PET technique visualizes amyloid deposits in heart
PET with 11C-PIB provides a noninvasive method for visualizing amyloid deposits in the heart, according to a study published in the February issue of the Journal of Nuclear Medicine. The researchers suggest that 11C-PIB eventually may be used in the clinical setting as both a diagnostic tool and a treatment follow-up method.
Systemic amyloidosis is a life-threatening disease that disrupts organ functions. In the heart, it can lead to cardiac insufficiency and arrhythmias. Physicians rely on echocardiography for imaging cardiac amyloidosis, followed by a cardiac biopsy to confirm the diagnosis. Early diagnosis—before heart tissue is damaged—and monitoring to assess the efficacy of treatment are important in the prognosis of the disease.
Noting that PET is used to evaluate amyloid deposits in the brain, Gunnar Antoni, PhD, of the PET Centre at Uppsala University Hospital in Uppsala, Sweden, and colleagues wanted to apply the noninvasive technique to cardiac amyloidosis. Their goal was to see if 11C-PIB (N-[methyl-11C]2-(49-methylamino-phenyl)-6-hydroxybenzothiazole) PET provided a method for direct visualization and quantification of amyloid deposits in the heart.
They enrolled 10 patients (mean age 66 years) diagnosed with systemic amyloidosis and five healthy volunteers (mean age 64 years) as controls. Cardiac amyloidosis diagnosis was established by myocardial biopsy or positive biopsy results from subcutaneous abdominal fat and echocardiography findings. They used PET/CT with 11C-PIB to visualize amyloid deposits in the heart and 11C-acetate to measure myocardial blood flow (MBF).
Myocardial uptake of 11C-PIB was visibly detected at all 10 patients 15 to 25 minutes after injection and there was obvious uptake of 11C-PIB in the left ventricle wall of all patients with cardiac amyloidosis. The healthy volunteers showed no uptake. 11C-PIB was also detected in the right ventricle wall in five of the patients and nine of the patients had signs of reversible uptake. The maximum concentration was seen at 10 to 15 minutes after injection.
MBF was significantly lower in patients with cardiac amyloidosis, but there was no significant correlation between MBF and 11C-PIB uptake in either the patients or healthy volunteers. An in vitro analysis in postmortem heart tissue from one patient confirmed specific binding of 11C-PIB in heart tissue with amyloid deposits.
“There was a significantly larger 11C-PIB RI [retention index] in the patients with known amyloidosis than in healthy volunteers,” Antoni et al wrote. “This finding is encouraging in terms of establishing an objective method in a clinical routine, to document cardiac amyloidosis in patients for whom cardiac biopsy material is not available.”
They pointed out that their study sample was small and did not include patients with diastolic heart failure and no cardiac amyloidosis. To be applied in a clinical setting, more studies are needed to ensure that 11C-PIB uptake did not occur in these patients, as well as several validation studies.
Their study showed that 11C-PIB could be used to visualize amyloid deposits in the heart, they concluded, and potentially may serve as a noninvasive method for diagnosing and follow-up treatment for cardiac amyloidosis.