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Magic Angle in Cardiac CT

Rationale and Objective

To identify the influence of various parameters for reducing artifacts in computed tomography (CT) of commonly used pacemakers or implantable cardioverter-defibrillator (ICD) lead tips.

Materials and Methods

This ex vivo phantom study compared two CT techniques (Dual-Energy CT [DECT] vs. Dual-Source CT [DSCT]), as well as the influence of incremental alterations of current-time product and pacemaker lead-tip angle with respect to the gantry plane. Four pacemaker leads and one ICD lead were evaluated. The images were assessed visually on a five-point Likert scale (1 = artifact free to 5 = massive artifacts). Likert values 1–3 represent clinically relevant, diagnostic image quality.

Results

344 of 400 total images were rated with diagnostic image quality. The DECT and dual-source DSCT technique each scored 86% diagnostic image quality. Statistically, DECT images showed significantly improved image quality ( P < .05). Concerning the current-time product, no statistically significant change was found. Regarding lead-tip positioning, an angle of ≤70° yielded 100% diagnostic image quality. Pacemaker and ICD leads were assessed to have statistically significant differences.

Conclusions

Surprisingly, the lead-tip angle of 70° has been established as the key angle under which diagnostic image quality is always ensured, regardless of the imaging technique. Thus, we call 70° the “Magic angle” in CT pacemaker imaging.

Introduction

Patients with implanted metallic devices are a common sight in clinical practice using computed tomography (CT). In particular, more than one million cardiovascular implantable electronic devices such as pacemakers (PMs) and implantable cardioverter-defibrillators (ICDs) are being implanted in patients with cardiovascular diseases every year, and this number is rising .

These devices are usually implanted in an infraclavicular subcutaneous or submuscular pocket with a transvenous lead. Most ventricular leads are placed in the apex of the right ventricle (RV), and most atrial leads are implanted in the right atrial appendage. There is a 4.4% incidence of a lead dislodgement or malfunctioning (~44,000 patients) 1 year after implantation from which approximately 10,000 patients are suffering from possible lead perforation.

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Materials and Methods

CT Data Acquisition and Experimental Setup

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Figure 1, Experimental setup: positioning of the lead tip with regard to the gantry plane.

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Image Post-Processing or Evaluation

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Statistics

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Result

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Technique or Protocol

Evaluation DECT versus DSCT

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TABLE 1

Mean Likert Values ± Standard Deviation of Each Pacemaker Lead Are Shown with Regard to the Specific CT Technique Setting.

Pacemaker 1 Pacemaker 2 † Pacemaker 3 Pacemaker 4 ICD ‡ Boston Scientific CapSure SP Novus 4592 CapSure Sense 4074 CapSureFix Novus 5076 St Jude Medical DECT 1 \* (65 mAs) 2.2 ± 1.4 2.0 ± 1.2 2.0 ± 1.0 2.4 ± 0.8 2.3 ± 1.3 2.2 ± 1.1 (for DECT) DECT 2 \* (125 mAs) 2.2 ± 1.4 2.0 ± 1.2 2.1 ± 1.0 2.3 ± 0.9 2.3 ± 1.3 DECT 3 \* (185 mAs) 2.2 ± 1.4 2.0 ± 1.2 2.3 ± 1.0 2.3 ± 0.9 2.3 ± 1.3 DSCT 1 (150 mAs) 2.3 ± 1.3 2.0 ± 1.2 2.3 ± 1.0 2.4 ± 0.8 2.6 ± 1.0 2.3 ± 1.0 (for DSCT) DSCT 2 (200 mAs) 2.3 ± 1.3 2.0 ± 1.2 2.3 ± 1.0 2.4 ± 0.8 2.6 ± 1.0 DSCT 3 (250 mAs) 2.3 ± 1.3 2.0 ± 1.2 2.3 ± 1.0 2.4 ± 0.8 2.6 ± 1.0 DSCT 4 (300 mAs) 2.3 ± 1.3 2.0 ± 1.2 2.3 ± 1.0 2.4 ± 0.8 2.7 ± 0.8 DSCT 5 (370 mAs) 2.3 ± 1.3 2.0 ± 1.2 2.3 ± 1.0 2.4 ± 0.8 2.7 ± 0.8 2.26 ± 1.3 2.00 ± 1.1 2.21 ± 0.9 2.37 ± 0.8 2.51 ± 1.0

No significant differences are evident between protocols of the same technique (eg, DSCT 1 vs. DSCT 2) (significance level: P < .05).

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Evaluation of Increasing Increments of Current-Time Product

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Evaluation Regarding Lead-tip Angle

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Figure 2, Amount of diagnostic or nondiagnostic values with regard to lead tip angle: With an angle equal or below 70°, entirely diagnostic image quality was ensured.

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Evaluation with Regard to Lead Design: Pacemaker versus ICD

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Observer

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Discussion

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Technique

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Angle

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Figure 3, Artifact burden of Boston Scientific pacemaker lead with an angle of 0° versus 90° toward the gantry.

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Pacemaker

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Observer

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Limitations

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Conclusion

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Acknowledgments

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