeled as a mixture of Gaussians, the parameters of which are estimated from the labeled atlases. The structure-specific feature vector is then used to parcellate the test image. For each atlas, a likelihood is iteratively computed based on the structure-specific vector feature. The likelihoods from multiple atlases are then fused. The updating and fusing of the likelihoods is achieved based on the expectation-maximization (EM) algorithm for maximum a posteriori (MAP) estimation problems. We first demonstrate the performance of the algorithm by examining the parcellation accuracy of 18 structures from 25 subjects with a varying degree of structural abnormality. Dice values ranging 0.8–0.9 were obtained. In addition, strong correlation was found between the volume size of the automated and the manual parcellation. Then, we present scan-rescan reproducibility based on another dataset of 16 DTI images – an average of 3.73%, 1.91%, and 1.79% for volume, mean FA, and mean MD respectively. Finally, the range of anatomical variability in the normal population was quantified for each structure.

RV work efficiency is greatly reduced in patients with pulmonary arterial hypertension as evidenced by 4D flow cardiac MRI

Background The dynamic assessment of intracardiac flow remained challenging until the recent development of timeresolved 3D phase-contrast CMR (PC-CMR), which allows for assessment of multi-dimensional whole heart and great vessel flow. Previous studies have used this technique in the ventricles to quantify flow type of the ventricle and the kinetic energy of each flow component. In the great vessels, parameters such as total flow, peak systolic velocity, and wall shear stress have excellent scan-rescan, inter-observer, and intra-observer reproducibility. In disease conditions, pathological vortices have been reported both in the ventricles and great vessels. We propose to use time-resolved 3D PC-CMR to study right ventricular (RV) work in patients with pulmonary arterial hypertension (PAH) as compared to normal subjects.

Reproducibility and accuracy of optic nerve sheath diameter assessment using ultrasound compared to magnetic resonance imaging

BackgroundQuantification of the optic nerve sheath diameter (ONSD) by transbulbar sonography is a promising non-invasive technique for the detection of altered intracranial pressure. In order to establish this method as follow-up tool in diseases with intracranial hyper- or hypotension scan-rescan reproducibility and accuracy need to be systematically investigated.MethodsThe right ONSD of 15 healthy volunteers (mean age 24.5 ± 0.8 years) were measured by both transbulbar sonography (9 – 3 MHz) and 3 Tesla MRI (half-Fourier acquisition single-shot turbo spin-echo sequences, HASTE) 3 and 5 mm behind papilla. All volunteers underwent repeated ultrasound and MRI examinations in order to assess scan-rescan reproducibility and accuracy. Moreover, inter- and intra-observer variabilities were calculated for both techniques.ResultsScan-rescan reproducibility was robust for ONSD quantification by sonography and MRI at both depths (r > 0.75, p ≤ 0.001, mean differences < 2%). Comparing ultrasound- and MRI-derived ONSD values, we found acceptable agreement between both methods for measurements at a depth of 3 mm (r = 0.72, p = 0.002, mean difference < 5%). Further analyses revealed good inter- and intra-observer reliability for sonographic measurements 3 mm behind the papilla and for MRI at 3 and 5 mm (r > 0.82, p < 0.001, mean differences < 5%).ConclusionsSonographic ONSD quantification 3 mm behind the papilla can be performed with good reproducibility, measurement accuracy and observer agreement. Thus, our findings emphasize the feasibility of this technique as a non-invasive bedside tool for longitudinal ONSD measurements.

Abstract 9803: Optimization and Comparison of Myocardial T1 Techniques at 3T in Patients With Aortic Stenosis

BACKGROUND: T1 mapping is an emerging cardiac magnetic resonance imaging technique to assess diffuse myocardial fibrosis. However, the optimal approach remains uncertain, especially at 3T. We sought to optimize and compare the most widely-used techniques. METHODS: T1 mapping was performed at 3T using the modified-look-locker-inversion sequence in 20 healthy volunteers and 20 patients with aortic stenosis (AS). Pre- and post-contrast myocardial T1, the partition coefficient (λ) and interstitial contrast volume of distribution (Vd) were assessed. After establishing the optimal time-point and myocardial region for analysis, we compared the reproducibility of these T1 measures and their ability to differentiate asymptomatic patients with AS from healthy volunteers. RESULTS: There was no segmental variation across the ventricle in any of the T1 measures evaluated. λ and Vd did not vary with time, while post-contrast T1 was relatively constant between 15-30min. Thus, mid-cavity myocardium at 20min was used for subsequent analyses. Vd displayed excellent intra-, inter-observer, and scan-rescan reproducibility (intra-class correlation coefficients (ICC) 1.00, 0.97 and 0.96 respectively), as did λ (ICC 0.99, 0.94, 0.93 respectively). Moreover, Vd and λ were both higher in patients with AS compared to controls (Vd 28.3±1.7 versus 26.0±1.6%, p &lt;0.001; λ 0.46±0.03 versus 0.44±0.03, p =0.02) (Figure 1A). By comparison, scan-rescan reproducibilities for pre- and post-contrast myocardial T1 values were only modest (ICC 0.72 and 0.56) with no differences observed between cases and controls (both p&gt;0.05) (Figure 1B). CONCLUSIONS: We recommend Vd and λ to assess diffuse myocardial fibrosis at 3T based upon their superior reproducibility and ability to identify disease states.

Optimization and comparison of myocardial T1 techniques at 3T in patients with aortic stenosis

AimsTo determine the optimal T1 mapping approach to assess myocardial fibrosis at 3T.Methods and resultsT1 mapping was performed at 3T using the modified look-locker-inversion sequence in 20 healthy volunteers and 20 patients with aortic stenosis (AS). Pre- and post-contrast myocardial T1, the partition coefficient (λ; ΔRmyocardium/ΔRblood, where ΔR = 1/post-contrast T1 − 1/pre-contrast T1), and extracellular volume fraction [ECV; λ (1 − haematocrit)] were assessed. After establishing the optimal time point and myocardial region for analysis, we compared the reproducibility of these T1 measures and their ability to differentiate asymptomatic patients with AS from healthy volunteers. There was no segmental variation across the ventricle in any of the T1 measures evaluated. λ and ECV did not vary with time, while post-contrast T1 was relatively constant between 15 and 30 min. Thus, mid-cavity myocardium at 20 min was used for subsequent analyses. ECV displayed excellent intra-, inter-observer, and scan–rescan reproducibility [intra-class correlation coefficients (ICC) 1.00, 0.97, and 0.96, respectively], as did λ (ICC 0.99, 0.94, 0.93, respectively). Moreover, ECV and λ were both higher in patients with AS compared with controls (ECV 28.3 ± 1.7 vs. 26.0 ± 1.6%, P < 0.001; λ 0.46 ± 0.03 vs. 0.44 ± 0.03, P = 0.02), with the former offering improved differentiation. In comparison, scan–rescan reproducibilities for pre- and post-contrast myocardial T1 were only modest (ICC 0.72 and 0.56) with no differences in values observed between cases and controls (both P> 0.05).ConclusionsECV appears to be the most promising measure of diffuse myocardial fibrosis at 3T based upon its superior reproducibility and ability to differentiate disease from health.

Automated longitudinal intra-subject analysis (ALISA) for diffusion MRI tractography

Fiber tractography (FT), which aims to reconstruct the three-dimensional trajectories of white matter (WM) fibers non-invasively, is one of the most popular approaches for analyzing diffusion tensor imaging (DTI) data given its high inter- and intra-rater reliability and scan-rescan reproducibility. The major disadvantage of manual FT segmentations, unfortunately, is that placing regions-of-interest for tract selection can be very labor-intensive and time-consuming. Although there are several methods that can identify specific WM fiber bundles in an automated way, manual FT segmentations across multiple subjects performed by a trained rater with neuroanatomical expertise are generally assumed to be more accurate. However, for longitudinal DTI analyses it may still be beneficial to automate the FT segmentation across multiple time points, but then for each individual subject separately. Both the inter-subject and intra-subject automation in this situation are intended for subjects without gross pathology. In this work, we propose such an automated longitudinal intra-subject analysis (dubbed ALISA) approach, and assessed whether ALISA could preserve the same level of reliability as obtained with manual FT segmentations. In addition, we compared ALISA with an automated inter-subject analysis. Based on DTI data sets from (i) ten healthy subjects that were scanned five times (six-month intervals, aged 7.6–8.6years at the first scan) and (ii) one control subject that was scanned ten times (weekly intervals, 12.2years at the first scan), we demonstrate that the increased efficiency provided by ALISA does not compromise the high degrees of precision and accuracy that can be achieved with manual FT segmentations. Further automation for inter-subject analyses, however, did not provide similarly accurate FT segmentations.

Suitability of Pharmacokinetic Models for Dynamic Contrast-Enhanced MRI of Abdominal Aortic Aneurysm Vessel Wall: A Comparison

PurposeIncreased microvascularization of the abdominal aortic aneurysm (AAA) vessel wall has been related to AAA progression and rupture. The aim of this study was to compare the suitability of three pharmacokinetic models to describe AAA vessel wall enhancement using dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI).Materials and MethodsPatients with AAA underwent DCE-MRI at 1.5 Tesla. The volume transfer constant (Ktrans), which reflects microvascular flow, permeability and surface area, was calculated by fitting the blood and aneurysm vessel wall gadolinium concentration curves. The relative fit errors, parameter uncertainties and parameter reproducibilities for the Patlak, Tofts and Extended Tofts model were compared to find the most suitable model. Scan-rescan reproducibility was assessed using the interclass correlation coefficient and coefficient of variation (CV). Further, the relationship between Ktrans and AAA size was investigated.ResultsDCE-MRI examinations from thirty-nine patients (mean age±SD: 72±6 years; M/F: 35/4) with an mean AAA maximal diameter of 49±6 mm could be included for pharmacokinetic analysis. Relative fit uncertainties for Ktrans based on the Patlak model (17%) were significantly lower compared to the Tofts (37%) and Extended Tofts model (42%) (p<0.001). Ktrans scan-rescan reproducibility for the Patlak model (ICC = 0.61 and CV = 22%) was comparable with the Tofts (ICC = 0.61, CV = 23%) and Extended Tofts model (ICC = 0.76, CV = 22%). Ktrans was positively correlated with maximal AAA diameter (Spearman’s ρ = 0.38, p = 0.02) using the Patlak model.ConclusionUsing the presented imaging protocol, the Patlak model is most suited to describe DCE-MRI data of the AAA vessel wall with good Ktrans scan-rescan reproducibility.

Reproducibility study of four‐dimensional flow MRI of arterial and portal venous liver hemodynamics: Influence of spatio‐temporal resolution

To evaluate influence of variation in spatio-temporal resolution and scan-rescan reproducibility on three-dimensional (3D) visualization and quantification of arterial and portal venous (PV) liver hemodynamics at four-dimensional (4D) flow MRI. Scan-rescan reproducibility of 3D hemodynamic analysis of the liver was evaluated in 10 healthy volunteers using 4D flow MRI at 3T with three different spatio-temporal resolutions (2.4 × 2.0 × 2.4 mm(3), 61.2 ms; 2.5 × 2.0 × 2.4 mm(3), 81.6 ms; 2.6 × 2.5 × 2.6 mm(3), 80 ms) and thus different total scan times. Qualitative flow analysis used 3D streamlines and time-resolved particle traces. Quantitative evaluation was based on maximum and mean velocities, flow volume, and vessel lumen area in the hepatic arterial and PV systems. 4D flow MRI showed good interobserver variability for assessment of arterial and PV liver hemodynamics. 3D flow visualization revealed limitations for the left intrahepatic PV branch. Lower spatio-temporal resolution resulted in underestimation of arterial velocities (mean 15%, P < 0.05). For the PV system, hemodynamic analyses showed significant differences in the velocities for intrahepatic portal vein vessels (P < 0.05). Scan-rescan reproducibility was good except for flow volumes in the arterial system. 4D flow MRI for assessment of liver hemodynamics can be performed with low interobserver variability and good reproducibility. Higher spatio-temporal resolution is necessary for complete assessment of the hepatic blood flow required for clinical applications.

970Optimization of T1 Mapping at 3T in Patients with Aortic Stenosis

Objectives: To assess and to optimize T1 mapping at 3T in healthy subjects and patients with aortic stenosis (AS). Methods: T1 mapping was performed at 3T using the modified look-locker inversion sequence in 20 healthy control subjects and 20 patients with AS (10 with delayed enhancement). Gadobutrol was administered at 0.1 mmol/kg and the following T1 measures were compared at contrast equilibrium: pre- and post-contrast T1 relaxation times; the partition coefficient (λ; ΔRmyocardium/ΔRblood, where ΔR = 1/post-contrast T1 – 1/pre-contrast T1) and the extracellular contrast volume of distribution (Vd; λ x [1-hematocrit]). Results: Contrast equilibrium occurred in regions of myocardial fibrosis by 20 min and this time-point was used for all subsequent analyses. Vd demonstrated excellent measures of intra-observer, inter-observer, and scan-rescan reproducibility (intra-class correlation coefficients (ICC) 1.00, 0.97 and 0.93 respectively), and λ had similar reproducibility (ICC 0.99, 0.94, 0.90 respectively). However, pre- and post-contrast T1 had poorer scan-rescan reproducibility (ICC 0.72 and 0.57 respectively). Vd values were higher in patients with AS compared to control subjects (29.0±2.1 vs. 26.3±1.7%, p < 0.01) and females compared to males (28.6 ± 2.2 vs. 26.6 ± 2.0%, p < 0.01).

Improved MRI quantification of spinal cord atrophy in multiple sclerosis

To identify an improved method for measuring spinal cord cross-sectional area (CSA) using magnetic resonance imaging (MRI) in multiple sclerosis (MS). MRI was performed on 15 controls and 15 MS patients and repeated in nine controls and nine patients after 6 months. At this timepoint, an additional scan was acquired to evaluate scan-rescan reproducibility. Two sequences were acquired in the cervical cord: 3D phase sensitive inversion recovery (PSIR) and 3D magnetization prepared rapid acquisition T1-weighted gradient echo. CSA was outlined at C2-C3 using two methods: a semiautomated edge detection method and active surface model (ASM). We evaluated reproducibility for all combinations of sequences and analysis methods using coefficient of variation (COV) and intraclass correlation coefficient and performed sample size calculations for clinical trials to reduce longitudinal cord atrophy. PSIR/ASM combination provided the lowest values of COV for intrarater, interrater, scan-rescan reproducibility (0.002%, 0.03%, and 0.1% respectively). At 6-month follow-up no significant changes were seen in CSA of controls, and a trend towards significance was observed in patients. PSIR/ASM proved more reproducible than established methods of evaluating CSA in MS and also provides the lowest number of subjects per arm for 6-month and 1-year clinical trials.

Experimentally and computationally fast method for estimation of a mean kurtosis

Results from several recent studies suggest the magnetic resonance diffusion-derived metric mean kurtosis (MK) to be a sensitive marker for tissue pathology; however, lengthy acquisition and postprocessing time hamper further exploration. The purpose of this study is to introduce and evaluate a new MK metric and a rapid protocol for its estimation. The protocol requires acquisition of 13 standard diffusion-weighted images, followed by linear combination of log diffusion signals, thus avoiding nonlinear optimization. The method was evaluated on an ex vivo rat brain and an in vivo human brain. Parameter maps were compared with MK estimated from a standard diffusion kurtosis imaging (DKI) data set comprising 160 diffusion-weighted images. The new MK displays remarkably similar contrast to MK, and the proposed protocol acquires the necessary data in less than 1 min for full human brain coverage, with a postprocessing time of a few seconds. Scan-rescan reproducibility was comparable with MK. The framework offers a robust and rapid method for estimating MK, with a protocol easily adapted on commercial scanners, as it requires only minimal modification of standard diffusion-weighting protocols. These properties make the method feasible in practically any clinical setting.

Effect of Sampling Frequency on Perfusion Values in Perfusion CT of Lung Tumors

The purpose of this study was to assess as a potential means of limiting radiation exposure the effect on perfusion CT values of increasing sampling intervals in lung perfusion CT acquisition. Lung perfusion CT datasets in patients with lung tumors (> 2.5 cm diameter) were analyzed by distributed parameter modeling to yield tumor blood flow, blood volume, mean transit time, and permeability values. Scans were obtained 2-7 days apart with a 16-MDCT scanner without intervening therapy. Linear mixed-model analyses were used to compare perfusion CT values for the reference standard sampling interval of 0.5 second with those of datasets obtained at sampling intervals of 1, 2, and 3 seconds, which included relative shifts to account for uncertainty in preenhancement set points. Scan-rescan reproducibility was assessed by between-visit coefficient of variation. Twenty-four lung perfusion CT datasets in 12 patients were analyzed. With increasing sampling interval, mean and 95% CI blood flow and blood volume values were increasingly overestimated by up to 14% (95% CI, 11-18%) and 8% (95% CI, 5-11%) at the 3-second sampling interval, and mean transit time and permeability values were underestimated by up to 11% (95% CI, 9-13%) and 3% (95% CI, 1-6%) compared with the results in the standard sampling interval of 0.5 second. The differences were significant for blood flow, blood volume, and mean transit time for sampling intervals of 2 and 3 seconds (p ≤ 0.0002) but not for the 1-second sampling interval. The between-visit coefficient of variation increased with subsampling for blood flow (32.9-34.2%), blood volume (27.1-33.5%), and permeability (39.0-42.4%) compared with the values in the 0.5-second sampling interval (21.3%, 23.6%, and 32.2%). Increasing sampling intervals beyond 1 second yields significantly different perfusion CT parameter values compared with the reference standard (up to 18% for 3 seconds of sampling). Scan-rescan reproducibility is also adversely affected.

High field carotid vessel wall imaging: A study on reproducibility

PurposeCurrently, a multi-contrast protocol, including a combination of five MR-sequences is used as reference standard for morphologic imaging and quantitative measurements of the carotid artery vessel wall. The purpose of this study is to investigate the scan–rescan reproducibility together with intra- and inter-observer reproducibility of each of the five MR-sequences. MethodsTwenty healthy volunteers (55% male, mean age=26 years) underwent repeated MR-examinations (3T-Philips-MRI) of the left carotid artery vessel wall with five sequences; T1-TFE, T2-TSE, PD-TSE, T1-TSE and 3D TOF. A standard phased-array coil with two flexible elements of 14cm×17cm was used to obtain nine transverse imaging sections of the left carotid artery with identical in-plane resolution (0.46mm×0.46mm). Reproducibility analysis was performed in 3 slices of the common carotid artery for all sequences. ResultsFor, scan–rescan reproducibility, intra class correlation coefficients (ICC) were excellent for all sequences and ranged from 0.79 to 0.95. The intra-observer ICC ranged from 0.89 to 0.98 and the inter-observer ICC ranged from 0.84 to 0.96, for both lumen and vessel wall assessment. ConclusionsBy high field MR imaging, vessel wall and lumen area of the carotid artery can be assessed with excellent scan–rescan, intra- and inter-observer reproducibility for all five sequences.

Hippocampal Magnetization Transfer Ratio at 3T: Validation of Automated Postprocessing and Comparison of Quantification Metrics

To investigate the reliability of a novel magnetization transfer ratio (MTR) postprocessing technique for the hippocampus using histogram analysis, and compare results to more established volumetric measurements. This study is conducted in healthy volunteers as a precursor to future applications regarding progressive neurologic diseases, such as Alzheimer's disease. Eight healthy subjects were scanned twice with interval of 1 week using quantitative magnetic resonance imaging (MRI). Automated pixel-wise analysis was performed for the hippocampal regions of each patient. Reliability was assessed using intraclass correlation coefficients (ICCs), coefficients of variation (COVs), and instrumental standard deviation (ISD). Reliable metrics were 25th percentile, median, 75th percentile, peak location, and mean approach (ranges: ICC = .93-.96, COV = 2.71-3.88%, ISD .78-1.01). Histogram peak height had ICC below .7, and a COV above 10%. Volumetric measurements had (ICC = .95-.97, COV = 1.43-3.39%). Excellent scan-rescan reproducibility (ICC > .9, COV < 10%) was observed for specific MTR histogram metrics and the mean MTR approach. These results are comparable to the volumetric approach. Future studies can examine the possibility that MTR changes precede morphological changes as this study suggests that both MTR and volumetric measurements of the hippocampus can be used as reliable imaging tools.

Liver T1ρ MRI measurement in healthy human subjects at 3 T: a preliminary study with a two-dimensional fast-field echo sequence.

The aim of this study was to explore the technical feasibility of T(1)ρ MRI for the liver, and to determine the normal range of liver T(1)ρ in healthy subjects at clinical 3 T. There were 15 healthy volunteers. Three representative axial slices were selected to cut through the upper, middle and lower liver. A rotary echo spin-lock pulse was implemented in a two-dimensional fast-field echo sequence. Spin-lock frequency was 500 Hz, and the spin-lock times of 1, 10, 20, 30, 40 and 50 ms were used for T(1)ρ mapping. The images were acquired slice by slice during breath-holding. Regions of interest (ROIs; n=5) were manually placed on each slice of the liver parenchyma region, excluding artefacts and vessels. The mean value of these ROIs (n=15) was regarded as the liver T(1)ρ value for the subject. Six subjects were scanned once at fasting status; six subjects were scanned once 2 h post meal; three subjects were scanned twice at fasting status; and seven subjects were scanned twice 2 h post meal. When two readers measured the same 10 data sets, the interreader reproducibility (ICC: intraclass correlation coefficient) was 0.955. With the 10 subjects scanned twice, the ICC for scan-rescan reproducibility was 0.764. There was no significant difference for the liver T(1)ρ value at the fasting status (43.08±1.41 ms) and post-meal status (42.97±2.38 ms, p=0.867). Pooling together all the 32 scans in this study, the normal liver T(1)ρ value ranged from 38.6 to 48.3 ms (mean 43.0 ms, median 42.6 ms). It is feasible to obtain consistent liver T(1)ρ measurement for human subjects at 3 T.

Experimental Evaluation of Accelerated T1rho Relaxation Quantification in Human Liver Using Limited Spin-Lock Times

ObjectiveIt was reported lately that to obtain consistent liver T1rho measurement, at 3T MRI using six spin-lock times (SLTs), is feasible. In this study, the feasibility of using three or two SLT points to measure liver T1rho relaxation time was explored.Materials and MethodsSeventeen healthy volunteers underwent 36 examinations. Three representative axial slices were selected to cut through the upper, middle, and lower liver. A rotary echo spin-lock pulse was implemented in a 2D fast field echo sequence. Spin-lock frequency was 500 Hz and the spin-lock times of 1, 10, 20, 30, 40, and 50 milliseconds (ms) were used for T1rho mapping. T1rho maps were constructed by using all 6 SLT points, three SLT points of 1, 20, and 50 ms, or two SLTs of 1 and 50 ms, respectively. Intra-class correlation coefficient (ICC) and Bland and Altman plot were used to assess the measurement agreement.ResultsTwo examinations were excluded, due to motion artifact at the SLT of 50 ms. With the remaining 34 examinations, the ICC for 6-SLT vs. 3-SLT T1rho measurements was 0.922, while the ICC for 6-SLT vs. 2-SLT T1rho measurement was 0.756. The Bland and Altman analysis showed a mean difference of 0.19 (95% limits of agreement: -1.34, 1.73) for 6-SLT vs. 3-SLT T1rho measurement, and the mean difference of 0.89 (95% limits of agreement: -1.67, 3.45) for 6-SLT vs. 2-SLT T1rho measurement. The scan re-scan reproducibility ICC (n = 11 subjects) was 0.755, 0.727, and 0.528 for 6-SLT measurement, 3-SLT measurement, and 2-SLT measurement, respectively.ConclusionAdopting 3 SLTs of 1, 20, and 50 ms can be an acceptable alternative for the liver T1rho measurement, while 2 SLTs of 1 and 50 ms do not provide reliable measurement.

A new sulcus-corrected approach for assessing cerebellar volume in spinocerebellar ataxia

Precise volumetry of the cerebellum still remains challenging, due to thin sulci and gyri. We present a new fast and reliable sulcus-corrected approach for quantitative assessment of cerebellar atrophy, evaluated on patients with spinocerebellar ataxia (SCA). Thin-sliced T1-weighted magnetic resonance images (MPRAGE) were acquired in 11 genetically confirmed SCA6 patients and in a group of age-matched control subjects ( n = 14). Post-processing involves a morphological image segmentation pipeline as a basis for a sulcus-corrected cerebellar volume measurement. Cerebellar volumes and intra-rater, inter-rater and scan–rescan reproducibility were quantified. Reliability of the measurements was validated using an anatomical preparation of the cerebellum. Repeatability coefficients (RC: intra-rater/inter-rater/scan–rescan) of the method were 1.07%/1.11%/1.35%. Absolute cerebellar volumes showed good agreement with the actual volume of the anatomical preparation. The cerebellar volume of the SCA 6 was 96.3 ± 12.1 ml (mean ± S.D.), which was significantly lower than the results of the corresponding control groups. The cerebellar volume correlated significantly to clinical dysfunction in SCA6. This is the first study to demonstrate the feasibility of a new sulcus-corrected approach to assess cerebellar volume. In contrast to currently used methods, this new approach may be more sensitive even to small atrophic changes affecting sulcal widening.

HIGH FIELD MR CAROTID VESSEL WALL IMAGING: REPRODUCIBILITY OF FIVE DIFFERENT MR WEIGHTINGS

Magnetic Resonance Imaging (MRI) has emerged as a promising noninvasive imaging modality for the serial assessment of vessel wall thickness in the carotid artery as an early marker of atherosclerosis. For clinical application of this technique, Scan-Rescan reproducibility is paramount. Currently, a multicontrast protocol, including a combination of MR-weightings is used as reference standard for quantitative and morphologic measurements.

Reproducibility of flow and wall shear stress analysis using flow‐sensitive four‐dimensional MRI

To systematically investigate the scan-rescan reproducibility and observer variability of flow-sensitive four-dimensional (4D) MRI in the aorta for the assessment of blood flow and global and segmental wall shear stress. ECG and respiration-synchronized flow-sensitive 4D MRI data (spatio-temporal resolution = 1.7 × 2.0 × 2.2 mm(3) /40.8 ms) were acquired in 12 healthy volunteers. To analyze scan-rescan variability, flow-sensitive 4D MRI was repeated in 10 volunteers during a second visit. Data analysis included calculation of time-resolved and total flow, peak systolic velocity, and regional and global wall shear stress (WSS) in up to 24 analysis planes distributed along the aorta. Scan-rescan, inter-observer, and intra-observer agreement was excellent for the calculation of total flow and peak systolic velocity (mean differences <5% of the average flow parameter). Global WSS demonstrated moderate agreement and increased variability regarding wall shear stress (scan-rescan, inter-observer, and intra-observer agreement; mean differences <10% of the average WSS parameters). The segmental distribution of wall shear stress in the thoracic aorta could reliably be reproduced (r > 0.87; P < 0.001) for different observers and examinations. Flow-sensitive 4D MRI-based analysis of aortic blood flow can be performed with good reproducibility. Robustness of global and regional WSS quantification was limited, but spatio-temporal WSS distributions could reliably be replicated.