Developing blood-brain barrier arterial spin labelling as a non-invasive early biomarker of Alzheimer's disease (DEBBIE-AD): a prospective observational multicohort study protocol

INTRODUCTION

Loss of blood-brain barrier (BBB) integrity is hypothesised to be one of the earliest microvascular signs of Alzheimer's disease (AD). Existing BBB integrity imaging methods involve contrast agents or ionising radiation, and pose limitations in terms of cost and logistics. Arterial spin labelling (ASL) perfusion MRI has been recently adapted to map the BBB permeability non-invasively. The DEveloping BBB-ASL as a non-Invasive Early biomarker (DEBBIE) consortium aims to develop this modified ASL-MRI technique for patient-specific and robust BBB permeability assessments. This article outlines the study design of the DEBBIE cohorts focused on investigating the potential of BBB-ASL as an early biomarker for AD (DEBBIE-AD).

METHODS AND ANALYSIS

DEBBIE-AD consists of a multicohort study enrolling participants with subjective cognitive decline, mild cognitive impairment and AD, as well as age-matched healthy controls, from 13 cohorts. The precision and accuracy of BBB-ASL will be evaluated in healthy participants. The clinical value of BBB-ASL will be evaluated by comparing results with both established and novel AD biomarkers. The DEBBIE-AD study aims to provide evidence of the ability of BBB-ASL to measure BBB permeability and demonstrate its utility in AD and AD-related pathologies.

ETHICS AND DISSEMINATION

Ethics approval was obtained for 10 cohorts, and is pending for 3 cohorts. The results of the main trial and each of the secondary endpoints will be submitted for publication in a peer-reviewed journal.

Arachidonic and docosahexaenoic acid supplementation and brain maturation in preterm infants; a double blind RCT

BACKGROUND

Arachidonic acid (ARA) and docosahexaenoic acid (DHA) are important structural components of neural cellular membranes and possess anti-inflammatory properties. Very preterm infants are deprived of the enhanced placental supply of these fatty acids, but the benefit of postnatal supplementation on brain development is uncertain. The aim of this study was to test the hypothesis that early enteral supplementation with ARA and DHA in preterm infants improves white matter (WM) microstructure assessed by diffusion-weighted MRI at term equivalent age.

METHODS

In this double-blind, randomized controlled trial, infants born before 29 weeks gestational age were allocated to either 100 mg/kg ARA and 50 mg/kg DHA (ARA:DHA group) or medium chain triglycerides (control). Supplements were started on the second day of life and provided until 36 weeks postmenstrual age. The primary outcome was brain maturation assessed by diffusion tensor imaging (DTI) using Tract-Based Spatial Statistics (TBSS) analysis.

RESULTS

We included 120 infants (60 per group) in the trial; mean (range) gestational age was 26+3 (22+6 - 28+6) weeks and postmenstrual age at scan was 41+3 (39+1 - 47+0) weeks. Ninety-two infants underwent MRI imaging, and of these, 90 had successful T1/T2 weighted MR images and 74 had DTI data of acceptable quality. TBSS did not show significant differences in mean or axial diffusivity between the groups, but demonstrated significantly higher fractional anisotropy in several large WM tracts in the ARA:DHA group, including corpus callosum, the anterior and posterior limb of the internal capsula, inferior occipitofrontal fasciculus, uncinate fasciculus, and the inferior longitudinal fasciculus. Radial diffusivity was also significantly lower in several of the same WM tracts in the ARA:DHA group.

CONCLUSION

This study suggests that supplementation with ARA and DHA at doses matching estimated fetal accretion rates improves WM maturation compared to control treatment, but further studies are needed to ascertain any functional benefit.

CLINICAL TRIAL REGISTRATION

www.

CLINICALTRIALS

gov; ID:NCT03555019.

Evidence for widespread alterations in cortical microstructure after 32 h of sleep deprivation

Cortical microstructure is influenced by circadian rhythm and sleep deprivation, yet the precise underpinnings of these effects remain unclear. The ratio between T₁-weighted and T₂-weighted magnetic resonance images (T₁w/T₂w ratio) has been linked to myelin levels and dendrite density and may offer novel insight into the intracortical microstructure of the sleep deprived brain. Here, we examined intracortical T₁w/T₂w ratio in 41 healthy young adults (26 women) before and after 32 h of either sleep deprivation (n = 18) or a normal sleep-wake cycle (n = 23). Linear models revealed significant group differences in T₁w/T₂w ratio change after 32 h in four clusters, including bilateral effects in the insular, cingulate, and superior temporal cortices, comprising regions involved in attentional, auditory and pain processing. Across clusters, the sleep deprived group showed an increased T₁w/T₂w ratio, while the normal sleep-wake group exhibited a reduced ratio. These changes were not explained by in-scanner head movement, and 95% of the effects across clusters remained significant after adjusting for cortical thickness and hydration. Compared with a normal sleep-wake cycle, 32 h of sleep deprivation yields intracortical T₁w/T₂w ratio increases. While the intracortical changes detected by this study could reflect alterations in myelin or dendritic density, or both, histological analyses are needed to clarify the precise underlying cortical processes.

Association between myocardial fibrosis, as assessed with cardiac magnetic resonance T1 mapping, and persistent dyspnea after pulmonary embolism

Background

Persistent dyspnea is a common symptom after pulmonary embolism (PE). However, the pathophysiology of persistent dyspnea is not fully clarified. This study aimed to explore possible associations between diffuse myocardial fibrosis, as assessed by cardiac magnetic resonance (CMR) T1 mapping, and persistent dyspnea in patients with a history of PE.

Methods

CMR with T1 mapping and extracellular volume fraction (ECV) calculations were performed after PE in 51 patients with persistent dyspnea and in 50 non-dyspneic patients. Patients with known pulmonary disease, heart disease and CTEPH were excluded.

Results

Native T1 was higher in the interventricular septum in dyspneic patients compared to non-dyspneic patients; difference 13 ms (95% CI: 2–23 ms). ECV was also significantly higher in patients with dyspnea; difference 0.9 percent points (95% CI: 0.04–1.8 pp). There was no difference in native T1 or ECV in the left ventricular lateral wall. Native T1 in the interventricular septum had an adjusted Odds Ratio of 1.18 per 10 ms increase (95% CI: 0.99–1.42) in predicting dyspnea, and an adjusted Odds Ratio of 1.47 per 10 ms increase (95% CI: 1.10–1.96) in predicting Incremental Shuttle Walk Test (ISWT) score < 1020 m.

Conclusion

Septal native T1 and ECV values were higher in patients with dyspnea after PE compared with those who were fully recovered suggesting a possible pathological role of myocardial fibrosis in the development of dyspnea after PE. Further studies are needed to validate our findings and to explore their pathophysiological role and clinical significance.

Hepatic magnetic resonance T1-mapping and extracellular volume fraction compared to shear-wave elastography in pediatric Fontan-associated liver disease

BACKGROUND

Children with Fontan circulation are at risk of developing hepatic fibrosis/cirrhosis. Reliable noninvasive monitoring techniques are lacking or under development.

OBJECTIVE

To investigate surrogate indicators of hepatic fibrosis in adolescents with Fontan circulation by evaluating hepatic magnetic resonance (MR) T1 mapping and extracellular volume fraction measurements compared to US shear-wave elastography.

MATERIALS AND METHODS

We analyzed hepatic native T1 times and extracellular volume fractions with modified Look-Locker inversion recovery. Liver stiffness was analyzed with shear-wave elastography. We compared results between 45 pediatric patients ages 16.7±0.6 years with Fontan circulation and 15 healthy controls ages 19.2±1.2 years. Measurements were correlated to clinical and hemodynamic data from cardiac catheterization.

RESULTS

MR mapping was successful in 35/45 patients, revealing higher hepatic T1 times (774±44 ms) than in controls (632±52 ms; P<0.001) and higher extracellular volume fractions (47.4±5.0%) than in controls (34.6±3.8%; P<0.001). Liver stiffness was 1.91±0.13 m/s in patients vs. 1.20±0.10 m/s in controls (P<0.001). Native T1 times correlated with central venous pressures (r=0.5, P=0.007). Native T1 was not correlated with elastography in patients (r=0.2, P=0.1) or controls (r = -0.3, P=0.3). Extracellular volume fraction was correlated with elastography in patients (r=0.5, P=0.005) but not in controls (r=0.2, P=0.6).

CONCLUSION

Increased hepatic MR relaxometry and shear-wave elastography values in adolescents with Fontan circulation suggested the presence of hepatic fibrosis or congestion. Central venous pressure was related to T1 times. Changes were detected differently with MR relaxometry and elastography; thus, these techniques should not be used interchangeably in monitoring hepatic fibrosis.

Noise dependency in vascular parameters from combined gradient-echo and spin-echo DSC MRI

Dynamic susceptibility contrast (DSC) imaging is a widely used technique for assessment of cerebral blood volume (CBV). With combined gradient-echo and spin-echo DSC techniques, measures of the underlying vessel size and vessel architecture can be obtained from the vessel size index (VSI) and vortex area, respectively. However, how noise, and specifically the contrast-to-noise ratio (CNR), affect the estimations of these parameters has largely been overlooked. In order to address this issue, we have performed simulations to generate DSC signals with varying levels of CNR, defined by the peak of relaxation rate curve divided by the standard deviation of the baseline. Moreover, DSC data from 59 brain cancer patients were acquired at two different 3 T-scanners (N = 29 and N = 30, respectively), where CNR and relative parameter maps were obtained. Our simulations showed that the measured parameters were affected by CNR in different ways, where low CNR led to overestimations of CBV and underestimations of VSI and vortex area. In addition, a higher noise-sensitivity was found in vortex area than in CBV and VSI. Results from clinical data were consistent with simulations, and indicated that CNR < 4 gives highly unreliable measurements. Moreover, we have shown that the distribution of values in the tumour regions could change considerably when voxels with CNR below a given cut off are excluded when generating the relative parameter maps. The widespread use of CBV and attractive potential of VSI and vortex area, makes the noise-sensitivity of these parameters found in our study relevant for further use and development of the DSC imaging technique. Our results suggest that the CNR has considerable impact on the measured parameters, with the potential to affect the clinical interpretation of DSC-MRI, and should therefore be taken into account in the clinical decision-making process.

Responses in the diffusivity and vascular function of the irradiated normal brain are seen up until 18 months following SRS of brain metastases

Background

MRI may provide insights into longitudinal responses in the diffusivity and vascular function of the irradiated normal-appearing brain following stereotactic radiosurgery (SRS) of brain metastases.

Methods

Forty patients with brain metastases from non-small cell lung cancer (N = 26) and malignant melanoma (N = 14) received SRS (15–25 Gy). Longitudinal MRI was performed pre-SRS and at 3, 6, 9, 12, and 18 months post-SRS. Measures of tissue diffusivity and vascularity were assessed by diffusion-weighted and perfusion MRI, respectively. All maps were normalized to white matter receiving less than 1 Gy. Longitudinal responses were assessed in normal-appearing brain, excluding tumor and edema, in the LowDose (1–10 Gy) and HighDose (>10 Gy) regions. The Eastern Cooperative Oncology Group (ECOG) performance status was recorded pre-SRS.

Results

Following SRS, the diffusivity in the LowDose region increased continuously for 1 year (105.1% ± 6.2%; P < .001), before reversing toward pre-SRS levels at 18 months. Transient reductions in microvascular cerebral blood volume (P < .05), blood flow (P < .05), and vessel densities (P < .05) were observed in LowDose at 6–9 months post-SRS. Correspondingly, vessel calibers in LowDose transiently increased at 3–9 months (P < .01). The responses in HighDose displayed similar trends as in LowDose, but with larger interpatient variations. Vascular responses followed pre-SRS ECOG status.

Conclusions

Our results imply that even low doses of radiation to normal-appearing brain following cerebral SRS induce increased diffusivity and reduced vascular function for up until 18 months. In particular, the vascular responses indicate the reduced ability of the normal-appearing brain tissue to form new capillaries. Assessing the potential long-term neurologic effects of SRS on the normal-appearing brain is warranted.

P5288Slice position vulnerability in the basal and apical parts for right ventricular circumferential strain measurement with feature tracking cardiac magnetic resonance

Background

Strain is a more sensitive and precise parameter than ejection fraction (EF) for detection and characterization of subclinical left ventricular (LV) dysfunction and remodeling. Similar relationship is expected for right ventricle (RV); however RV functional parameters are less validated. Feature tracking strain analysis based on standard cardiac magnetic resonance (CMR) cine imaging is available for both ventricles. We experience a large slice-to-slice variation for RV global circumferential strain (GCS), possibly making the parameter vulnerable to minute position changes.

Purpose

To evaluate slice-to-slice differences in RV GCS for identification of the least variation region in a patient group without regional RV disease, in order to achieve a robust method for measurement.

Hypothesis

The slice-to-slice difference in peak GCS is lower in the mid-ventricular part of the RV than in the basal and apical parts.

Methods

50 patients 6–72 months after pulmonary embolism without other major cardiopulmonary disease were included; mean age 60 years (range: 18–75 years); 68% men.

Standard 2D cine CMR was obtained in longitudinal planes and in 10–12 consecutive 10 mm short axis planes for complete coverage of the RV. RV free wall and the inner contour of the septum were manually segmented on every end-diastolic and end-systolic slice from the pulmonary valve to the apex for feature tracking strain analysis.

Peak RV GCS for every short axis slice and GCS difference (absolute percentage points) between adjacent slices were calculated. RV EF and peak RV GLS from the 4-chamber image were measured for correlation to RV GCS. Wilcoxon signed rank test and Pearson correlation were performed. Confidence intervals of means are based on 1000 bootstrap samples.

Results

RV EF was 46.6% (95% CI: 44.3; 48.8), RV peak GLS was −17.6% (95% CI: −18.6; −16.6). RV mid-ventricular GCS was −10.9% (95% CI: −12.0; −9.9). RV peak GCS slice-to-slice difference was 6.8 absolute percentage points (95% CI: 6.0; 7.6) in the basal part, 2.7 (95% CI: 2.4; 3.0) in the mid-ventricular part and 4.6 (95% CI: 3.9; 5.3) apically. Difference was significantly lower in mid-ventricular (p<0.001) compared to both basal and apical.

RV EF correlated to RV peak GLS (r: −0.397, p=0.004) and mid-ventricular peak GCS (r: −0.356, p=0.01) but not to basal or apical peak GCS. RV peak GLS correlated to basal and mid-ventricular peak GCS (r: 0.313, p=0.03 and r: 0.301, p=0.03 respectively) but not to apical peak GCS.

Figure 1 shows slice-to-slice difference (expressed in absolute percentage points) in right ventricular peak GCS.

Conclusion

Slice-to-slice difference in RV peak GCS was significantly lower in the mid-ventricular region. Large differences in the basal and apical parts indicate that measurements largely depend on slice positioning.

Brain metastases with poor vascular function are susceptible to pseudoprogression after stereotactic radiation surgery

Purpose

This study aimed to investigate the hemodynamic status of cerebral metastases prior to and after stereotactic radiation surgery (SRS) and to identify the vascular characteristics that are associated with the development of pseudoprogression from radiation-induced damage with and without a radionecrotic component.

Methods and materials

Twenty-four patients with 29 metastases from non-small cell lung cancer or malignant melanoma received SRS with dose of 15 Gy to 25 Gy. Magnetic resonance imaging (MRI) scans were acquired prior to SRS, every 3 months during the first year after SRS, and every 6 months thereafter. On the basis of the follow-up MRI scans or histology after SRS, metastases were classified as having response, tumor progression, or pseudoprogression. Advanced perfusion MRI enabled the estimation of vascular status in tumor regions including fractions of abnormal vessel architecture, underperfused tissue, and vessel pruning.

Results

Prior to SRS, metastases that later developed pseudoprogression had a distinct poor vascular function in the peritumoral zone compared with responding metastases (P < .05; number of metastases = 15). In addition, differences were found between the peritumoral zone of pseudoprogressing metastases and normal-appearing brain tissue (P < .05). In contrast, for responding metastases, no differences in vascular status between peritumoral and normal-appearing brain tissue were observed. The dysfunctional peritumoral vasculature persisted in pseudoprogressing metastases after SRS.

Conclusions

Our results suggest that the vascular status of peritumoral tissue prior to SRS plays a defining role in the development of pseudoprogression and that advanced perfusion MRI may provide new insights into patients' susceptibility to radiation-induced effects.

Abstract 1471: Immunotherapy revised: Ipilimumab potentiates the vascular response to stereotactic radiosurgery in patients with brain metastases

Introduction: While immunotherapy is a promising treatment option for advanced metastatic disease, the survival benefit of adding ipilimumab to stereotactic radiosurgery (SRS) in unselected patients with metastases to the brain seems limited [1, 2]. Moreover, because conventional diagnostic methods for assessing treatment response were not designed for these therapies, the mechanisms of action in vivo are poorly understood. To reveal potential synergistic effects of adding ipilimumab to SRS, we here present preliminary data on the vascular response to SRS and ipilimumab in patients with brain metastases from malignant melanomas and non-small cell lung cancer.

Methods: Voxel-wise estimations of blood volume and vessel calibers were acquired by perfusion MRI and Vessel Architectural Imaging [3], respectively, in 13 patients with brain metastases from lung cancer receiving SRS only (N = 6; 7 lesions) and malignant melanomas receiving SRS only (N = 4; 5 lesions) or SRS and ipilimumab (N = 3; 5 lesions). Regions of enhancing tumor were identified on contrast-enhanced MRIs, whereas peri-tumoral tissue regions included a region containing a 2mm wide dilation of the enhancing tumor and outside the SRS target area. MRIs were performed at baseline (pre SRS) and repeated every three months. Ipilimumab (3mg/kg) were administered intravenously over 90 min every third week for four cycles. SRS was delivered to the tumor (visual metastasis + 2 mm margin) with a peripheral dose of 18 Gy or 25 Gy, depending on tumor size.

Results: For patients treated with SRS only, the vessel calibers decreased with a median value of 15% in the peri-tumoral area at 3 months following SRS (P&lt;0.05, Wilcoxon signed rank test) and more in metastases from lung cancer than in melanomas (75% vs 95%, P&lt;0.05, Mann-Whitney U test). In contrast, for patients treated with SRS and ipilimumab, there was almost a two-fold increase in the average vessel caliber size in the peri-tumoral area at 3 months (P&lt;0.05 vs SRS only, Mann-Whitney U test). Non-significant trends towards lower blood volume values and tumor volumes were observed in all groups at 3 months.

Conclusion: The enlarged average vessel calibers and the subsequent lack of an increase in blood volume suggest ipilimumab helps clean up the vascular bed by removing small caliber vessels and effectively reducing the capillary vessel density. Our advanced MRI data provide valuable and novel insights into the biological mechanisms of response to ipilimumab and at study end may help identify patients with metastatic disease that benefit from this therapy by prolonged survival.

References:

1. Mathew et al, Melanoma Res 2013. 23(3):191-5

2. Patel et al, Am J Clin Oncol 2015. May 16:[Epub]

3. Emblem et al, Nat Med 2013. 19(9):1178-83

Citation Format: Ingrid Digernes, Cathrine Saxhaug, Oliver Geier, Edmund Reitan, Einar Waldeland, Kunt Håkon Hole, Kari Dolven Jacobsen, Åslaug Helland, Kyrre Eeg Emblem. Immunotherapy revised: Ipilimumab potentiates the vascular response to stereotactic radiosurgery in patients with brain metastases. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1471.

Aqueductal Stroke Volume: Comparisons with Intracranial Pressure Scores in Idiopathic Normal Pressure Hydrocephalus

BACKGROUND AND PURPOSE

Aqueductal stroke volume from phase-contrast MR imaging has been proposed for predicting shunt response in normal pressure hydrocephalus. However, this biomarker has remained controversial in use and has a lack of validation with invasive intracranial monitoring. We studied how aqueductal stroke volume compares with intracranial pressure scores in the presurgical work-up and clinical score, ventricular volume, and aqueduct area and assessed the patient's response to shunting.

MATERIALS AND METHODS

Phase-contrast MR imaging was performed in 21 patients with probable idiopathic normal pressure hydrocephalus. Patients were selected for shunting on the basis of pathologically increased intracranial pressure pulsatility. Patients with shunts were offered a second MR imaging after 12 months. Ventricular volume and transverse aqueductal area were calculated, as well as clinical symptom score.

RESULTS

No correlations between aqueductal stroke volume and preoperative scores of mean intracranial pressure or mean wave amplitudes were observed. Preoperative aqueductal stroke volume was not different between patients with shunts and conservatively treated patients (P = .69) but was correlated with ventricular volume (R = 0.60, P = .004) and aqueductal area (R = 0.58, P = .006) but not with the severity or duration of clinical symptoms. After shunting, aqueductal stroke volume (P = .006) and ventricular volume (P = .002) were reduced. A clinical improvement was seen in 16 of 17 patients who had shunts (94%).

CONCLUSIONS

Aqueductal stroke volume does not reflect intracranial pressure pulsatility or symptom score, but rather aqueduct area and ventricular volume. The results do not support the use of aqueductal stroke volume for selecting patients for shunting.

Reproducibility of manual and semi-automated late enhancement quantification in patients with Fabry disease

BACKGROUND

Late enhancement (LE) imaging is increasingly used for diagnosis of non-ischemic cardiomyopathy. However, the mostly patchy appearance of LE in this context may reduce the reproducibility of LE measurement.

PURPOSE

To report intra- and inter-observer variabilities of LE measurements in Fabry disease using manual and semi-automated quantification.

MATERIAL AND METHODS

Twenty MRI data-sets of male patients aged 44 ± 7 years were analyzed twice (interval 12 months) by one observer and additionally once by a second observer. Left ventricular (LV) parameters were determined using cine MRI. Gradient-echo LE images were analyzed by manual planimetry and by a semi-automatic prototype software. Variabilities were determined by Bland-Altman analyses and additionally intra-class correlation coefficient (ICC) values were calculated to survey intra- and inter-observer reproducibility.

RESULTS

The amount of LE was 5.2 ± 5.1 mL or 2.8 ± 2.6 % of LV mass (observer 2). LE was detected predominantly intramurally in a patchy pattern. All patients had LE restricted to the basal infero-lateral parts of the LV. The extent of LE correlated to LV mass (207 ± 70 g, P < 0.05, r = 0.6). The intra- and inter-observer variabilities were -0.6 to 1.0 mL and -0.7 to 1.6 mL, respectively (95% confidence intervals). ICC values were 0.981-0.999. The semi-automatic software allowed quantification of LE areas in all patients. The comparison of LE amount determined by semi-automatic software versus manual planimetry yielded an intra-observer variability ranging from -1.9 to 2.3 mL.

CONCLUSION

Semi-automatic planimetry of patchy LE in patients with Fabry disease is feasible. The determined intra- and inter-observer variabilities for manual and semi-automatic planimetry were in the range of 20-40% of LE amount with high ICC values.

Diffusion-weighted magnetic resonance imaging for pretreatment prediction and monitoring of treatment response of patients with locally advanced breast cancer undergoing neoadjuvant chemotherapy

BACKGROUND

For patients with locally advanced breast cancer (LABC) undergoing neoadjuvant chemotherapy (NACT), the European Guidelines for Breast Imaging recommends magnetic resonance imaging (MRI) to be performed before start of NACT, when half of the NACT has been administered and prior to surgery. This is the first study addressing the value of flow-insensitive apparent diffusion coefficients (ADCs) obtained from diffusion-weighted (DW) MRI at the recommended time points for pretreatment prediction and monitoring of treatment response.

MATERIALS AND METHODS

Twenty-five LABC patients were included in this prospective study. DW MRI was performed using single-shot spin-echo echo-planar imaging with b-values of 100, 250 and 800 s/mm(2) prior to NACT, after four cycles of NACT and at the conclusion of therapy using a 1.5 T MR scanner. ADC in the breast tumor was calculated from each assessment. The strength of correlation between pretreatment ADC, ADC changes and tumor volume changes were examined using Spearman's rho correlation test.

RESULTS

Mean pretreatment ADC was 1.11 + or - 0.21 x 10(-3) mm(2)/s. After 4 cycles of NACT, ADC was significantly increased (1.39 + or - 0.36 x 10(-3) mm(2)/s; p=0.018). There was no correlation between individual pretreatment breast tumor ADC and MR response measured after four cycles of NACT (p=0.816) or prior to surgery (p=0.620).

CONCLUSION

Pretreatment tumor ADC does not predict treatment response for patients with LABC undergoing NACT. Furthermore, ADC increase observed mid-way in the course of NACT does not correlate with tumor volume changes.

A simulation of MRI based dose calculations on the basis of radiotherapy planning CT images

BACKGROUND

The advantage of MRI-based radiotherapy planning is the superior soft tissue differentiation. However, for accurate patient dose calculations, a conversion of the MR images into Hounsfield CT maps is necessary. The aim of the present study was to investigate the dose accuracy that can be achieved with segmented MR-images derived from the planning CT images by assigning fixed densities to different classes of tissues.

METHODS

Treatment plans for ten prostate cancer patients were selected. A collapsed cone algorithm was used to calculate patient dose distributions. The dose calculations were based on four different image sets: (1) the original CT-series (DD(DP)), (2) a simulated MR series with all tissue set to a homogenous water equivalent material of density 1.02 g/cm(3) (DD(W)), (3) a simulated MR series with soft tissue set to a water equivalent material with density 1.02 g/cm(3) and the bone set to a density of 1.3 g/cm(3) (DD(W+B1.3)), and (4) a simulated MR series identical to (3) but with a bone density equal to 2.1 g/cm(3) (DD(W+B2.1)). The dose distributions were compared by analysing dose difference histograms as well as through a visual display of spatial dose deviations.

RESULTS

The population based minimum, mean and maximum dose difference between the DD(DP) and DD(W) in the target volume was -2.8, -1.0 and 0.6%, respectively. Corresponding differences between DD(DP) and DD(W+B1.3) were -1.6, 0.2 and 1.5%, respectively, and between DD(DP) and DD(W+B2.1) -4.3, 4.2 and 9.7%, respectively. For the rectum, the differences between CT(DP) and the other image sets were in the range of -19.5 to 8.8%. For the bladder, the differences were in the range of -9.6 to 7.0%.

CONCLUSIONS

A systematic study using segmented MR images was undertaken. To achieve an acceptable accuracy in the CTV dose, the MR images should be segmented into bone and water equivalent tissue. Still, significant dose deviation for the organs at risk may be present. As tissue segmentation in real MR images is introduced, segmentation errors and errors that stem from geometrical non-linearities may further reduce the accuracy.

Functional and Metabolic Recovery of the Right Ventricle During Bosentan Therapy in Idiopathic Pulmonary Arterial Hypertension

An impaired high-energy phosphate metabolism might play a critical role in the pathogenesis of right ventricular (RV) failure due to chronic pulmonary arterial hypertension (PAH). 31P-NMR spectroscopy is well established for measurements of high-energy phosphate metabolites in various left ventricular heart diseases, however, mainly for technical and sensitivity reasons, its successful transfer for measurements in the RV is currently missing. In the present study, the usefulness of this non-invasive approach is not only shown in RV failure due to PAH but also tested during subsequent therapy.

Boundary effects of molecular diffusion in nanoporous materials: A pulsed field gradient nuclear magnetic resonance study

The boundary conditions of intraparticle diffusion in nanoporous materials may be chosen to approach the limiting cases of either absorbing or reflecting boundaries, depending on the host-guest system under study and the temperature of measurement. Pulsed field gradient nuclear magnetic resonance is applied to monitor molecular diffusion of n-hexane and of an n-hexane-tetrafluoromethane mixture adsorbed in zeolite crystallites of type NaX under either of these limiting conditions. Taking advantage of the thus-established peculiarities of mass transfer at the interface between the zeolite bulk phase and the surrounding atmosphere, three independent routes for probing the crystal size are compared. These techniques are based on (i) the measurement of the effective diffusivity under complete confinement, (ii) the application of the so-called NMR tracer desorption technique, and (iii) an analysis of the time dependence of the effective diffusivity in the short-time limit where, by an appropriate variation of the adsorbate and the measuring conditions, the limiting cases of reflecting and adsorbing boundaries could be considered. All these techniques are found to yield coinciding results, which are in excellent agreement with the crystal sizes determined by microscopy.

Cation diffusion in cartilage measured by pulsed field gradient NMR

In this study, the pulsed field gradient (PFG) nuclear magnetic resonance (NMR) technique was used for the investigation of (1) concentration and compression effects on cation self-diffusion, and (2) restricted diffusion of cations in cartilage. Since physiologically relevant cations like Na+ are difficult to investigate owing to their very short relaxation times, the cations tetramethylammonium (TMA) and tetraethylammonium (TEA) were employed for diffusion studies in samples of explanted cartilage. Results indicated that the diffusion of monovalent cations shows strong similarities to observations already made in studies of the diffusion of water in cartilage: with increasing compression, i.e. decreasing water content, the diffusion coefficient of the cation decreases concomitantly. The diffusion coefficients also showed a decrease with increasing cation concentrations, basically reflecting the corresponding decrease in the water content. Both results could be explained by the well-established model of Mackie and Meares. This, together with the similarity of the diffusion coefficient D in cartilage relative to free solution (about 50%) for both cations, is consistent with the view that the water content and not the charge is the most important determinant of the intratissue diffusivity of monovalent cations. Diffusion studies with increasing observation times showed strong evidence of restricted diffusion, allowing the estimation of the geometry of barriers within cartilage.

NMR studies of water diffusion and relaxation in hydrating slag-based construction materials

The NMR relaxation properties of hydrating blast-furnace slag cements have recently been shown to be dominated by the effect of water self-diffusion in internal magnetic field gradients in the pastes. While this was suggested on the basis of NMR relaxometry and magnetic susceptibility data, we report here the results from first direct studies of the water self-diffusion in the hydrating paste using a specialized PFG sequence and very intensive magnetic field gradient pulses.

Determination of genuine diffusivities in heterogeneous media using stimulated echo pulsed field gradient NMR

Pulsed field gradient (PFG) NMR diffusion measurements in heterogeneous media may lead to erroneous results due to the disturbing influence of internal magnetic field gradients. Here, we present a simple theoretical model which allows one to interpret data obtained by stimulated spin echo PFG NMR in the presence of spatially varying internal field gradients. Using the results of this theory, the genuine self-diffusion coefficients in heterogeneous media may be extrapolated from the dependence of the apparent diffusivities on the dephasing time of the simulated echo PFG NMR sequence. Experimental evidence that such extrapolation yields satisfactory results for self-diffusion of hexadecane in natural sediments (sand) and of n-octanol in doped MgO pastes is provided.