Medical device-grade T1 phantom for T1 mapping quality assurance


Myocardial T1 mapping and extracellular volume (ECV) have the potential to guide patient care and serve as surrogate end-points in clinical trials in many cardiac pathologies. Several T1 mapping sequences implementations are available, on different platforms, at 1.5T and 3T. The majority of these sequences rely on measuring tissue T1 relaxation times by fitting an exponential recovery curve to a series of images following an inversion pulse.

Acquired Raw Image
Figure 1. (a) Acquired raw images. (b) Calculated T1 map with ShMOLLI

T1 mapping can aid in the study and understanding of several cardiac pathologies such as myocarditis or amyloid (figure 2):

Native T1 Maps
Figure 2. Native T1 maps and late gadolinium-enhancement (LGE) images in some cardiac pathologies.

Although factors influencing T1 mapping stability and inter-sequence comparisons are well understood, measurements differ between different cardiac-MRI scanners and pulse sequences used. Additionally, little is known about T1 mapping delivery at a larger scale over many sites and there is no global quality assurance (QA) system. The main aim of this project was to form a collaboration of a specialist MRI small-medium enterprise (Resonance Health, Australia), clinicians, physicist and metrology institutes (work led by Prof. James Moon). Therefore, a phantom covering clinically relevant ranges of T1 and T2 in blood and myocardium (pre and post contrast at 1.5T and 3T) was designed. A schematic representation of the T1MES phantom is shown in figure 3:

Intenal Phantom Structure
Figure 3. Internal and external phantom structure.

Phantom
Figure 4. Phantom T1 quantification. Each phantom consists of 9 tubes with various T1 and T2 values.

Worldwide phantom data was analysed at the BHC by cardiology research fellows and physics students with an analysis toll developed in-house.

Quality Assurance T1
Figure 5. Quality assurance of T1 mapping: the initial T1MES CMR centers

Analysis of all phantom data is currently being undertaken. Future results will explore T1 mapping sequences, platform performance, stability and the potential for standardisation.