Intraoperative Imaging and Image Fusion

Image Guiding Therapy (IGT)

What is image guiding therapy?

Image-guided therapy, a central concept of 21st century medicine, is the use of any form of medical imaging to plan, perform, and evaluate surgical procedures and therapeutic interventions. Image-guided therapy techniques help to make surgeries less invasive and more precise, which can lead to shorter hospital stays and fewer repeated procedures. [1]

[2] [1]

How does IGT works?

IGT is a innovation in cancer treatment field. One of the most known type of IGT is Image guiding radiation therapy (IGRT). IGRT is the use of imaging during radiation therapy to improve the precision and accuracy of treatment delivery but also limiting radiation exposure to nearby healthy brain tissues. Radiation therapy machines are equipped with imaging technology to allow the doctor to image the tumor before and during treatment. These images will help define the exact location, size and orientation of your brain tumor and also By comparing these images to the reference images taken during simulation, the patient’s position and/or the radiation beams may be adjusted to more precisely target the radiation dose to the tumor. There are several types of scans that may be used to help gather these images like:

Computerized Tomography (CT)
Magnetic Resonance Imaging (MRI)
Magnetic Resonance Spectroscopy (MRS)
Perfusion MRI
Position Emission Tomography (PET) [3], [4], [5], [6]

Side effects of IGRT

As almost every other treatment, IGRT has it's own side effects especially since the treatment is based on radiation. Even though scientists are trying day after day that the equipment used for IGRT, limites the damage of the tissue surrounding the treated area, that is still an issue. Side effects of radiation treatment include problems that occur as a result of the treatment itself as well as from radiation damage to healthy cells in the treatment area. The number and severity of side effects patients experience will depend on the type of radiation and dosage they receive and the part of their body being treated. Radiation therapy can cause early and late side effects. Early side effects occur during or immediately after treatment and are typically gone within a few weeks. Common early side effects of radiation therapy include tiredness or fatigue and skin problems. Skin in the treatment area may become more sensitive, red, irritated, or swollen. Other skin changes include dryness, itching, peeling and blistering. Depending on the area being treated, other early side effects may include: [4]

hair loss in the treatment area
mouth problems and difficulty swallowing
eating and digestion problems
diarrhea
nausea and vomiting
headaches
soreness and swelling in the treatment area
urinary and bladder changes

Late side effects, which are rare, occur months or years following treatment and are often permanent. They include:

brain changes
spinal cord changes
lung changes
kidney changes
colon and rectal changes
infertility
joint changes
lymphedema
mouth changes
secondary cancer

Intraoperative imaging

As mentioned earlier in this page, doctors need to use imaging procedures may be used to help determine the exact shape and location of the tumor, and a special device may be created to help the patient maintain the same exact position during each treatment because as it is already known, they must not move during the procedure so the images are not blurry. Intraoperative imaging means that doctors use imaging during the surgery. This helps them with targeting the tumor, navigating and also treating the tumor without causing other possible damages. This method has also increased the number of survival cases. Some of these imaging modalities are CT, iMRI (intraoperative MRI), ultrasound etc. We decided to explain some of this imaging modalities.

Intraoperative MRI (iMri)

Operating under interactive image guidance offers advantages over traditional guidance systems that use only preoperative data and therefore they can not provide accurate localization and navigation. Intraoperative magnetic resonance imaging (iMRI) is a procedure to create images of the brain during surgery. Neurosurgeons rely on iMRI technology to create accurate pictures of the brain that guide them in removing brain tumors and other abnormalities during operations. There are some advantages that IMri has, like locate abnormalities if the brain has shifted and also distinguish abnormal brain tissue from normal brain tissue. The MRI equipment is mounted onto strong rails in the ceiling to allow it to move into and out of the active surgical area of the operating room during the surgical procedure, without requiring the patient to be moved at all. This lets neurosurgeons see real-time images of the brain, so they can check the progress of surgery and make adjustments as necessary. Despite its increasing usefulness, there are some disadvantages to ioMR (very expansive, time consuming, only nonferromagnetic instruments are possible in the magnetic field, not possible for patients with ferromagnetic implants). MR-guided brain biopsy has been proved to be a safer and faster procedure than frame-based stereotaxy. Schulz et al. reported that, in biopsies of the petroclival region, MRI guidance provides maximum patient safety and a level of diagnostic accuracy not attainable with other guiding systems. Good results have been published from biopsies performed in a conventional closed-bore scanner without any special IMRI instrumentation. The contrast and visibility of the needle permitted more than 400 uncomplicated punctures and interventions. The mean duration of a biopsy was 19 min. Due to its good sensitivity, MRI is able to detect bone lesions not seen at all in other modalities. [7], [12]

Video showing how iMri works [9] The setup of iMri equipment into OR [8]

CT (iCT)

The intraoperative CT (iCT) and image-guided surgery system create unmatched surgical vision and precision, allowing surgeons to see things others can’t see during complex brain, spine and trauma surgeries. All images from the iCT are available in real time to the surgeon and operating room team. This surgical navigation system provides the highest level of accuracy for image guided surgery. High CT image quality increases surgeon confidence and supports advanced minimally invasive surgery. The iCT works like a traditional CT scanner that is used in a typical radiation room, however it is more advanced and completely mobile. It can be moved from one operating room to another, and has a much larger opening than a traditional CT scanner, making it easier to position around the patient during surgery. Intraoperative CT scan is safe, efficacious, cheaper and a fast procedure that helps reducing the time of evaluation of DBS lead position.Also there is an adjustment of <1 mm as shown in a paper from December 2016. It was laso stated that iCT was less time consuming that iMri. As what we read about ICT from a group of researches who had tried intraoperative CT with a considerable number of patients, they stated that intraoperative CT can replace or the proper word would be substitute the post-operative CT scan, but it can not substitute the post-operative MRI scan especially for targets clearly visible on MRI that can not be seen properly or not at all on a CT scan. [11], [13], [15], [16]

Intraoperative CT Operation Room [14]

Ultrasound (IOUS)

A procedure that uses ultrasound (high-energy sound waves that are bounced off internal tissues and organs) during surgery. Sonograms (pictures made by ultrasound) of the inside of the body are viewed on a computer in real-time to help a surgeon find tumors or other problems during the operation. Also called IOUS. [17]

Intraoperative Contrast-Enhanced Ultrasound for Brain Tumor Surgery [18]

Intraoperative Fluorescence

Fluorescence-guided surgery is one of the rapidly emerging methods of surgical “theranostics.” Fluorescence-guided brain tumor surgery is either routinely applied in some centers or is under active study in clinical trials. Besides the trinity of commonly used drugs (fluorescein sodium, 5-aminolevulinic acid, and indocyanine green), less studied fluorescent stains, such as tetracyclines, cancer-selective alkylphosphocholine analogs, cresyl violet, acridine orange, and acriflavine, can be used for rapid tumor detection and pathological tissue examination. FGS is performed using imaging devices with the purpose of providing real time simultaneous information from color reflectance images (bright field) and fluorescence emission. One or more light sources are used to excite and illuminate the sample. Light is collected using optical filters that match the emission spectrum of the fluorophore. Imaging lenses and digital cameras (CCD or CMOS) are used to produce the final image. [19]

Fluorescent image guided surgery explanation (©Mount Sinai Health System)

Image Registration/Fusion

The aim of image fusion procedure is to construct a more detailed and representative output image from some images with different modalities. In general, image fusion procedure consists of some steps that help in achieving such goal. The first step in image fusion procedure is to register the input images. Image registration is defined as the process of mapping the input images with the help of reference image. Images can be from the same or different modalities. The goal of such mapping is to match the corresponding images based on certain features to assist in the image fusion process. The ultimate benefit of image fusion is the quality of the information contained in the output image. Other benefits involve extending the range of operations, extending spatial and temporal coverage, reducing uncertainty, increasing reliability, achieving robust system performance, and representing the information more compactly. [20]

The image registration steps [20]

The main steps of image fusion procedure [20]

Multiple fusion algorithms [21]

Rigid fusion – no compensation for motion or patient position

Photo courtesy of Mirada Solutions Ltd software Reveal MVS supplied to Oxford projects

Deformable fusion – crucial when structures have changed position or shape between or during scans due to voluntary or physiological motion or imperfect scanning protocols

Photo courtesy of Mirada Solutions Ltd software Reveal MVS supplied to Oxford projects

Many Clinical Applications of Fusion

Cancer staging
Biopsy planning
Radiotherapy treatment planning
Quantitative assessment of treatment response
Pre-surgical assessment of other conditions e.g. epilepsy
As an effective communication tool when reporting to clinical meetings, referring physicians or to patients
Whenever multiple data sources may be better assessed together

Some fusion examples

MRI-CT image fusion [21]

MRI CT

Fusing the two volumes, to find the most probable image transformation is the core of automed radiation therapy planning

PET data identifies a region of hypometabolism due to epilepsy. Fusion with MR localises the damage to the anterior and medial areas of the right temporal gyrus

Example courtesy of Mirada Solutions Ltd software Reveal MVS supplied to Oxford projects [21]

Fusion of information = registration plus combination in a single representation: PET/CT [21]

Deformable fusion- PET shows increased metabolism in lesions identified on CT, consistent with active tumor growth rather than necrosis post-radiotherapy.

CT – PET registration

Example courtesy of Mirada Solutions Ltd software Reveal MVS supplied to Oxford projects

Non-rigid image registration [21]

Bibliography:

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