AB0796 Quantitative bone marrow lesion characterization at the sacroiliac joint with T1-mapping

Background

Conventional magnetic resonance imaging (MRI) uses T1-weighted and short-tau inversion recovery (STIR) sequences to characterize bone marrow lesions in axial spondyloarthritis. However, quantification is restricted to the extent of marrow lesions because signal intensities are highly variable within and across patients and scanners. Furthermore, some marrow lesions are less visible in MRI and need further characterization with computed tomography (CT), e.g. sclerosis. Quantitative MRI in form of mapping sequences might help to better characterize bone marrow lesions.

Objectives

To evaluate the performance of T1-mapping for differentiating different bone marrow lesions at the sacroiliac joints in patients with suspected axial spondyloarthritis.

Methods

Sixty-two patients (mean age 41±12.5; thirty-two were finally diagnosed with axial spondyloarthritis and 30 with another condition) underwent CT and MRI of the sacroiliac joints. Besides standard oblique coronal T1 and STIR sequences a T1-mapping sequence (Modified Look-Locker Inversion Recovery) was added to the protocol. Bone marrow lesions (maximum 4 lesions per patient, 1 lesion of the same type per joint) were characterized by an expert radiologist into four groups, namely sclerosis (lesion type (LT) 1), osteitis (LT2), fat lesion (LT3) and mixed marrow lesions (LTm). Relaxation times on T1-maps were compared using Kruskal-Wallis test correcting for multiple comparisons and correlated to quantitative measures from conventional MRI sequences and CT.

Results

119 lesions were selected (LT1: 38, LT2: 27, LT3: 40; LTm: 14). T1-map showed highly significant differences between LT1-3 with the lowest values for sclerosis (1522±227 ms), followed by osteitis (1906±82 ms) and fat lesions (2391±200 ms); p<0.0005. However, mixed lesions showed a broad distribution of values (1869±670), irrespective of their characteristics. T1-map correlated to a high degree with conventional T1-values (r = 0.74) and Hounsfield units in CT (r = -0.69) with p < 0.0001, respectively, but not with STIR (p = 0.8).

Conclusion

T1-Mapping allows for accurately characterizing lesions at the sacroiliac joint in patients with suspected axial spondyloarthritis and, thus, may combine information from two conventional sequences and CT into one in the future while providing superior capacity for quantification. However, in our study mixed lesions and inhomogeneous bone marrow remained problematic. Thus, further sequence development is needed before its implementation in clinical routine.

Figure 1.

T1-mapping values of the different lesions, LT1: Sclerosis, LT2: Osteitis, LT3: Fat lesion, LTm: Mixed lesion. Differences are highly significant, which allows T1-mapping to characterize those different lesions in one sequence.

Disclosure of Interests

Torsten Diekhoff Speakers bureau: Novartis, Eli Lilly, MSD, Canon MS, Consultant of: Novartis, Dominik Deppe: None declared, Denis Poddubnyy: None declared, Katharina Ziegeler: None declared, Fabian Proft: None declared, Kay-Geert Hermann: None declared, Mikhail Protopopov: None declared, Felix Radny: None declared, Marcus Makowski: None declared

OP0256 CHOOSE WISELY: IMAGING FOR DIAGNOSIS OF AXIAL SPONDYLOARTHRITIS

Background:

To date, the European Alliance of Associations for Rheumatology (EULAR) guidelines recommend X-ray (XR) as first line imaging in axial Spondyloarthritis (axSpA) and magnetic resonance imaging (MR) if the diagnosis cannot be established by XR and clinical features. However, much knowledge has been gained recently strengthening the applicability of MR for the detection of structural lesions and raising the question, whether XR is still necessary. Also, several publications used low-dose computed tomography (CT) as reference standard and imaging test.

Objectives:

In light of this complex diagnostic situation, the aim of this study was to compare the three major modalities, XR, MR and CT of SIJ, in their diagnostic performance of axSpA and differential diagnosis in a cohort of patients with low back pain using the final judgment of the rheumatologist as standard of reference.

Methods:

163 patients (89 with axSpA; 74 with degenerative diseases) underwent XR, CT and MR. Three blinded experts categorized the imaging into axSpA, other diseases or normal in 5 separate reading rounds (XR, CT, MR, XR+MR, CT+MR, respectively). The results were compared to the clinical diagnosis. Sensitivity and specificity values for axSpA and interrater reliability were compared.

Results:

XR showed lower sensitivity and specificity (66.3%/67.6% respectively) compared to MR (82.0%/86.5%) and CT (77.5%/97.3%). Sensitivity and specificity of XR+MR was similar to MR alone (77.5% / 87.8%). However, CT+MR was superior to MR alone (75.6% / 97.3%) (see Figure). CT had the best interrater reliability (kappa = 0.875) followed by MR (0.665) and XR (0.517). CR+MR reliability was similar (0.662) compared to MR alone, while CT+MR reliability (0.732) was superior.

Figure 1.

Frequency of positive and negative findings in radiography (XR), computed tomography (CT), magnetic resonance imaging (MR) and combinations and resulting diagnostic accuracy values. SE: Sensitivity, SP: Specificity, LR-/+: negative/positive likelihood ratio.

Conclusion:

In conclusion, XR is inferior to cross-sectional imaging and should be replaced by MR or CT for differential diagnosis. While MR is the most sensitive imaging technique, it lacks specificity when compared to CT. CT alone has high diagnostic accuracy, despite being insensitive to bone marrow lesions such as fatty metaplasia or osteitis. Adding CT to MR leads to an increase in specificity at a minor expense of sensitivity.

References:

[1]Sieper J, Rudwaleit M, Baraliakos X, et al. The Assessment of SpondyloArthritis international Society (ASAS) handbook: a guide to assess spondyloarthritis. Ann Rheum Dis. 2009;68 Suppl 2:ii1-44.

[2]Mandl P, Navarro-Compán V, Terslev L, et al. EULAR recommendations for the use of imaging in the diagnosis and management of spondyloarthritis in clinical practice. Ann Rheum Dis. 2015;74(7):1327-39.

[3]Diekhoff T, Hermann KA, Greese J, et al. Comparison of MRI with radiography for detecting structural lesions of the sacroiliac joint using CT as standard of reference: results from the SIMACT study. Ann Rheum Dis. 2017.

[4]Diekhoff T, Greese J, Sieper J, Poddubnyy D, Hamm B, Hermann KA. Improved detection of erosions in the sacroiliac joints on MRI with volumetric interpolated breath-hold examination (VIBE): results from the SIMACT study. Ann Rheum Dis. 2018;77(11):1585-89.

[5]Baraliakos X, Hoffmann F, Deng X, Wang YY, Huang F, Braun J. Detection of Erosions in Sacroiliac Joints of Patients with Axial Spondyloarthritis Using the Magnetic Resonance Imaging Volumetric Interpolated Breath-hold Examination. The Journal of rheumatology. 2019;46(11):1445-49.

[6]Wu H, Zhang G, Shi L, et al. Axial Spondyloarthritis: Dual-Energy Virtual Noncalcium CT in the Detection of Bone Marrow Edema in the Sacroiliac Joints. Radiology. 2019;290(1):157-64.

Disclosure of Interests:

Torsten Diekhoff Speakers bureau: Canon MS, Roche, Novartis, MSD, Grant/research support from: Assessment of Spondyloarthritis International Society, Iris Eshed: None declared, Felix Radny: None declared, Katharina Ziegeler: None declared, Fabian Proft: None declared, Juliane Greese: None declared, Dominik Deppe: None declared, Robert Biesen: None declared, Kay-Geert Hermann: None declared, Denis Poddubnyy: None declared

A fully synthetic human Fab antibody library based on fixed VH/VL framework pairings with favorable biophysical properties

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Spontaneous lifetime in a dielectrically-apertured Fabry-Perot microcavity

We present calculations of the modification of the spontaneous emission rate from a point source dipole in a Fabry-Perot microcavity containing an optically thin dielectric aperture. The dielectric aperture is described as a passive current source which is driven by the spontaneous point source. The spontaneous emission rate is shown to depend on the details of the aperture design, and shows a strong enhancement on resonance due to 3-dimensional optical confinement by the dielectric aperture.