Interventional Magnetic Resonance Systems - Essay Example

Name: Institution: Title: Interventional MR Systems Professor: Course: Date of Submission: Table of Contents Table of Contents 2 Abstract 3 Introduction 4 Findings 5 Working mechanism of interventional MR systems 5 Illustration and examples 12 Significance and liabilities 13 Typical iMR system room 16 Conclusion 16 Bibliography 17 Abstract IMRI is used mainly in the adult neurosurgical population. These systems are vital in resection control and intra-operative navigation. In this report I present my experience of iMRI systems areas of clinical applications, working concepts and mechanism, merits and demerits. Methodology: I reviewed neurosurgical procedures in which the system was employed in resection control for instance during tumor removal and needle biopsy. The systems hence are vitally reliable in real-time basic resection and safe resection control procedures. Introduction Interventional Magnetic Resonance systems are systems that use medical imaging principles mainly employed in radiology to view detailed internal structures in the body. The recent trends in the medical field have created robust interest in the use of MR imaging for guidance in radiologic and surgical procedures. The system uses great magnetic fields for alignment of atoms in the internal body structure and conversely for alteration, radio frequency. MR systems enhance the contrast between different soft tissues making it essential in imaging the brain, muscles and the heart. This principle is employed and results obtained compared with other imaging procedures such as the CT or X-rays. The only contrasting feature is MR systems use no ionization radiation. Due to the rising instances of neurological disorders there has been increasing emphasis on neuroradiologists playing a vital role in patients with such. This has led to the development of sophisticated radiologic procedures parallel to endovascular and percutaneous methods to minimize the traditional neurosurgery which is being phased out (Hendee & Morgan, 1984,). Magnetic Resonance Imaging or NMRI or MRT through the combination of both hardware and software have made MR imaging a reality. These advances include: various concepts in MR system design, supplementary developments in MR pulsation sequence. In the past patients used to wait for a long time for results moreover, spending set backs faced during the time spend in large closed-bore superconducting systems. This is not the cases anymore due the developments made. With the advancement of pulse sequence express imaging has been made promising on open systems with minimal invasiveness. Comprehension of the varying MR systems needs a clear distinction between image guidance and procedural monitoring. Therefore data disseminated by the MR systems are used to scrutinize therapeutic intervention for instance: surgical or thermal intervention in which the condition of the tumor resection may be erratically monitored and thermal energy dissipated and impacting tissue transitioning are examined respectively. These interventional MR systems need minimal changes to an ideal imaging system; this is because access to the patient is not a necessity during the procedure. In this event application of interventional MR imaging includes the use of radiologists during the operation catheters, electrodes, needles and surgeon guided endoscopes. This active intervention leads to the abandonment of conventional diagnostic concepts and traditional procedures (Damadian, 1971). Findings Working mechanism of interventional MR systems About three quarters of the human body is composed mainly of water molecules. Each molecule contains 2 hydrogen nuclei or protons. Therefore when a person is inside the strong magnetic fields composed within the system that is the scanner, magnetic moments become aligned in the field direction. When a transmitter containing radio frequency is turned on periodically it produces an unstable electromagnetic field. Due to resonance frequency, photons are absorbed and thereby flipping the gyrate of the aligned body photons in the body. The resonance of the photons highly depends on the application strength of the magnetic field. After turning the field the energized protons regress to the ideal lower-energy gyrate-down condition. In this way the hydrogen dipole has two spins that is a high and low one, one respectively. At low spin both dipole and magnetic field are oriented parallel to each other and conversely anti-parallel at high gyrate. Energy is therefore released during this rapid low and high gyrate producing photons which are then detected by the scanner as electromagnetic signal which are similar to radio waves. Due to energy conservation the resonance frequency also monitors the frequency of the photons that are released. Photons released are characterized by energy and frequency hence drawing a relationship between field strength and frequency which facilitate the use of nuclear magnetic resonance for imaging (Brown & Selmelke, 1999). Figure: 1 Source: Hendee & Morgan, (1984). Figure: 1 relays a workstation which controls the three dimensional slicer which interprets the location and alignment of the locator. It therefore receives real-time images and relays it to the surgeon via the VDU. Scempp (1998) asserts that image construction is due to variation of detectable return to equilibrium state of the protons on different tissues. For instance five different tissue variables gyrating density that is TS1 and TS2 relaxation times, stream and spectral alteration can be essentially used to construct images. Variation in the scanner settings generates a contrasting distinction between different body tissues or other elements like dispersion MRI and fMRI. Through adding extra fields during the scan you obtain the 3 dimensional positions. It is done through transmitting electric currents through gradient coils. Variation of the magnetic field is then due to the fields depending on the positions within the administered person. Therefore the frequency of the released photons can then be traced backed by inverse mathematical Fourier transformations. Contrasting agents that are conspicuous can be introduced intravenously to make tumors, fluid tracts (veins, arteries and capillaries) and inflammations to make them distinct. In the case of arthrograms the fluids may be directly injected into a joint. Abdominal area of the body injected with contrasting agents. Figure: 2 Source: Brown, M. (1999). Figure: 3, shows how the organs would look like when conspicuous agents are injected into them thus showing varying perspectives of the organs. Mental implants can be affected by strong magnetic fields and radio pulsation for example cochlear implant and cardiac pacemakers hence the compatibly approval of the cochlear implants for specifically for MRI. While the cardiac pace makers the outcome may sometimes be devastating making patients with such not recommended for MRI. The gradients coils that are within the bore of the scanner have strong forces between them and main solenoid that produces noise during operation. Dumping the noise diminishes it from reaching an optimum of 130 decibels with very strong magnetic fields. The principle used enhances viewing of all body parts particularly brain, connective tissues, tumors and the brain with numerous hydrogen nuclei and little density disparity. Figure 4 Source: Brown, M. (1999). IMRI medical Applications IMRI systems are employed in various procedures for instance: pituitary, spinal cord and brain tumors; epileptic surgery, severe intracranial hemorrhage, cystic lesions, syrongomyelia, chiari deformity and biopsy of the small brain or spinal lesions among others. The iMRI feedback time relays its data in real-time therefore the physician is able to precisely locate the either brain or spinal lesions for a detailed exposure. Before leaving the operating suite tumors can easily be detected. While in the treatment of complex cystic lesions of either the brain or spinal canal iMRI systems are used in combination of endoscopes. During severe hemorrhage on the cranial part of the head MRI easily detects blood clots enhancing complete evacuation without eventually injuring the surrounding brain. For predictability iMRI are able to recognize immediate postoperative and intraoperative complications before unending injury posed to the brain or spinal injury. For biopsies MRI guided ultrasound is focused similar to a magnifying glass focusing light. The waves as a result of the ultrasound are then transmitted to a transducer for conversion of electrical signals to ultrasound energy to a diminutive central degree. When the procedure is carried out the beam of ultrasound is targeted towards the soft tissues (sonication), in which it penetrates generating a detailed section of protein denaturation, unrecyclable distortion of cells and coagulative necrosis at definite regions (Friebe, 2005). MRI applications for instance biopsy: Figure: 5 Source: Brown, M. (1999). Before the procedure is carried out MR imaging principles are used to produce images of the affected area and surrounding organs. In this event it is used to plan procedure and orient the patient in order to achieve the right angle for treatment. During this the temperature of the region is monitored through MR thermal mapping system displays depicted as a color map. Through it the physician is able to administer treatment ensuring the safety of the patient that is effectual thermal ablation. Moreover the results are monitored through real-time anatomical MR images and T1 weighted images characterized by Gadolinium contrasting agents are used to establish ablated areas. MRI also can be used to determining blood flow through phase contrast flow mapping techniques. With the ultra fast echo and echo planar data acquisition allows the imaging close to real-time (Jost & Kumar, 1998). Figure: 6 Source: Brown, M. (1999). Illustration and examples The basis of potential complex library of pulse sequences which is mainly based on the chemical sensitivity of the MRI. For instance with values of the echo time say Te and the repetition time Tr are the fundamental constraints of generation and eventual acquisition of the image taking place in the T2-weighting. On this situation tissues containing water and fluids are bright and tissues with lots of fat are dark. Figure: 7 Source: Schempp, (1998). Hence the converse is true for T2-weighted imagery. Tissues which are to a large extent dented develop edema making T2-weighted sequence sensitive for pathological procedures. Addition of RF pulsation and manipulation of the gradients T2-weighted is modified into a FLAIR sequence in which a distinction can be drawn between free water (dark) and edematous tissues (bright). The principle is employed in demyelinating diseases for the brain like multiple sclerosis. During MRI assessment which consists of 5-20 sequences each specifically provide information, concerning the target tissue. The information is then combined for analysis (Jost & Kumar, 1998). There are various types of MRI scans which include: 1. Diffusion MRI 2. Magnetized transfer MRI 3. Fluid attenuated inversion recovery 4. Magnetic resonance angiography Significance and liabilities The interventional MR systems are less harmful to both the patient and the operator hence apt for interventional radiology. Images produced during the procedure can be used in performing less invasive procedures interactively. Strong magnetic radio frequency and quasi static fields produced by the physical part of the system needs strategic locations free from magnetic properties. For instance Titanium surgical apparatus; MR compatible examination accessories and IMRI scanner make it very costly to obtain. For appropriate access to the patient the operator is provided with an open bore magnet. Such magnets have low magnetic fields that is 0.001 - 0.2 T range. This reduces the sensitivity of the system by decreasing the radio frequency power which is absorbed by the patient on a protracted operation. However with the advent of integrated high field magnetic systems through incorporation of MRI, CT and surgical suite interconnected in different rooms to counter the lowered sensitivity of the open bore. Advantages of IMR monitoring therapeutic procedures: 1. There is less or completely no ionization radiation for both the patient and the physician. 2. Draws clear distinctions between various kinds of tissues. 3. Has a multi-planar capability that is unlimited orientation of the image plane and thus can easily acquire 3D data sets. 4. It is thermometry hence detect both adverse and ideal temperature conditions (Rosen, 2007). Therefore the patient’s safety, efficacy procedures, minimized complication and improved clinical outcome are closely and well monitored. Moreover the physician has advantageous control of the system and hence reduced manpower. In this event patients have a less duration spent in hospital than the previous traditional trend. This is cost effective since the latter spends less. For a complete IMRI setup one needs all necessary tools to perform a less invasive surgery. This includes: anesthesia, screening devices and surgical tools. The major problem is due to very high magnet field the system has that is greater than 1.0 T thereby having great attraction force accessing the patient inside the bore (Friebe, 2005). Essentially tools meant for surgical procedures used in conjunction with this system should be non-magnetic or non-ferrous. However, the recommended tools are very many inflating the cost to assemble the system. Moreover IMR systems are usually installed and assembled in a room shielded from radio frequency. Therefore all the signals to and fro the room require electrical filtration. For instance AC linkages carry radio frequency signals which distort MRI imaging. This means that any tool used within the shielded perimeter create no MRI metal artifact which limits the interpretation of the image. For example a 3mm coronary stent is diametrically 10mm on an MRI image hence because of the material property and shielding offered by the implants allows no internal view. It is necessary to assemble the system from Nitinol or precious alloys to counter incompatibility of the device. Furthermore iMRS rooms ought to be similar to theatres considering the hygienic factors, air circulation and accessibility. In this case it is quite difficult in regards to RF shielding constructed from aluminum and filters for aesthetic gases and AC. Also some of the patients who have metallic implants (neuro simulators and pacemakers) are among other hardships. Hence patients with such cases cannot undergo iMRI procedures rendering them stagnate in their prevailing condition (Friebe, 2005). Typical iMR system room Figure: 8 Source: Schempp, (1998). Conclusion Intervention MRI systems have transitioned the traditional mechanisms into a cutting edge techniques with more safety assurance. Many mechanical dilemmas have been solved such as moving the surgical table. This has been eliminated as movement of the system would throw the electrodes off target. Therefore accuracy has been highly appreciated by this MRI principle. However, the dissemination of this procedure faces an economical setback. Thus outside the academic setting the acquisition of such is considered insurmountable predicament. The costs inflate due to improvement on MRI guided techniques. On the positive side the encroachment of iMRI systems have led to rapid cost effectiveness allied to the treatment of various illnesses. Mostly patients who have used MR image guided biopsy, thermal or chemical ablation have evaded open surgical procedures rendering the patient less vulnerable to related risks. This has potentially motivated the use of this principle in radiological practices. MR guidance thus reduces the size of craniotomy hence shortening hospital stay. This hence is the landmark of clinical safety procedures. Bibliography Brown, M. (1999). MRI Basic Principles and Applications. 2 ed. New York : Wisely-Liss. Damadian, R. V. (1971, March 19). Tumor Detection by Nuclear Magnetic Resonance. Science, 171 , pp. 1151–1153. Friebe, M. (2005, October 20). Therapy Applications in the Magnet. Interventional MRI: IAMERS Newsletter , pp. 1-2. Hendee, W. R., & Morgan, C. J. (1984). —Physical PrinciplesMagnetic Resonance Imaging Part . West J Med , 141 (4): 491–500. Jost, C. &. (1998). Are Current Cardiovascular Stents MRI Safe? The Journal of invasive cardiology , 10 (8): 477–479. Rosen, L. (2007). The Recent advances in magnetic resonance neurospectroscopy. Neurotherapeutics , 27 (3): 330–45. Schempp, W. (1998). Magnetic Resonance Imaging, Mathematical Foundations and Applications. New York: Wiley-Liss. Appendices MRI- Magnetic Resonance Imaging NMRI- Nuclear Magnetic Resonance Imaging MRT- Magnetic Resonance Tomography CT- Computer Tomography T- Tesla AC- Alternating Current FLAIR- Fluid attenuated inversion recovery VDU- Visual Display Unit Read More