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Pitfalls of blinded T1-map image analysis by human operator and impact on measured stress T1 responses

Session Poster session 1

Speaker Ambra Masi

Congress : EuroCMR 2019

  • Topic : imaging
  • Sub-topic : T1 and T2 Mapping, T2*
  • Session type : Poster Session
  • FP Number : P172

Authors : A Masi (Oxford,GB), Q Zhang (Oxford,GB), R Soundarajan (Oxford,GB), J Leal Pelado (Oxford,GB), C Baker (Oxford,GB), S Neubauer (Oxford,GB), VM Ferreira (Oxford,GB), SK Piechnik (Oxford,GB)

Authors:
A Masi1 , Q Zhang1 , R Soundarajan1 , J Leal Pelado1 , C Baker1 , S Neubauer1 , VM Ferreira1 , SK Piechnik1 , 1University of Oxford Centre for Clinical Magnetic Resonance Research, Division of Cardiovascular Medicine, Radcliffe Department of Medicine, John Radcliffe Hospital - Oxford - United Kingdom of Great Britain & Northern Ireland ,

Citation:
European Heart Journal - Cardiovascular Imaging ( 2019 ) 20 ( Supplement 2 ), ii129

Background
Stress T1-mapping is a novel technique for ischaemia testing without the need for gadolinium-based contrast agents. We investigate pitfalls of blinded T1-map analysis, using inter-method agreement between MOLLI and ShMOLLI T1-maps as an illustrative example of their impact on stress T1 results.

Methods
We prospectively scanned 18 patients (61±15 years; 72% male) referred for clinical stress CMR for inducible ischaemia, with varied pathology. All patients underwent CMR at 1.5 Tesla including cine, rest and Regadenoson stress T1-mapping using both ShMOLLI and MOLLI 5(3)3, perfusion and LGE imaging. Rest and stress T1-maps were analysed in the mid-ventricular short-axis view by a single human operator, blinded to other CMR images. T1 reactivity (T1stress - T1rest)/T1rest was analysed using original and eroded (mid-wall myocardium) contours on the segmental basis (n=108 segments).

Results
Stress T1 responses were clearly detectable (Table 1). ShMOLLI T1  measurements had a higher T1 reactivity (4%±4%) compared with MOLLI (3%±4%; p<0.01), with both methods showing similar intragroup variability. Head-to-head comparison of ShMOLLI versus MOLLI revealed low positive correlation R=0.15. Minimizing the partial volume as one known source of noise in T1, improved inter-method correlation to R=0.27. Inevitably linked reduction in sample volumes increased the SD and slightly reduced the statistical significance of the apparent difference in reactivity between methods (p<0.03). Inspection of cases with major discrepancies, intended to shed light on unexpectedly weak inter-method correlation, revealed pitfalls in blinded T1-map analysis, such as significant variations in the ROI thickness and failures to include subendocardial infarctions at the blood-myocardium interface (Figure 1).

Conclusion
T1-map analysis blinded to LGE imaging by a human operator affects the stress T1 results using both ShMOLLI and MOLLI techniques. Clear pitfalls identified include significant variations in the ROI wall thickness and missing subendocardial infarctions. Multi-stage image analysis approaches with robust quality control are required to deliver more reliable stress T1-mapping for clinical applications.

Whole myocardium Mid-wall myocardium

ShMOLLI

MOLLI

ShMOLLI

MOLLI

T1 rest (ms)

941±74

982±77

933±75

1014±58

T1 stress (ms)

982±77

1025±55

976±79

1045±61

ΔT1 (%)

4.5±4

2.9±4

4.7±5

3.2±5

Table 1. Comparison of segmental ShMOLLI and MOLLI rest-stress T1 (mean±SD) using Regadenoson in 18 patients referred for clinical stress CMR for inducible ischaemia.


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