The inflammatory arthritides are systemic disorders that can result in long-term deformity and disability. The occurrence of severe long term sequelae in affected patients has reduced, which is attributable to earlier detection of disease and advances in treatment, with increased use of disease modifying anti-rheumatic drugs (DMARDs) and biologic agents.
Synovitis is well understood as the hallmark of rheumatoid arthritis (RA) and responsible for joint destruction \cite{Chang2016}. Synovial angiogenesis has been proposed as one of the earliest markers of inflammatory arthritis and a critical early stage in the progression of synovitis and joint destruction. \cite{Gaffney1998,Vasanth2010}. In addition to nurturing the hyperplastic synovium, angiogenesis promotes persistence of synovial inflammation through the influx of inflammatory cells to create the disease-specific microenvironment in RA \cite{Pap2005} \cite{Connell2002}. Some effector molecules such as tumour necrosis factor-alpha (TNF-\(\alpha\)), vascular endothelial growth factor (VEGF) and angiopoietin 1 (Ang-1) have been identified as key elements in the development of new blood vessel formation. Inhibition of these angiogenic factors could reduce the progression of synovial hyperplasia and joint destruction \cite{Clavel2003}. Therefore, imaging identification of angiogenesis would allow early therapeutic intervention as a means of preventing joint destruction and improve the course of the disease \cite{Ostendorf2001}.
Magnetic Resonance Imaging (MRI) is highly sensitive in detecting the classic features of inflammatory arthritis, specifically synovitis and tendon related disease, erosions and Bone Marrow Oedema (BMO) as a precursor of erosive change\cite{Østergaard2005}. It is also sensitive for detection of enthesitis, one of the three key criteria (apart from dactylitis and peripheral arthritis) required to diagnose seronegative peripheral inflammatory disease \cite{Chang2016}. Contrast enhanced MRI is routinely used in our practice for early detection of disease and in diagnostically challenging cases. It is particularly useful in the small subgroup of patients that are in clinical remission but demonstrate radiological evidence of disease\cite{Østergaard2005} \cite{Molenaar2004}. Early treatment in this group confers a better outcome for patients and underpins the therapeutic strategy in inflammatory arthritides.
The synovial enhancement rate in contrast enhanced MRI has been shown to correlate with synovial volume, erosion, vascularity, capillary permeability and metabolic activity, and has been a classical marker of active disease \cite{Hodgson2008}. Magnetic Resonance Angiography (MRA) sequences, such as Time-resolved Imaging of Contrast KineticS (TRICKS, GEHC, Milwaukee, WI, USA), allow detection of newly recruited vessels in the early phase of disease, prior to diffuse synovial enhancement \cite{Vasanth2010}. Dynamic contrast enhancement also allows analysis of perfusion parameters, specifically, the peak or maximum enhancement. This measure has been shown to correlate with patient rated pain and the degree of synovitis on histology \cite{Vordenbäumen2014}. When fused to a structural volumetric T1 sequence, this can provide a pictorial representation of areas of synovitis.
Utilising these techniques can prove difficult in a clinical environment, particularly as there is an increased amount of imaging for the radiographers and interpreting radiologists to process and analyse. Therefore, the utility and practicality when compared to post-contrast imaging must be evaluated. This pilot study describes our initial experience and evaluates the benefit of TRICKS magnetic resonance angiographic (MRA) imaging and peak enhancement fusion images in the assessment of synovitis at the metacarpophalangeal joints.
Methods and materials
Patient selection:
We retrospectively collected data from consecutive patients who had local institutional MR imaging to assess for synovitis over a period of 1 year (August 2015 to August 2016). Patients who did not have complete TRICKS sequences where excluded.
MRI Imaging:
Patients were positioned with the hand of interest elevated above the head on the scanning table with a small field of view coil (knee coil) applied. All imaging was acquired on a GE 3T Discovery 750 MR scanner (GEHC, Milwaukee, WI, USA).
The standard protocol included: axial and coronal T1, T2 fat-saturated (FS) and post-contrast T1 FS sequences. Dynamic contrast enhanced MRA images were acquired at the same time using the TRICKS sequence . Only a single injection of 10ml of MR contrast, Gadavist (Bayer Healthcare Pharmaceuticals Inc, Wayne NJ, USA) was required. Although a standard field of view for the TRICKS sequence was specified, this was altered in some patients due to subject size differences.