Clinical Research - Collection of image data from normal patient treatment


Preparation to clinical research has included the coordination of the protocols for image acquisition during patient treatments with the protocols for pre-clinical animal experiments. Animal experiments are conducted to mirror standard patients treatment as close as possible.

The following protocol for image data acquisition has been agreed upon:

  1. as close as possible before RFA, contrast-enhanced, multiphase (venous, portal venous and arterial) CT imaging of the liver will be performed for therapy planning;
  2. immediately before RFA, native CT images are acquired to plan the positioning of the probe;
  3. after RFA, a whole-liver contrast-enhanced CT scan captures the electrodes in situ;
  4. in the following days and depending on the state of health, the patient will undergo MRI scanning in both inspiration and expiration using a liver-specific contrast medium;
  5. about one month after RFA, multiphase control CT imaging is performed to depict the final lesion size and detect possible residual tumour.

However, the standard protocol didn't give the required contrast to segment the liver veins in the portal venous phase after contrast injection. The contrast could be improved by using a longer delay time (+ 5 sec) until the start of the scan in the portal venous phase. This should allow a sufficient depiction of both the liver veins as well as the intrahepatic branches of the portal vein for the purpose of segmentation.

The final size of an RFA-induced lesion is still difficult to predict, especially in the vicinity of vessels which will act as heat sinks. Computed tomography is not capable to visualize the heating effect and a thermal monitoring during ablation is not possible. Therefore, any physiological model that could properly simulate the shape of the ablation lesion would provide valuable information for the radiologists.
However, the prediction has to meet certain requirements with respect to the spatial accuracy. The clinically relevant accuracy depends on tumour location and tumour type. For critical locations such as the liver hilus near large vessels, for sub-capsular lesions close to the lung or the stomach and for metastases of a colorectal carcinoma the required accuracy is below 5 mm. For other more intraparenchymal tumour locations and for HCCs, an accuracy of 10 mm would be sufficient. For the present project, the required accuracy limit for the prediction of the ablation size was set to 5 mm.
Another, clinically important piece of information is the correspondence between the ablation lesion as it is seen and reconstructed from the CECT images and the histologically defined lesion. Currently, there is no reliable clinical data available that would relate these two different measures. The CECT lesion is characterized by reduced signal intensity with respect to the surrounding non-damaged tissue and therefore appears darker. The border between ablated and healthy tissue, however, is not a sharp one. One main objective of the image analysis is therefore to draw the histologically justified border over the blurred region seen in the CECT images.
Benchmark for such a definition, however, is a tissue section in which alive and dead cells have been appropriately stained. The key question for the radiologist is to which extent the CT border corresponds to that defined by histology. This is necessary for an early detection of areas that are under treated and possibly require another RF ablation. The most beneficial scenario would be to avoid a second RFA and the associated risk of complications by using simulation software to predict the ablated volume and to control the RF ablation procedure in order to provide the required security margins.

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