ECG‐correlated image reconstruction from subsecond multi‐slice spiral CT scans of the heart

Abstract

Subsecond spiral computed tomography (CT) offers great potential for improving heart imaging. The new multi‐row detector technology adds significantly to this potential. We therefore developed and validated dedicated cardiac reconstruction algorithms for imaging the heart with subsecond multi‐slice spiral CT utilizing electrocardiogram (ECG) information. The single‐slice cardiac z‐interpolation algorithms 180°CI and 180°CD [Med. Phys.25, 2417–2431 (1998)] were generalized to allow imaging of the heart for M‐slice scanners. Two classes of algorithms were investigated: 180°MCD (multi‐slice cardio delta), a partial scan reconstruction of data with(fan angle) resulting in effective scan times of 250 ms (central ray) when a 0.5 s rotation mode is available, and 180°MCI (multi‐slice cardio interpolation), a piecewise weighted interpolation between successive spiral data segments belonging to the same heart phase, potentially providing a relative temporal resolution of 12.5% of the heart cycle when a four‐slice scanner is used and the table increment is chosen to be greater than or equal to the collimated slice thickness. Data segments are selected by correlation with the simultaneously recorded ECG signal. Theoretical studies, computer simulations, as well as patient measurements were carried out for a multi‐slice scanner providing slices to evaluate these new approaches and determine the optimal scan protocol. Both algorithms, 180°MCD and 180°MCI, provide significant improvements in image quality, including extremely arythmic cases. Artifacts in the reconstructed images as well as in 3D displays such as multiplanar reformations were largely reduced as compared to the standard z‐interpolation algorithm 180°MLI (multi‐slice linear interpolation). Image quality appears adequate for precise calcium scoring and CT angiography of the coronary arteries with conventional subsecond multi‐slice spiral CT. It turned out that for heart rates the partial scan approach 180°MCD yields unsatisfactory results as compared to 180°MCI. Our theoretical considerations show that a freely selectable scanner rotation time chosen as a function of the patient's heart rate, would further improve the relative temporal resolution and thus further reduce motion artifacts. In our case an additional 0.6 s mode besides the available 0.5 s mode would be very helpful. Moreover, if technically feasible, lower rotation times such as 0.3 s or even less would result in improved image quality. The use of multi‐slice techniques for cardiac CT together with the new z‐interpolation methods improves the quality of heart imaging significantly. The high temporal resolution of 180°MCI is adequate for spatial and temporal tracking of anatomic structures of the heart (4D reconstruction).