Examples of Earlier Detection of Disease
• Bone scan detects metastases earlier than X-rays: more sensitive, but less specific
• I123 mIBG detects pheochromocytoma metastatic to lymph nodes that can not be visualized on a CT scan
Examples of Molecular Imaging:
Imaging of neuroendocrine tumors with I123 mIBG identifies lymph nodes containing metastatic pheochromocytoma long before they appear on CT scans This patient had only 1 tumor (arrow) evident on a CT scan.
Imaging of hyperthyroidism (Graves Disease) using I123 NaI. Note uniformity of uptake with no hot spots of cold spots
Imaging of hot nodules using I123 NaI. Note suppression of uptake in the remainder of the thyroid gland.
Skeletal imaging with Tc-99m MDP or another labeled phosphate analog provides planar and/or tomographic images of bony metastases months or years before they can be identified by any other imaging modality. It traces phosphate uptake by hydroxyapatite molecules in bone tissue.
In-111 Octreoscan Study positive for liver metastases. The tumor has somatostatin receptor sites which readily take up this somatostatin analog.
Following injection of F18 FDG, a sugar analog, a PET scan can reveal the presence of breast cancer cells in specific areas of the body, in particular, lymph nodes that have not yet changed size or shape. These tumors are frequently missed by other imaging modalities since molecular changes predate structural changes. This is a breast cancer patient with a normal CT scan.
Prostate Cancer imaging with In111 ProstaScint involves a radiolabeled antibody specific for a tumor membrane surface antigen on prostate cancer cells. The resulting antigen-antibody complex is precipitated at the tumor site and permits external detection of both primary and metastatic disease. Although disliked by patients, this is considered to be the best diagnostic procedure available for detecting recurrent prostate cancer. This is a Whole Body ProstaScint Scan of a Patient with Rising PSA while undergoing Hormonal Therapy. ProstaScint activity in a left supraclavicular lymph node and in many central abdominal lymph nodes (arrows) indicates a high likelihood of metastatic disease and hormone resistant.
Bone Imaging with F-18 NaF provides excellent quality images of bony metastases by tracing the absorption of fluoride ion by bone tissue, with preferential uptake in metastases. F-18 NaF PET scans have improved anatomic detail compared with conventional gamma camera systems, with higher accuracy in detecting both osteolytic and osteoblastic metastases. They have a greater differentiation rate of benign versus malignant lesions and improved ability to identify the extent of bone metastases.