Hypothesis & Rationale • Controversy exists in the specificity of dynamic contrast enhanced (DCE) MRI. We have previously shown (Aref et al, Invest Radiol. 2002. 37:178-92) that the spatial resolution greatly affects the values of contrast agent transfer rates calculated from DCE MRI data using a two-compartment model. In DCE MRI spatial resolution is sacrificed for temporal resolution. We and others (Su et al, JMRI. 2003. 18:467-77) have hypothesized that this partial volume effect is the reason for the controversy as different groups use vastly different spatial and temporal resolutions. As a possible means of increasing temporal resolution without sacrificing spatial resolution, many investigators (Kucharczyk et al, AJR. 1994. 163:671-9, Liang et al, IEEE Trans Med Imaging. 2003. 22:1026-30) have tried using reduced encoding techniques. Below we analyze the limits of spatial resolution and three reduced encoding techniques on quantitative measurements of contrast agent transfer rates. • We are testing the hypothesis that dynamic reference sets in reduced-encoding techniques have spatial resolution limits for accurate quantitative tumor typing based on volume normalized contrast agent transfer rates between tumor plasma and extravascular extracellular space (EES), K pt /V T , obtained from dynamic contrast enhanced (DCE) MRI.
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2004 ISMRM E-poster Effect of Reduced Encoding Dynamic Data Size on Permeability-Surface Area Estimation
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Hypothesis & Rationale • Controversy exists in the specificity of dynamic contrast enhanced (DCE) MRI.
We have previously shown (Aref et al, Invest Radiol. 2002. 37:178-92) that the spatial resolution greatly affects the values of contrast agent transfer rates calculated from DCE MRI data using a two-compartment model. In DCE MRI spatial resolution is sacrificed for temporal resolution. We and others (Su et al, JMRI. 2003. 18:467-77) have hypothesized that this partial volume effect is the reason for the controversy as different groups use vastly different spatial and temporal resolutions. As a possible means of increasing temporal resolution without sacrificing spatial resolution, many investigators (Kucharczyk et al, AJR. 1994. 163:671-9, Liang et al, IEEE Trans Med Imaging. 2003. 22:1026-30) have tried using reduced encoding techniques. Below we analyze the limits of spatial resolution and three reduced encoding techniques on quantitative measurements of contrast agent transfer rates.
• We are testing the hypothesis that dynamic reference sets in reduced-encoding techniques have spatial resolution limits for accurate quantitative tumor typing based on volume normalized contrast agent transfer rates between tumor plasma and extravascular extracellular space (EES), Kpt/VT, obtained from dynamic contrast enhanced (DCE) MRI.
• Thirty-six 30-day old female Sprague-Dawley rats were injected with n-ethyl-n-nitrosourea. Ten of these animals with infiltrating ductal carcinomas were analyzed in this study.
• Two-compartment model with Kp↔t PS (F >> PS)
Materials & Methods
Distribution
Excretion Injection
The two-compartment model (above) and a plot of the plasma compartment (right).
Table 3: The p-value of the t-test adjusted step down Bonferroni for Kp↔t/VT obtained from the top five FFT “hot spot” locations in Keyhole, RIGR, and TRIGR reconstructed with PEDYN = 128, 64, 32, 24, 16, and 4 compared to fully reconstructed FFT (PE = 128) (n = 10).
Conclusions • Keyhole: the top five Kpt/VT “hot spots” from fully reconstructed FFT and
Keyhole are statistically the same only at PEDYN = 128 and 64. • RIGR: the top five Kpt/VT “hot spots” are statistically the same as FFT for all
PEDYN, as a result of very large standard deviations. • TRIGR: the top five Kpt/VT “hot spots” from TRIGR and FFT are the same at
PEDYN = 128, 64, 32, and 24. In addition, using reduced dynamic data, PEDYN = 64 and 24, TRIGR localizes statistically similar “hot spots” as those obtained from FFT maps.
• As PEDYN decreases the generalized-series techniques are better able to accurately estimate image data and hence provide more accurate quantitative dynamic contrast information than Keyhole.
• Although RIGR agrees with FFT at all PEDYN and appears statistically superior to TRIGR, RIGR has unrealistic outlier Kpt/VT “hot spots” and large standard deviations at lower PEDYN not seen with TRIGR. Furthermore, RIGR does not localize statistically similar “hot spots” as FFT.
• Keyhole has the most limited dynamic data threshold and TRIGR more accurately obtains clinical low-resolution dynamic data, PEDYN = 64, 32, and 24, and more accurately localizes “hot spots”, PEDYN = 64 and 24, than both Keyhole and RIGR.
• This implies that one can gain at least a fivefold (5.33) improvement in spatial resolution without sacrificing the necessary temporal resolution.