Cardiac MRI Tagging & Strain Simulator

Cardiac Cycle

Phase in cycle 0%

Mechanical phaseDiastole

Myocardial Mechanics

Peak contractility 20%

Peak transmural twist 12°

Tag-Derived Strain (live)

Circumferential E_cc

0.0%

Radial E_rr

0.0%

Transmural twist

0.0°

Wall thickness

0.60

How it works

SPAMM (Spatial Modulation of Magnetization) tagging saturates a grid of thin parallel planes in the myocardium immediately after the R-wave. Because the grid is burned into the tissue's own magnetization, each intersection is a real material (Lagrangian) marker that moves with the heart muscle for ~200–300 ms before the tags fade by T1 relaxation — long enough to capture systolic contraction.

Deformation gradient:  F = ∂x/∂X
Green–Lagrangian strain: E = ½(FᵀF − I)
Reported clinically (engineering form):
  Ecc = (L − L0)/L0   (circumferential, mid-wall arc)
  Err = (h − h0)/h0    (radial, wall thickness)

This simulator drives a simplified but physically consistent transmural deformation field: the endocardial border moves inward more than the epicardial border (so the wall thickens as it contracts — Err > 0), the circumference shortens as the radius shrinks (Ecc < 0), and a twist angle is applied that decays linearly from full at the endocardium to zero at the epicardium, reproducing the transmural shear that real HARP/feature-tracking analysis of tagged cine MRI recovers as LV torsion. Grid points inside the myocardial ring bend with this field; points in the blood pool and background stay fixed, exactly as static tissue looks on a real tagged image.

Peak contractility — how far the endocardium moves inward at peak systole, which sets the magnitude of both Ecc and Err (they are coupled through wall geometry, as in real myocardium).
Peak transmural twist — endocardial rotation relative to the epicardium at peak systole; reduced twist is an early marker of subclinical dysfunction even when ejection fraction is still normal.
Phase slider / Play — scrub or auto-play one cardiac cycle; the mechanical phase follows a rapid-contraction / slower-relaxation envelope, as in a real pressure–volume cycle.

Clinical relevance: tagging-derived strain and twist detect regional myocardial dysfunction (e.g. after infarction, or in early cardiomyopathy) before global measures like ejection fraction change, which is why strain imaging is used alongside standard cine cardiac MRI.

Myocardium (deforming) Tag grid (material markers)

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