Ultrasound-assisted carbon ion dosimetry and range measurement using injectable polymer-shelled phase-change nanodroplets: in vitro study.

Methods allowing for in situ dosimetry and range verification are essential in radiotherapy to reduce the safety margins required to account for uncertainties introduced in the entire treatment workflow. This study suggests a non-invasive dosimetry concept for carbon ion radiotherapy based on phase-change ultrasound contrast agents. Injectable nanodroplets made of a metastable perfluorobutane (PFB) liquid core, stabilized with a crosslinked poly(vinylalcohol) shell, are vaporized at physiological temperature when exposed to carbon ion radiation (C-ions), converting them into echogenic microbubbles.

Ultrasound-assisted investigation of photon triggered vaporization of poly(vinylalcohol) phase-change nanodroplets: A preliminary concept study with dosimetry perspective.

Purpose: We investigate the vaporization of phase-change ultrasound contrast agents using photon radiation for dosimetry perspectives in radiotherapy.

Methods: We studied superheated perfluorobutane nanodroplets with a crosslinked poly(vinylalcohol) shell. The nanodroplets' physico-chemical properties, and their acoustic transition have been assessed firstly.

Effect of a Radiotherapeutic Megavoltage Beam on Ultrasound Contrast Agents.

Collateral damage to healthy surrounding tissue during conventional radiotherapy increases when deviations from the treatment plan occur. Ultrasound contrast agents (UCAs) are a possible candidate for radiation dose monitoring. This study investigated the size distribution and acoustic response of two commercial formulations, SonoVue/Lumason and Definity/Luminity, as a function of dose on clinical megavoltage photon beam exposure (24 Gy).

Modulating ultrasound contrast generation from injectable nanodroplets for proton range verification by varying the degree of superheat.

Purpose: Despite the physical benefits of protons over conventional photon radiation in cancer treatment, range uncertainties impede the ability to harness the full potential of proton therapy. While monitoring the proton range in vivo could reduce the currently adopted safety margins, a routinely applicable range verification technique is still lacking. Recently, phase-change nanodroplets were proposed for proton range verification, demonstrating a reproducible relationship between the proton range and generated ultrasound contrast after radiation-induced vaporization at 25°C.

Characterization of an inorganic scintillator for small-field dosimetry in MR-guided radiotherapy.

Introduction: Aim of this study is to dosimetrically characterize a new inorganic scintillator designed for magnetic resonance-guided radiotherapy (MRgRT) in the presence of 0.35 tesla magnetic field (B).

Methods: The detector was characterized in terms of signal to noise ratio (SNR), reproducibility, dose linearity, angular response, and dependence by energy, field size, and B orientation using a 6 MV magnetic resonance (MR)-Linac and a water tank.

Proton range verification with ultrasound imaging using injectable radiation sensitive nanodroplets: a feasibility study.

Technologies enabling in vivo range verification during proton therapy are actively sought as a means to reduce the clinical safety margins currently adopted to avoid tumor underdosage. In this contribution, we applied the semi-empirical theory of radiation-induced vaporization of superheated liquids to coated nanodroplets. Nanodroplets are injectable phase-change contrast agents that can vaporize into highly echogenic microbubbles to provide contrast in ultrasound images.

Phase Change Ultrasound Contrast Agents with a Photopolymerized Diacetylene Shell.

Phase change contrast agents for ultrasound (US) imaging consist of nanodroplets (NDs) with a perfluorocarbon (PFC) liquid core stabilized with a lipid or a polymer shell. Liquid ↔ gas transition, occurring in the core, can be triggered by US to produce acoustically active microbubbles (MBs) in a process named acoustic droplet vaporization (ADV). MB shells containing polymerized diacetylene moiety were considered as a good trade off between the lipid MBs, showing optimal attenuation, and the polymeric ones, displaying enhanced stability.

Attenuation estimation by repeatedly solving the forward scattering problem.

Estimation of the attenuation is important in medical ultrasound not only for correct time-gain compensation but also for tissue characterization. In this paper, the feasibility of a new method for attenuation estimation is tested. The proposed method estimates the attenuation by repeatedly solving the forward wave propagation problem and matching the simulated signals to the measured ones.

Modeling the dose dependence of the vis-absorption spectrum of EBT3 GafChromic™ films.

Purpose: The aim of this work was to model the dose dependence of the darkening of GafChromic™ EBT3 films by combining the optical properties of the polydiacetylene polymer phases, and a modified version of the single-hit model, which will take the stick-like shape of the monomer microcrystals into account. Second, a comparison is made between the quantification of the film darkening by flatbed scanning and by UV-vis absorption spectroscopy.

Method: GafChromic EBT3 films were irradiated with a 6 MV photon beam at dose levels between 0 and 50 Gy.

A multidisciplinary approach unravels early and persistent effects of X-ray exposure at the onset of prenatal neurogenesis.

Background: In humans, in utero exposure to ionising radiation results in an increased prevalence of neurological aberrations, such as small head size, mental retardation and decreased IQ levels. Yet, the association between early damaging events and long-term neuronal anomalies remains largely elusive.

Methods: Mice were exposed to different X-ray doses, ranging between 0.

Longitudinal in vivo microcomputed tomography of mouse lungs: No evidence for radiotoxicity.

Before microcomputed tomography (micro-CT) can be exploited to its full potential for longitudinal monitoring of transgenic and experimental mouse models of lung diseases, radiotoxic side effects such as inflammation or fibrosis must be considered. We evaluated dose and potential radiotoxicity to the lungs for long-term respiratory-gated high-resolution micro-CT protocols. Free-breathing C57Bl/6 mice underwent four different retrospectively respiratory gated micro-CT imaging schedules of repeated scans during 5 or 12 wk, followed by ex vivo micro-CT and detailed histological and biochemical assessment of lung damage.

Geometric regularization for 2-D myocardial strain quantification in mice: an in-silico study.

Myocardial strain quantification in the mouse based on 2-D speckle tracking using real-time ultrasound datasets is feasible but remains challenging. The major difficulty lies in the fact that the frame rate-to-heart rate ratio is relatively low, causing significant decorrelation between subsequent frames. In this setting, regularization is therefore particularly important to discard motion estimates that are improbable.

Hippocampal malrotation in pediatric patients with epilepsy associated with complex prefrontal dysfunction.

Purpose: The cognitive consequences of hippocampal malrotation (HIMAL) were investigated in a matched control study of children with epilepsy.

Methods: Seven children with HIMAL were compared on a range of memory and attention tasks with 21 control children with epilepsy without temporal role pathology and 7 children with epilepsy and magnetic resonance imaging (MRI)-documented hippocampal sclerosis. In addition, in a statistical morphometric analysis, MRI studies from four children with HIMAL were compared to similar images of 20 age-matched typically developing control children.

On the construction of an inter-subject diffusion tensor magnetic resonance atlas of the healthy human brain.

Voxel based morphometry (VBM) has been increasingly applied to detect diffusion tensor (DT) image abnormalities in patients for different pathologies. An important requisite for a robust VBM analysis is the availability of a high-dimensional non-rigid coregistration technique that is able to align both the spatial and the orientational DT information. Consequently, there is a need for an inter-subject DTI atlas as a group specific reference frame that also contains this orientational DT information.

Nonrigid coregistration of diffusion tensor images using a viscous fluid model and mutual information.

In this paper, a nonrigid coregistration algorithm based on a viscous fluid model is proposed that has been optimized for diffusion tensor images (DTI), in which image correspondence is measured by the mutual information criterion. Several coregistration strategies are introduced and evaluated both on simulated data and on brain intersubject DTI data. Two tensor reorientation methods have been incorporated and quantitatively evaluated.

Atlas-to-image non-rigid registration by minimization of conditional local entropy.

In this paper an algorithm for atlas-to-image non-rigid registration based on regional entropy minimization is presented. Tissue class probabilities in the atlas are registered with the intensities in the target image. The novel aspect of the paper consists in using tissue class probability maps that include the three main regions (for the brain, white matter, gray matter and csf) and a further partitioning thereof.

Construction and validation of mean shape atlas templates for atlas-based brain image segmentation.

In this paper, we evaluate different schemes for constructing a mean shape anatomical atlas for atlas-based segmentation of MR brain images. Each atlas is constructed and validated using a database of 20 images for which detailed manual delineations of 49 different subcortical structures are available. Atlas construction and atlas based segmentation are performed by non-rigid intensity-based registration using a viscous fluid deformation model with parameters that were optimally tuned for this particular task.

Linear normalization of MR brain images in pediatric patients with periventricular leukomalacia.

The feasibility of linear normalization of child brain images with structural abnormalities due to periventricular leukomalacia (PVL) was assessed in terms of success rate and accuracy of the normalization algorithm. Ten T1-weighted brain images from healthy adult subject and 51 from children (4-11 years of age) were linearly transformed to achieve spatial registration with the standard MNI brain template. Twelve of the child brain images were radiologically normal, 22 showed PVL and 17 showed PVL with additional enlargement of the lateral ventricles.

An information theoretic approach for non-rigid image registration using voxel class probabilities.

We propose two information theoretic similarity measures that allow to incorporate tissue class information in non-rigid image registration. The first measure assumes that tissue class probabilities have been assigned to each of the images to be registered by prior segmentation of both of them. One image is then non-rigidly deformed to match the other such that the fuzzy overlap of corresponding voxel object labels becomes similar to the ideal case whereby the tissue probability maps of both images are identical.

Atypical neuropsychological profile in a boy with 22q11.2 Deletion Syndrome.

In this article the general and specific cognitive impairments of the boy R.H. with a de novo deletion 22q11.

A viscous fluid model for multimodal non-rigid image registration using mutual information.

We propose a multimodal free-form registration algorithm based on maximization of mutual information. The warped image is modeled as a viscous fluid that deforms under the influence of forces derived from the gradient of the mutual information registration criterion. Parzen windowing is used to estimate the joint intensity probability of the images to be matched.