PET-MRI Scanners: A Further Evolution in Diagnostic Imaging
Scanners that combine the capability of positron emission tomography (PET) with magnetic resonance imaging (MRI) are now being developed. PET evaluates metabolic aspects of disease, while MRI provides high-resolution anatomical information. The PET-MRI scanner is a further evolution of an earlier hybrid, PET–CT, which combines PET with computed tomography (CT) imaging.
Engineering Challenges and Opportunities
Black and white MRI images beside coloured MRI-PET fusion images.
Photo courtesy of GE Healthcare.
There are technical difficulties in engineering a hybrid that has PET and MRI scanners in a single unit.
A process known as image fusion has been used for some time, where a composite picture is produced by overlaying images obtained after patients are scanned in separate PET and MRI machines. The composite image is then used to help guide diagnosis, treatment planning and follow-up.
A hybrid PET–MRI scanner would reduce imaging time and potentially increase patient throughput. A combined unit might also avoid errors due to a partial mismatch of images caused by variations in patient position in the separate scanners.
Clinical Applications of PET–MRI Image Fusion
PET–MRI fusion has been used for the initial evaluation of brain tumours, as well as treatment planning and follow-up after therapy.[1] Diagnosis with PET–MRI fusion has been associated with increased survival times for patients with recurrent high grade gliomas treated by radiotherapy,[2] and with more specific diagnoses of brain tumours in children.[3]
PET–MRI fusion has been used to manage the treatment of patients with some types of brain tumours and those with intractable epilepsy, sometimes with the use of additional images from CT or single photon emission computed tomography (SPECT). The combined images provide additional information on the volume of the brain to be treated, permitting more complete destruction of the target lesion and potentially reducing adverse events associated with the treatment (surgery or radiotherapy).
The use of PET–MRI has improved the detection of epileptogenic regions in children with a genetic disorder who are being evaluated for epilepsy surgery.[4] PET–MRI fusion has also been used with a frameless surgical guidance system to permit more precise excision of epileptogenic tissue and minimize damage to normal tissue.[5]
Cost
The cost of a PET–MRI machine is unknown, but it is likely to be higher than the US$2.5 to US$3 million for a hybrid PET–CT scanner.[6] A cost-effectiveness evaluation of the technology would need to take into account the cost offsets gained through faster imaging.
Future Directions
Comparative clinical benefits for existing PET-MRI or PET-CT approaches need to be established, as well as the caseload and casemix required for effective utilization of a hybrid PET-MRI scanner.
References
[1] Wong TZ, et al. Cancer J 2004;10(4):234-42.
[2] Grosu AL, et al. Int J Radiat Oncol Biol Phys 2005;63(2):511-9.
[3] Borgwardt L, et al. J Clin Oncol 2005;23(13):3030-7.
[4] Asano E, et al. Neurology 2000;54(10):1976-84.
[5] Murphy M, et al. J Clin Neurosci 2001;8(6):534-8.
[6] Hibbs CW, et al. Academy Journal 2004;1. Available: http://www.aia.org/aah_a_jrnl_0401_article5&grandCh=yes.