Detecting low blood concentrations in joints using T1 and T2 mapping at 1.5, 3, and 7 T: an in vitro study

Abstract

Background: Intra-articular blood causes irreversible joint damage, whilst clinical differentiation between haemorrhagic joint effusion and other effusions can be challenging. An accurate non-invasive method for the detection of joint bleeds is lacking. The aims of this phantom study were to investigate whether magnetic resonance imaging (MRI) T1 and T2 mapping allows for differentiation between simple and haemorrhagic joint effusion and to determine the lowest blood concentration that can be detected.

Methods: Solutions of synovial fluid with blood concentrations ranging from 0 to 100% were scanned at 1.5, 3, and 7 T. T1 maps were generated with an inversion recovery technique and T2 maps from multi spin-echo sequences. In both cases, the scan acquisition times were below 5 min. Regions of interest were manually drawn by two observers in the obtained T1 and T2 maps for each sample. The lowest detectable blood concentration was determined for all field strengths.

Results: At all field strengths, T1 and T2 relaxation times decreased with higher blood concentrations. The lowest detectable blood concentrations using T1 mapping were 10% at 1.5 T, 25% at 3 T, and 50% at 7 T. For T2 mapping, the detection limits were 50%, 5%, and 25%, respectively.

Conclusions: T1 and T2 mapping can detect different blood concentrations in synovial fluid in vitro at clinical field strengths. Especially, T2 measurements at 3 T showed to be highly sensitive. Short acquisition times would make these methods suitable for clinical use and therefore might be promising tools for accurate discrimination between simple and haemorrhagic joint effusion in vivo.

Keywords: Haemarthrosis; Image interpretation (computer-assisted); Magnetic resonance imaging; Phantoms (imaging); Synovial fluid.

Fig. 1

a Nuclear magnetic resonance tubes with different ratios of synovial fluid and blood. Blood percentage from left to right: 0%, 2.5%, 5%, 10%, 25%, 50%, 75%, and 100%. b Phantom setup: a cylindrical water-filled holder with six samples, horizontally placed in a 16-channel knee coil using a 3-T MRI system. The phantom was equipped with a fiberoptic thermometer (the asterisk in all images) and a heating system based on heat exchange between water in the heating system (black arrows) and the water or oil volume in the phantom. c Scan image from the T1 mapping sequence. For each tube, a region of interest was manually placed within the tube region (example in yellow). d Scan image from the T2 mapping sequence

Fig. 2

Mean T1 and T2 value estimates for the different blood concentrations, at 3 field strengths. For 7 T, some of the estimates were not available, because artefacts or relaxation times were too short to be measured

Fig. 3

Effect of different acceleration techniques on T2 estimates at 1.5 T. T2 exhibited an inverse dependence on the blood concentration with all acceleration techniques. The three accelerated T2 mapping methods showed good agreement with the reference scan (echo spacing 30 ms), except from the 5% blood concentration measurement using the EPI acceleration technique. EPI, echo-planar imaging; TSE, turbo spin-echo; TSE+SENSE, turbo spin-echo with sensitivity encoding

Fig. 4

Bland-Altman plots for interobserver agreement regarding T1 and T2 measurements at 1.5 and 3 T. Horizontal dashed lines indicate the upper and lower limit of agreement from the mean by the two observers (ULoA/LLoA). For T1 measurements, the mean was − 28.99 ms, with a limit of agreement (LoA) equal to 143 ms. For T2 measurements, the mean was − 1.164 ms with LoA equal to 148 ms