POS0958 RESPONSIVENESS OF CONVENTIONAL, SEMI-AUTOMATIC AND FULL-AUTOMATIC METHODS TO QUANTIFY MARROW BONE EDEMA LESIONS IN MRI OF AXIAL SPONDYLOARTHRITIS PATIENTS: A PILOT STUDY

Background:

The presence or absence of marrow bone edema (MBE) in the sacroiliac joints (SIJ) is very important in the diagnosis of axial Spondyloarthritis (axSpA). The quantification of this lesion and its extension may be important to analyze responsiveness of the treatment. Several scoring systems have been proposed for MRI images of SIJ, some of them being observer dependent (Berlin, SPARCC). Others, works in a semi-automatically way, such as the s-SCAISS[1], which makes it possible to quantify the size of the lesion, based on the indication of the expert. Recently, methods like the KITs4R[2], based on a deep patch-based classification network. allow a fully automated detection and quantification of the MBE lesions.

Objectives:

To analyze responsiveness of several scores (observer independent, semiautomatic and full automatic) for quantify MBE in SIJ of axSpA patients.

Methods:

Two rheumatologists independently quantified SIJ images from axSpA patients by visual inspection methods (Berlin and SPARCC indexes) and a semiautomatic system (s-SCAISS) on a single semi-coronal MRI slide (STIR). Full semi-coronal MRI images (15 to 18 slices) were used for an automatic detection algorithm (KITs4R), where total MBE was calculated as sum of areas of MBE in each slice. Patients were assessed before TNF-α therapy (PRE) and 3 months later (POST). Spearman correlations was used to analyze relationship between variables, Wilcoxon signed-rank test for significant differences and Cohen’s d for calculating the effect size of improvement. Figure 1 shows processing of the MRI images: A) Area of MBE selected by the SCAISS, when the rheumatologist “click” on each MBE; B) Lesions detected automatically by KITs4R; C) Automated deep segmentation of bones and subchondral regions (with split into quadrants with central axes of joints also shown. D) Superposed A, B and C images.

Results:

12 axSpA patients were recruited from the CASTRO cohort (42% female, age 46±11 years, disease duration 16±13 years, BMI 28±5). Results PRE and POST are shown in Table 1: mean values (sd), statistical significance (NS, not significant; *, p<0.05; **, p<0.01), and effect size. Activity indexes and CRP were lower. ASDAS and CRP shown significant differences and a large effect size. All MRI scores showed good responsiveness (ES medium-large, p<0.01), specially KITs4R. Agreement between all MRI scores were high (r>0.8;p<0.01). Between semiautomatic and automatic methods, this agreement was also excellent (r=0.92;p<0.001). Correlation in improvements (reductions in scores) were also significant between all MRI scores (r>0.7;p<0.05).

PREPOSTSignESBASDAI6.12 (2.45)4.96 (2.74)N.S.0.44-SmallASDAS3.61 (1.04)2.58 (1.25)*0.89-LargeCRP11.26 (8.93)4.81 (4.08)**0.84-LargeBERLIN2.58 (1.98)1.17 (1.85)**0.74-MediumSPARCC3.92 (3.42)1.58 (2.43)**0.69-MediumSCAISS295 (332)95 (163)**0.68-MediumKITs4R1671 (1596)258 (421)**1.04-Large

NS, not significant; *, p<0.05; **, p<0.01

Conclusion:

All MRI scores have good level of agreement between them and good responsiveness. Berlin and SPARCC are observer dependent, and do not quantify the extension of the MBE area. s-SCAIS helps to this quantification. KITs4R is not observer dependent but clinimetric validation, analizing agreement level with human expert, is necessary. New advanced tools are improving quantitative and objective measurement of BME which is important to analyze responsiveness.

References:

[1]Development and validation of SCAISS, a tool for semi-automated quantification of sacroilitis by magnetic resonance in spondyloarthritis. Rheumatol Int. 2018 Oct;38(10):1919-1926.

[2]The semi-automated algorithm for the detection of bone marrow oedema lesions in patients with axial spondyloarthritis. Rheumatol Int. 2020 Apr;40(4):625-633.

Disclosure of Interests:

None declared.

From simple to complex networks: inherent structures, barriers, and valleys in the context of spin glasses

Given discrete degrees of freedom (spins) on a graph interacting via an energy function, what can be said about the energy local minima and associated inherent structures? Using the lid algorithm in the context of a spin glass energy function, we investigate the properties of the energy landscape for a variety of graph topologies. First, we find that the multiplicity N(s) of the inherent structures generically has a log-normal distribution. In addition, the large volume limit of ln <N(s)>/<ln N(s)> differs from unity, except for the Sherrington-Kirkpatrick model. Second, we find simple scaling laws for the growth of the height of the energy barrier between the two degenerate ground states and the size of the associated valleys. For finite connectivity models, changing the topology of the underlying graph does not modify qualitatively the energy landscape, but at the quantitative level the models can differ substantially.

Stochastic simulations of remodeling applied to a two-dimensional trabecular bone structure

In this investigation the stochastic dynamics of trabecular bone remodeling (which is a key concept in a range of remodeling models) is verified. For this purpose, two-dimensional binary images of horizontal histological sections of lumbar vertebral bone (L-3) were collected from young and old subjects. Then the stochastic algorithm of remodeling was applied to the images of young trabecular bone. The resulting images of "simulated" old structures and those of "real" old structures were analyzed to evaluate the following architectural parameters: bone volume/trabecular volume; mean area of marrow cavities; mean trabeculae length; marrow space star volume; Euler number density; trabecular thickness; trabecular number; trabecular separation; mean two-point distance along the skeleton of trabecular structure; probability of disconnection; the ratio of marrow space star volume to geometrical volume and dimensionless ratio of mean area of marrow cavities; and mean trabecular length squared (form factor). Using the parametric t-test, the groups of simulated and real old bone images were compared. It is found that the p value of the t-test is never less than 0.20. For eight parameters the p value is >0.45. It is concluded that, as long as the horizontal sections of lumbar vertebrae are considered (sections perpendicular to the direction of the main spine load), the stochastic algorithm of bone remodeling will properly reproduce the architectural properties of trabecular bone.

Optimizing the assessment of age-related changes in trabecular bone

The goal of this study was to develop an optimal procedure to determine age-related changes in trabecular bone. The investigations were based on two-dimensional images of the human vertebral trabecular bone specimens. The following indices of trabecular structure were considered: bone volume/total volume, star volume of the marrow cavity, Euler number and the probability of disconnection (straightforwardly connected with the number of separated parts of the network). To follow precisely the changes in the trabecular structure with age, a computer simulation model was used. Up to 35 years of physiological remodelling were simulated. The validation of the model calculations was based on a quantitative comparison with the data measured for older individuals. The simulations confirmed that the description of the age-related changes in the trabecular bone by means of the architectural parameter (star volume) constitutes a promising tool for subjects older than approximately 50 years. For individuals younger than approximately 50 years bone mineral density (bone volume/total volume) seems to be the best suited descriptor. The results suggest that the optimal diagnostic procedure is age-dependent and should not be limited to the bone mineral density measurement. The clinical usefulness of the procedure has been validated by examination of the CT images.

Comparison of trabecular bone architecture in young and old bones

In this study, different parameters currently applied for the description of trabecular bone architecture in young and old subjects are compared. Moreover, new parameters are proposed and assessed. For the investigations, the two-dimensional images of vertebral body sections are acquired with the use of a low-magnification digital camera. The parameters were calculated both for the skeleton and for the bone/marrow interface distinguished in the images of the trabecular network. The following methods of the descriptions of the trabecular bone architecture were considered: histomorphometric analysis (BV/TV, asymmetry, mean trabeculae length), fractal geometry technique, Euler characteristic, star volume of the marrow cavity, the mean distance between two points of the trabecular network, and the probability of disconnection (is straightforwardly connected with the number of separated parts of the network). Moreover, bone mineral density (BMD) was determined for comparative purposes. The quantities directly extracted form the images are also combined to produce new indexes, which better differentiate young and old bones. It was found that the BMD, the BV/TV, the star volume, the Euler number, and the probability of disconnection might be used as indicators of the age-related changes of trabecular bone. The parameters could be measured with the precision comparable to that of the BMD. The only exception is the probability of disconnection. Highly significant correlations were demonstrated between bone density (BMD, BV/TV) and trabecular architecture (SV/GV, probability of disconnection).