Data Quantification and Limitations

Tracer kinetic principles can be used to provide estimates of relative blood volume (rBV), relative blood flow (rBF) and mean transit time (MTT) derived from the first-pass of contrast agent through the microcirculation (Rosen et al. 1991; Sorensen et al. 1997; Barbier et al. 2001) (Fig. 10.2). These variables are related by the central volume theorem equation (BF = BV/MTT). Quantification of T2*-weighted DCE-MRI and its application for leaky vasculature is discussed in detail elsewhere in this book (see Chap. 4). The most robust parameter which can be extracted reliably from first pass techniques is rBV, which is obtained from the integral of the time

Fig. 10.1 Typical T2*-weighted DCE-MRI study. 30-year old woman with a grade 3 invasive ductal cancer of the right breast. The same patient is illustrated in Figures 10.2, 10.3, 10.6, 10.8 and 10.12. 22 ml of IV contrast Gd-DTPA was given after the 10th data point (arrow). First pass T2* susceptibility effects cause darkening of the tumour (arrows) (subtle but the effect is better appreciated in the subtraction image (insert)). No darkening of the breast parenchyma is seen. The first pass and recirculation phases are indicated. Signal intensity changes for 2 regions of interest are shown on the subtraction image of the nadir point for ROI corresponding to the tumour.

Fig. 10.1 Typical T2*-weighted DCE-MRI study. 30-year old woman with a grade 3 invasive ductal cancer of the right breast. The same patient is illustrated in Figures 10.2, 10.3, 10.6, 10.8 and 10.12. 22 ml of IV contrast Gd-DTPA was given after the 10th data point (arrow). First pass T2* susceptibility effects cause darkening of the tumour (arrows) (subtle but the effect is better appreciated in the subtraction image (insert)). No darkening of the breast parenchyma is seen. The first pass and recirculation phases are indicated. Signal intensity changes for 2 regions of interest are shown on the subtraction image of the nadir point for ROI corresponding to the tumour.

series data during the first pass of the contrast agent (Ostergaard et al. 1996). This cannot readily be done for the breast because of the loss of compart-mentalisation of the contrast medium. Solutions to counter Tj enhancing effects of gadolinium chelates include pre-dosing with contrast medium to saturate the leakage space and idealised model fitting (Fig. 10.2); the time series data is fitted to a gamma-variate function from which the parameters rBV, rBF and MTT are derived. This is the methodology that we employ using custom analysis software called Magnetic Resonance Imaging Workbench (MRIW) which has been developed at the Institute of Cancer Research, Royal Marsden Hospital, London (D'Arcy et al. 2004). This software is also used to analyse T1-weighted DCE-MRI data (see Sect. 10.4.4.4). From a practical perspective, it is not always necessary to quantify T2*-weighted DCE-MRI data to obtain insights of the spatial distribution of tissue perfusion. Simple subtraction images can demonstrate the maximal signal attenuation (also termed rela-

Average R2* Curve

Average R2* Curve

Fig. 10.2 Model fitting of T2*-weighted data. Same patient as illustrated in Figures 10.1, 10.3, 10.6, 10.8 and 10.12. T2* signal intensity data from the tumour ROI in Figure 10.1 are converted into R2* (1/T2*) and then fitted with a gamma variate function. The computed values of rBV, rBF and MTT for this region of interest are 265, 10.6 arbitrary units and 25.1 seconds. Parametric maps representing blood flow kinetics are shown in Figure 10.3.

Time (seconds)

Fig. 10.2 Model fitting of T2*-weighted data. Same patient as illustrated in Figures 10.1, 10.3, 10.6, 10.8 and 10.12. T2* signal intensity data from the tumour ROI in Figure 10.1 are converted into R2* (1/T2*) and then fitted with a gamma variate function. The computed values of rBV, rBF and MTT for this region of interest are 265, 10.6 arbitrary units and 25.1 seconds. Parametric maps representing blood flow kinetics are shown in Figure 10.3.

tive maximum signal drop, rMSD), which has been strongly correlated with relative blood flow and volume in tumours (Liu et al. 2002). Subtraction analysis should only be done, however, if there is a linear relationship between rBV and rBF, that is when MTT is in a narrow range; this is often the case in non-necrotic breast tumours (Fig. 10.3).

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