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Parametric mapping of the hepatic perfusion index with gadolinium-enhanced volumetric MRI

¹ Cancer Research UK Clinical Magnetic Resonance Research Group, Royal Marsden NHS Trust & Institute of Cancer Research, Downs Road, Sutton, Surrey SM2 5PT, Departments of ² Neuroimaging, ³ Medical Engineering and Physics and ⁴ Radiology, King's College Hospital, London SE5 9RS, ⁵ Brain & Body Centre, University of Nottingham, Nottingham NG7 2RD, ⁶ Centre for Medical Image Computing, Department of Medical Physics, UCL, London WC1E 6BT, UK

View larger version (19K): [in this window] [in a new window]   Figure 1. Directvs indirect methods of hepatic perfusion index (HPI) estimation. The shaded area represents the liver enhancement curve, while the dotted and dashed lines depict the arterial and portal contributions, respectively. The liver curve is separated into arterial and portal phases according to the time of peak splenic enhancement, and the peak gradients are superimposed as heavy black lines. For both methods the hepatic arterial perfusion is derived from the peak gradient of the arterial phase of the liver curve. (a) The "indirect" method calculates the portal perfusion from the peak enhancement of the portal phase of the liver curve, while (b) the "direct" method first subtracts the arterial component and then calculates the portal venous perfusion from the peak gradient of the derived portal liver curve.

View larger version (12K): [in this window] [in a new window]   Figure 2. Box-and-whisker plot showing overall hepatic perfusion index (HPI) calculated (using the "combined" method) from controls and from patients with confirmed primary colorectal cancer and metastatic liver disease evident on imaging. Points more than one and a half times the interquartile ranges from the median are plotted as outliers.

View larger version (53K): [in this window] [in a new window]   Figure 3. Hepatic perfusion index(HPI) map from a control subject. (a) A T1 weighted image acquired just after the peak arterial enhancement, for comparison. (b) The same T1 image is shown in the background, overlaid with an HPI map of the liver. The HPI scale is shown to the right.

View larger version (47K): [in this window] [in a new window]   Figure 4. Hepatic perfusion index map(and corresponding post-contrast T1 weighted image) from a patient with multiple confirmed metastases in the right liver. A bright area is visible along the posterior border of the liver (arrow) corresponding to an area of abnormal arterialization.

View larger version (11K): [in this window] [in a new window]   Figure 5. Perfusion estimation from enhancement gradient in a single parenchyma voxel. In each figure the dashed line shows the splenic arterial peak, separating arterial from portal phase; the red line shows the smoothed uptake curve from which gradients are taken; the black line shows measured gradient. (a) Peak uptake gradient during the arterial phase. (b) The estimated portal contribution (after subtraction of a scaled spleen curve), and peak gradient measured from this during the portal phase. The measured gradient during the portal phase in this parenchyma voxel exceeds that in the arterial phase.

View larger version (11K): [in this window] [in a new window]   Figure 6. Perfusion estimation in a single voxel in the tumour periphery(see Figure 5 caption for explanation). The measured gradient during arterial phase is considerably higher than that in the portal phase.

View larger version (53K): [in this window] [in a new window]   Figure 7. Hepatic perfusion index(HPI) map (and corresponding post-contrast T1 weighted image) from a patient with confirmed metastases in segments II and III of the left liver. A bright area on the HPI map extends around the margins of the metastasis visible on the T1 weighted post-contrast image (arrow).

View larger version (49K): [in this window] [in a new window]   Figure 8. Hepatic perfusion index(HPI) map (and corresponding post-contrast T1 weighted image) from a patient with a large mass occupying much of segments VI–VIII of the right liver. Considerable heterogeneous structure is visible within the mass in the HPI map, including increased HPI around the perimeter. An area of normal-appearing parenchyma is also visible (arrow). Although this area is bright in post-contrast T1, indicating greater total gadolinium uptake than in the large mass, enhancement occurs mainly during the portal phase, and the corresponding HPI is correctly shown as low.