Oesophageal IGRT considerations for SBRT of LA-NSCLC: barium-enhanced CBCT and interfraction motion

Background To determine the optimal volume of barium for oesophageal localisation on cone-beam CT (CBCT) for locally-advanced non-small cell lung cancers (NSCLC) and quantify the interfraction oesophageal movement relative to tumour. Methods Twenty NSCLC patients with mediastinal and/or hilar disease receiving radical radiotherapy were recruited. The first five patients received 25 ml of barium prior to their planning CT and alternate CBCTs during treatment. Subsequent five patient cohorts, received 15 ml, 10 ml and 5 ml. Six observers contoured the oesophagus on each of the 107 datasets and consensus contours were created. Overall 642 observer contours were generated and interobserver contouring reproducibility was assessed. The kappa statistic, dice coefficient and Hausdorff Distance (HD) were used to compare barium-enhanced CBCTs and non-enhanced CBCTs. Oesophageal displacement was assessed using the HD between consensus contours of barium-enhanced CBCTs and planning CTs. Results Interobserver contouring reproducibility was significantly improved in barium-enhanced CBCTs compared to non-contrast CBCTs with minimal difference between barium dose levels. Only 10 mL produced a significantly higher kappa (0.814, p = 0.008) and dice (0.895, p = 0.001). The poorer the reproducibility without barium, the greater the improvement barium provided. The median interfraction HD between consensus contours was 4 mm, with 95% of the oesophageal displacement within 15 mm. Conclusions 10 mL of barium significantly improves oesophageal localisation on CBCT with minimal image artifact. The oesophagus moves substantially and unpredictably over a course of treatment, requiring close daily monitoring in the context of hypofractionation.

Comparison between Widefield Optical Coherence Tomography Devices in Eyes with High Myopia

Background: To compare four different optical coherence tomography (OCT) devices for visualization of retinal and subretinal layers in highly myopic eyes. Methods: In this prospective, observational, cross-sectional study, consecutive patients with high myopia and control subjects were imaged by four OCT devices: Spectralis OCT2, PlexElite 2.0 100 kHz, PlexElite 2.0 200 kHz and the Canon Xephilio OCT-S1. The acquisition protocol for comparison consisted of single vertical and horizontal line scans centered on the fovea. Comparison between the devices in the extent of visible retina, presence of conjugate image or mirror artifacts, visibility of the sclerochoroidal interface and retrobulbar tissue. Results: 30 eyes with high myopia and 30 control subjects were analyzed. The visualized RPE length was significantly different between the OCT devices with Xephilio OCT-S1 imaging the largest extent (p < 0.0001). The proportion of eyes with conjugate image artifact was significantly higher with the Spectralis OCT (p < 0.0001), and lower with the PlexElite 200 kHz (p < 0.0001). No difference in visibility of the sclerochoroidal interface was noted among instruments. The retrobulbar tissue was visible in a higher proportion of eyes using swept-source PlexElite 100 kHz and 200 kHz (p < 0.007) compared to the other devices. Conclusions: In highly myopic eyes, the four OCT devices demonstrated significant differences in the extent of the retina imaged, in the prevalence of conjugate image artifact, and in the visualization of the retrobulbar tissue.

Anterior Mediastinal Lesion Segmentation Based on Two-Stage 3D ResUNet With Attention Gates and Lung Segmentation

ObjectivesAnterior mediastinal disease is a common disease in the chest. Computed tomography (CT), as an important imaging technology, is widely used in the diagnosis of mediastinal diseases. Doctors find it difficult to distinguish lesions in CT images because of image artifact, intensity inhomogeneity, and their similarity with other tissues. Direct segmentation of lesions can provide doctors a method to better subtract the features of the lesions, thereby improving the accuracy of diagnosis.MethodAs the trend of image processing technology, deep learning is more accurate in image segmentation than traditional methods. We employ a two-stage 3D ResUNet network combined with lung segmentation to segment CT images. Given that the mediastinum is between the two lungs, the original image is clipped through the lung mask to remove some noises that may affect the segmentation of the lesion. To capture the feature of the lesions, we design a two-stage network structure. In the first stage, the features of the lesion are learned from the low-resolution downsampled image, and the segmentation results under a rough scale are obtained. The results are concatenated with the original image and encoded into the second stage to capture more accurate segmentation information from the image. In addition, attention gates are introduced in the upsampling of the network, and these gates can focus on the lesion and play a role in filtering the features. The proposed method has achieved good results in the segmentation of the anterior mediastinal.ResultsThe proposed method was verified on 230 patients, and the anterior mediastinal lesions were well segmented. The average Dice coefficient reached 87.73%. Compared with the model without lung segmentation, the model with lung segmentation greatly improved the accuracy of lesion segmentation by approximately 9%. The addition of attention gates slightly improved the segmentation accuracy.ConclusionThe proposed automatic segmentation method has achieved good results in clinical data. In clinical application, automatic segmentation of lesions can assist doctors in the diagnosis of diseases and may facilitate the automated diagnosis of illnesses in the future.

Magnetic resonance microscopy of samples with translational symmetry with FOVs smaller than sample size

In MRI, usually the Field of View (FOV) has to cover the entire object. If this condition is not fulfilled, an infolding image artifact is observed, which suppresses visualization. In this study it is shown that for samples with translational symmetry, i.e., those consisting of identical objects in periodic unit cells, the FOV can be reduced to match the unit cell which enables imaging of an average object, of which the signal is originated from all unit cells of the sample, with no punishment by a loss in signal-to-noise ratio (SNR). This theoretical prediction was confirmed by experiments on a test sample with a 7 × 7 mm2 unit cell arranged in a 3 × 3 matrix which was scanned by the spin-echo and by single point imaging methods. Effects of experimental imperfections in size and orientation mismatch between FOV and unit cell were studied as well. Finally, this method was demonstrated on a 3D periodic sample of tablets, which yielded well-resolved images of moisture distribution in an average tablet, while single tablet imaging provided no results. The method can be applied for SNR increase in imaging of any objects with inherently low signals provided they can be arranged in a periodic structure.

The effect of device configuration and patient’s body composition on image artifact and RF heating of deep brain stimulation devices during MRI at 1.5T and 3T

BACKGROUNDPatients with deep brain stimulation (DBS) implants have limited access to MRI due to safety concerns associated with RF-induced heating. Currently, MRI in these patients is allowed only in 1.5T horizontal scanners and with pulse sequences with reduced power. Nevertheless, off-label use of MRI at 3T is increasingly reported based on limited safety assessments. Here we present results of systematic RF heating measurements for two commercially available DBS systems during MRI at 1.5T and 3T.PURPOSETo assess the effect of imaging landmark, DBS lead configuration, and patient body composition on RF heating of DBS leads during MRI at 1.5 T and 3T.STUDY TYPEPhantom study.POPULATION/SUBJECTS/PHANTOM/SPECIMEN/ANIMAL MODELGel phantoms and cadaver brain.FIELD STRENGTH/SEQUENCE1.5T and 3T, T1-weighted turbo spin echo.ASSESSMENTRF heating was measured at tips of DBS leads implanted in brain-mimicking gel.STATISTICAL TESTSNone.RESULTSWe observed substantial fluctuation in RF heating mainly affected by phantom composition and DBS lead configuration, ranging from 0.14°C to 23.73°C at 1.5 T, and from 0.10°C to 7.39°C at 3T. The presence of subcutaneous fat substantially altered RF heating at electrode tips (−3.06°C < ΔT < 19.05°C). Introducing concentric loops in the extracranial portion of the lead at the surgical burr hole reduced RF heating by up to 89% at 1.5T and up to 98% at 3T compared to worst case heating scenarios.DATA CONCLUSIONDevice configuration and patient body composition significantly altered the RF heating of DBS leads during MRI at 1.5T and 3T. Interestingly, certain lead trajectories consistently reduced RF heating and image artifact over different imaging landmarks, RF frequencies, and phantom compositions. Such trajectories could be implemented in patients with minimal disruption to the surgical workflow.