Consistency and variability in functional localisers

A critical assumption underlying the use of functional localiser scans is that the voxels identified as the functional region-of-interest (fROI) are essentially the same as those activated by the main experimental manipulation. Intra-subject variability in the location of the fROI violates this assumption, reducing the sensitivity of the analysis and biasing the results. Here we investigated consistency and variability in fROIs in a set of 45 volunteers. They performed two functional localiser scans to identify word- and object-sensitive regions of ventral and lateral occipito-temporal cortex, respectively. In the main analyses, fROIs were defined as the category-selective voxels in each region and consistency was measured as the spatial overlap between scans. Consistency was greatest when minimally selective thresholds were used to define “active” voxels (p < 0.05 uncorrected), revealing that approximately 65% of the voxels were commonly activated by both scans. In contrast, highly selective thresholds (p < 10^− 4 to 10^− 6) yielded the lowest consistency values with less than 25% overlap of the voxels active in both scans. In other words, intra-subject variability was surprisingly high, with between one third and three quarters of the voxels in a given fROI not corresponding to those activated in the main task. This level of variability stands in striking contrast to the consistency seen in retinotopically-defined areas and has important implications for designing robust but efficient functional localiser scans.     

Effects of model-based physiological noise correction on default mode network anti-correlations and correlations

Previous studies have reported that the spontaneous, resting-state time course of the default-mode network is negatively correlated with that of the “task-positive network”, a collection of regions commonly recruited in demanding cognitive tasks. However, all studies of negative correlations between the default-mode and task-positive networks have employed some form of normalization or regression of the whole-brain average signal (“global signal”); these processing steps alter the time series of voxels in an uninterpretable manner as well as introduce spurious negative correlations. Thus, the extent of negative correlations with the default mode network without global signal removal has not been well characterized, and it is has recently been hypothesized that the apparent negative correlations in many of the task-positive regions could be artifactually induced by global signal pre-processing. The present study aimed to examine negative and positive correlations with the default-mode network when model-based corrections for respiratory and cardiac noise are applied in lieu of global signal removal. Physiological noise correction consisted of (1) removal of time-locked cardiac and respiratory artifacts using RETROICOR (Glover, G.H., Li, T.Q., Ress, D., 2000. Image-based method for retrospective correction of physiological motion effects in fMRI: RETROICOR. Magn. Reson. Med. 44, 162–167), and (2) removal of low-frequency respiratory and heart rate variations by convolving these waveforms with pre-determined transfer functions (Birn et al., 2008; Chang et al., 2009) and projecting the resulting two signals out of the data. It is demonstrated that negative correlations between the default-mode network and regions of the task-positive network are present in the majority of individual subjects both with and without physiological noise correction. Physiological noise correction increased the spatial extent and magnitude of negative correlations, yielding negative correlations within task-positive regions at the group-level (p < 0.05, uncorrected; no regions at the group level were significant at FDR = 0.05). Furthermore, physiological noise correction caused region-specific decreases in positive correlations within the default-mode network, reducing apparent false positives. It was observed that the low-frequency respiratory volume and cardiac rate regressors used within the physiological noise correction algorithm displayed significant (but not total) shared variance with the global signal, and constitute a model-based alternative to correcting for non-neural global noise.     

Relationship between respiration, end-tidal CO2, and BOLD signals in resting-state fMRI

A significant component of BOLD fMRI physiological noise is caused by variations in the depth and rate of respiration. It has previously been demonstrated that a breath-to-breath metric of respiratory variation (respiratory volume per time; RVT), computed from pneumatic belt measurements of chest expansion, has a strong linear relationship with resting-state BOLD signals across the brain. RVT is believed to capture breathing-induced changes in arterial CO₂, which is a cerebral vasodilator; indeed, separate studies have found that spontaneous fluctuations in end-tidal CO₂ (PETCO₂) are correlated with BOLD signal time series. The present study quantifies the degree to which RVT and PETCO₂ measurements relate to one another and explain common aspects of the resting-state BOLD signal. It is found that RVT (particularly when convolved with a particular impulse response, the “respiration response function”) is highly correlated with PETCO₂, and that both explain remarkably similar spatial and temporal BOLD signal variance across the brain. In addition, end-tidal O₂ is shown to be largely redundant with PETCO₂. Finally, the latency at which PETCO₂ and respiration belt measures are correlated with the time series of individual voxels is found to vary across the brain and may reveal properties of intrinsic vascular response delays.     

Does estrogen receptor gene polymorphism play a role in Parkinson's disease?

This study was designed to investigate the frequency of estrogen receptor (ER) gene polymorphism in Chinese patients with Parkinson's disease (PD). Polymerase chain reaction (PCR) method and restriction fragment length polymorphism (RFLP) were used to detect the ER gene polymorphisms in 158 PD patients and 146 healthy controls. In the PD and control groups, “x” accounted for 83.5% and 80.8%, respectively (P > 0.05). “xx” was found in 77.2% of the PD group and in 69.9% of the control group (P > 0.05). The frequency of “p” in the PD and control group was 67.7% and 64.0%, respectively (P > 0.05). “pp” was 51.9% in the PD group and 43.8% in the control group (P > 0.05). “ppxx” was found in 49.4% of the PD and 43.0% of the control subjects (P > 0.05). There was no significant difference in the “x”, “xx”, “p”, “pp” or “ppxx” between males and females within the PD or control groups. In conclusion, we found no significant differences in the genotype or allele frequencies between patients with Parkinson's disease and healthy subjects. These findings suggest that the estrogen receptor gene polymorphism may not play a key role in the pathogenesis PD in Chinese patients.     

Factors contributing to large analgesic effects in placebo mechanism studies conducted between 2002 and 2007

Recent meta-analyses find various magnitudes of placebo analgesia effects in placebo mechanism trials versus placebo control trials, which have led to debate. To further investigate the magnitude of placebo analgesia in placebo mechanism trials the databases “PubMed”, “PsycINFO” and “Web of Science” (2002–2007) were searched with the term “placebo analgesia”. Twenty-one articles including 24 studies fulfilled the selection criteria (concerning: mechanisms, control, placebo treatment, randomization and pain measures). The validity of studies was assessed by the authors and effect sizes were calculated via difference scores. The magnitude of placebo analgesia in placebo mechanism studies was large (d = 1.00) and about five times larger than placebo analgesia effects in placebo control studies (d = 0.15–0.27). Differences in magnitude between the two types of studies appear to result from different types of suggestions given for pain relief. The magnitude of placebo effects was larger in studies that used long-term pain stimuli >20 s (d = 0.96) as opposed to short-term stimuli (d = 0.81) and the largest placebo effects were found in studies wherein hyperalgesia was present (d = 1.88). These results replicate our previous finding that placebo analgesic effects are higher in mechanism studies than in placebo control studies. However, since magnitudes of placebo analgesic effects are highly variable it may be valuable to investigate the factors and mechanisms that contribute to this variability as well as differences in magnitudes across types of studies.     

Neural substrates of letter fluency processing in young adults who were born very preterm: Alterations in frontal and striatal regions

Several studies have described poorer performance in executive-type tasks in individuals who were born very preterm compared to controls. As there is evidence that high-order executive functions may be underpinned by neuronal activity in frontal–striatal circuits, we investigated with functional MRI a group of young adults who were born very preterm (n = 28, gestational age < 33 weeks) and controls (n = 26) in order to detect possible alterations in brain activation during completion of a letter fluency task with differential cognitive loading (“easy” and “hard” letter trials). Structural MRI data were also collected to clarify whether any functional changes were associated with structural brain volume changes. Group membership, level of task difficulty and gestational age had significant effects on brain activation. In the absence of significant between-group differences in task performance, during “easy” letter trials, very preterm-born individuals showed attenuated activation in anterior cingulate gyrus, right caudate nucleus and left inferior frontal gyrus compared to controls. During “hard” letter trials, very preterm-born individuals showed both decreased and increased BOLD signal compared to controls, in left middle frontal and anterior cingulate gyrus, respectively. BOLD signal in caudate nucleus and anterior cingulate gyrus, in regions with peaks close to areas where between-group differences were observed, was linearly associated with gestational age. Analysis of structural MRI data showed altered grey matter distribution in the preterm-born group compared to controls. However, fMRI results were only partly explained by structural changes, and may reflect processes of functional plasticity for the successful completion of executive-type operations.     

In-vivo quantitative T2 mapping of carotid arteries in atherosclerotic patients: segmentation and T2 measurement of plaque components

Background

Atherosclerotic plaques in carotid arteries can be characterized in-vivo by multicontrast cardiovascular magnetic resonance (CMR), which has been thoroughly validated with histology. However, the non-quantitative nature of multicontrast CMR and the need for extensive post-acquisition interpretation limit the widespread clinical application of in-vivo CMR plaque characterization. Quantitative T₂ mapping is a promising alternative since it can provide absolute physical measurements of plaque components that can be standardized among different CMR systems and widely adopted in multi-centre studies. The purpose of this study was to investigate the use of in-vivo T₂ mapping for atherosclerotic plaque characterization by performing American Heart Association (AHA) plaque type classification, segmenting carotid T₂ maps and measuring in-vivo T₂ values of plaque components.

Methods

The carotid arteries of 15 atherosclerotic patients (11 males, 71 ± 10 years) were imaged at 3 T using the conventional multicontrast protocol and Multiple-Spin-Echo (Multi-SE). T₂ maps of carotid arteries were generated by mono-exponential fitting to the series of images acquired by Multi-SE using nonlinear least-squares regression. Two reviewers independently classified carotid plaque types following the CMR-modified AHA scheme, one using multicontrast CMR and the other using T₂ maps and time-of-flight (TOF) angiography. A semi-automated method based on Bayes classifiers segmented the T₂ maps of carotid arteries into 4 classes: calcification, lipid-rich necrotic core (LRNC), fibrous tissue and recent IPH. Mean ± SD of the T₂ values of voxels classified as LRNC, fibrous tissue and recent IPH were calculated.

Results

In 37 images of carotid arteries from 15 patients, AHA plaque type classified by multicontrast CMR and by T₂ maps (+ TOF) showed good agreement (76% of matching classifications and Cohen’s κ = 0.68). The T₂ maps of 14 normal arteries were used to measure T₂ of tunica intima and media (T₂ = 54 ± 13 ms). From 11865 voxels in the T₂ maps of 15 arteries with advanced atherosclerosis, 2394 voxels were classified by the segmentation algorithm as LRNC (T₂ = 37 ± 5 ms) and 7511 voxels as fibrous tissue (T₂ = 56 ± 9 ms); 192 voxels were identified as calcification and one recent IPH (236 voxels, T₂ = 107 ± 25 ms) was detected on T₂ maps and confirmed by multicontrast CMR.

Conclusions

This carotid CMR study shows the potential of in-vivo T₂ mapping for atherosclerotic plaque characterization. Agreement between AHA plaque types classified by T₂ maps (+TOF) and by conventional multicontrast CMR was good, and T₂ measured in-vivo in LRNC, fibrous tissue and recent IPH demonstrated the ability to discriminate plaque components on T₂ maps.     

Plasmaviskositat und gerinnung bei leberzirrhosekranken

In 31 patients with liver cirrhosis the following parameters were determined: Factor I (fibrinogen), Factor II, Factor VII and Factor X according to the Normotest of Owren, Factor VIII, the thromboplastin time, the partial thromboplastin time (PTT), the thrombin time and the thromboelastogram. These parameters were compared with the plasma viscosity. A significant correlation was found between the plasma viscosity and Factor I, Factor VIII, the “maximal thromboelasticity” (m), the Normotest and the thrombin time; a reversely proportional, however, significant correlation was observed for the “reaction time” (r) and the “clot formation time” (k).The possible importance of these findings and the correlation between the plasma viscosity, the parameters of the hypercoagulability and the liver function are discussed according to a clinical example.

Zusammenfassung

Bei 31 Patienten mit einer Leberzirrhose wurden Faktor I, Faktor II, VII, X als Normotest nach Owren, Faktor VIII, der Quick-Wert, die partielle Thromboplastinzeit (PTT), die Thrombinzeit und das Thrombelastogramm (r, k, m) untersucht und der Plasmaviskosität gegenübergestellt.Dabei wurde eine signifikante Korrelation zwischen der Plasmaviskosität und dem Faktor I, Faktor VIII, der maximalen Thrombuselastizität (m), dem Normotest und der Thrombinzeit sowie eine umgekehrt proportionale signifikante Korrelation zur Reaktionszeit (r) und Gerinnselbildungszeit (k) im Thrombelastogramm gefunden.An einem klinischen Beispiel wird die mögliche Bedeutung und der Zusammenhang zwischen der Plasmaviskosität, den Parametern der Hyperkoagulobilität sowie der Leberfunktion diskutiert.     

Problem-based learning in clinical practice: employment and education as development partners

In this project tutorial small group working sessions of problem-based learning were carried out in the long-term care practice period of nursing students. The purpose was to describe nursing students’ learning when tutorial work was carried out during their first clinical practice period. The students had one PBL cycle during their four weeks’ clinical practice consisting of two tutorial sessions where clinical mentors and the teacher worked together as tutors. The students were pre-tested before the clinical practice and post-tested afterwards using a questionnaire. The questionnaire had been used in pilot projects during 2004–2005. Altogether, 40 nursing students participated in the study. There were statistically significant differences between pre- and post-test in “PBL-learning skills” (p < 0.001) and “interaction with old patients” (p < 0.001). The means of items “Interested in work in long-term care” and “Own attitude towards long-term care” had increased between pre- and post-test. In conclusion it can be suggested that carrying out tutorials in nursing students’ clinical practice is beneficial.     

Optimization of Improved Motion-sensitized Driven-equilibrium (iMSDE) blood suppression for carotid artery wall imaging

Background

Improved motion-sensitized driven-equilibrium (iMSDE) preparations have been successfully used in carotid artery wall imaging to achieve blood suppression, but it causes notable signal loss, mostly due to inherent T₂ decay, eddy current effects and B₁⁺ inhomogeneity. In this study, we investigate the signal to noise ratio (SNR) and blood suppression performance of iMSDE using composite RF pulses and sinusoidal gradients. Optimized first moment (m₁) values for iMSDE prepared T₁- and T₂- weighted (T₁- and T₂-w) imaging are presented.

Methods

Twelve healthy volunteers and six patients with carotid artery disease underwent iMSDE and double inversion recovery (DIR) prepared T₁- and T₂-w fast spin echo (FSE) MRI of the carotid arteries. Modified iMSDE module using composite RF pulses and sinusoidal gradients were evaluated with a range of m₁. SNR of adjacent muscle, vessel wall and the lumen were reported. The optimized iMSDE module was also tested in a 3D variable flip angle FSE (CUBE) acquisition.

Results

The SNR of muscle was highest using sinusoidal gradients, and the relative improvement over the trapezoidal gradient increased with higher m₁ (p<0.001). Optimal SNR was observed using an iMSDE preparation scheme containing two 180° composite pulses and standard 90° and -90° pulses (p=0.151). iMSDE produced better blood suppression relative to DIR preparations even with a small m₁ of 487 mT*ms²/m (p<0.001). In T₁-w iMSDE, there was a SNR decrease and an increased T₂ weighting with increasing m_1. In T₂-w iMSDE, by matching the effective echo time (TE), the SNR was equivalent when m₁ was <= 1518 mT*ms²/m, however, higher m₁ values (2278 – 3108 mT*ms²/m) reduced the SNR. In the patient study, iMSDE improved blood suppression but reduced vessel wall CNR efficiency in both T₁-w and T₂-w imaging. iMSDE also effectively suppressed residual flow artifacts in the CUBE acquisition.

Conclusions

iMSDE preparation achieved better blood suppression than DIR preparation with reduced vessel wall CNR efficiency in T_1-w and T₂-w images. The optimized m₁s are 487 mT*ms²/m for T₁-w imaging and 1518 mT*ms²/m for T₂-w imaging. Composite 180° refocusing pulses and sinusoidal gradients improve SNR performance. iMSDE further improves the inherent blood suppression of CUBE.     

The use of surface electromyography as a tool in differentiating temporomandibular disorders from neck disorders

The aim of this study was to assess the electromyographic characteristics of the masticatory muscles (masseter and temporalis) of patients with either “temporomandibular joint disorder” or “neck pain”. Surface electromyography of the right and left masseter and temporalis muscles was performed during maximum teeth clenching in 38 patients aged 21–67 years who had either (a) temporomandibular joint disorder (24 patients); (b) “neck pain” (13 patients). Ninety-five control, healthy subjects were also examined. During clenching, standardized total muscle activities (electromyographic potentials over time) were significantly different in the three groups: 75 μV/μV s % in the temporomandibular joint disorder patients, 124 μV/μV s % in the neck pain patients, and 95 μV/μV s % in the control subjects (analysis of variance, P<0.001). The temporomandibular joint disorder patients also had significantly (P<0.001) more asymmetric muscle potentials (78%) than either neck pain patients (87%) or control subjects (92%). A linear discriminant function analysis allowed a significant separation between the two patient groups, with a single patient error of 18.2%. Surface electromyographic analysis during clenching allowed to differentiate between patients with a temporomandibular joint disorder and patients with a neck pain problem.     

Chronic pain reconsidered

Chronic pain has been traditionally defined by pain duration, but this approach has limited empirical support and does not account for chronic pain’s multi-dimensionality. This study compared duration-based and prospective approaches to defining chronic pain in terms of their ability to predict future pain course and outcomes for primary care patients with three common pain conditions: back pain (n = 971), headache (n = 1078), or orofacial pain (n = 455). At baseline, their chronic pain was classified retrospectively based on Pain Days in the prior six months and prospectively with a prognostic Risk Score identifying patients with “possible” or “probable” chronic pain. The 0–28 Risk Score was based on pain intensity, pain-related activity limitations, depressive symptoms, number of pain sites, and Pain Days. Pain and behavioral outcomes were assessed at six-month follow-up, and long-term opioid use was assessed two to five years after baseline. Risk Score consistently predicted clinically significant pain at six months better than did Pain Days alone (area under the curve of 0.74–0.78 for Risk Score vs. 0.63–0.73 for Pain Days). Risk Score was a stronger predictor of future SF-36 Physical Function, pain-related worry, unemployment, and long-term opioid use than Pain Days alone. Thus, for these three common pain conditions, a prognostic Risk Score had better predictive validity for pain outcomes than did pain duration alone. However, chronic pain appears to be a continuum rather than a distinct class, because long-term pain outcomes are highly variable and inherently uncertain.     

An investigation on nursing, midwifery and health care students' learning motivation in Turkey

The aim was to determine differences between the dimensions of motivational learning and sociodemographic characteristics of nursing, midwifery and health care students. For the purpose of collecting data on learning-oriented motivations, occupational learning motivation scale (OLMS) was used. The OLMS was designed to assess the constructs of extrinsic, intrinsic and negative factors for learning, cognitive and lifelong learning goals. The mean levels of the items “willingness to help people”, “fear of making mistakes” and “willingness to work with those likely to motivate them” were all determined to be high. Significant differences were revealed for the sex of the students (p < 0.05).     

Use of peak Doppler gradient across ventricular septal defects leads to underestimation of right-sided pressures in patients with “sloped” Doppler signals

In patients with “sloped” appearance of the Doppler signal across a ventricular septal defect (VSD), the peak Doppler velocity seems to overestimate the catheterization-derived peak-to-peak gradient, resulting in underestimation of right-sided heart pressures. In 11 patients with sloped Doppler signals across the VSD, ventricular pressure tracings were compared with simultaneous recordings of the Doppler signal. The average peak Doppler gradient (40.2 ± 19.2 mm Hg) overestimated the catheterization-derived peak-to-peak gradient (20.2 ± 13.6 mm Hg) significantly (P ≤ .001). Doppler mean gradient (20.2 ± 11.3 mm Hg; P = ns) and end-systolic gradient (17.0 ± 12.5 mm Hg; P ≤ .05) were closer estimates of the catheterization peak-to-peak gradient. All Doppler gradients showed good correlation to the catheterization peak-to-peak gradient with r² values of 0.77, 0.73, and 0.91. We conclude that Doppler mean or end-systolic gradients should be used for calculation of right-sided heart pressures in this patient population. (J Am Soc Echocardiogr 2001;14:1197-202.)     

Weaning from mechanical ventilation: a cross-sectional study of reference values and the discriminative validity of aging

[Purpose] To evaluate pre-extubation variables and check the discriminative validity of age as well as its correlation with weaning failure in elderly patients. [Subjects and Methods] Two hundred thirty-nine consecutive patients (48% female) who were on mechanical ventilation and had undergone orotracheal intubation were divided into four subgroups according to their age: <59 years, 60–69 years, 70–79 years, and >80 years old. The expiratory volume (V_E), respiratory frequency (f), tidal volume (V_T), and respiratory frequency/tidal volume ratio (f/V_T) were used to examine differences in weaning parameters between the four subgroups, and age was correlated with weaning failure. [Results] The rate of weaning failure was 27.8% in patients aged >80 years and 22.1% in patients aged <60 years old. Elderly patients presented higher f/V_T and f values and lower V_T values. The areas under the receiver operating characteristic curves for f/V_T ratio were smaller than those published previously. [Conclusion] Our results indicate that aging influences weaning criteria without causing an increase in weaning failure.Key words: Weaning, Mechanical ventilation, Aging     

MP2RAGE,a self bias-field corrected sequence for improved segmentation and T1-mapping at high field

The large spatial inhomogeneity in transmit B₁ field (B₁⁺) observable in human MR images at high static magnetic fields (B₀) severely impairs image quality. To overcome this effect in brain T₁-weighted images, the MPRAGE sequence was modified to generate two different images at different inversion times, MP2RAGE. By combining the two images in a novel fashion, it was possible to create T₁-weigthed images where the result image was free of proton density contrast, T₂? contrast, reception bias field, and, to first order, transmit field inhomogeneity.MP2RAGE sequence parameters were optimized using Bloch equations to maximize contrast-to-noise ratio per unit of time between brain tissues and minimize the effect of B₁⁺ variations through space. Images of high anatomical quality and excellent brain tissue differentiation suitable for applications such as segmentation and voxel-based morphometry were obtained at 3 and 7 T.From such T₁-weighted images, acquired within 12 min, high-resolution 3D T₁ maps were routinely calculated at 7 T with sub-millimeter voxel resolution (0.65–0.85 mm isotropic). T₁ maps were validated in phantom experiments. In humans, the T₁ values obtained at 7 T were 1.15 ± 0.06 s for white matter (WM) and 1.92 ± 0.16 s for grey matter (GM), in good agreement with literature values obtained at lower spatial resolution. At 3 T, where whole-brain acquisitions with 1 mm isotropic voxels were acquired in 8 min, the T₁ values obtained (0.81 ± 0.03 s for WM and 1.35 ± 0.05 for GM) were once again found to be in very good agreement with values in the literature.     

Quantitation of cannabinoid CB1 receptors in healthy human brain using positron emission tomography and an inverse agonist radioligand

[¹¹C]MePPEP is a high affinity, CB₁ receptor-selective, inverse agonist that has been studied in rodents and monkeys. We examined the ability of [¹¹C]MePPEP to quantify CB₁ receptors in human brain as distribution volume calculated with the “gold standard” method of compartmental modeling and compared results with the simple measure of brain uptake. A total of 17 healthy subjects participated in 26 positron emission tomography (PET) scans, with 8 having two PET scans to assess retest variability. After injection of [¹¹C]MePPEP, brain uptake of radioactivity was high (e.g., 3.6 SUV in putamen at  60 min) and washed out very slowly. A two-tissue compartment model yielded values of distribution volume (which is proportional to receptor density) that were both well identified (SE 5%) and stable between 60 and 210 min. The simple measure of brain uptake (average concentration of radioactivity between 40 and 80 min) had good retest variability ( 8%) and moderate intersubject variability (16%, coefficient of variation). In contrast, distribution volume had two-fold greater retest variability ( 15%) and, thus, less precision. In addition, distribution volume had three-fold greater intersubject variability ( 52%). The decreased precision of distribution volume compared to brain uptake was likely due to the slow washout of radioactivity from brain and to noise in measurements of the low concentrations of [¹¹C]MePPEP in plasma. These results suggest that brain uptake can be used for within subject studies (e.g., to measure receptor occupancy by medications) but that distribution volume remains the gold standard for accurate measurements between groups.     

T2 mapping of the heart with a double-inversion radial fast spin-echo method with indirect echo compensation

Background

The abnormal signal intensity in cardiac T₂-weighted images is associated with various pathologies including myocardial edema. However, the assessment of pathologies based on signal intensity is affected by the acquisition parameters and the sensitivities of the receiver coils. T₂ mapping has been proposed to overcome limitations of T₂-weighted imaging, but most methods are limited in spatial and/or temporal resolution. Here we present and evaluate a double inversion recovery radial fast spin-echo (DIR-RADFSE) technique that yields data with high spatiotemporal resolution for cardiac T₂ mapping.

Methods

DIR-RADFSE data were collected at 1.5 T on phantoms and subjects with echo train length (ETL) = 16, receiver bandwidth (BW) = ±32 kHz, TR = 1RR, matrix size = 256 × 256. Since only 16 views per echo time (TE) are collected, two algorithms designed to reconstruct highly undersampled radial data were used to generate images for 16 time points: the Echo-Sharing (ES) and the CUrve Reconstruction via pca-based Linearization with Indirect Echo compensation (CURLIE) algorithm. T₂ maps were generated via least-squares fitting or the Slice-resolved Extended Phase Graph (SEPG) model fitting. The CURLIE-SEPG algorithm accounts for the effect of indirect echoes. The algorithms were compared based on reproducibility, using Bland-Altman analysis on data from 7 healthy volunteers, and T₂ accuracy (against a single-echo spin-echo technique) using phantoms.

Results

Both reconstruction algorithms generated in vivo images with high spatiotemporal resolution and showed good reproducibility. Mean T₂ difference between repeated measures and the coefficient of repeatability were 0.58 ms and 2.97 for ES and 0.09 ms and 4.85 for CURLIE-SEPG. In vivo T₂ estimates from ES were higher than those from CURLIE-SEPG. In phantoms, CURLIE-SEPG yielded more accurate T₂s compared to reference values (error was 7.5-13.9% for ES and 0.6-2.1% for CURLIE-SEPG), consistent with the fact that CURLIE-SEPG compensates for the effects of indirect echoes. The potential of T₂ mapping with CURLIE-SEPG is demonstrated in two subjects with known heart disease. Elevated T₂ values were observed in areas of suspected pathology.

Conclusions

DIR-RADFSE yielded TE images with high spatiotemporal resolution. Two algorithms for generating T₂ maps from highly undersampled data were evaluated in terms of accuracy and reproducibility. Results showed that CURLIE-SEPG yields T₂ estimates that are reproducible and more accurate than ES.     

Endogenous assessment of chronic myocardial infarction with T1ρ-mapping in patients

Background

Detection of cardiac fibrosis based on endogenous magnetic resonance (MR) characteristics of the myocardium would yield a measurement that can provide quantitative information, is independent of contrast agent concentration, renal function and timing. In ex vivo myocardial infarction (MI) tissue, it has been shown that a significantly higher T_1ρ is found in the MI region, and studies in animal models of chronic MI showed the first in vivo evidence for the ability to detect myocardial fibrosis with native T_1ρ-mapping. In this study we aimed to translate and validate T_1ρ-mapping for endogenous detection of chronic MI in patients.

Methods

We first performed a study in a porcine animal model of chronic MI to validate the implementation of T_1ρ-mapping on a clinical cardiovascular MR scanner and studied the correlation with histology. Subsequently a clinical protocol was developed, to assess the feasibility of scar tissue detection with native T_1ρ-mapping in patients (n = 21) with chronic MI, and correlated with gold standard late gadolinium enhancement (LGE) CMR. Four T_1ρ-weighted images were acquired using a spin-lock preparation pulse with varying duration (0, 13, 27, 45 ms) and an amplitude of 750 Hz, and a T_1ρ-map was calculated. The resulting T_1ρ-maps and LGE images were scored qualitatively for the presence and extent of myocardial scarring using the 17-segment AHA model.

Results

In the animal model (n = 9) a significantly higher T_1ρ relaxation time was found in the infarct region (61 ± 11 ms), compared to healthy remote myocardium (36 ± 4 ms) . In patients a higher T_1ρ relaxation time (79 ± 11 ms) was found in the infarct region than in remote myocardium (54 ± 6 ms). Overlap in the scoring of scar tissue on LGE images and T_1ρ-maps was 74%.

Conclusion

We have shown the feasibility of native T_1ρ-mapping for detection of infarct area in patients with a chronic myocardial infarction. In the near future, improvements on the T_1ρ -mapping sequence could provide a higher sensitivity and specificity. This endogenous method could be an alternative for LGE imaging, and provide additional quantitative information on myocardial tissue characteristics.