Magnetic Resonance Imaging (MRI) is a technique that uses the principle of nuclear magnetic resonance (NMR) to detect the electromagnetic waves emitted by an applied gradient magnetic field based on the different attenuation of the energy released in different structural environments within a substance. The position and type of atomic nuclei that make up the object can be mapped to the internal structure of the object. The use of this technique for imaging the internal structure of the human body has resulted in a revolutionary medical diagnostic tool that has greatly contributed to the rapid development of medicine, neurophysiology and cognitive neuroscience.
In 2003, American chemist Lauterbur and British physicist Mansfield were awarded the Nobel Prize in Physiology or Medicine for their groundbreaking achievements in magnetic resonance imaging (MRI) technology. This is the sixth Nobel Prize to date for research on the topic of MRI. Currently, MRI main magnets for clinical applications have evolved from 0.015 Tesla (T) to 3.0 T, and up to 7.0 T for experimental MRI.
MRI has become the reference image of choice for neuronavigation surgery because of its high soft tissue contrast, precise spatial and temporal resolution, arbitrary planar three-dimensional imaging capability, sensitivity to flow and temperature, functional brain imaging, and absence of ionizing radiation.
Intraoperative magnetic resonance
Intraoperative MRI (iMRI) refers to the preoperative, intraoperative and postoperative MRI scans, image acquisition and image processing, and the ability to perform true real-time navigational surgery, which is a major technological revolution in the field of neurosurgery in the mid- to late-1990s. The advent of open MRI has made intraoperative “real-time” imaging possible. With innovations in the basic design of magnets and scanners, MRI systems have been successfully introduced into the neurosurgical operating room. iMRI has revolutionized the traditional neurosurgical procedure in which the surgeon relies on subjective experience to guide the procedure and determine the outcome of the procedure. The combination of iMRI and neuronavigation systems has significantly improved the accuracy and safety of surgery, and is regarded as a milestone in the history of neurosurgery. At present, only a few large neurosurgery centers in Europe and the United States have this equipment.
In 2006, the Department of Neurosurgery of Huashan Hospital of Fudan University introduced the world’s most advanced PoleStar? N20 portable open low field strength (0.15 T) iMRI system, which has accumulated more than 500 cases of various surgeries with remarkable clinical efficacy.
In 2009, Huashan Hospital installed and applied the ultra-high field strength (3.0 T) iMRI, which can be freely moved within the operating room by using the patented air track technology. And with iMRI as the center, the digital integrated neurosurgery center is integrated. Within the iMRI Digital Integrated Neurosurgery Center, intraoperative real-time imaging can be performed without moving the patient, guiding the surgeon to perform surgical operations from any angle and introducing a whole new stage of micro-invasive neurosurgery.
Application of iMRI in neurosurgery
iMRI navigation is widely used in neurosurgery, especially in gliomas, giant pituitary tumors, cerebrovascular bypass surgery, functional neurosurgery, and intracerebral directional puncture biopsy surgery. iMRI has the following advantages: (1) Real-time imaging to navigate surgery and improve tumor resection rate. (2) Intraoperative functional brain imaging can help reduce the incidence of postoperative neurological dysfunction such as hemiplegia and aphasia. (3) Provide real-time guidance and precise positioning for stereotactic puncture, biopsy, implantation and other procedures. (4) Intraoperative detection of certain occult or early complications, such as cerebral ischemia and hemorrhage.
For example, when a neurosurgeon visually determines that a glioma has been completely excised, there are still tumor remnants in 33-67% of cases. Even with the application of conventional neuronavigation, tumor residual occurs in nearly 1/3 of cases. The extent of resection is one of the most important prognostic correlates of glioma. Minimizing tumor load intraoperatively not only facilitates subsequent standardized and comprehensive treatment, but also prolongs the tumor progression-free period and survival time. For glioma, iMRI can monitor the extent of surgical resection in real time, precisely and quantitatively, which represents the highest technology of current microsurgery for glioma and its long-term clinical efficacy has been affirmed by the international medical community.
In our unit, 0.15T iMRI-guided transnasal-pterineal resection was used for pituitary macroadenoma. The results showed that the total surgical resection rate increased from 58.2% to 83.6%, and the postoperative endocrine cure rate reached about 70%. In Germany, 1.5T iMRI-guided transsphenoidal pituitary tumor resection was reported, and the total tumor resection rate increased from 58% to 82%. High-field intensity iMRI provides immediate feedback on the extent of tumor resection and reveals important structures such as the adjacent cavernous sinus, internal carotid artery, optic cross and hypothalamus, improving surgical accuracy and safety.
The iMRI enables the puncture target to be seen instead of invisible, resulting in a 97.4% diagnosis rate for biopsies of brain lesions and only 2.7% postoperative complications.
iMRI Safety
MRI is one of the least harmful clinical diagnostic imaging methods available. Today, MRI technology is used to examine at least 60 million cases worldwide each year. However, MRI systems can also cause harm to humans in certain situations, including the following.
(1) Strong static magnetic fields: In the presence of ferromagnetic material, whether embedded in the patient or within the magnetic field, this can be a risk factor.
(2) Gradient fields that vary with time: can excite nerves or muscles by inducing an electric field in the subject. At sufficient intensity, it can produce peripheral nerve excitation (e.g., tingling or percussive sensation) or even cause cardiac excitation or ventricular vibration.
(3) Thermogenic effects of radiofrequency fields (RF): The large-angle RF field emissions used during MRI focusing or measurement are converted to heat in the patient’s tissues by the electromagnetic energy, which can increase the tissue temperature.
(4) Noise: The various noises generated during MRI operation may cause hearing damage in some patients.
Therefore, it is important to first consult with your primary care physician for both MRI examinations and iMRI procedures.
Patient Precautions
All patients undergoing iMRI-guided surgery are subject to personal safety screening prior to entering the iMRI Digital Integrated Neurosurgery Center to eliminate potential risk factors and ensure medical safety. An explanation of the iMRI environment and the rationale that accompanies the iMRI safety screening form will be given by the attending physician.
Do you have or have you ever had any of the following?
1.□Yes □No Heart surgery, heart valves, pacemakers, cardiac defibrillators, coronary stents.
2. □Yes □No Brain surgery, cerebral aneurysm clips, shunts, deep stimulator (DBS).
3. □Yes □No Vascular bypass, endovascular stents, spring coils, etc.
4. □Yes □No Eye surgery, implants
5. □Yes □No Injury to the eye from metal or metal flakes
6. □Yes □No Orthopedic metal needles, screws, rods, etc.
7. □Yes □No Previous spinal surgery (lumbar or cervical)
8. □Yes □No Ear surgery, cochlear implants, hearing aids
9. □Yes □No Metal mesh implants, metal sutures, metal staples, internal electrodes
10.□Yes □No Any electrical, mechanical or magnetic implants
11 . □Yes □No implanted drug input pump, insulin pump
12 .□Yes □No Metal tattoos such as metal eyeliner, lip liner, etc.
13 . □Yes □No Pregnancy, breastfeeding, metal contraceptive ring, uterine cap, etc.
14. □Yes □No Any surgery that results in an implant in the body or results in a legacy in the body (prosthesis, prosthetic eyes, dentures, etc.)
If “yes” to any of 1-14, please provide an explanation to your supervising physician.
Do I need an intraoperative MRI procedure and how do I request one?
We are committed to providing quality, individualized care and value your input and the needs of your family. You can request an iMRI procedure from your primary care physician, who will respect your wishes and use his or her discretion to determine whether an iMRI procedure is necessary.