Ultrasound-guided therapeutic focused ultrasound: Current status and future directions

Figures & data

Figure 1. Diagnostic ultrasound image of the target vessel and surrounding tissue used for the determination of the treatment planning model parameters. The target vessel was the femoral artery of a FH pig used in the study described in Shehata et al. [65]. Reproduced with permission from Almekkawy [111]. S, skin; F, fat; M, muscle; CT, connective tissue; A, artery.

Figure 2. An integrated USgFUS system for real-time visualisation of lesion formation based on echogenicity change. Reproduced from Vaezy et al. [125]. Reproduced with permission from IEEE and Elsevier Science and Technology Journals.

Figure 3. Schematic diagram of a USgFUS system designed for monitoring changes in lesion stiffness using localised harmonic motion (LHM). Reproduced with permission from Curiel et al. [143,178].

Figure 4. Maximum temperature change due to the application of 1.7-s sub-therapeutic HIFU ‘shots’ before and after the application of a 5-s therapeutic HIFU ‘shot’. Reproduced from Liu and Ebbini [85] with permission.

Table 1. FUS-induced lesion parameter imaging using MRgHIFU and USgHIFU.

	MRgHIFU		USgHIFU
Feature/parameter  to be imaged	Treatment planning	Real time treatment monitoring	Treatment planning	Real time treatment monitoring
Tumour boundaries	T1, T2, T2*, DWI	T1, T2, T2*, DWI	B-mode, CEUS	B-mode
Bone	T1, T2, T2*,  DWI, UTE	T1, T2, T2*, DWI	B-mode	B-mode (greyscale changes in soft tissue surrounding bone)
Hypoxia	DWI, DCE	DWI, DCE	–	(CEUS)
Perfusion	DSC, DCE	DSC, DCE	CEUS	CEUS
Temperature	–	EPI, T2*	–	Speed of sound
	–	GRE	–
Tissue changes		DWI, MR elastography	B-mode	B-mode (greyscale changes), Elastography, RFI, harmonic motion imaging

DWI, diffusion weighted imaging; UTE, ultrashort echo time; DCE, dynamic contrast enhanced imaging – requires gadolinium contrast agents so only used prior to treatment session or post-treatment; DSC, dynamic susceptibility contrast – only used in brain applications at present, requires gadolinium; EPI, echo planar imaging – fast acquisition, sensitive to susceptibility artefacts and magnetic field inhomogeneities; GRE, gradient recalled echo sequence – slower than EPI; CEUS, contrast enhanced ultrasound – uses microbubble contrast agents to provide scattering contrast.

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