Regional tidal volume assessed by gated lung imaging

Area of Science:

• Nuclear Medicine
• Pulmonary Physiology
• Medical Imaging

Background:

• Traditional xenon-133 imaging has limitations due to poor physical properties and radiation dose.
• Technetium-99m microspheres offer improved imaging but may not accurately reflect ventilation and preclude simultaneous perfusion scans.
• Krypton-81m gas has suitable energy but generator supply and short half-life pose challenges for ventilation index calculation.

Purpose of the Study:

• To measure regional lung tidal volumes and functional residual capacities using xenon-127 (127Xe).
• To develop a method for correcting geometric changes during ventilation using simultaneous technetium-99m (99Tcm) perfusion data.
• To evaluate the utility of the derived regional function ratios in differentiating normal from abnormal lung function.

Main Methods:

• Regional lung volumes were measured by accumulating iso-volumic images during 127Xe rebreathing.
• Geometric changes during ventilation were corrected using simultaneous 99Tcm counts from gated perfusion scans.
• Regions of interest were dynamically adjusted to maintain constant 99Tcm counts, allowing derivation of regional tidal volumes (TVr) and functional residual capacities (FRCr).

Main Results:

• Patients with chronic bronchitis and emphysema showed increased FRCr and a decreased TVr/FRCr ratio compared to normal subjects.
• Preliminary data indicate the TVr/FRCr ratio is a more effective discriminator of regional lung function than xenon washout estimates.
• Xenon-127 (127Xe) offers improved dosimetry and allows simultaneous ventilation/perfusion imaging with 99Tcm.

Conclusions:

• The developed method using 127Xe and dynamic 99Tcm correction accurately measures regional lung volumes.
• The TVr/FRCr ratio shows promise as a sensitive indicator for detecting abnormal regional lung function, particularly in obstructive lung diseases.
• 127Xe imaging provides a superior alternative to 133Xe for ventilation studies, enabling simultaneous ventilation-perfusion imaging.