Radiofrequency　ablation　(RFA)　is　an　alternative　treatment　for　early-stage　hepatocellular　carcinoma　(HCC).　The　production　of　gas　bubbles　by　RFA　indicates　threshold　temperature　of　tissue　necrosis　and　results　in　changes　in　backscattered　energy　(CBE)　when　ultrasound　monitors　RFA.　In　this　study,　ultrasound　single-phase　CBE　imaging　was　used　as　a　means　of　monitoring　RFA　of　the　liver　tumor　by　analyzing　the　backscattering　of　ultrasound　from　gas　bubbles　in　the　liver.　A　total　of　19　HCC　patients　were　enrolled　in　the　study.　An　ultrasound　system　was　used　during　RFA　to　monitor　the　ablation　process　and　acquire　raw　image　data　consisting　of　backscattered　signals　for　single-phase　CBE　imaging.　On　the　basis　of　single-phase　CBE　imaging,　the　area　corresponding　to　the　range　of　gas　bubbles　was　compared　with　the　tumor　sizes　and　ablation　zones　estimated　from　computed　tomography.　During　RFA,　ultrasound　single-phase　CBE　imaging　enabled　improved　visualization　of　gas　bubbles.　Measured　gas　bubble　areas　by　CBE　were　related　to　tumor　size　(the　Spearman　correlation　coefficient　r(s)　=　0.86;　p　＜　0.05);　less　dependent　on　the　ablation　zone.　Approximately　95%　of　the　data　fell　within　the　limits　of　agreement　in　Bland-Altman　plots,　and　58%　of　the　data　fell　within　the　95%　CI.　This　study　suggests　that　single-phase　CBE　imaging　provides　information　about　liver　tumor　size　because　of　the　abundant　vessels　in　liver　tumors　that　promote　the　generation　of　gas　bubbles,　which　serve　as　natural　contrast　agents　in　RFAs　to　enhance　ultrasound　backscattering.　Ultrasound　single-phase　CBE　imaging　may　allow　clinicians　to　determine　if　the　required　minimum　RFA　efficacy　level　is　reached　by　assessing　gas　bubbles　in　the　liver　tumors.