technetium-tc-99m-pyrophosphate and Pulmonary-Embolism

A simple technique is described for generating ventilation/perfusion ratio and perfusion/ventilation ratio images from the posterior Tc-99m PYP aerosol inhalation and Tc-99m MAA perfusion images obtained during routine lung scintigraphy. These images highlight areas of ventilation/perfusion incongruence--mismatch or reverse mismatch--that may sometimes be difficult to detect on conventional images.

Topics: Aerosols; Humans; Image Processing, Computer-Assisted; Lung; Pulmonary Embolism; Radionuclide Imaging; Technetium Tc 99m Aggregated Albumin; Technetium Tc 99m Pyrophosphate; Ventilation-Perfusion Ratio

Although [99mTc] diethylenetriaminepentaacetic acid (DTPA) is currently the most widely used radioaerosol, rapid alveolar clearance limits its usefulness for single photon emission computed tomography (SPECT) ventilation lung imaging. Previous research has shown that [99mTc]phosphate compounds have high alveolar deposition and slow clearance and thus provide suitable aerosols for pulmonary ventilation studies. We have compared the pulmonary retention and blood levels of [99mTc]pyrophosphate (PYP) and [99mTc]DTPA in eight normal nonsmoking male volunteers. These two radioaerosols have comparable pulmonary deposition. Technetium-99m PYP, however, has a much slower pulmonary clearance which allows sufficient time (20 or more minutes) for SPECT data acquisition using a single-headed rotating gamma camera. While the radiation absorbed dose to the lungs for [99mTc]PYP (0.31 rad/mCi) is greater than for [99mTc]DTPA (0.11 rad/mCi), it is at a clinically acceptable and safe level.

Topics: Administration, Inhalation; Adult; Aerosols; Diphosphates; Humans; Lung; Male; Organometallic Compounds; Pentetic Acid; Pulmonary Embolism; Technetium; Technetium Tc 99m Pentetate; Technetium Tc 99m Pyrophosphate; Tomography, Emission-Computed