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• 
           Hypothesis & Rationale
     Controversy exists in the specificity of dynamic contrast enhanced (DCE) MRI.
  ...
Plasma compartment equation
                                  Materials & Methods
                                        ...
Materials & Methods
                Heart   

                            Liver   
    
Tumor   Image
            
       ...
Results
FFT    Keyhole Difference Images       FFT      TRIGR Difference Images




      128   64   32    24    16    4  ...
Results



          PEDYN  
    Keyhole     
     RIGR
    TRIGR      
           64
       0.0016   
       0.0016
   0....
Conclusions
•    Keyhole: the top five Kpt/VT “hot spots” from fully reconstructed FFT and
     Keyhole are statistically...
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2004 ISMRM E-poster Effect of Reduced Encoding Dynamic Data Size on Permeability-Surface Area Estimation

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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), Kp↔t/VT, obtained from dynamic contrast enhanced (DCE) MRI. Specifically, we compared Kp↔t/VT “hot
spot” values of ten infiltrating ductal carcinomas, obtained with fully reconstructed FFT to those obtained from Keyhole, reduced-
encoding imaging by generalized-series reconstruction (RIGR), and two-reference RIGR (TRIGR), using dynamic data of decreasing
size, PEDYN = 128, 64, 32, 24, 16, and 4. Preliminary data suggests that TRIGR has lower resolution limits on dynamic data for
obtaining accurate Kp↔t/VT “hot spots” than Keyhole or RIGR.

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2004 ISMRM E-poster Effect of Reduced Encoding Dynamic Data Size on Permeability-Surface Area Estimation

  1. 1. •  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), Kpt/VT, obtained from dynamic contrast enhanced (DCE) MRI.
  2. 2. Plasma compartment equation Materials & Methods •  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) Plasma compartment curve Distribution The two-compartment model (above) and a Excretion plot of the plasma Injection compartment (right). Tumor compartment equation
  3. 3. Materials & Methods Heart Liver Tumor Image Ref. Bladder
  4. 4. Results FFT Keyhole Difference Images FFT TRIGR Difference Images 128 64 32 24 16 4 128 64 32 24 16 4 FFT RIGR Difference Images •  Keyhole shows “blurring” in the PE direction, due to averaging. •  RIGR is more robust, but the difference images have quality losses with decreasing dynamic data PE. •  TRIGR has qualitatively better difference images with fewer 128 64 32 24 16 4 dynamic data PE, than Keyhole or RIGR.
  5. 5. Results PEDYN Keyhole RIGR TRIGR 64 0.0016 0.0016 0.053 32 0.00 0.00 0.0055 24 0.00 0.00 0.053 16 0.00 0.00 0.00047 4 0.00 0.00 0.00047 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).
  6. 6. Conclusions •  Keyhole: the top five Kpt/VT “hot spots” from fully reconstructed FFT and Keyhole are statistically the same only at PEDYN = 128 and 64. •  RIGR: the top five Kpt/VT “hot spots” are statistically the same as FFT for all PEDYN, as a result of very large standard deviations. •  TRIGR: the top five Kpt/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 Kpt/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.

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