Accuracy of combined PET/CT in image-guided interventions of liver lesions: an ex-vivo study

Abstract

Aim: Positioning of interventional devices in liver lesions is a challenging task if only CT is available. We investigated the potential benefit of combined PET/CT images for localization of interventional devices in interventional liver studies.

Methods: Thirty lesions each of hyperdense, isodense and hypodense attenuation compared to normal liver parenchyma were injected into 15 ex-vivo pig livers. All lesions were composed of the same amounts of gelatine containing 0.5 MBq of (18)F-FDG. Following lesion insertion, an interventional needle was placed in each lesion under CT-guidance solely. After that, a PET/CT study was performed. The localization of the needle within the lesion was assessed for CT alone and PET/CT and the root mean square (RMS) was calculated. Results were compared with macroscopic measurements after lesion dissection serving as the standard of reference.

Results: In hypo- and isodense lesions PET/CT proved more accurate in defining the position of the interventional device when compared with CT alone. The mean RMS for CT and PET/CT differed significantly in isodense and hypodense lesions. No significant difference was found for hyperdense lesions.

Conclusion: Combined FDG-PET/CT imaging provides more accurate information than CT alone concerning the needle position in FDG-PET positive liver lesions. Therefore combined PET/CT might be potentially beneficial not only for localization of an interventional device, but may also be beneficial for guidance in interventional liver procedures.

Figure 1

A 7-gauge biopsy needle and a syringe were used for insertion of the gelatine/FDG mixture into the liver. The mixture hardened as it cooled in the ex-vivo-liver.

Figure 2

A: This shows a hypodense lesion. The margins of the hypodense lesion are barely seen (fine black arrows). In comparison, the combined PET/CT image of the same lesion shows exactly the margins of the lesion (Figure 2D). Furthermore, the combined PET/CT suggests a different location and extent of the lesion, which was confirmed by the standard of reference. B: This shows a hyperdense lesion. The margins of the lesions are well seen. The combined PET/CT shows the same location and extent of the lesion within the liver tissue (Figure 2E). Thus, in hyperdense lesions, a high correlation of CT and combined PET/CT measurements was found. C: This shows a nearly isodense lesion. The margins of the lesions can only be anticipated (fine black arrows). The corresponding PET/CT (Figure 2 F) of the same lesion shows a different extent of the same lesion with well defined and sharp margins.

Figure 3

This shows the different mean RMS values for hyper-, iso-, and hypodens lesions. A statistically significant difference was found between the mean RMS values in CT and PET/CT in isodense lesions (P < 0.05, grey bars). Additionally, a statistically significant difference was found between the mean RMS values of CT and PET/CT in hypodense lesions (P < 0.05, black bars). No difference was found in hyperdense lesions (white bars).

Figure 4

It shows the measurements on the commercially available computer workstation for CT alone (A/B) and combined PET/CT (C/D). The lesions´ width and height was measured in coronal direction (Figure 4A and C, X/Z), the lesions´ length in sagittal direction (black arrow (Y) in Figure 4 B and D).

Figure 5

It shows an example of two isodense lesions on CT alone and combined PET/CT with the inserted biopsy needles. The lesions margins are barely seen on CT images alone (fine black arrows, A and C). In comparison, the true extent and localisation of the lesion are well shown on the combined PET/CT images. Based on poor visibility on CT alone, the lesion in the bottom row was nearly missed (D).

Figure 6

This shows the mean Hounsfield Units (HU) of all measured lesion types, the compared liver background and the corresponding standard deviation. A: hyperdense lesions; LB: liver background; C: isodense lesions; D: hypodense lesions.