In five patients with acute multilobar pulmonary embolism (PE) who were imaged with multi-detector row CT angiography, maximum intensity projection images were reformatted from axial images into rotated paddlewheel and coronal planes with three slab thicknesses and were reviewed for evidence of PE on a per-vessel basis with consensus of two readers. Paddlewheel reformations had a significantly higher percentage of overall detection of PE than did coronal reformations obtained with equivalent slab thickness (P < .0001). Paddlewheel reformations with 5.0-mm slab thickness had no significantly different percentage of overall detection of PE compared with that of axial images obtained with 2.5-mm collimation.
Computed tomographic (CT) pulmonary angiography is gaining widespread acceptance as a first-line study for the diagnosis of pulmonary embolism (PE) (1). Multi-detector row helical CT is an important recent advance in helical CT technology (2-8). Compared with single-detector row CT, advantages of multi-detector row CT include faster scanning time, decreased respiratory and cardiac motion, improved vascular con-spicuity, and enhanced quality of reformatted images (2-8). These advantages have especially important implications for CT angiography. A relative disadvantage of multi-detector row CT is that it generates large data sets. Recently, there has been considerable interest in the use of multiplanar volume reformation (MPVR) methods in CT angiography, both as a mechanism for enhancing display of vascular structures and for improving the efficiency of interpretation by decreasing the number of images necessary for review (9).
With regard to CT pulmonary angiography, a limitation of MPVR images is that the traditional coronal and sagittal reformation planes are not ideal for following the branching patterns of the pulmonary arteries. Most of the images tend to "slice" the pulmonary vessels into small fragments of varying lengths. Recently, a new image display method has been described in which a set of planar slabs is arranged in a paddlewheel or rotational pattern that pivots on a central horizontal axis between the lung hila (Fig la, Ib) (10). The paddlewheel reformation technique provides a continuous display of branching vessels that radiate from both hila (Fig Ic) (10). However, the optimal slab thickness for the paddle-wheel method and its accuracy for detection of PE have not yet been established.
The purpose of our study was threefold: to compare the effect of different slab thicknesses used to detect PE with the paddlewheel and coronal MPVR methods, to determine the percentage of overall detection of PE by using paddle-wheel and coronal MPVR methods, and to compare the percentage of overall detection of PE achieved with these methods with that achieved with standard axial CT.