The goal of this research study is to determine whether changes in organ-specific uptake of 124I- AT-01 can be measured by PET/CT imaging and further, whether these values correlate with changes in a subject's disease status and thereby enable monitoring of disease response over time in terms of organ-specific amyloid load.

This is a single center, open label, prospective study using 124I-AT-01 PET/CT imaging to evaluate changes in amyloid load in patients with systemic amyloidosis who had undergone 124I-AT-01 imaging.

Consented eligible patients will provide 3 tablespoons of blood for the following laboratory tests: CMP, CBC, CRP, Troponin, NT-proBNP, LDH, FLC and anti-drug antibody (ADA) analyses. A urine sample will also be collected to assess renal function. If required, a pregnancy test will be administered.

Patients will then undergo a transthoracic echocardiographic examination and vital sign assessment before receiving an intravenous injection of no more than 2 mCi 124I-AT-01 followed, 5 h thereafter, by repeat vital sign measurements and PET/CT imaging from crown to thighs with a dynamic PET acquisition over the heart. Previously acquired 124I- AT-01 PET/CT images will be used as baseline values to determine quantitative changes in uptake of the radiotracer in the heart, liver, spleen, and kidney (and other organs deemed positive following visual inspection of the baseline and repeat imaging) as a measure of changes in amyloid load. Optionally, if the patients can return to the study site within ~30 days post injection of 124I-AT-01, a second (post-injection) blood draw and ADA evaluation will be performed.

Inclusion Criteria:

• Must have given written informed consent (signed and dated) and any authorizations required by local law and be able to comply with all study requirements.
• Must have a diagnosis of systemic amyloidosis based on the patient's medical record.
• Must have undergone PET/CT imaging with 124I-AT-01 as part of the AMY1001 study (IND #132282) with visually positive uptake of radiotracer in at least one abdominothoracic organ.
• Must have been imaged with 124I-AT-01 as part of the AMY1001 study (IND #132282) more than 12 months prior to repeat imaging.
• Females: must be non-pregnant and non-lactating and either: surgically sterile (e.g., tubal occlusion, hysterectomy, bilateral salpingectomy, bilateral oophorectomy); post-menopausal (defined as 12 months of spontaneous amenorrhea in females > 55 years of age or, in females ≤ 55 years, 12 months of spontaneous amenorrhea without an alternative medical cause and follicle-stimulating hormone (FSH) levels in the post-menopausal range for the laboratory involved).

Exclusion Criteria:

• Disabling dementia or other mental or behavioral disease.
• Patients on dialysis.
• Inability or unwillingness to comply with the study requirements.
• Patients taking heparin, or heparin derivatives (e.g. low molecular weight heparins) for anticoagulation.
• Other reason that would make the subject inappropriate for entry into this study.
• Inability to lie still for 60 minutes on the PET/CT scanner.
• History of iodine (potassium iodide) allergy.
• Positive ADA finding defined as significantly higher than normal human serum mean values AND with a mean value at least five times greater than the mean value of the normal human serum control.