Quantification of myocardial extracellular volume without blood sampling

Area of Science:

• Cardiovascular Imaging
• Biomedical Engineering
• Radiology

Background:

• Cardiac magnetic resonance (CMR) T1 relaxation time mapping is crucial for assessing diffuse interstitial fibrosis and edema.
• Myocardial extracellular volume (ECV) quantification, derived from T1 mapping, reflects non-cardiomyocyte tissue proportion.
• Conventional ECV calculation necessitates blood sampling for hematocrit (HCT), limiting clinical routine due to HCT variability.

Purpose of the Study:

• To evaluate the accuracy and applicability of synthetic ECV measurement derived from CMR without blood sampling.
• To analyze the impact of regression models on the bias of synthetic ECV compared to conventional methods.
• To explore the potential of non-invasive ECV in conditions with expected large alterations, such as cardiac amyloidosis.

Main Methods:

• Systematic review and meta-analysis of published studies on synthetic ECV.
• Secondary analysis of existing data to assess the influence of regression modeling on bias.
• Investigation of the inverse relationship between blood T1 relaxation rate (R1) and HCT to estimate synthetic HCT.

Main Results:

• A good overall correlation and minimal bias were observed between synthetic and conventional ECV measurements across reviewed studies.
• Despite promising results, questions regarding the absolute accuracy of the synthetic ECV method persist.
• Linear regression using local T1 relaxation time data is recommended for calculating synthetic ECV formulas.

Conclusions:

• Synthetic ECV offers a non-invasive quantitative assessment of myocardial extracellular space, especially when timely HCT measurements are impractical.
• This method is particularly valuable in clinical scenarios with expected significant ECV changes, like cardiac amyloidosis.
• Local formula calculation via linear regression is advised due to the dependence of T1 relaxation times on specific imaging setups.