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Pitfalls in MR measurement of tissue blood flow with intravascular tracers: which mean transit time?
R M Weisskoff1, D Chesler, J L Boxerman
1Massachusetts General Hospital, Department of Radiology, Charlestown 02129.
Abstract:
Measuring tissue blood flow with NMR imaging of intravascular tracers is more difficult than measurements of tissue blood volume. One major obstacle to the application of the Central Volume Principle is the direct measurement of the mean transit time. In this note, we demonstrate that mean transit time (MTT), which relates tissue blood volume to blood flow via the Central Volume Principle, is not the first moment of the concentration-time curve for MR or CT imaging of purely intravascular tracers. However, while first moment methods cannot be used by themselves to determine absolute flow, we show that transit curves may provide a useful relative measure of flow, for example, by considering ratios of the first moments.
Insights
Measuring tissue blood flow using intravascular tracers is challenging. This study shows mean transit time (MTT) is not the first moment in imaging, but transit curves offer relative flow measurements.
Area of Science:
- Medical Imaging
- Physiology
- Biophysics
Background:
- Measuring tissue blood flow using intravascular tracers presents significant challenges.
- The Central Volume Principle, relating blood volume to blood flow, is hindered by difficulties in directly measuring mean transit time (MTT).
Purpose of the Study:
- To investigate the relationship between mean transit time (MTT) and the first moment of the concentration-time curve for intravascular tracers in NMR and CT imaging.
- To explore alternative methods for assessing relative tissue blood flow when absolute flow measurement is difficult.
Main Methods:
- Analysis of concentration-time curves derived from MR or CT imaging of purely intravascular tracers.
- Theoretical demonstration that MTT is not the first moment of these curves.
Main Results:
- The mean transit time (MTT) is demonstrated not to be the first moment of the concentration-time curve for purely intravascular tracers in MR or CT imaging.
- While first moment methods alone cannot determine absolute blood flow, transit curves can provide a useful relative measure of flow.
Conclusions:
- Direct measurement of mean transit time (MTT) using first moment analysis is not feasible for purely intravascular tracers in standard imaging techniques.
- Relative blood flow assessment can be achieved by analyzing ratios of the first moments from transit curves, offering a practical alternative for certain applications.