#nucmed

Clinical trials are also underway for PSMA-targeted therapy with alpha-emitting radionuclides. Alpha particles are much more energetic and thus cause more localized damage than beta particles. They do not travel as far in tissue, so they tend to have less toxicity. Image shows a patient with metastatic prostate cancer who had excellent response after 2 cycles of actinium-225-PSMA targeted alpha therapy (TAT). Reference: Zacherl et al. J. Nucl. Med. 2021, 62, 669-674.

#TeachingRounds#FOAMed#FOAMRad#Radiology#NuclearMedicine#PETCT

This patient is an 80 year-old man with elevated PSA. Whole body bone scan demonstrates non-focal uptake in the left tibia. Radiograph reveals thickened cortex and trabecular thickening. Findings are compatible with Paget's disease; a good reminder that just because a patient has prostate cancer doesn't mean everything on their scan is prostate cancer. 

As mentioned yesterday, vesicoureteric reflux is a complication of many congenital GU abnormalities. Most commonly, voiding cystourethrogram (VCUG) is the study of choice to evaluate for reflux. Reflux is graded according to the diagram shown.

Nuclear cystography can also be used. Radiation dose is lower, but less anatomic information is obtained, and grading reflux is less precise (mild, moderate, severe).

A patient with thyrotoxicosis and this thyroid scan is said to have thyroiditis. The gland is hypofunctioning, RAIU is near zero and no thyroid tissue is seen in the neck. Uptake is decreased due to inflammation or suppression of the thyroid axis.

This patient had subacute thyroiditis, which has a differential of granulomatous (de Quervain) thyroiditis, post-partum thyroiditis, and silent thyroiditis.

Other differential diagnoses for thyroiditis include: 1. Iodine-induced thyroiditis (usually from iodinated contrast) 2. Type 2 amioadarone induced thyrotoxicosis (type 1 has elevated RAIU) 3. Factitious thyroiditis 4. Ectopic thyroid tissue (struma ovarii, functioning follicular carcinoma)

Nuclear thyroid scintigraphy provides both functional and anatomic information in the workup of thyroid disease. Tc-99m-pertechnetate, I-123, or I-131 can be used (iodine is used if measurement of radioactive iodine uptake – RAIU - is desired, useful in most cases). Indications for thyroid scan are as follows:

1. Thyrotoxicosis, including subclinical hyperthyroidism (usually with RAIU) 2. Evaluating functional status of a thyroid nodule (usually with RAIU) 3. Thyroid cancer (typically I-131): RAIU and whole body scan after thyroidectomy, to evaluate for residual disease in neck, lymph nodes, and for distant metastases (also assists in planning RAI therapy) 4. Evaluation of mediastinal masses (i.e. substernal goiter) 5. Detection of ectopic thyroid tissue (i.e. lingual thyroid, esp. in the evaluation of neonatal hypothyroidism)

Today's less common nuclear medicine study is Tc-99m-pyrophosphate (PYP) for evaluation of suspected cardiac amyloidosis. In such patients, PYP has excellent specificity for TTR amyloidosis.

Case shows a planar image (left) from a PYP scan of an elderly patient with suspected cardiac amyloidosis. SPECT CT (right) confirms that the uptake localizes to the myocardium. Based on ASNC guidelines, this is "strongly suggestive" of TTR amyloidosis (myocardial uptake greater than rib uptake).