Measurement accuracy. Applications in X-ray computed tomography (CT) dose reduction and magnetic resonance spectroscopy (MRS) volume selection

X-ray computed tomography (CT) images of transaxial cross sections of the body can be used to determine tissue volumes. However, the considerable radiation dose associated with high-quality clinical images has greatly limited the use of CT for this application. The relationship between the accuracy of the volume measurement and the radiation dose to the patient was analysed. A simple method to evaluate the X-ray-exposure-to-accuracy performance of the CT system was developed and applied. Finally, a manual procedure for radiation exposure control was designed, in which the largest diameter of the patient's cross section is used to determine the CT scan parameters for minimal radiation dose. This procedure was evaluated in clinical routine and resulted in substantially reduced radiation doses with maintained accuracy in the volume determination. Depending on the thickness of the patient, radiation dose levels of 1-45 % of that of a standard CT examination of the abdomen were achieved. This exposure control procedure could be applied to achieve dose reduction in most CT applications. Furthermore, radiation exposure control can and should be a standard feature of every CT system, to allow automatic optimisation of scan parameters for each patient resulting in minimal radiation dose.The potential success of 1H and 31P magnetic resonance spectroscopy (MRS) as a clinical and research tool depends on several factors. One is the ability to accurately restrict the MRS measurement to a tissue volume of interest (e.g. a tumour), despite the fact that the receiver coil of the magnetic resonance (MR) system collects the MR signal from a much larger part of the body. This requires that MRS be used with a volume selection technique, usually combined with MR imaging of the body region to plan the position and size of the MRS volume. A method was developed to experimentally evaluate volume selection performance of the MR system. A new test phantom was designed for point-wise measurements of high precision, and was used to obtain high spatial resolution signal profiles of 31P MRS volume selections with ISIS. Detailed information was obtained of the size, shape and position of the actual MRS volume. Position errors of several mm, signal loss and transition zones of the actual volume in question were demonstrated. The position errors were analysed and significant contributions from off-resonance effects were found, due to measurement parameters that are controllable by the user in both MR imaging and MRS. The spatial inaccuracy, due to magnetic field distortions of the test phantom itself, was analysed and found to be very small, typically a few hundredths of a mm. The mechanical inaccuracy of the phantom was 0.5 mm. The test method developed can be applied to MRS under clinical conditions and requires no special test functionality or adaptation of the MR system. The detailed information provided by this measurement technique can aid the development of more efficient volume selection techniques. It can also be utilised to increase the efficiency of volume-selective MRS in clinical practise

A Novel Framework for repeated measurements in diffusion tensor imaging

In the context of diffusion tensor imaging (DTI), the utility of making repeated measurements in each diffusion sensitizing direction has been the subject of numerous stud- ies. One can estimate the true signal value using either the raw complex-valued data or the real-valued magnitude signal. While conventional methods focus on the former strategy, this paper proposes a new framework for acquiring/processing repeated measurements based on the latter strategy. The aim is to enhance the DTI processing pipeline by adding a diffusion signal estimator (DSE). This permits us to exploit the knowledge of the noise distribution to estimate the true signal value in each direction. An extensive study of the proposed framework, including theoretical analysis, experiments with synthetic data, performance evaluation and comparisons is presented. Our results show that the precision of estimated diffusion parameters is dependent on the number of available samples and the manner in which the DSE accounts for noise. The proposed framework improves the precision in estimation of diffusion parameters given a sufficient number of unique measurements. This encourages future work with rich real datasets and downstream applications

Abnormal brain processing of gentle touch in anorexia nervosa

Body image disturbance is a core symptom in anorexia nervosa (AN). Recent research suggests that abnormalities in touch perception may contribute to the disease mechanisms in AN. Here, we used functional magnetic resonance imaging (fMRI) to study possible abnormalities in cortical processing of affective touch in AN. Gentle skin strokes were applied to the right forearm during fMRI scanning in women diagnosed with AN (n = 25) and in matched healthy controls (HC; n = 25). Blocks of skin stroking were alternated with blocks of static skin indentation. Participants provided ratings of the pleasantness of skin stroking stimulation. AN participants perceived skin stroking as significantly less pleasant than HC. We observed no group differences for the contrast between skin stroking and skin indentation in primary tactile regions. We did find, however, significantly less activity in the AN group in areas including left caudate nucleus. Also, we found less activity in the AN group in bilateral lateral occipital cortex for the main effect of skin stroking. Our results suggest that abnormal functioning of the dorsal striatum could affect evaluation of pleasant tactile stimuli, and that abnormal functioning of the lateral occipital cortex might be related to disturbed body image perception.Funding Agencies|European Union Seventh Framework Program (FP7/2007-2013) [PIOF-GA-2012-302896]; Soderstrom Konig Foundation; Linnea and Joself Carlssons Foundation; Fredrik och Ingrid Thuring Foundation; O. E. och Edla Johanssons Foundation; Stiftelsen Wilhelm och Martina Lundgrens vetenskapsfond; ALF Vastra Gotaland</p

Image Fusion of Reconstructed Digital Tomosynthesis Volumes From a Frontal and a Lateral Acquisition

Digital tomosynthesis (DTS) has been used in chest imaging as a low radiation dose alternative to computed tomography (CT). Traditional DTS shows limitations in the spatial resolution in the out-of-plane dimension. As a first indication of whether a dual-plane dual-view (DPDV) DTS data acquisition can yield a fair resolution in all three spatial dimensions, a manual registration between a frontal and a lateral image volume was performed. An anthropomorphic chest phantom was scanned frontally and laterally using a linear DTS acquisition, at 120 kVp. The reconstructed image volumes were resampled and manually co-registered. Expert radiologist delineations of the mediastinal soft tissues enabled calculation of similarity metrics in regard to delineations in a reference CT volume. The fused volume produced the highest total overlap, implying that the fused volume was a more isotropic 3D representation of the examined object than the traditional chest DTS volumes

MRI diffusion and perfusion alterations in the mesencephalon and pons as markers of disease and symptom reversibility in idiopathic normal pressure hydrocephalus.

IntroductionCore symptomatology in idiopathic normal pressure hydrocephalus (iNPH) points at dysfunction in the mesencephalon and pons indicating pathological changes in these regions, but only a few studies have addressed the issue. The aim of this study was to investigate diffusion (ADC) and perfusion patterns pre- and postoperatively in these areas in iNPH.MethodsTwenty iNPH patients and 15 healthy controls were included. Patients underwent a clinical examination and brain MRI pre- and 3-6 months postoperatively. The MRI-scan included diffusion and dynamic susceptibility contrast perfusion weighted sequences. Regions of interest in the mesencephalon and pons were drawn on a FLAIR sequence and co-registered to ADC maps and perfusion data.ResultsThere were no significant differences in pre or postoperative ADC compared to the control group, however postoperative ADC increased by 10% (p = 0.026) in the mesencephalon and 6% (p = 0.016) in the pons in all patients and also in the subgroup of shunt responders by 11% (p = 0.021) and 4% (p = 0.020), respectively. Preoperative relative cerebral blood flow (rCBF) was similar in iNPH patients and controls. Postoperatively, rCBF increased in shunt responders by 6% (p = 0.02) in the mesencephalon and 11% (p = 0.004) in the pons. This increase correlated with the degree of clinical improvement (rs = 0.80, p = 0.031 and rs = 0.66, p = 0.021, respectively).ConclusionThe postoperative increase in ADC and the correlation between postoperative increase in rCBF and clinical improvement in the mesencephalon and pons shown in this study point at an involvement of these areas in the core pathophysiology and its reversibility in iNPH

Absolute quantification of cerebral blood flow in neurologically normal volunteers: Dynamic-susceptibility contrast MRI-perfusion compared with computed tomography (CT)-perfusion

To improve the reproducibility of arterial input function (AIF) registration and absolute cerebral blood flow (CBF) quantification in dynamic-susceptibility MRI-perfusion (MRP) at 1.5T, we rescaled the AIF by use of a venous output function (VOF). We compared CBF estimates of 20 healthy, elderly volunteers, obtained by computed tomography (CT)-perfusion (CTP) and MRP on two consecutive days. MRP, calculated without the AIF correction, did not result in any significant correlation with CTP. The rescaled MRP showed fair to moderate correlation with CTP for the central gray matter (GM) and the whole brain. Our results indicate that the method used for correction of partial volume effects (PVEs) improves MRP experiments by reducing AIF-introduced variance at 1.5T. Magn Reson Med, 2009

Hippocampal volumes in patients exposed to low-dose radiation to the basal brain. A case–control study in long-term survivors from cancer in the head and neck region

Abstract Background An earlier study from our group of long time survivors of head and neck cancer who had received a low radiation dose to the hypothalamic-pituitary region, with no signs of recurrence or pituitary dysfunction, had their quality of life (QoL) compromised as compared with matched healthy controls. Hippocampal changes have been shown to accompany several psychiatric conditions and the aim of the present study was to test whether the patients’ lowered QoL was coupled to a reduction in hippocampal volume. Methods Patients (11 men and 4 women, age 31–65) treated for head and neck cancer 4–10 years earlier and with no sign of recurrence or pituitary dysfunction, and 15 matched controls were included. The estimated radiation doses to the basal brain including the hippocampus (1.5 – 9.3 Gy) had been calculated in the earlier study. The hippocampal volumetry was done on coronal sections from a 1.5 T MRI scanner. Measurements were done by two independent raters, blinded to patients and controls, using a custom method for computer assisted manual segmentation. The volumes were normalized for intracranial volume which was also measured manually. The paired t test and Wilcoxon’s signed rank test were used for the main statistical analysis. Results There was no significant difference with respect to left, right or total hippocampal volume between patients and controls. All mean differences were close to zero, and the two-tailed 95% confidence interval for the difference in total, normalized volume does not include a larger than 8% deficit in the patients. Conclusion The study gives solid evidence against the hypothesis that the patients’ lowered quality of life was due to a major reduction of hippocampal volume.</p