Any methodologies, which enables localization, targeting and controlling during interventional processes are summarized to image-guided therapy. It includes image-guided surgery and interventional radiology. For example, surgeons can navigate through the body or just use it as an extended view into the body structures. We will cover assistance by imaging in detail in the section intraoperative imaging. IGT is also used in order to model a patient’s anatomy for surgery planning or for giving additional functional information while the treatment process.[1]
In the beginning of treatment, several scans of the patient are made. These scans are then combined before they are converted to a 3D model, which can be used in a further stage of the treatment. For example, motion during surgeries are visualized via simulations, which are based on the 3D model.
IGT is used for[6]:
- Craniotomy
- Navigation
- intracranial electrical stimulation testing (ECS)
- Removal of tissue
Intraoperative Imaging[1,2]
During brain surgeries, imaging extends the possibilities to monitor every step the surgeon is doing. As these treatment option is very risky and critical, intraoperative imaging enables increased safety and accuracy of every action. Now, lets dive deep into several techniques which are used in these processes.
The main advantage of Ultrasound in this purpose is providing a monitor feature real-time, which is also given by MRI. A surgery in order to resect brain tumor cells was accompanied by a 3D ultrasound rendering. As imaging qualty of ultrasound improved over time, a consideration as the single navigation monitor during surgeries is examined. In this context, the most-used imaging techniques are the Doppler imaging and the B-mode imaging. Doppler imaging is best for visualizing blood flow, whereas the latter imaging technique helps identifying the needle used in biopsies.
Besides Ultrasound imaging, MRI does not generate harmful radiation to the patient and is the most used technology for detecting and grading tumor cells. During the surgery, a MRI setting is built which can easily be adjusted to the patient. This avoids the necessity of the patient’s movement. Especially in a brain surgery, a complete movement of the patient to a MRI-machine is not possible, so integrating MRI-imaging in the surgical environment is a big plus. For example. while resecting tumor cells from a critical area in the brain, real-time MRI-images helps the surgeon in deciding whether his actions are sucessful or not. Although being the most efficient way of assistance during the brain tumor surgery procedure, it is demanding a lot of energy and thus causes high costs. Also generating images and its preprocessing can be time-consuming, causing a longer surgery duration.
High availability, ease of use and high image quality leads us to CT. All these points substantiate CT as the most-used technique during surgeries although producing radiation which affects the patient. In order to take CT scans, the radiologist has to move the CT device to the patient and starts it from the control room. Often, CT accompanies biopsies, where it helps to monitor the position of the needle throughout the whole procedure. Research is done in order to achieve a lower scan time and a lower dose of radiation, which results in less harm to the scanned patient.
A way of visualising the tumor cells and to able to distinguish them from normal brain cells, tumor cells are marked by flourescent dyes. After injection, the dye accumulates in high concentration in tumor tissue. The three most used dyes are indocyanine green, 5-aminolevulinic acid and flourescein. Indocyanin Green shows blood flow and vessels, whereas the last two dyes are collected at gliomas. This high concentration marks the tumor cells. With the help of CT and MRI, a surgeon is in a better initial position for resecting tumor cells.
Bibliography
- Jolesz, Ferenc, ed. Intraoperative imaging and image-guided therapy. Springer Science & Business Media, 2014.
- Haigron, P., Dillenseger, J.-L., Luo, L., & Coatrieux, J.-L. (2010). Image-guided therapy: evolution and breakthrough. Ieee Engineering in Medicine and Biology Magazine, 29(1), 100–104.
- Moiyadi, Aliasgar V., and Prakash Shetty. "Direct navigated 3D ultrasound for resection of brain tumors: a useful tool for intraoperative image guidance." Neurosurgical focus 40.3 (2016): E5.
- http://www.mottchildren.org/conditions-treatments/intraoperative-mri-university-michigan
- Belykh E, Martirosyan NL, Yagmurlu K, et al. Intraoperative Fluorescence Imaging for Personalized Brain Tumor Resection: Current State and Future Directions. Frontiers in Surgery. 2016;3:55.
- https://ncigt.org/brain-tumor-resection
- http://veterinarymedicine.dvm360.com/forefront-frameless-stereotactic-ct-guided-needle-brain-biopsy