Breathing-Adapted Imaging Techniques for Rapid 4-Dimensional Lung Tomosynthesis

Abstract

Purpose: This article presents enhancements to a 4-dimensional (4D) lung digital tomosynthesis (DTS) model introduced in a 2018 paper. That model was proposed as an adjunct to 4D computed tomography (4DCT) to improve tumor localization through artifact reduction achieved by imaging the entire lung in all projections, reducing the projection collection time duration for each phase compared with 4DCT, and requiring only a single-breath cycle to capture all phases. This is applicable to SABR treatment planning. Enhancements comprise customized patient 4D-DTS x-ray scanning parameters.

Methods and materials: Imaging parameters derived with the 4D-DTS model were arc duration, frames per second, pulse duration, and tube current normalized to single-chest radiographic milliampere-seconds (mA/mAs_AEC). Optimized phase-specific DTS projections imaging parameters were derived for volunteer respiration-tracking surrogate waveforms and for sinusoidal waveforms. These parameters are temporally matched to the respiratory surrogate waveform and presented as continuous data plots during a period of 20 seconds. Comparison is made between surrogate excursions during a single-phase CT and 4D-DTS reconstructions.

Results: 4D-DTS imaging techniques were customized to volunteer respiratory waveforms and sinusoidal waveforms. Technique settings at the highest velocity portions of the volunteer waveforms were arc duration 0.066 seconds, frame rate 921 Hz, pulse duration 1.076 ms, and normalized tube current 76.2 s^-1. Technique settings at the highest velocity portions of the sinusoidal waveforms were arc duration 0.029 seconds, frame rate 2074 Hz, pulse duration 0.472 ms, and normalized tube current 173.6 s^-1. Sinusoidal surrogate excursion distance at the highest velocity portion of the waveform during a CT rotation of 0.5 seconds ranged from 2.68 to 21.09 mm, all greater than the limiting excursion distance chosen in the 4D-DTS model.

Conclusions: 4D-DTS image technique settings can be customized to individual patient breathing patterns so that captured range of motion satisfies an operator-selected value.

Figure 1

Volunteers’ surrogate breathing waveforms 1 through 3 and associated imaging technique plots for D = 1 mm and f = 5. (A) Breathing displacement (cm) versus time. (B) Arc duration (seconds). (C) Frame rate (Hz). (D) Pulse duration (ms). (E) Normalized tube current (mA/mAs_AEC).

Figure 2

Simulated sinusoidal breathing waveforms and associated imaging techniques plots for D = 1 mm and f = 5. Left: 1 cm displacement, 12 bpm. Right: 4 cm displacement, 25 bpm. (A) Breathing displacement (cm) versus time. (B) Arc duration (seconds). (C) Frame rate (Hz). (D) Pulse duration (ms). (E) Normalized tube current (mA/mAs_AEC). Abbreviation: bpm = breaths per minute.

Figure 3

Imaging technique extreme values derived from simulated sinusoidal breathing waveforms using instantaneous analytical velocity at 12, 15, 20, and 25 breaths per minute and 10 to 40 mm breathing displacements for D = 1 mm and f = 5. (A) Minimum arc duration (seconds). (B) Maximum frame rate (Hz). (C) Minimum pulse duration (ms). (D) Maximum normalized tube current (mA/mAs_AEC).