Iodine Mapping of the Lung Using Subtraction Imaging for Pulmonary Embolism: Technique and Initial Clinical Experience

PURPOSE/AIM To describe a technique of deriving iodine maps of the lungs using subtraction CTA. To provide our initial clinical experience of this technique and comparison to iodine maps derived from dual energy imaging CONTENT ORGANIZATION A. Principles B. Data acquisition C. Postprocessing: Registration, motion correction and filtering D. Clinical examples E. Comparison with dual energy CT F. Advantages and limitations SUMMARY Iodine maps derived from dual energy CT have been successfully used for assessment of acute pulmonary embolism. We present technical principles and initial results of a technique deriving iodine maps from subtracting precontrast scans from pulmonary CTA. Accurate image registration is crucial: Artifacts may arise from pulsation, motion or differences in inspiratory level. With good registration, partially obstructed vessels can be distinguished from complete occlusions and correlated with perfusion defects in the lung parenchyma. Color coding of lung parenchyma can enhance perfusion differences at a quality that is superior to iodine maps from dual energy imaging. Radiation dose can be kept below 5 mSv for standard size patients. This subtraction technique allows for excellent evaluation of lung parenchyma and pulmonary vessels and achieves a more than 3 times higher contrast-to-noise ratio than dual energy images at identical dose.