In-Line Phase Contrast Imaging of Hepatic Portal Vein Embolization with Radiolucent Embolic Agents in Mice: A Preliminary Study

et al. (2013) In-Line Phase Contrast Imaging of Hepatic Portal Vein Embolization with Radiolucent Embolic Agents in Mice: A Preliminary Study. PLoS ONE 8(12): e80919. doi:10.1371/journal.pone.0080919 In-Line Phase Contrast Imaging of Hepatic Portal Vein Embolization with Radiolucent Embolic Agents in Mice: A Preliminary Study Rongbiao Tang 0 Wei Huang 0 Fuhua Yan 0 Yong Lu 0 Wei-Min Chai 0 Guo-Yuan Yang 0 Ke-Min Chen 0 Jonathan A. Coles, Glasgow University, United Kingdom 0 1 Department of Radiology, Rui Jin Hospital, Shanghai Jiao Tong University School of Medicine , Shanghai , People's Republic of China, 2 Neuroscience and Neuroengineering Center, Med-X Research Institute, Shanghai Jiao Tong University , Shanghai , People's Republic of China It is crucial to understand the distribution of embolic agents inside target liver during and after the hepatic portal vein embolization (PVE) procedure. For a long time, the problem has not been well solved due to the radiolucency of embolic agents and the resolution limitation of conventional radiography. In this study, we first reported use of fluorescent carboxyl microspheres (FCM) as radiolucent embolic agents for embolizing hepatic portal veins. The fluorescent characteristic of FCM could help to determine their approximate location easily. Additionally, the microspheres were found to be fairly good embolizing agents for PVE. After the livers were excised and fixed, they were imaged by in-line phase contrast imaging (PCI), which greatly improved the detection of the radiolucent embolic agents as compared to absorption contrast imaging (ACI). The preliminary study has for the first time shown that PCI has great potential in the pre-clinical investigation of PVE with radiolucent embolic agents. - Preoperative portal vein embolization (PVE) is an effective modality to induce hepatic hypertrophy by obstructing the selective portal vein supplying the diseased segment of the liver [14]. In order to prevent blockage in the wrong region, it is quite essential to determine the distribution of the embolic agents inside target liver during and after the embolization. Clinically, gelatin sponge (GS) and polyvinyl alcohol particles (PVA) are the most commonly used embolic agents [5,6]. However, GS and PVA are low-absorption materials which are hardly visualized by conventional radiography. Therefore, embolic agents are always injected by combining them with iodine contrast agent to enhance image contrast. Nevertheless, iodine-enhanced method only indirectly shows the embolization site, and can not accurately verify the distribution of embolic agents. Additionally, it is still difficult to show fine embolized vessels with a diameter of 200 mm or less by conventional angiography due to the limitation of spatial resolution [7]. To overcome the challenges, novel imaging method should be applied. Currently, synchrotron radiation (SR) phase contrast imaging (PCI) has been widely utilized to provide excellent image contrast for soft tissues [811]. PCI, utilizing the phase shift, can produce higher contrast images than absorption contrast imaging (ACI) [12,13]. Also, PCI is considered as a powerful preclinical imaging modality to observe fine structures with its resolution higher than any available clinical radiography [14,15]. Using PCI, hepatic vessels down to micron level can be clearly shown without using contrast agents [16,17]. The values of these applications raise the possibility of using PCI for clearly imaging lowabsorption embolic materials. In this study, GS and PVA were imaged by SR imaging. PCI and ACI were performed and compared. We evaluated the feasibility of using PCI for imaging PVE with radiolucent fluorescent carboxyl microspheres (FCM). Materials and Methods Sample Preparation All experiments were conducted in accordance with the guidelines established and approved by Shanghai Jiao Tong Universitys Institutional Animal Care and Use Committee. 6 male ICR mice were anesthetized using an intraperitoneal injection of ketamine (100 mg kg21) and xylazine (10 mg kg21). The main portal trunk was dissected, and then punctured with a thin PE-50 catheter through a midline laparotomy. Then PVE was performed by injecting 100 FCM (in 0.1 ml PBS) into the portal vein via the catheter attached to a 1 ml syringe. 5 minutes after the PVE, mice were sacrificed by cervical dislocation under anesthesia. The livers were harvested and placed in 4% formaldehyde solution. The numbers of FCM in main lobes of liver were counted under fluorescence microscope. Data were expressed in mean 6 standard deviation. Three non-dehydrated livers were randomly chosen to scan by phase contrast CT imaging. For imaging dehydrated livers, the other three livers were placed in a 4% formaldehyde solution for 72 hours, dehydrated with 100% ethanol for 48 hours, and then placed in the air for 2 hours. SR Imaging Parameters Imaging was performed at the BL13W1 beamline in Shanghai Synchrotron Radiation Facility (SSRF, China). X-rays were derived from a 3.5 GeV electron storage ring. The beamline covered an energy range of 8 to 72.5 keV. X-Ray was monochromatized at 19 keV energy using a double-crystal monochromator with Si(111) and Si(311) crystals. The energy resolution was gE/E,561023. The transmitted x-rays were first converted to visible light by a scintillator consisting of a 100 mm thick CdWO4 cleaved single crystal, and then captured by a CCD camera with the pixel size of 3.7 mm. (Photonic Science, UK). Samples were positioned on a translation/rotation stage at a distance of 34 m from the synchrotron source. The distance between the sample and the detector had a changeable range of 8 m (Fig. 1). Comparison between ACI and PCI Clinically utilized 150350-mm GS (Eric Kang, China) and 90 180-mm PVA (PVA-100, Cook) were purchased for imaging. FCM (ACMEmicrospheres, USA) were used for hepatic PVE. FCM had a mean diameter of 100 mm, ranging from 90 to 105 mm. ACI and PCI were performed with the same imaging parameters except sample-to-detector distance (d = 1 cm and 60 cm, respectively). The distance was changed by moving the CCD camera on a rail. Relative densities were evaluated by line profile analysis via Image-Pro Plus 6.0. Phase Contrast CT Imaging 1000 projection images were obtained from each sample over 180u in rotation steps of 0.18u. The projections were recorded with sample-to-detector distance of 60 cm and exposure time of 1 s. The raw data were processed by applying the filtered back projection (FBP) algorithm with PITRE software [18]. 3D phase contrast reconstructed images were acquired by using the Amira 5.2 software (Mercury Computer Systems, USA). SR Imaging of GS and PVA The radiolucent characteristic of GS and PVA was demonstrated in Fig. 2. No distinct contrast between GS or PVA and its surrounding air could be observed on the absorption images (Figs. 2c and g). After adjusting the distance to 60 cm, we were able to clearly vis (...truncated)