Recent SPECT/CT Imaging Studies using ORNL/JLAB instrumentation Bethesda May 20, 2005

Overview Systemic AA-Amyloidosis New contrast agent studies

Motivation Serum amyloid P component (SAP) is a normal plasma protein and a universal constituent of amyloid deposits. I-123 labeled SAP has been used clinically to diagnose and monitor systemic Amyloidosis. ORNL/UT collaboration is the first group to image I-125 labeled SAP in murine Amyloidosis models. Using iodine-labeled SAP as the “gold standard” our goal is to identify new imaging compounds for improved diagnosis and therapy.

Balb/c mice constitutively express the human IL-6 gene The mice have high circulating concentrations of sAA (~ 1 mg/mL) and develop severe AA-amyloid disease at 8 mos. of age Administering amyloid enhancing factor to 8 wk old mice results in severe (usually fatal) pathology within 10 wks post-injection Amyloid deposits found in spleen, liver, pancreas, kidney, heart, tongue and vasculature The huIL-6 Transgenic Mouse as a Model of Systemic AA-Amyloidosis

Autoradiography- Splenic Amyloid Deposits Congo red (Mag. 160 x) 125 I-SAP Autoradiography - hematoxylin and eosin counterstain (Mag. 160 x) 125I-SAP Co-localizes with AA-Amyloid Deposits in the Mouse

6 Balb/c huIL-6 mice 3 mice Inject with 100 μg AA-AEF Inject with 100 μL PBS 1% Lugol’s solution as drinking water 300 μCi 125 I-huSAP Sacrifice and Image Mice Biodistribution & Autoradiography Day 0 Wk 7 – 48 hours Wk 7 Wk hours SAP Imaging Protocol

Dual-Modality Imaging of Mice with AA-Amyloid Axial section through spleen and liver SPECT SPECT/CT 3D- SPECT/CT

Enlarged spleen is a consistent pathology

Rendering and Determining Organ Volumes from SPECT Data-sets

% Counts per organ % Injected Dose/gram tissue Biodistribution (spleen:liver) ratio Image Count (spleen:liver) ratio Mouse 10.6 Mouse * Mouse * Image analysis cannot discern the pancreas from the liver which leads to an overestimation of the hepatic deposits and a decrease in the ratio. Comparison of Amyloid Quantitation by Biodistribution and Image Analysis

Conclusions 125 I-SAP provides high resolution mapping of AA-amyloid in mice using a microSPECT imager. Amyloid burden can be quantified at various levels of resolution using autoradiography, biodistribution or SPECT image analysis. CT-directed, 3-dimensional volumetric rendering of the organs will provide organ-restricted specific activities and a greater level of “internal resolution” than the SPECT images alone.

But, SAP scintigraphy has been criticized for: 1.Its inability to image cardiac amyloid in AL patients 2.Its overestimation of hepatic involvement due to its catabolism in the liver So, A small proteinase inhibitor, aprotinin, has been evaluated, clinically and compared to SAP SPECT imaging in our model.

99m Tc-Aprotinin Scintigraphy for Amyloidosis Heart Intestine Joints carpal tunnel IgGκ MM Patient Tongue and submandibular gland Renal AL PatientPlasmacytoma Patient Heart Liver Left sinus Left femur 64 yr old ♂ 86 yr old ♀78 yr old ♀ J. Nuc. Med. Vol. 44 No

125 I-Aprotinin SPECT Imaging for AA- Amyloidosis in Mice SPECT images of 125 I-aprotinin in AA-amyloidotic mice- sagital SPECT images of 125 I-aprotinin in AA-amyloidotic mice- coronal I-Aprotinin is not an efficient tracer for detecting AA-amyloid deposits in our mouse model. However, it can detect renal dysfunction.

Iodine labeled SAP remains the “gold standard” huIL-6 control (20x lower window) control (20x lower window)

Contrast agents are required for CT-based image segmentation water soluble contrast agent injected ip

Segmented spleen and liver (CT) vs. SPECT distribution

Open Challenge… Need to “bloat” CT data to capture lower resolution SPECT activity

Newly developed contrast agent specifically targets the spleen and liver

Liver/Spleen contrast agent (in vivo study)

Contrast agent can also be configured as a blood pool agent

In Vivo blood pool imaging study

Summary SPECT and CT instrumentation are in routine use. Representative SPECT/CT study of AA amyloidosis model presented. Recent contrast agent studies presented.