47 research outputs found
Application of Laplacian-based Methods to Multi-echo Phase Data for Accurate Susceptibility Mapping
In Susceptibility Mapping (SM) using multi-echo gradient-echo phase data, unwrapping and/or background-Ăeld removal is often performed using Laplacian-based methods.
However, SM pipelines in the literature have applied these methods at diĂerent stages. Here, using simulated and acquired images, we compared the performance of three pipelines that apply Laplacian-based methods at diĂ erent stages. We showed that Laplacian-based methods alter the linearity of the phase over time. We demonstrated that only a processing pipeline that takes this into account, i.e. by Ătting the multi-echo data over time to correctly
estimate a Ăeld map before applying Laplacian-based methods, gives accurate susceptibility values
Investigating the accuracy and precision of TEâdependent versus multiâecho QSM using Laplacianâbased methods at 3 T
Purpose:
Multiâecho gradientârecalled echo acquisitions for QSM enable optimizing the SNR for several tissue types through multiâecho (TE) combination or investigating temporal variations in the susceptibility (potentially reflecting tissue microstructure) by calculating one QSM image at each TE (TEâdependent QSM). In contrast with multiâecho QSM, applying Laplacianâbased methods (LBMs) for phase unwrapping and background field removal to single TEs could introduce nonlinear temporal variations (independent of tissue microstructure) into the measured susceptibility. Here, we aimed to compare the effect of LBMs on the QSM susceptibilities in TEâdependent versus multiâecho QSM.
Methods:
TEâdependent recalled echo data simulated in a numerical head phantom and gradientârecalled echo images acquired at 3 T in 10 healthy volunteers. Several QSM pipelines were tested, including four distinct LBMs: sophisticated harmonic artifact reduction for phase data (SHARP), variableâradius sophisticated harmonic artifact reduction for phase data (VâSHARP), Laplacian boundary value background field removal (LBV), and oneâstep total generalized variation (TGV). Results from distinct pipelines were compared using visual inspection, summary statistics of susceptibility in deep gray matter/white matter/venous regions of interest, and, in the healthy volunteers, regional susceptibility bias analysis and nonparametric tests.
Results:
Multiâecho versus TEâdependent QSM had higher regional accuracy, especially in highâsusceptibility regions and at shorter TEs. Everywhere except in the veins, a processing pipeline incorporating TGV provided the most temporally stable TEâdependent QSM results with an accuracy similar to multiâecho QSM.
Conclusions:
For TEâdependent QSM, carefully choosing LBMs can minimize the introduction of LBMârelated nonlinear temporal susceptibility variations
Investigating the effect of flow compensation and quantitative susceptibility mapping method on the accuracy of venous susceptibility measurement
Quantitative susceptibility mapping (QSM) is a promising non-invasive method for obtaining information relating to oxygen metabolism. However, the optimal acquisition sequence and QSM reconstruction method for reliable venous susceptibility measurements are unknown. Full flow compensation is generally recommended to correct for the influence of venous blood flow, although the effect of flow compensation on the accuracy of venous susceptibility values has not been systematically evaluated. In this study, we investigated the effect of different acquisition sequences, including different flow compensation schemes, and different QSM reconstruction methods on venous susceptibilities.
Ten healthy subjects were scanned with five or six distinct QSM sequence designs using monopolar readout gradients and different flow compensation schemes. All data sets were processed using six different QSM pipelines and venous blood susceptibility was evaluated in whole-brain segmentations of the venous vasculature and single veins. The quality of vein segmentations and the accuracy of venous susceptibility values were analyzed and compared between all combinations of sequences and reconstruction methods.
The influence of the QSM reconstruction method on average venous susceptibility values was found to be 2.7â11.6 times greater than the influence of the acquisition sequence, including flow compensation. The majority of the investigated QSM reconstruction methods tended to underestimate venous susceptibility values in the vein segmentations that were obtained.
In summary, we found that multi-echo gradient-echo acquisition sequences without full flow compensation yielded venous susceptibility values comparable to sequences with full flow compensation. However, the QSM reconstruction method had a great influence on susceptibility values and thus needs to be selected carefully for accurate venous QSM
Evaluating the Accuracy of Susceptibility Maps Calculated from Single-echo versus Multi-echo Gradient-echo Acquisitions
For Susceptibility Mapping (SM), Laplacian-based methods (LBMs) can be used on single- or multi-echo gradient echo phase data. Previous studies have shown the advantage of using multi-echo versus single-echo data for noise reduction in susceptibility-weighted images and simulated data. Here, using simulated and acquired images, we compared the performance of two SM pipelines that used multi- or single-echo phase data and LBMs. We showed that the pipeline that fits the multi-echo data over time first and then applies LBMs gives more accurate local fields and $\chi$ maps than the pipelines that apply LBMs to single-echo phase data
Quantitative Susceptibility Mapping (QSM) is Sensitive to Hippocampal and Subcortical Gray Matter Changes in Temporal Lobe Epilepsy
Although temporal lobe epilepsy (TLE) results in widespread changes in MRI measures of tissue volume, diffusion and functional connectivity, changes in tissue composition in TLE have not been investigated with MRI. Quantitative susceptibility mapping (QSM) is sensitive to changes in tissue composition, in particular to iron and myelin. Here, we show for the first time that QSM is sensitive to gray matter abnormalities in 31patients with temporal lobe epilepsy (TLE) compared to 23 healthy controls, and showed significant susceptibility changes in the hippocampus in left TLE patients, and in the bilateral thalamus in both left and right TLE
Intra-abdominal Adiposity In Preterm Infants: An Explorative Study
Objective: The aim of the present study was to compare the total body fat mass and the intra-abdominal adipose tissue between preterm infants assessed at term corrected age and full-term newborns. Methods: An observational explorative study was conducted. 25 preterm and 10 full term infants were evaluated at 0-1 month of corrected and postnatal age, respectively. The total body fat mass was assessed by means of an air displacement plethysmography system (Pea Pod COSMED, USA) and the intra-abdominal adipose tissue by means of magnetic resonance imaging (software program SliceOMatic, Version 4.3,Tomovision, Canada). Results: Total body fat mass (g) of preterm and term infants was 633 (±183) and 538 (±203) respectively while intra-abdominal fat mass (g) was 14.2 (±4.9) and 19.9 (±11.4). Conclusions: Preterm infants, although exhibiting a total body fat mass higher than full term infants, do not show an increased intra-abdominal adipose tissue
A radiological visual scale to predict the potentially recruitable lung in ALI/ARDS patients
Introduction In ALI/ARDS patients the amount of potentially
recruitable lung is extremely variable and it is poorly predictable by
the changes of oxygenation, carbon dioxide or compliance during a
PEEP trial [1]. At the present time the gold standard to compute the
lung recruitability is the quantitative lung CT scan, in which each lung image, after being manually drawn, is analyzed by dedicated software.
However, this is both a laborious and time-consuming technique. The
aim of this study was to evaluate the ability of a visual radiological scale
compared with lung CT scan analysis to predict the lung recruitability
in ALI/ARDS patients.
Methods A whole lung CT scan was performed at 5 and 45 cmH2O
airway pressure. For CT scan analysis each lung image was manually
outlined and analyzed by a dedicated software. The potentially
recruitable lung was defi ned as the proportion of the nonaerated
lung tissue in which aeration was restored [1]. For radiological visual
scale analysis, two radiologists performed a blinded evaluation of the
consolidation/collapsed areas in each lobe by visual inspection [2]. The
overall lung change in consolidation/collapsed was obtained by the
sum of each lobe and computed as the diff erence between the two
conditions.
Results Twenty-four ALI/ARDS patients (age 59 \ub1 15 years, BMI
26 \ub1 4 kg/m2, PaO2/FiO2 170 \ub1 60, PEEP 10 \ub1 2 cmH2O) were enrolled.
The percentage of potentially recruitable lung was 16.2 \ub1 7.1% and
14.7 \ub1 7.0%, computed by CT scan and by the visual radiological scale,
respectively. The mean diff erence between CT scan analysis and visual
radiological analysis was 3.3 \ub1 4.6% (median: 2.91, interquartile range:
0.38 to 6.56). The error of the visual method was lower than 5% in 14
patients (58.3%), between 5% and 10% in eight patients (33.3%) and
between 10% and 15% in two patients (8.3%).
Conclusions The application of a radiological visual scale is able to
predict the amount of potentially recruitable lung similarly to those
obtained by a dedicated software avoiding the need of manually
drawing each lung image.
References
1. Gattinoni L, et al.: N Engl J Med 2006, 354:1775-1786.
2. Pierce RJ, et al.: Thorax 1980, 35:773-780
Sarcopenia is associated with reduced survival in patients with advanced hepatocellular carcinoma undergoing sorafenib treatment
Background: Sarcopenia has been associated with poor outcomes in patients with cirrhosis and solid tumours. Objective: Analyse the influence of sarcopenia on survival and treatment duration in patients with advanced hepatocellular carcinoma (HCC) treated with sorafenib. Methods: We conducted a multicentre, retrospective study on 96 patients with advanced HCC treated with sorafenib, all with available abdominal computed tomography (CT) scan within 30 days from treatment start. Anthropometric, laboratory, treatment and follow-up data were collected. Sarcopenia was defined by reduced skeletal muscle index calculated from an L3 section CT image. Results: Sarcopenia was present in 49% of patients. Patients were divided into two groups according to sarcopenia: age was significantly higher in the sarcopenic group (SG) (66 years (31â87) versus 72 years (30â84), p = 0.04], with no difference in other baseline characteristics. The SG showed shorter overall survival (OS) (39 (95% confidence interval (CI) 26â50) versus 61 (95% CI 47â77) weeks (p = 0,01)) and shorter time on treatment (12.3 (95% CI 8â19) versus 25.9 (95% CI 15â33) weeks (p = 0.0044)). At multivariate analysis, sarcopenia was independently associated to reduced OS (p = 0.03) and reduced time on treatment (p = 0.001). Conclusion: Sarcopenia is present in almost half of patients with advanced HCC, and is associated with reduced survival and reduced duration of oral chemotherapy
Spatiotemporal changes in substantia nigra neuromelanin content in Parkinsonâs disease
This study aimed to investigate the spatiotemporal changes in neuromelanin-sensitive MRI signal in the substantia nigra and their relation to clinical scores of disease severity in patients with early or progressing Parkinsonâs disease and patients with idiopathic rapid eye movement sleep behaviour disorder (iRBD) exempt of Parkinsonian signs compared to healthy control subjects. Longitudinal T1-weighted anatomical and neuromelanin-sensitive MRI was performed in two cohorts, including patients with iRBD, patients with early or progressing Parkinsonâs disease, and control subjects. Based on the aligned substantia nigra segmentations using a study-specific brain anatomical template, parametric maps of the probability of a voxel belonging to the substantia nigra were calculated for patients with various degrees of disease severity and controls. For each voxel in the substantia nigra, probability map of controls, correlations between signal-to-noise ratios on neuromelanin-sensitive MRI in patients with iRBD and Parkinsonâs disease and clinical scores of motor disability, cognition and mood/behaviour were calculated. Our results showed that in patients, compared to the healthy control subjects, the volume of the substantia nigra was progressively reduced for increasing disease severity. The neuromelanin signal changes appeared to start in the posterolateral motor areas of the substantia nigra and then progressed to more medial areas of this region. The ratio between the volume of the substantia nigra in patients with Parkinsonâs disease relative to the controls was best fitted by a mono-exponential decay. Based on this model, the pre-symptomatic phase of the disease started at 5.3 years before disease diagnosis, and 23.1% of the substantia nigra volume was lost at the time of diagnosis, which was in line with previous findings using post-mortem histology of the human substantia nigra and radiotracer studies of the human striatum. Voxel-wise patterns of correlation between neuromelanin-sensitive MRI signal-to-noise ratio and motor, cognitive and mood/behavioural clinical scores were localized in distinct regions of the substantia nigra. This localization reflected the functional organization of the nigrostriatal system observed in histological and electrophysiological studies in non-human primates (motor, cognitive and mood/behavioural domains). In conclusion, neuromelanin-sensitive MRI enabled us to assess voxel-wise modifications of substantia nigraâs morphology in vivo in humans, including healthy controls, patients with iRBD and patients with Parkinsonâs disease, and identify their correlation with nigral function across all motor, cognitive and behavioural domains. This insight could help assess disease progression in drug trials of disease modification