Thrombus imaging

Figure 7.15 The P280 thrombus imaging agent peptide for labeling with technetium-99m. Possible Tc ligand atoms shown in hold type. (Adapted with permission from Figure 23 of Liu, S. Edwards, D. S. Chem. R(.v., 1999, 99(9), 2235-2268. Copyright 1999, American Chemical Society.)...

Technetium-labeled peptides and proteins have been investigated as potential thrombus-imaging agents. Complex 70, which combines 99mTc with the tripeptide motif Arg-Gly-Asp, binds GP Iib/IIIa recep-... 

MRX408/phospholipid + RGD peptide-PEG-lipid Thrombus imaging and accelerated thrombolysis [94]... 

Dougan H, Weitz JI, Stafford AR, Gillespie KD, Klement P, Hobbs JB, Lyster DM, Evaluation of DNA aptamers directed to thrombin as potential thrombus imaging agents, Nucl. Med. Biol., 30 61-72, 2003. 

The third class of thrombus-imaging peptides are natural polypeptides (disintegrins), with high affinity for the receptor. Disintegrins are usually composed of 48-84 amino acids, and are rich in cysteine residues. The formation of disulfide bridges confer to the polypeptides a defined structure where the RGD motif is exposed at the tip of a flexible loop. Radioactively labeled Bitistatin [127] produced images of intense uptake at the thrombus site which corresponded to the true dimension of the lesion. 

Lister-James, J., Knight, L. C., Maurer, A. H., Bush, L. R., Moyer, B.R., and Dean, R.T. (1996) Thrombus imaging with a techne-tium-99m-labeled activated platelet receptorbinding peptide, J Nud Med 37, 775-781. 

Fig. 5.8a,b. Assumed signal intense plaque (a). Source image of TOF-MRA at the level of the carotid bulb displays bright material, ultrasound showed no evidence of a thrombus. On CE-MRA there is a short eccentric stenosis of the left ICA (b)... 

Fig. 5. 9a,b. Subacute wall-adherent thrombus (a). After embolic infarction of the middle cerebral artery ultrasound has identified an echolucent structure within the ICA, highly suggestive of thrombus. Tl-weighted spin echo image with fat saturation confirms an intraluminal thrombus (a) with a mild stenosis (a, b), gradually resolving over weeks... 

Fig. 5.20a-d. Subacute thrombus formation in a large fusiforme aneurysm of the basilar artery. Parts of the thrombus are still isoin-tense to brain, while others are moderately hyperintense on spin echo Tl-weighted image (a). Residual flow within the vessel is outlined against thrombus much better on post-contrast Tl-weighted spin echo (c) and post-contrast TOF-MRA (d) than on unenhanced TOF-MRA (b)... 

Non-thrombotic intraluminal notches as present in hypertrophic Pacchioni granulations might also mimick thrombus (Fig. 18.12). On MRI, these intraluminal granulations are hypo- or isointense in T1 and hyperintense in T2-weighted images and well defined (Giraud et al. 2001). 

Fig. 18.12. Circumscript filling defects within a dural sinus, a Incidental finding in contrast-enhanced CT. The bilateral well-defined filling defects in the lateral sinuses (arrows) most probably represent Pacchioni granulations, b Contrast-enhanced Tl-weighted image with incidentally demonstrated hypointense, round and circumscript structures within the lateral sinus (arrow). They most likely represent hypertrophic Pacchioni granulations and not thrombus, c In the T2-weighted images of the same patient the structures appear strongly hyperintense (arrow)...

The suitability of aptamers as in vivo imaging agents is demonstrated in references [39-41], who used anti-neutrophil elastase and anti-thrombin aptamers for imaging of inflammation and thrombus in vivo, respectively. 

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