MRI and PET CT- An introduction

Dr MA Hashmi, MRI- Incharge and Dr Somanath Pandey, Nuclear Medicine Consultant, Saroj Gupta Cancer Centre & Research Institute, talk on MRI and PET CT’s role in improving patient care

Magnetic resonance imaging (MRI) is used in radiology to investigate the anatomy and physiology of the body in both health and disease by help of magnetic fields and radio waves to form images of the body. It is widely used for medical diagnosis, staging of disease and for follow-up without exposure to ionising radiation. Since MRI does not use any ionising radiation its use is recommended in preference to CT. MRI is, in general, a safe technique. Contraindications to MRI include most cochlear implants and cardiac pacemakers, shrapnel and metallic foreign bodies in the orbits. MRI is the tool of choice for neurological cancers as it is more sensitive than CT for small tumours and offers better visualisation of the posterior fossa. The contrast provided between grey and white matter makes it the optimal choice for many conditions of the central nervous system like demyelinating diseases, dementia, cerebrovascular disease, infectious diseases and epilepsy. It is also used in radio surgery to treat intracranial tumours, arteriovenous malformations and other surgically treatable conditions.

Hepatobiliary MR is used to detect and characterise lesions of the liver, pancreas and bile ducts. Focal or diffuse disorders of the liver may be evaluated. Anatomical imaging of the bile ducts is achieved by using a heavily T2-weighted cholangiopancreatography (MRCP). It is also used in the pre-operative staging of rectal and prostate cancer. Applications in the musculoskeletal system are spinal imaging, assessment of joint disease and soft tissue tumours.

PET-CT scan

PET, fused with CT scan, is a new modality that combines functional and anatomic imaging. PET-CT scan using 18F-Fluorodeoxyglucose (18F-FDG) is an integral part of cancer management due to its importance in staging, treatment planning (surgery as well as radiation therapy), evaluation of treatment response, detection of recurrence and long term follow up. FDG PET-CT scan is more sensitive in tumour detection than conventional imaging modalities. For e.g. tumours are not detected by CT scan alone until they reach a size of 10 – 100 gm; whereas PET-CT can detect tumours having a size as low as 0.1 gm. Moreover, PET-CT is a whole body scan, therefore it can detect tumours/ lesions in unexpected/ unusual locations. Apart from the field of oncology, FDG PET-CT has important role in infection; neurology, cardiology etc.

Saroj Gupta Cancer Centre & Research Institute, Thakurpukur, Kolkata has recently installed MRI, multi-slice CT and PET. They will help in better investigation, treatment and follow–up of the patients.