Tc-99m MAA Liver Perfusion Scan

Indication

Tc-99m MAA liver perfusion scan is combined with diagnostic angiography and it is indicated for treatment planning in patients who are candidates of Y-90 microsphere therapy.

What is Tc-99m MAA Liver Perfusion Scan? How Does It Show Tumor Focus?

Theranostics is a recently developing field of the medicine. This approach takes body images using a tumor-specific agent to locate the tumor and its metastasis and their potential future locations and it also uses a specific agent with pre-determined therapeutic efficiency for the diseased tissue. This approach enables switching from traditional medicine to contemporary personalized medical procedures.

Regarding liver cancers, Tc-99m MAA liver perfusion scan allows pre-treatment trial, helps us plan the optimal dose of treatment and detects pulmonary and gastrointestinal shunts with high sensitivity. On the other hand, tumor tissues can be treated with a targeted therapy approach with Yttrium-90 (Y-90) microsphere. This is a rather new and successful method of theranostic procedures.

If a therapeutic agent is administered into the hepatic artery, we have some advantages, as liver has dual blood supply and 80 to 90% of tumors measuring larger than 3 mm in diameter are fed by the hepatic artery. On the other hand, healthy hepatic parenchyma is mainly fed by the portal vein. For more than 3 decades this variation has been used when chemotherapy agents are administered through intra-arterial pumps and for tumor embolization. Y-90 microsphere therapy, also called Transarterial Radioembolization (TARE), is an effective treatment for both primary and metastatic malignancies of the liver and it may be used for better survival and to for decreasing the tumor burden in patients for whom surgery or other regional therapies are contraindicated.

Once a patient is considered to be a candidate for Y-90 microsphere therapy, the initial assessment is angiography. The procedure identifies the visceral anatomy and anatomical variations; circulation of liver is assessed, extra-hepatic vessels are occluded/embolized. Once vascular mapping is completed through angiography; Tc-99m MAA liver perfusion scan is performed as a simulation of Y-90 microsphere therapy, through which pulmonary/gastrointestinal system shunts are investigated and the optimal treatment dose is determined.

Similar to Y-90 microspheres, 99mTc-labeled macroaggregated albumin (MAA) particles that measure 15-100 μm in size settle in hepatic capillaries and precapillaries and cause microembolisms. Thus, arterial perfusion of healthy hepatic tissues and tumoral foci are accurately mapped with MAA particles administered into the hepatic artery.

Who are the Candidates for Tc-99m MAA Liver Perfusion Scan?

Tc-99m MAA liver perfusion scan is employed for candidates of Y-90 microsphere therapy. This is an imaging technology that allows to develop a personalized plan before the treatment and is performed during diagnostic angiography.

Is Tc-99m MAA Liver Perfusion Scan Safe?

Vascular mapping through Tc-99m MAA liver perfusion scan is a safe imaging technique which uses low doses of radiation. Patients will be informed by our interventional radiologist about recommendations for a simultaneous angiography procedure. Both procedures are contra-indicated for pregnant women due to radiation exposure.

Preparation for Tc-99m MAA Liver Perfusion Scan

Special preparation is not required for Tc-99m MAA liver perfusion scan. However, patients will be informed by our interventional radiologist about recommendations for simultaneous angiography procedure.

Tc-99m MAA Liver Perfusion Scintigraphy Procedure

One of the basic phases prior to Y-90 microsphere therapy is the angiography, which is performed at the interventional radiology unit in order to map feeders of the tumor, embolize collaterals and assess patency of the portal vein. After the procedure is completed, approximately 150-185 MBq (4-5 mCi) Tc-99m MAA is infused into the artery through a microcatheter. In order to prevent image artifacts secondary to in vivo MAA fragmentation, the patient is transferred to the Nuclear Medicine Clinic in a short time; anterior, posterior and right lateral static images, also including lungs and liver, and SPECT/CT images are acquired within the first hour. These images help not only withevaluation of pulmonary and gastrointestinal shunts, but also with a dosimetric plan that allows to determine the optimal therapeutic activity for Y-90 microsphere therapy.

Administration Site Options for Tc-99m MAA

The planned infusion site of Y-90 microsphere;

• To lobar artery of the hepatic lobe, which poses the highest risk for elevated pulmonary shunt (e.g. with vascular invasion or higher tumor load),
• To hepatic artery or proper hepatic artery; Tc-99m MAA may be administered;

If variations of the hepatic artery are faced, MAA doses are divided into smaller aliquots in order to assess the entire hepatic perfusion in a single angiography procedure (e.g. 1-5 mCi) and the agent is administered into right and left hepatic arteries.

Supraumbilical subcutaneous soft tissue leakage can be observed in Tc-99m MAA liver perfusion scan. If leakage is detected on the anterior abdominal wall; vasospasm with cold compress on anterior abdominal wall is recommended during treatment in order to eliminate post-treatment subcutaneous inflammation and radiation damage.

Tc-99m MAA Liver Perfusion Scan – Quantitative Measurements

Tumor/Liver uptake ratio = [Tumor count (count/pixel)]/[Liver count (count/pixel)] threshold value should be greater than 2.

Hepatopulmonary shunt ratio = √[(Anterior Pulmonary Count) x (Posterior Pulmonary Count)] / √[(Anterior Pulmonary Count + Anterior Hepatic Count) x (Posterior Lung Count + Posterior Hepatic Count)] x100