3D visualization of vertebrate soft tissues using spiceCT (Selectively Perfusable Iodine‐based Contrast‐Enhanced CT) as a rapid alternative to diceCT

Abstract

The treatment of vertebrate specimens with radio‐opaque substances to enhance soft‐tissue contrast in CT scans has revolutionized morphological analysis. DiceCT has produced spectacular results and involves immersing specimens in Lugol's iodine. A shortcoming of diceCT is that diffusion (the “d” in “diceCT”) can take days, weeks, or months in large, intact, unskinned specimens. Moreover, long diffusion times can cause marked shrinkage. Alternatively, our team has developed spiceCT, which involves perfusing specimens with Lugol's iodine, yielding excellent results—literally within hours. The vascular system of thawed, unfixed, unskinned specimens (mostly birds and reptiles thus far) is cannulated, and then hypertonic (2.5 or 5%) aqueous Lugol's iodine is injected with a syringe. The solution perfuses well, easily filling capillary beds. Perfusion can be visually monitored in key areas, as well as tactilely via syringe pressure. Staining is rapid, and specimens can be scanned immediately, yielding same‐day results. There is no time for shrinkage, which is a well‐known problem for diceCT specimens immersed in iodine for long periods. The absence of prior fixation shortens processing time and also opens new avenues for final storage in that the specimen can be fixed, refrozen, or even skeletonized. Perfusion rather than diffusion also allows targeting of tissues—selective perfusion (the “sp” of “spiceCT”)—by injecting their vascular supply. One shortcoming of spiceCT is that iodine is too large to cross the blood‐brain barrier (BBB), even in cadaveric specimens. Our team is currently exploring ways to overcome this problem, experimenting with adding EDTA to the Lugol's injection medium to disrupt the cadherins forming the tight junctions of the endothelial cells of the cerebral vasculature. Initial results are promising. SpiceCT is intended to supplement, not replace, diceCT in the toolkit of morphologists.Support or Funding InformationUS National Science Foundation (IOB‐0517257, IOS‐1050154, IOS‐1456503)This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The inferior alveolar nerve and its relationship to the mandibular canal

“…Soft tissue structures like nervous tissues are not visible in a standard microCT scan and thus a staining procedure—known as diceCT (diffusible iodine‐based contrast enhanced tomography)—was utilized (Gignac et al, 2016; Hedrick et al, 2018; Vickerton et al, 2013; Witmer et al, 2018). The diceCT process involves submerging a specimen in a series of chemicals to allow the tissues to uptake the iodine molecules and make the tissues radiopaque.…”

“…However, because the soft tissues are not radiopaque until after staining has occurred, there is no way to measure shrinkage in these specific specimens during this process. DiceCT is an excellent procedure for rare specimens or museum specimens because, although the chemical composition is changed due to the staining process, the specimen undergoes no gross dissection or physical changes after the iodine has been rendered colorless (Gignac et al, 2016; Jain, 2017; O'Brien & Bourke, 2015; O'Brien & Williams, 2014; Witmer et al, 2018). This means that a specimen can be used many times in digital format and could be used for projects in the future due to the non‐destructive nature of the staining process.…”