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Quantitative 3D myocardial perfusion at systole and diastole with a dual echo arterial input function

Jason K Mendes¹, Ganesh Adluru¹, Devavrat Likhite¹, Apoorva Pedgaonkar¹, Merlin J Fair^2,3, Peter D Gatehouse^2,3, Brent Wilson⁴, and Edward V DiBella¹

¹Radiology and Imaging Sciences, University of Utah, Salt Lake City, UT, United States, ²Cardiovascular Magnetic Resonance Unit, Royal Brompton Hospital, London, United Kingdom, ³National Heart & Lung Institute, Imperial College London, London, United Kingdom, ⁴Cardiology, University of Utah, UT, United States

Synopsis

Quantitative 3D myocardial perfusion is a clinically realistic goal and this work further develops and combines several innovative sequence designs to achieve this goal. These developments include an optimized 3D stack of stars readout (150ms per beat), acquisition and T2* correction of an arterial input function, tailored saturation pulse design and potential whole heart coverage at both systole and diastole at heart rates up to 109 bpm. Implementation and quantitative perfusion results are shown for healthy volunteers and a patient with known coronary disease.

Purpose

While the feasibility of 2D quantitative cardiac perfusion has been established^1-3 the increased coverage and slice resolution of 3D methods aid in identifying ischemic burden, increase confidence that any defects have been identified, and may offer improved handling of respiratory motion⁴. However, reduced clinical utility of 3D methods⁵ has been observed because the increased acquisition time of 3D data typically requires a decrease in spatial resolution. In addition, a measured Arterial Input Function (AIF)^6-7 with T2* correction of the AIF to reduce the over estimation of myocardial blood flow⁸ , and quantification of blood flow at different cardiac phases⁹ would provide further diagnostic benefit and make 3D cardiac perfusion more clinically viable. Free-breathing acquisition would also make the studies easier to perform. The combination of all these concepts is further complicated by the fact that perfusion is often required during a stressed state where heart rates exceed 100bpm. Consequently, only a limited number of 3D perfusion studies have been reported^10-13 with none addressing all the problems and concepts discussed above. This work demonstrates the feasibility of free-breathing 3D perfusion (at systole and diastole) with a measured and T2* corrected AIF.

Methods

All studies were performed on a Siemens Prisma 3T MRI scanner. Data was acquired with an ECG gated/free breathing hybrid sequence (2D radial AIF combined with 3D radial stack of stars). For 3D, the resolution was 1.8mm x 1.8mm x 5mm, 8 partitions, TE/TR=0.77/1.54ms, 98 rays per beat (25 in the central partition) and a total readout time of 150ms (325ms including the 6 RF saturation pulses¹⁴ and a 150ms saturation recovery time (SRT)). The 2D AIF data was acquired with a resolution of 1.8mm x 1.8mm x 8mm, 20 rays per beat and TE1/TE2/TR=0.99/1.87/2.75ms for a total readout time of 55ms (99ms including the saturation block and a 20ms SRT). The total time per beat for the AIF and both systolic and diastolic 3D data sets (Figure 1a) is 750ms (80bpm) and is sufficient for most rest perfusion studies. However, a more efficient technique (Figure 1b) can embed the AIF acquisition into the 3D perfusion SRT time resulting in a total time of just over 650ms (92 bpm) and is more appropriate for stress studies. For even higher heart rates, using a 3D perfusion SRT of 100ms allows acquisition up to 109bpm. Data was reconstructed using a joint multi-slice and multi-coil algorithm with temporal¹ and spatial¹⁵ total variation constraints, and processed with Matlab software¹⁶ to obtain quantitative perfusion values. Systolic and diastolic 3D perfusion data were acquired in 10 subjects (53±19 years) with 0.075 mmol/kg of ProHance (gadoteridol, Bracco Diagnostics) injected at 5 ml/s with a 20ml saline flush.

Results and Discussion

The efficient AIF method (Figure 1) does not measure the AIF in the same volume as the 3D perfusion but rather in an adjacent basal slice. For validation purposes, the AIF was acquired both within the 3D perfusion volume and in the basal slice during the same injection (Figure 2). Each AIF was acquired at two echo times to allow proper T2* correction (Figure 2a). The basal AIFs agree well with the standard AIF with the bolus arriving slightly sooner in the left atrium as expected. Perfusion was quantified in the 3D volume for this subject using each AIF (Figure 2b) with good agreement between the standard and efficient methods. Source images at both systole and diastole (at the beginning of myocardial enhancement) for a normal volunteer and a patient with quadruple bypass surgery and a known infarct are shown in Figure 3. The quantified mean blood flow for the inner 6 slices are summarized by the bull’s eye plots in Figure 4.

Conclusion

We have demonstrated the feasibility of performing quantitative 3D perfusion at systole and diastole with heart rates up to 109 bpm. We have confirmed that even at these high heart rates, it is possible to acquire a measured and T2* corrected AIF. Initial perfusion values are consistent with those published in literature.

Acknowledgements

No acknowledgement found.

References

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Figures

Figure 1: Standard and efficient methods of acquiring an AIF. For the standard method (top row), the AIF (yellow slice) is measured at the center of the 3D volume (blue volume) and consequently must occur outside the non-selective saturation pulse (NS-Sat) and delay of the 3D acquisition. In the efficient method (bottom row), the AIF is acquired basal to the 3D volume and shares the saturation pulse of the 3D volume and overlap with the 3D Saturation Recovery Time (TD3D). The diagram is scaled to time appropriately with the efficient method reducing the acquisition time per beat by about 100ms.

Figure 2: Comparison of the AIF obtained from the standard and efficient methods. The first and second echoes (a) are shown for both the standard (left column) and the efficient methods (right column). The efficient method AIF measured in the ascending aorta (red line and arrow) has slightly better agreement with the standard method (blue line and arrow) than the efficient method measured in the left atrium (green line and arrow). Average blood flows at systole and diastole calculated from all three AIFs are shown in the corresponding colored boxes (b).

Figure 3: Quantitative 3D perfusion source images at the beginning of myocardial enhancement. Shown are all 8 slices in both systole and diastole for a 31 year old female volunteer (a) and a 63 year old male patient (b) with quadruple bypass surgery and a known infarct.

Figure 4: Regional mean blood flow for the normal volunteer and quadruple bypass patient with known infarct. Average blood flow over the whole volume is shown below each bull’s eye plot.

Proc. Intl. Soc. Mag. Reson. Med. 25 (2017)

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