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Final Program


Program-At-A-Glance

Rapid Fire Session

Session: Rapid Fire Session 4: New Contrast Techniques (Monitor 14)

Quantifying Myocardial Perfusion without Exogenous Contrast Agents Through Arterial Oxygen Tension Modulation

Friday, February 6, 2026
4:13 PM - 4:20 PM  
Location: Galapagos / Aruba / Ilhabela (2nd Lower Level)
Background: First-pass CMR is a proven method for evaluating myocardial perfusion; however, it requires GBCAs, which are contraindicated in patients with severe renal dysfunction, a source of hypersensitivity, and in consideration of environmental pollution1,2. To address these limitations, recent efforts have exploited the susceptibility effect of deoxygenated hemoglobin (dOHb) as an endogenous contrast agent for quantifying perfusion in brain and kidney3,4. However, this approach has not yet been studied in the heart. We developed a free-running, high-temporal-resolution, simultaneous multi-slice (SMS), T2-CMR technique to test whether a prospective arterial oxygen modulation protocol can also be used to quantify myocardial perfusion.

Methods: Ten healthy canines (20-25kg) were studied in a 3T MRI system (Biograph mMR, Siemens, Germany). Arterial blood gases were targeted using an automated prospective blood gas system (Thornhill Research Inc., Canada)5. A free-running, SMS, T2 CMR sequence (T2-prep:60ms, voxel size:1.6×1.6×6mm3, MB factor:3, total scan time:7 mins) was prescribed, and images were reconstructed at every 5 heartbeats via the CMR multitasking framework6. Images were then processed to quantify MBF, MBV, and MTT via the DSC framework with the 16-segment AHA model3,4,7. During the gas modulation, T2w signal changes in the myocardium and LV were converted into dOHb using the T2-relaxation model: ΔR2(t) = -(1/TET2-prep)ln[S(t)/S0] and a reported ΔR2-dOHB model8. The LV dOHb curve served as an arterial input function(AIF), and MBV was computed as the area-under-the-curve ratio of the tissue to the AIF per segment. MBF was estimated by deconvolving the tissue curve with the AIF, and MTT was defined as MBV/MBF.

Results: Fig. 1A shows measured end-tidal oxygen pressure (PETO2) and oxygen saturation (SO2) tracked the target waveform. Fig. 1B shows representative short-axis T2w images acquired using the SMS method. Fig. 1C illustrates highly time-resolved mid-slice images, demonstrating signal fluctuations in both the LV and myocardium consistent with P<sub>ETO2 modulations. T2w signals measured in the myocardium and LV, and changes in dOHb are shown in the signal traces below. In addition to qualitative signal tracking, the method enabled quantitative perfusion mapping. Fig. 2 shows regional rest perfusion metrics, with average values (MBF: 1.19 ± 0.16 ml/g/min; MBV: 0.10 ± 0.01 ml/g; MTT: 5.32 ± 0.51 s).

Conclusion: This study is the first to assess myocardial perfusion using free-running, T2 CMR combined with precise dOHb modulation. Our measures of perfusion metrics are consistent with those determined in healthy canines using other methods, including first-pass CMR and ¹³N-ammonia PET9-11. While our findings are early and the methods need to be validated under disease conditions, dynamic alterations in dOHb have the potential to evolve as a safe, inexpensive, noninvasive, repeatable, and environmentally sustainable alternative to GBCA-based quantitative myocardial perfusion imaging.

Figure 1. Free-running T2 CMR during controlled PETO₂ modulation: spatial coverage and oxygenation-driven signal dynamics. (A) Measured PETO₂ from the RespirAct system and SO₂ closely tracked the target PETO₂ waveform, indicating excellent protocol adherence. (B) Representative images from apical, mid, and basal slices demonstrate the spatial coverage of the proposed imaging technique. (C) Mid-slice images (mid-diastole and end-expiration) during the gas modulation show dynamic signal changes in the left ventricular (LV) blood pool and myocardium. Corresponding T2 signal and derived dOHb concentration for the LV blood pool (red) and septal myocardium (blue) exhibit consistent oxygenation-driven variations, supporting the method’s sensitivity and temporal resolution.
Figure 2. Segmental myocardial perfusion metrics in healthy canines at rest. Segment-wise perfusion measurements, including myocardial blood flow (MBF: 1.19 ± 0.16 ml/g/min, A), myocardial blood volume (MBV: 0.10 ± 0.01 ml/g, B), and mean transit time (MTT: 5.32 ± 0.51 s, C), are shown for healthy canine models based on the AHA 16-segment model.