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  • Poster presentation
  • Open Access

Metabolic imaging of in vivo myocardium

  • 1, 2,
  • 3, 2 and
  • 1, 2
Journal of Cardiovascular Magnetic Resonance201517 (Suppl 1) :P251

https://doi.org/10.1186/1532-429X-17-S1-P251

  • Published:

Keywords

  • Ventricular Septal Defect
  • Normal Myocardium
  • Extracellular Volume Fraction
  • Efflux Rate Constant
  • Nominal Voxels

Background

The equilibrium cellular water efflux rate constant [kio; mean water lifetime inverse] from contrast agent [CA]-enhanced MRI measures on-going cellular Na+,K+-ATPase activity [turnover]. Good literature [4 different labs] agreement shows substantial kio decreases in myocardial ischemia, hypertension, or infarct regions (Table). The 3 methods used differ in extracellular ("outside") CAo level manipulation to change the MR shutter-speed relative to kio and the MR exchange condition reached: A) CAo steady-state, slow-exchange-regime; B) CAo titration, fast-exchange-regime [FXR]; and C) CAo wash-out, FXR. The independent intracellular volume fraction [ICV] - cell density•volume product and ≈ 1 - ECV [extracellular volume fraction] - also decreases in pathology. We hypothesize that kio mapping shows metabolic compromise most effectively. We report initial experience with tissue near a repaired ventricular septal defect [VSD].

Methods

We acquired serial 1.5T 1H2O T1-weighted data from a 27 yo male before and 3 times after a bolus IV 0.15 mmol/kg CA [Omniscan] injection. Quantitative Look-Locker T1 measurements [non-selective inversion, 21 recovery times] imaged an 8 mm slice with a mid-ventricular short axis location inferior to the VSD patch. Method C (CAo wash-out, FXR) determined kio and ICV values in six LV wall segments.

Results

The Figure shows a post-CA T1-w image: the endo- and epicardial LV wall edges as bright orange and green, respectively [light orange circle, an LV ROI]. Segmental ICV and kio values are given (yellow). Segments S5 and S6 comprise the septum. The ICV values for segments S1 - S4 are reasonable for normal myocardium (Table). Thus, we have indicated (*) a control myocardial kio value [5 s-1, Table], since the CA wash-out data quantity [3 points] and quality from these normal myocardium segments yielded insufficient precision. Interestingly, the kio value is reduced [4.5 s-1] in segment S6, and dramatically so [1.7 s-1; 66%↓] in segment S5, immediately inferior to the VSD patch.
Figure 1
Figure 1

Literature reports of active trans-membrane water cycling [kio] and intracellular volume fraction [ICV] values in normal and pathological myocardia.

Figure 2
Figure 2

Short axis T1-w image slice inferior to VSD patch. The kio and ICV values of six LV wall segments are given. kio and ICV are reduced (66% and 30%, respectively) in segment S5,immediately below the patch.

Conclusions

The kio biomarker is a sensitive measure of on-going myocardial metabolic activity. Our result suggests that tissue nearby a VSD patch can be, or become, metabolically compromised.

The ultimate goal is pixel-wise kio and ICV maps. [Here, nominal voxels are 2x2x8 mm3 = 32 μL.] For this, one needs data with good S/N and more than 3 wash-out points. Also, method C has systematic error absent in methods A and B, which cannot be used for humans. It assumes the CAo concentration equals that of CAp [in plasma] during wash-out. This is invalid for finite CA intravasation kinetics, which may be particularly slow in myocardial lesions due to common reduced vascularization. Possible kio and ICV underestimations can be corrected using Ktrans [the CA extravasation transfer constant] from the bolus tissue wash-in time-course to calculate the CA intravasation rate constant.

Funding

NIH: RO1-NS040801.

Authors’ Affiliations

(1)
Advanced Imaging Research Center, Oregon Health & Science University, Portland, OR, USA
(2)
Knight Cardiovascular Institute, Oregon Health & Science University, Portland, OR, USA
(3)
Division of Cardiovascular Medicine, Oregon Health & Science University, Portland, OR, USA

Copyright

© Springer et al; licensee BioMed Central Ltd. 2015

This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

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