High-intensity　focused　ultrasound　(HIFU)　is　a　well-accepted　tool　for　noninvasive　thermal　therapy.　To　control　the　quality　of　HIFU　treatment,　the　focal　spot　generated　in　tissues　must　be　localized.　Ultrasound　imaging　can　monitor　heated　regions;　in　particular,　the　change　in　backscattered　energy　(CBE)　allows　parametric　imaging　to　visualize　thermal　information　in　the　tissue.　Conventional　CBE　imaging　constructed　in　the　spatial　domain　may　be　easily　affected　by　noises　when　the　HIFU　focal　spot　is　visualized.　This　study　proposes　frequency-domain　CBE　imaging　to　improve　noise　tolerance　and　image　contrast　in　HIFU　focal　spot　monitoring.　Phantom　experiments　were　performed　in　a　temperature-controlled　environment.　HIFU　of　2.12MHz　was　applied　to　the　phantoms,　during　which　a　clinical　scanner　equipped　with　a　3-MHz　convex　array　transducer　was　used　to　collect　raw　image　data　consisting　of　backscattered　signals　for　B-mode,　spatial-,　and　frequency-domain　CBE　imaging.　Concurrently,　temperature　changes　were　measured　at　the　focal　spot　using　a　thermocouple　for　comparison　with　CBE　values　by　calculating　the　correlation　coefficient　r.　To　further　analyze　CBE　image　contrast　levels,　a　contrast　factor　was　introduced,　and　an　independent　t-test　was　performed　to　calculate　the　probability　value　p.　Experimental　results　showed　that　frequency-domain　CBE　imaging　performed　well　in　thermal　distribution　visualization,　enabling　quantitative　detection　of　temperature　changes.　The　CBE　value　calculated　in　the　frequency　domain　also　correlated　strongly　with　that　obtained　using　the　conventional　spatial-domain　approach　(r=0.97).　In　particular,　compared　with　the　image　obtained　through　the　conventional　method,　the　contrast　of　the　CBE　image　obtained　using　the　method　based　on　frequency-domain　analysis　increased　by　2.5-fold　(4dB;　p＜0.05).　Frequency-domain　computations　may　constitute　a　new　strategy　when　ultrasound　CBE　imaging　is　used　to　localize　the　focal　spot　in　HIFU　treatment　planning.