Selecting registration schemes in case of interstitial lung disease follow-up in CT

CALIPER: A deformable image registration algorithm for large geometric changes during radiotherapy for locally advanced non-small cell lung cancer

PURPOSE

Locally advanced non-small cell lung cancer (NSCLC) patients may experience dramatic changes in anatomy during radiotherapy and could benefit from adaptive radiotherapy (ART). Deformable image registration (DIR) is necessary to accurately accumulate dose during plan adaptation, but current algorithms perform poorly in the presence of large geometric changes, namely atelectasis resolution. The goal of this work was to develop a DIR framework, named Consistent Anatomy in Lung Parametric imagE Registration (CALIPER), to handle large geometric changes in the thorax.

METHODS

Registrations were performed on pairs of baseline and mid-treatment CT datasets of NSCLC patients presenting with atelectasis at the start of treatment. Pairs were classified based on atelectasis volume change as either full, partial, or no resolution. The evaluated registration algorithms consisted of several combinations of a hybrid intensity- and feature-based similarity cost function to investigate the ability to simultaneously match healthy lung parenchyma and adjacent atelectasis. These components of the cost function included a mass-preserving intensity cost in the lung parenchyma, use of filters to enhance vascular structures in the lung parenchyma, manually delineated lung lobes as labels, and several intensity cost functions to model atelectasis change. Registration error was quantified with landmark-based target registration error and post-registration alignment of atelectatic lobes.

RESULTS

The registrations using both lobe labels and vasculature enhancement in addition to intensity of the CT images were found to have the highest accuracy. Of these registrations, the mean (SD) of mean landmark error across patients was 2.50 (1.16) mm, 2.80 (0.70) mm, and 2.04 (0.13) mm for no change, partial resolution, and full atelectasis resolution, respectively. The mean (SD) atelectatic lobe Dice similarity coefficient was 0.91 (0.08), 0.90 (0.08), and 0.89 (0.04), respectively, for the same groups. Registration accuracy was comparable to healthy lung registrations of current state-of-the-art algorithms reported in literature.

CONCLUSIONS

The CALIPER algorithm developed in this work achieves accurate image registration for challenging cases involving large geometric and topological changes in NSCLC patients, a requirement for enabling ART in this patient group.

Does obesity attenuate the beneficial cardiovascular effects of cardiorespiratory fitness?

BACKGROUND AND AIMS

Higher cardiorespiratory fitness is associated with lower pulse wave velocity and arterial stiffness in normal weight individuals, and this has not been examined in obese individuals. It is unclear whether an altered body composition acts as a modifier of the association between cardiorespiratory fitness and arterial stiffness. We examined the association between peak oxygen uptake and brachial-ankle pulse wave velocity and analysed whether body composition attenuates this association in obese middle-aged individuals.

METHODS

Bio-impedance analysis-derived body composition assessment in 212 healthy and sedentary either overweight or obese individuals was followed by measurement of brachial-ankle pulse wave velocity and spiroergometric peak oxygen uptake. Multivariate analysis was performed to analyse the association between peak oxygen uptake and brachial-ankle pulse wave velocity and to assess the moderating effect of several body composition-related interaction terms (BMI, total body mass, body fat mass, waist circumference, waist-to-height ratio) on this association.

RESULTS

Peak oxygen uptake was inversely associated with brachial-ankle pulse wave velocity (β = -0.059, 95% CI = -0.099; -0.018, p = 0.005). Testing for the impact of different body composition-related interaction terms on this association showed no significance, 95% CI lateralized towards positivity.

CONCLUSIONS

This study shows an inverse association between cardiorespiratory fitness and arterial stiffness in middle-aged obese individuals. We also found a tendency towards an attenuating impact of an obese body composition on this association. Physical fitness seems to be a stronger modulator of cardiovascular risk than body composition but the success of training efforts may be compromised by obesity.

A novel approach for local abdominal aortic aneurysm growth quantification

Although aneurysm size still remains the most accepted predictor of rupture risk, abdominal aortic aneurysms (AAAs) with maximum diameter smaller than 5 cm may also rupture. Growth rate is an additional marker for rupture risk as it potentially reflects an undesirable wall remodeling that leads to fast regional growth. Currently, an indication for surgery is an expansion rate >10 mm/year, measured as change in maximum diameter over time. However, as AAA expansion is non-uniform, it is questionable whether measurement of maximum diameter change over time can capture increased localized remodeling activity. A method for estimating AAA surface area growth is introduced, providing a better measure of local wall deformation. The proposed approach is based on the non-rigid iterative closest point algorithm. Optimization and validation is performed using 12 patient-specific AAA geometries artificially deformed to produce a target surface with known nodal displacements. Mesh density sensitivity, range of uncertainty, and method limitations are discussed. Application to ten AAA patient-specific follow-ups suggested that maximum diameter growth does not correlate strongly with the maximum surface growth (R ² = 0.614), which is not always colocated with maximum diameter, or uniformly distributed. Surface growth quantification could reinforce the quality of aneurysm surveillance programs.