Development of image segmentation methods for intracranial aneurysms.

Though providing vital means for the visualization, diagnosis, and quantification of decision-making processes for the treatment of vascular pathologies, vascular segmentation remains a process that continues to be marred by numerous challenges. In this study, we validate eight aneurysms via the use of two existing segmentation methods; the Region Growing Threshold and Chan-Vese model. These methods were evaluated by comparison of the results obtained with a manual segmentation performed. Based upon this validation study, we propose a new Threshold-Based Level Set (TLS) method in order to overcome the existing problems. With divergent methods of segmentation, we discovered that the volumes of the aneurysm models reached a maximum difference of 24%. The local artery anatomical shapes of the aneurysms were likewise found to significantly influence the results of these simulations. In contrast, however, the volume differences calculated via use of the TLS method remained at a relatively low figure, at only around 5%, thereby revealing the existence of inherent limitations in the application of cerebrovascular segmentation. The proposed TLS method holds the potential for utilisation in automatic aneurysm segmentation without the setting of a seed point or intensity threshold. This technique will further enable the segmentation of anatomically complex cerebrovascular shapes, thereby allowing for more accurate and efficient simulations of medical imagery.

Characterization of polyethyleneglycol-stabilized, manganese-substituted hydroxylapatite (MnHA-PEG). A potential MR blood pool agent.

PURPOSE: To optimize the performance (or efficacy) of a potential particulate blood pool agent for MR angiography by varying the particle size. The colloidal system under investigation was polyethylene glycol-stabilized manganese-substituted hydroxylapatite (MnHA-PEG). MATERIAL AND METHODS: Several MnHA-PEG formulations were prepared using various length PEGs (MW = 140-2000). Products were characterized in vitro by dynamic light scattering (DLLS), field flow fractionation (FFF), and relaxometry; and in vivo by blood clearance kinetics in rabbits, and by analytical electron microscopy (EM). RESULTS: The particle size distribution (PSD) consisted only of small particles (approximately 10-nm diameter) when approximately 40 mo1% PEG was used. At approximately 20 mo1% PEG, larger particles (approximately 100 nm), which are aggregates of the small ones, were also present. The water proton relaxation profiles of the particles in plasma were different from that of the free Mn2+. In plasma, the large aggregates were broken down into the smaller particles which were stable. Although the small particles were efficient relaxation enhancing agents, they were cleared from the blood approximately 3 times faster than the approximately 100-nm diameter aggregates, probably as a consequence of leakage into the extravascular space. Variation of PEG size had no effect on particle characteristics or on blood clearance. Analytical EM of rabbit liver specimens indicated some retention of Mn in mitochondria at the time point when Mn content of other subcellular structures returned to baseline. CONCLUSION: DLLS and FFF are complementary techniques for sizing particulate MR contrast media. Small MnHA particles are more efficient T1-shortening agents than large ones but they are prone to leakage from the vascular space. Within the MW range explored, the length of PEG molecule had no effect on blood clearance of the MnHA particles. Larger aggregates of MnHA-PEG break down into stable small particles in plasma. Mn clears from the subcellular structures within hepatocytes within 60 min after i.v. MnHA-PEG administration except from the mitochondria in which it appears to accumulate.

Detectability of hypervascular hepatocellular carcinoma by arterial phase images of MR and spiral CT.

The ability of arterial phase images of breath-hold MR imaging and spiral CT to detect hypervascular hepatocellular carcinomas (HCCs) was evaluated. Prior to transcatheter arterial chemoembolization (TACE) with iodized oil, MR images and spiral CT during i.v. bolus injection of contrast medium (IV-MR imaging and IV-spiral CT) and spiral CT during intraarterial injection of contrast media through catheter (IA-spiral CT) of the entire liver were obtained in 24 consecutive patients with 93 HCCs. In the detection of HCCs less than 1 cm in diameter, IA-spiral CT (87.3%) was superior to IV-MR imaging (63.5%) and IV-spiral CT (54.0%) (p < 0.001). There was no significant difference in detectability in any tumor size between IV-MR imaging and IV-spiral CT. IA-spiral CT was the best for detecting hypervascular HCCs, and there was no significant difference between IV-MR imaging and IV-spiral CT.