The using of 3Tesla in Clinical Settings - Essay Example

The last five years have seen a major push for the use of 3Tesla in clinical settings High strength magnetic field has become a prime topic of research in recent years. Current studies have shown that 3Tesla has captured almost entire market of imaging. Prior to this, 1.5T and below magnetic field strength were predominantly used. Latest developments in technology in terms of magnetic design and shielding have been offering an additional comfort to patients and improved imaging quality to clinicians. The market research (2004) stated, “3T systems made up 25% of new high field MRI scanner purchases” (Jerrold & Keene, 2009, pp 1-8). Benefits of 3T over old system have been discussed in detail further in the essay. 3T has provision for excellent imaging results of human body structures such as brain, abdominal organs, all the bony parts and abnormal masses (cancer). In addition, some complicated procedures such as diffuse tensor imaging (DTI) and MRI spectroscopy can also be administered easily with 3T (Haines & Quaddy, 2010, pp1-3). There is a scope of using many RF coils array for faster image processing in 3T. Basic physics of MRI and nuclear spin Here is a glance at the basic physics of MRI and correlation with nuclear spin. Magnetic field is a force generated by the electric currents or magnets. This force attracts other metallic and magnetic objects towards the field. Nucleus of the atom has magnetic properties. All the nuclei provide chemical information together throughout the magnetic field. Atomic chief constituents are proton, electron and neutron. They start revolving in an angular momentum. This is called as nuclear spin. This spin is suggestive of the direction of movements in magnetic field (James, 1998, pp1-31; Machann, Schlemmer&Schick, 2008, pp63-70). When two atoms come together in pair, they do not demonstrate a spin. However, in some nuclei, there are uneven number of protons and neutrons. These types of nuclei will have intrinsic angular momentum. In other incidences, when the unpaired nuclei spins are put in the magnetic field the magnetic field of the nucleus and surrounding field react with each other. These reactions are explained with Larmour frequency equations (James, 1998, pp1-31; Machann et.al., 2008, pp63-70). These nuclei momentums align either parallel or anti parallel with the surrounding magnetic field based on the law of quantum physics. Hence, this creates energy difference among the spins that in turn allows transition in between the states. Nucleus consumes energy and goes into excitement phase and further resting or relaxation phase. This relaxation period is important for calculation, as it indicates that any system requires equal time to go into relaxing phase after equal time of exciting phase throughout the magnetization. Total sum of the energy from every step transition is equated along with signal spatial frequency domain and spin density. This signal from spatial frequency is expressed into density in real place for the formation of MRI image (James, 1998, pp1-31; Machann et.al., 2008, pp63-70). Following picture shows the sample of 3T scanner machine with large bore. Picture curtsey- (Haines & Quaddy, 2010, pp1-3) Advantages of going to higher field Higher field means better imaging in shorter time. Transformation of scanning machines from1.5T to 3T also has many positive aspects: 1) SNR (Signal to noise ratio) The major advantage of using 3T technology is to have increased SNR, i.e. signal to noise ratio. “The FDA limits SAR by anatomical site based on the potential effects of heating” (Stafford, pp 1-5). SNR is almost double in 3T imaging. Raised SNR would certainly improve the image quality far better than before. In addition to this, higher SNR reduces the image acquiring time that helps in many ways such as reduced image producing time helps decrease the incidences of artefacts, especially motion. Many times posture of the patient for imaging makes him/her uncomfortable. Hence, reduced image acquisition time is quite helpful. 2) Spectral Resolution Improved SNR requires thinner slices and offers high resolution. Hence, better imaging and better clarity. 3T has made possible certain scans that were not so easy on previous systems due to their qualities. As per the experts, 3T has added many advantages to the imaging process offering highest quality resolution and maximum use of applications with less time and effort consumption. This further helps in accurate diagnosis in clinical set ups. As per Dr Don Mills, “When we saw the image quality and speed of the 3T, it became obvious to us that 3T is the wave of the future.” Moreover, he added that, “I think it will soon be the gold standard for MRI” (Siemens medical solutions, 2009, 1-6).With high field strength, there can be a massive spectral division of all different chemical species. This helps to get high spectral resolution. This has added benefit to MRI spectroscopy (Stafford, pp 1-5). 3) Contrast changes and its applications Increase in field sensitivity allows higher resolution in the same given time or increased speed of scanning in the same achieved resolution. However, with higher magnetic field such as 3T parameters for relaxation differ. Hence, high SNR cannot be utilised easily. Spin relaxation and shortening of T2 are noticed when higher field is applied. Moreover, susceptibility gradient is increased linearly causing more T2 shortening. All these things add to achieve better quality T2 contrast. In addition, BOLD (Blood oxygen level dependant) contrast has also received an advantage of high SNR and T2 contrast. However, drawback is short T2 measurements causes’ loss of signals at times especially in echo- train based scanners. However, gradually, all these difficulties have been sorted out with 3T with the help of parallel imaging that helps to lower down echo-train length with minimal compromise at resolution (Stafford, pp 1-5). Challenges in transition to 3T Transition to higher field is always a challenging task for all the technicians. When the industry decided to move from 1.5T to 3T, lot of challenges have come across them. It was not an easy transition. Entire MRI set up was adjusted to 1.5T. All the support systems were compatible with 1.5T. Before transition, vigorous research had taken place to establish 3T compatible equipments. Patient implants suitability for 3T was a very important issue. Not all the implants were tested on 3T. This was a big task as patients safety was the biggest concern. Another major obstacle was the amount of heat produced when 3T machine is in use. FDA has set up a standard limit for production of heat in human body during imaging process. As per the observation, 3T crosses this limit quickly and for cooling purpose, body has to rest inside for extended time (Jerrold & Keene, 2009, pp 1-8). Just like all other new experiments, 3T also had to pass through lot of discussions and trials before it got set into the clinical settings. Moving to higher field strength needs more weight, cryogen usage and fringe field managed for sitting purpose. Earlier, there were certain inhibitory factors that did not allow people to use 3T in full swing. Some limitations were physical, technical and safety oriented. Technical limitations were B0 and B1 homogeneity, high gradient coil performance, linearity and large radiofrequency coils whereas 3T also had to correct its limitation on physics ground such as susceptibility artifact, kinetic changes etc (Stanford, pp 1-5). If the patient is exposed to change of field or moving to higher field for small duration, he sometimes gets headache, nausea, vertigo with visual disturbances, tingling numbness and toothache (Stafford, pp 1-5; Kangarlu, Pierre-Marie & Robitaille, 2000, pp 321-355). These challenges were resolved by understanding of protocols and imaging procedure clearly that mainly differed from 1.5T. Hence, overcoming these challenges has helped everyone to enjoy the benefits of going to higher field without compromising patients’ safety (Stafford, pp1-5). 1) Specific absorption rate (SAR) – Specific absorption rate was the main obstacle in the row. SAR is depending upon the total amount of consumption and utilization of energy. SAR has a specific marker that has been set by FDA keeping in mind the patient’s safety. 3T used to consume more energy for longer duration in order to give good images. Hence, SAR measure used to be high resulted in low quality resolution and extended procedure time. However, with the developments in the imaging field technology and the modifications in softwares have created a significant change in the utility of 3T mechanism. Flip angles and parallel imaging methods are being used to reduce the amount of energy used in the process of 3T. In addition, true form hardware development has also made a significant reduction in the energy component of 3T imaging. With the help of all these positive changes, 3T has become a main choice for most of the technicians (Siemens medical solutions, 2009, 1-6). 2) Dielectric effects- Another big issue with 3T was dielectric effects. Dielectric effects include T1 relaxation changes and B1 homogeneities. In addition, problems such as susceptibility and increase of chemical shift were very common with 3T usage. However, gradually with the development of the technology and improvement of computer software as mentioned above about True Form software has fixed the related hassles with the 3T operation. T1 extension time was no more problem when multiple pulse sequences were added to T1 weighting. Eventually, this scenario helped 3T technique to establish in a positive environment. “We were concerned about the dielectric effect, particularly in body imaging,” said Dr. Bisese. “But with our 3T magnet, we have not had a problem with that kind of artifact at all.” (Siemens medical solutions, 2009, 1-6). Signal void in 3T due to dielectric effects Picture curtsey (Machann, Schlemmer, Schick, 2008, 64-70) 3) Acceptance- 3T scanner has helped introducing wider magnetic bore with 70mm dimension. Routine bore are available in 55-60 size. Hence, imaging heavy weight patients and claustrophobic patients is sometimes really very difficult. Many times a patient is advised for vertical scanner with low imaging field in such cases. MRI of obese and unconscious patient was a challenge before. Nevertheless, with the introduction of 3T with 70 mm bore all these problems have been resolved. Claustrophobics and obese patient can fit into 70mm bore without much difficulty. Some patients require more imaging time in case of head examination or abdominal examination. With 70 mm bore, patient can lie down for longer time without any fear. Hence, introduction of 3T was indeed very beneficial to have good quality imaging along with the desired time of examination (Siemens medical solutions, 2009, 1-6). 4) Patient’s safety- Patient’s safety has always a prime focus in MRI setups. Initially, imaging with 3T system was not advisable to the patients with metallic implants and other devices. “It is extremely important to note that medical devices declared “MR Safe” at 1.5 Tesla are not necessarily so at higher fields.” (Stafford, pp 1-5). It was observed that some devices or implants that were termed safe for 1.5T could have severe magnetic reaction with 3T. Hence, it could be a disaster (Shellock, 2008). 3T technique was not suitable to such patient and was a major health risk. However, as the world started realising the advantages of 3T scanners the need was felt among all for testing all the implants for 3T compatibility. Hence, most of the metallic implants had been tested and verified in 3T before they were tagged as 3T compatible (Siemens medical solutions, 2009, 1-6). 5) Noisy 3T is noisy. High magnetic field strength and length of the magnetic bore determine the amount of noise produced during the procedure. Noise increases with the gradient field of the high field strength. Noise in 3T approaches maximum limit faster than 1.5T. Moreover, it crosses the safety limit too. Hence, ear protection devices have been made compulsory to all the patients while undergoing examination with 3T (Jerrold & Keene, 2009, pp 1-8). 6) Education- Another important difficulty was awareness of this new activity in the imaging field. Bringing 3T from scientist room to clinic was a long journey. Radiographers and clinician were well worse with 1.5 T or below techniques and their protocols. While introducing 3T to clinical settings important step was to provide appropriate knowledge about the device and its applications in the clinical management to all the related staff. However, many training opportunities were made available in order to understand the exact difference in 3T and 1.5T. In current dates, maximum clinicians and imaging technicians are aware of the all details of 3T imaging and they find it convenient to read the results with 3T (Siemens medical solutions, 2009, 1-6). Conclusion 3T had to face many challenges before getting set into the most of MRI setups, as described above. 3T had to satisfy all those criteria that 1.5T had to fulfil when it was initially introduced in the market. Gradually, people have started showing acceptance towards 3T scanners and their beneficial applications. Higher field means higher resolution and contrast changes that altogether offer better imaging with maximum comfort to patient and technician. Moreover, 3T scanners are able to provide all of the above. However, discussion has already begun about the advanced version of 3T in magnetic field such as 5T or 7Twith improved results and we hope to see them in near future. References Gomez, E.F. (2008). In homogeneity Correction in High Field Magnetic Resonance Images: Human Brain Imaging at 7 Tesla. Haines, L. & Quaddy, T. (2010). 3 Tesla MRI to offer outstanding image detail in clinical setting. Siemens new release. James, T.L. (1998). Fundamentals of NMR. [Online]. Available from http://www.ias.ac.in/initiat/sci_ed/resources/chemistry/James.T.pdf [Accessed: May 18, 2012]. Jerrold, J. & Keene, S. (2009). MRI Safety at 3T versus 1.5T. The Internet Journal. Kangarlu, A., Pierre-Marie, L. & Robitaille (2000). Biological effects and health implications in magnetic resonance imaging. Concepts in Magnetic Resonance, vol. 12, no. 5, pp. 321-359. Machann, J., Schlemmer, H.P. & Schick, F. (2008). Technical challenges and opportunities of whole-body magnetic resonance imaging at 3 T. Physica Medica, vol. 24.pp. 63-70. Shellock, F. G. (2008). Reference manual for MR safety, implants, and devices. Biomedical Publishing Group. Siemens medical solution (2009). Incorporation of 3T MRI into clinical routine. Siemens healthcare. Stafford, R.J. High field MRI: Technology, applications, safety, and limitations. The University of Texas. Read More