acute brain injury. It is a well known fact that patients with cognitive difficulties after acute brain injury have abnormal pattern of brain activation. As the patients undergo cognitive behavioural therapy, their pattern of activation return towards normal, and through high field strength MR scanning, we can monitor how treatment engages cognitive processes to improve performance. The ability of 3 tesla machine to deliver
thinner slices with high spatial resolution and speed as compared to 1.5 tesla has also led to increased clinical preference for 3 tesla. This leads to isotropic image acquisition at desired physiological phases (e.g. early, late arterial and venous phases) and high resolution multiplanar reformatting. Due to reduced scan acquisition times,
small 10-second breath hold sequences can be acquired with 3 tesla field strength MRI, serving the purpose for high-resolution and multiphasic MR angiography images.
LIMITATIONS Inspite of emergence of above mentioned breakthrough advances in field of high- strength MR neuroimaging, few safety concerns have also been raised by medical professionals. A large number of implants, aneurysmal clips, stents that have been considered safe by the standards of 1.5 tesla MRI machine are not all cleared for 3 tesla system. Also FDA restricts the amount of heat that can be induced within human tissue. The acceptable levels reach more frequently in 3 tesla scanning, which requires longer scan times to allow the tissue to cool down to an acceptable level. Due to high amount of heat generated, the supporting equipment for the MRI suite needs to be more efficient and compatible, which also lead to the increase in installation cost. Howsoever the limitations, the benefit
versus risk ratio sways in favour of the opportunities 3 tesla MRI has opened in the terms of clinical application. With the strict
The greater signal intensity afforded at 3T is particularly enticing for diffusion-weighted imaging (DWI) needs
vigilance of MRI protocols required for these high field strength scanners e.g. automatic locking doors with badge access, ferromagnetic metal detectors, and professional education. The environment at MR scanning centre can be made safer and less accident prone.
CONCLUSION 3T MRI is clearly ready to meet the needs of clinical practice today. Specific absorption rate limitations (amounting to heat induction in human tissue) are minimized because of technical advances. Now we have specific surface coils for various applications. With appropriate adjustments to scanning protocols, modification of contrast dose, one can master the challenges of scanning at 3T. 3T MRI has twice the signal to noise.
Higher signal gives superior resolution and hence more flexibility. It makes the images sharp and clear and allows to do super high-resolution 1024x1024 studies and super fast studies for contrast MR angiograms in 10 seconds. Spectacular anatomical delineation
provided by high-definition scanning at true 1024 resolution can improve preoperative assessment and may improve sensitivity to smaller lesions. High spatial resolution obtained in 3T MR imaging gives useful information and superior image quality in carotid and cerebral angiography. Better lesion delineation, high speed
and multiphasic scanning gives 3 tesla MRI the cutting edge over standard 1.5 tesla MR machines in clinical neuroimaging. It gives the radiologists as well the purchasers the advantage that is increasingly sought by them in highly competitive market. Only cost considerations stand in the way of 3T systems eventually dominating the high- field market. ■
ID
REFERENCES References available on request (
magazine@informa.com)
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