Abstract：
To understand if unexplained signal artifacts in MRg-LITT proton resonance frequency- (PRF-) shift thermometry images are caused by air bubbles or hemorrhages, and to characterize their effects on temperature measurements.
Retrospective image data from an IRB-approved clinical trial of intracranial MRg-LITT were inspected for asymmetric distortions observed in phase data during ablations, which have been previously reported as likely hemorrhages. A total of eight patient cases were selected: seven with artifact occurrence and one without. Mathematical image models for air bubbles or hemorrhages were implemented to estimate the size of the air bubble or hemorrhage needed to explain the clinically observed phase artifacts. Correlations and Bland-Altman analyses were used to determine if an air bubble model or a hemorrhage model was better correlated to the clinical data. The model was used to inject bubbles into clean PRF phase data without artifacts to examine how temperature profile distortions change with slice orientation. The simulated air-bubble injected data were compared to clinical data containing artifacts to examine the bubbles\' effects on temperature and thermal damage estimates.
The model demonstrated that air bubbles up to approximately 1 cm in diameter could explain the clinically observed phase artifacts. The bubble model predicts that a hemorrhage would have to be 2.2 times as large as an air bubble in order to explain the same extent of phase distortion observed in clinical data. Air bubbles had 16% percent higher correlations to the clinical PRF phase data than hemorrhages, even after rescaling the hemorrhage phases to better match the data. The air bubble model also explains how the phase artifacts lead to both large positive and large negative temperature errors, up to ±100 °C, which could cascade to damage estimate errors of several millimeters.
Results showed that the artifacts are likely caused by air bubbles rather than hemorrhages, which may be introduced before heating or appear during heating. Manufacturers and users of devices that rely upon PRF-shift thermometry should be aware these phase distortions from bubble artifacts can result in large temperature errors.
Retrospective image data from an IRB-approved clinical trial of intracranial MRg-LITT were inspected for asymmetric distortions observed in phase data during ablations, which have been previously reported as likely hemorrhages. A total of eight patient cases were selected: seven with artifact occurrence and one without. Mathematical image models for air bubbles or hemorrhages were implemented to estimate the size of the air bubble or hemorrhage needed to explain the clinically observed phase artifacts. Correlations and Bland-Altman analyses were used to determine if an air bubble model or a hemorrhage model was better correlated to the clinical data. The model was used to inject bubbles into clean PRF phase data without artifacts to examine how temperature profile distortions change with slice orientation. The simulated air-bubble injected data were compared to clinical data containing artifacts to examine the bubbles\' effects on temperature and thermal damage estimates.
The model demonstrated that air bubbles up to approximately 1 cm in diameter could explain the clinically observed phase artifacts. The bubble model predicts that a hemorrhage would have to be 2.2 times as large as an air bubble in order to explain the same extent of phase distortion observed in clinical data. Air bubbles had 16% percent higher correlations to the clinical PRF phase data than hemorrhages, even after rescaling the hemorrhage phases to better match the data. The air bubble model also explains how the phase artifacts lead to both large positive and large negative temperature errors, up to ±100 °C, which could cascade to damage estimate errors of several millimeters.
Results showed that the artifacts are likely caused by air bubbles rather than hemorrhages, which may be introduced before heating or appear during heating. Manufacturers and users of devices that rely upon PRF-shift thermometry should be aware these phase distortions from bubble artifacts can result in large temperature errors.
摘要：
目的：了解MRg-LITT质子共振频率-（PRF-）位移测温图像中无法解释的信号伪影是否是由气泡或出血引起的，并表征它们对温度测量的影响。
方法：检查了IRB批准的颅内MRg-LITT临床试验的回顾性图像数据，检查了消融期间相位数据中观察到的不对称畸变，以前报道过的很可能是出血.总共选择了8例患者：7例发生伪影，1例没有伪影。实施了气泡或出血的数学图像模型，以估计解释临床观察到的相位伪影所需的气泡或出血的大小。相关性和Bland-Altman分析用于确定气泡模型或出血模型是否与临床数据更好地相关。该模型用于将气泡注入干净的PRF相位数据中，而没有伪影，以检查温度分布失真如何随切片方向变化。将模拟的气泡注入数据与包含伪影的临床数据进行比较，以检查气泡对温度和热损伤估计的影响。
结果：该模型表明，直径约1厘米的气泡可以解释临床观察到的相位伪影。气泡模型预测，出血必须是气泡的2.2倍，以解释临床数据中观察到的相同程度的相位失真。气泡与临床PRF阶段数据的相关性比出血高16%，即使在重新调整出血阶段以更好地匹配数据之后。气泡模型还解释了相位伪影如何导致较大的正温度误差和较大的负温度误差，高达±100°C，这可能会导致几毫米的损伤估计误差。
结论：结果表明，伪影可能是由气泡而不是出血引起的，可在加热前引入或在加热过程中出现。依赖于PRF偏移测温的设备的制造商和用户应该意识到这些来自气泡伪影的相位失真可能导致大的温度误差。
方法：检查了IRB批准的颅内MRg-LITT临床试验的回顾性图像数据，检查了消融期间相位数据中观察到的不对称畸变，以前报道过的很可能是出血.总共选择了8例患者：7例发生伪影，1例没有伪影。实施了气泡或出血的数学图像模型，以估计解释临床观察到的相位伪影所需的气泡或出血的大小。相关性和Bland-Altman分析用于确定气泡模型或出血模型是否与临床数据更好地相关。该模型用于将气泡注入干净的PRF相位数据中，而没有伪影，以检查温度分布失真如何随切片方向变化。将模拟的气泡注入数据与包含伪影的临床数据进行比较，以检查气泡对温度和热损伤估计的影响。
结果：该模型表明，直径约1厘米的气泡可以解释临床观察到的相位伪影。气泡模型预测，出血必须是气泡的2.2倍，以解释临床数据中观察到的相同程度的相位失真。气泡与临床PRF阶段数据的相关性比出血高16%，即使在重新调整出血阶段以更好地匹配数据之后。气泡模型还解释了相位伪影如何导致较大的正温度误差和较大的负温度误差，高达±100°C，这可能会导致几毫米的损伤估计误差。
结论：结果表明，伪影可能是由气泡而不是出血引起的，可在加热前引入或在加热过程中出现。依赖于PRF偏移测温的设备的制造商和用户应该意识到这些来自气泡伪影的相位失真可能导致大的温度误差。
