Analyzing the human liver vascular architecture by combining vascular corrosion casting and micro-CT scanning: a feasibility study

Abstract

Although a full understanding of the hepatic circulation is one of the keys to successfully perform liver surgery and to elucidate liver pathology, relatively little is known about the functional organization of the liver vasculature. Therefore, we materialized and visualized the human hepatic vasculature at different scales, and performed a morphological analysis by combining vascular corrosion casting with novel micro-computer tomography (CT) and image analysis techniques. A human liver vascular corrosion cast was obtained by simultaneous resin injection in the hepatic artery (HA) and portal vein (PV). A high resolution (110 μm) micro-CT scan of the total cast allowed gathering detailed macrovascular data. Subsequently, a mesocirculation sample (starting at generation 5; 88 × 68 × 80 mm³) and a microcirculation sample (terminal vessels including sinusoids; 2.0 × 1.5 × 1.7 mm³) were dissected and imaged at a 71-μm and 2.6-μm resolution, respectively. Segmentations and 3D reconstructions allowed quantifying the macro- and mesoscale branching topology, and geometrical features of HA, PV and hepatic venous trees up to 13 generations (radii ranging from 13.2 mm to 80 μm; lengths from 74.4 mm to 0.74 mm), as well as microvascular characteristics (mean sinusoidal radius of 6.63 μm). Combining corrosion casting and micro-CT imaging allows quantifying the branching topology and geometrical features of hepatic trees using a multiscale approach from the macro- down to the microcirculation. This may lead to novel insights into liver circulation, such as internal blood flow distributions and anatomical consequences of pathologies (e.g. cirrhosis).

Keywords: 3D reconstruction; hepatic vasculature; image processing; morphology; tree analysis.

Figure 1

Human liver vascular corrosion cast and micro-computer tomography (CT) scanner. (a) Total liver with indication of the dissection location of the mesocirculation sample; (b) mesocirculation sample; (c) scanning electron microscopic image of the microcirculation sample; (d) micro-CT scanner with a static X-ray tube, a static flat panel detector and a rotating liver cast to capture images during a 360 ° rotation. HA, hepatic artery; HV, hepatic venous system; PV, portal vein.

Figure 2

Three-dimensional reconstructions of the macrocirculation and mesocirculation. (a) Superposition of three macrovascular trees with indication of the dissection location of the mesocirculation sample; macrovascular HA (b), PV (c) and HV trees (d) with arrows indicating monopodial branches; (e) superposition of three mesovascular trees; mesovascular HA (f), PV (g) and HV trees (h) with brighter parts indicating four subsamples used to acquire geometrical data.

Figure 3

Results of the vascular tree analysis of the macro-and mesocirculation. Radius (a–c), length (d–f) and number of vessels (g–i) as a function of the generation number for the hepatic artery (HA), portal vein (PV) and hepatic venous system (HV) trees. Macrocirculation measurements (as obtained in Debbaut et al. 2011) and mesocirculation measurements are indicated by black and white markers, respectively. [Original and estimated numbers of vessels for the mesocirculation (Table 1) are indicated by gray and white dots, respectively.] Exponential trend lines are depicted by dashed lines when fitted to macro-and mesocirculation data. Equations and coefficients of determination (R²) of the exponential functions are given. The first HV generation (VCI) was not taken into accounted when fitting the radius trend line, as the VCI has a much larger diameter and is not really part of the hepatic vasculature. Length trend lines did not incorporate the first generation, as these vessels were cut to resect the liver, resulting in an underestimated length.

Figure 4

Liver microcirculation. (a) Single micro-CT slice showing bright spots (probably contrast agent particles); (b) indication of the most likely lobule borders; (c) 3D reconstruction of a liver lobule; and (d) of a virtually dissected subsample.