The increasing use of systemic and directed liver therapy for patients with hepatic metastasis has created a demand for improved accuracy of noninvasive imaging techniques. Computed tomography (CT) and magnetic resonance imaging (MRI) are the most common studies used for imaging the liver in oncology patients. Many studies have directly compared the diagnostic efficacy of MRI and CT in patients with focal hepatic malignancies. These reports determined that, although the spatial resolution of CT remains superior, MRI has better contrast resolution and has repeatedly been proven to detect and characterize focal liver lesions with greater accuracy than CT. Whereas iodinated CT contrast material is nephrotoxic, MR contrast has very favorable safety profiles.
In addition, Diffusion-Weighted Imaging is extremely sensitive for identifying sub-centimeter lesions in the liver not seen on conventional MR sequences.
An Ideal PET/CT scan comprises of a low dose whole body CT with PET acquisition. FDG non-avid lesions may be easily missed on PET/CT examination unless it is combined with a diagnostic multiphasic CECT examination which accounts for a large amount of patient radiation exposure and ionic contrast administration. Triple phase MRI for the liver with simultaneous acquisition of PET done using a Simultaneous PET/MRI, limits the exposure to radiation and to the ionic contrast agent used for CT.
PET/MRI gives a comprehensive evaluation of the disease with additional information from MRCP and MR angiography thus mitigating the need for separate 3 separate studies viz. PET/CT+Multiphasic CECT and an MRI with MRCP.
GI cancers are a heterogeneous group of neoplasms that differ in their biologic and physical behaviors depending on the organ of origin, location within the organ, and degree of differentiation. MRI remains the imaging modality of choice for liver, pancreas and rectum. With the development of newer faster single sequences like T2 HASTE, it is possible for imaging the small bowel with MR also K/a MR enterography and MR enteroclysis. This can be done after distending the bowel with plain water which provides excellent contrast with exquisite intraluminal details providing pictures much similar to or rather better than barium study done using x-ray.
With the development of the simultaneous PET/MR dual information can be obtained in a single study with unmatched registration of the PET and MR images which is especially useful in identifying small intraluminal polyps, NET’s, etc. So combining PET and MRI will help the multifaceted imaging required in GI cancers.
45 year old male diagnosed with autoimmune hepatitis and raised serum alpha-fetoprotein (AFP) level 350ng/ml.
Axial T2W(A) shows lobulated liver contour, the shrunken right lobe and fissural widening suggesting cirrhotic liver disease. Axial STIR (B) and diffusion (C) images showing a well-defined lesion in the right hepatic lobe with no significant FDG uptake on corresponding PET/MRI fused images (D) (white arrows).
Axial post-contrast images in arterial (A), porto-venous (B) and delayed (C)phases (white arrows)demonstrating an arterial phase enhancing lesion in the right hepatic lobe with washout in portal venous and delayed scans suggestive of Hepatocellular carcinoma.
50 year old female for staging workup of Hepatocellular carcinoma.
Coronal Post contrast VIBE (A) and axial post-contrast VIBE (B) reveals severe focal narrowing of the intrahepatic IVC (red arrow) with hepatosplenomegaly and multiple enlarged retroperitoneal, mesenteric and abdominal wall collaterals (green arrows) s/o Budd Chiari syndrome. Axial T2W (C) and PET MR fused (D) images shows an irregular hepatic outline with an FDG avid mass in segments V/IVA (white arrow)
Furthermore, the hepatic mass shows arterial phase enhancement (A) with washout on delayed scans (B, C). A small thrombus is seen in the right branch of portal vein (white arrow in C ). Multiple additional arterial enhancing satellite nodules are also seen (red arrows) in Post-contrast axial VIBE arterial phase images (D, E, F)
60 year old male with liver cirrhosis and suspected hepatocellular carcinoma.
Axial post contrast VIBE (arterial phase) (A) venous phase (B) PET MR fused( C) and DWI (D) images reveal three non-FDG avid arterial enhancing lesions (arrows in A) with washout on delayed scans. The lesions appear hyperintense on DWI, s/o possibility of Hepatocellular carcinoma.
Axial pre-contrast VIBE sections of the liver (A, B) in the same patient showing multiple predominantly T1 hyperintense nodules scattered in the liver parenchyma with no significant arterial phase enhancement(C). The lesions are not discernible on DWI (D) suggesting the possibility of Regenerative nodules or Low-grade Dysplastic nodules.
This short PET-MRI Scan case was compiled by Dr. Sangeeta Taneja and Dr. Amarnath Jena (Nuclear Medicine Physician at PET-Suite @ Indraprastha Apollo Hospital, Sarita Vihar).
Read More about PET-MRI Scan at House Of Diagnostics in Delhi and NCR.
The Simultaneous PET-MRI Scan is currently offered at PET-Suite at Apollo Hospital, Sarita Vihar.