First MRI application of an active breathing coordinator

Abstract

A commercial active breathing coordinator (ABC) device, employed to hold respiration at a specific level for a predefined duration, was successfully adapted for magnetic resonance imaging (MRI) use for the first time. Potential effects of the necessary modifications were assessed and taken into account. Automatic MR acquisition during ABC breath holding was achieved. The feasibility of MR-ABC thoracic and abdominal examinations together with the advantages of imaging in repeated ABC-controlled breath holds were demonstrated on healthy volunteers. Five lung cancer patients were imaged under MR-ABC, visually confirming the very good intra-session reproducibility of organ position in images acquired with the same patient positioning as used for computed tomography (CT). Using identical ABC settings, good MR-CT inter-modality registration was achieved. This demonstrates the value of ABC, since application of T1, T2 and diffusion weighted MR sequences provides a wider range of contrast mechanisms and additional diagnostic information compared to CT, thus improving radiotherapy treatment planning and assessment.

Figure 1.

Schematic MR-ABC diagram: the original ABC digital volume transducer in the MR scanner room is connected through the RF panel to the original ABC control module in the technical room using custom extension cables and connectors. The tubing of the original balloon valve is extended to reach the ABC control box and the purpose-built trigger adapter. Upon detection of full balloon valve inflation, the adapter activates a waveform generator that triggers MR acquisition. Patient alert signals from the MR patient alert button are intercepted by a custom adapter and fed into the patient switch input of the control module to abort breath holding. The module communicates with a control computer in the MR operator area, operating the standard ABC control software. Grey lines indicate air tubes while black lines denote electrical connections. Boxes with a darker hue represent components different from the standard ABC design.

Figure 2.

Patient setup for MR-ABC examinations: subjects lay supine on an Extended Wing Board fixed on a Perspex flatbed, with hands superior to their head and their nose clamped. The ABC breathing system, spirometer and balloon valve were supported by an adjustable purpose-built post. A modified MR alert button replaced the original patient switch and was retained in position by custom clamps on the handle bar.

Figure 3.

The same axial slice with (a) no ABC in the scanner room, (b) ABC transducer at the scanner isocentre plane and (c) ABC transducer 30 cm far from the isocentre in axial direction. All images are equally windowed. The circular ROI used for SNR calculations is drawn on (a) and (c).

Figure 4.

Three abdominal slices of a DW-EPI of a healthy volunteer acquired during multiple ABC breath holding with the same settings at two time points (a) and (b) during the same session (b = 0 s mm⁻², identical slice position) to demonstrate averaging with ABC breath holds. (c) is the average of (a) and (b). (d) ADC maps produced by aggregating the DW images from the time points (a) and (b) at each slice position (b = 0, 100, 500, 750 s mm⁻²). (e) Difference images (b) − (a). No image registration was used in any operation and displayed windowing is the same in all cases except for the ADC maps.

Figure 5.

Two coronally reformatted slices of a DW-EPI (b = 0 s mm⁻²) of a healthy volunteer acquired during (a) standard operator-instructed self-induced multiple breath holds; (b) ABC-controlled multiple breath holding and (c) repetition of (b). (d) Difference images (b) − (c), demonstrating good intra-session registration using the ABC. No image registration was used and the slice location and windowing is identical for all displayed images.

Figure 6.

MR images of a NSCLC patient acquired in ABC breath holds with the same inhalational threshold: (a) T1-w 3D VIBE (slice location 57.56 mm, thickness 3 mm); (b) DW-EPI2 with b = 750 s mm⁻² (slice location 57.17 mm, thickness 6 mm); (c) overlay of (a) and (b) in OsiriX. (d) T2-w HASTE (slice location 58.67 mm, thickness 3 mm); (e) DW-EPI1 with b = 200 s mm⁻² (slice location 58.67 mm, thickness 5 mm) and (f) their overlay in OsiriX. All original images were individually windowed.

Figure 7.

(a) Checkerboard view of the Pinnacle³ registration of an axial CT image (grey) with an axial 3D T1-w VIBE image (orange) of a NSCLC patient in ABC-controlled breath holding with the same settings and positioning. (b) Coronal and (c) sagittal reconstruction of the CT-VIBE fusion. (d) A more superior transversal slice of the CT image of the same patient (grey) fused with a b = 200 s mm⁻² DW-EPI1 (orange) acquired under the same ABC conditions. (e) and (f) denote the coronal and sagittal reconstruction of the CT-EPI fusion. All of these images demonstrate the good inter-modality registration achievable with the ABC system.