Local distortion as a pitfall of iterative MLEM reconstruction in myocardial perfusion imaging - A phantom study.

PURPOSE

To provide insight into appearance of local distortion as a pitfall and to assess performance of MLEM reconstruction in presence of a high-contrast object or hot spot and to quantify extent of involvement, specifically in myocardial perfusion imaging.

METHODS

A checkerboard image is reconstructed with MLEM with and without the presence of a high-contrast region or hot spot to demonstrate pattern of distortion in near and distant locations around it. Then, a cardiac NCAT phantom is constructed without ("control") and with a nearby hot spot or highly-intense object (as lung lesion close to lateral wall of LV). An in-house MLEM algorithm is implemented and utilized for reconstruction. Images are analyzed by creating error images and profile plotting.

FINDINGS

Pattern of distortion on a checkerboard image is like a two diagonal bands of the same width of the spot crossing perpendicularly. Higher relative intensity (5:1 vs. 2:1) results in more distortion both in extent and severity. Tomographic image of control NCAT phantom reveals an almost uniform intensity in lateral wall. However, as relative intensity of spot increases, distortion worsens. Circumferential curves of all walls are almost superimposed except for the wall close to object (or lateral wall of the LV).

CONCLUSION

Presence of a hot spot or object creates distortion its own periphery during MLEM reconstruction. The object-of-interest is influenced if located in that region. Degree of distortion depends on relative intensity of hot object to background. Likewise, an artifactual defect is created in LV wall in myocardial perfusion imaging.