Department of Mechanical Engineering, National University of Singapore, Singapore, Singapore.
Int J Comput Assist Radiol Surg. 2013 Jan;8(1):135-44. doi: 10.1007/s11548-012-0689-2. Epub 2012 Apr 24.
Cardiac strain calculated from tagged magnetic resonance (MR) images provides clinicians information about abnormalities of heart-wall motion in patients. It is important to develop an accurate method to determine the cardiac strain efficiently. An adaptive windowed harmonic phase (AWHARP) method is proposed for cardiac strain calculation.
AWHARP is based on adaptive windowed Fourier transform (AWFT) and 2D Gabor wavelet transform (2D-GWT). The AWFT provides a spatially varying representation of the signal spectra, which allows the harmonic phase (HARP) image to be extracted with high accuracy. Instantaneous spatial frequencies are calculated using 2D-GWT, and the widths of the adaptive windows are then determined according to the instantaneous spatial frequencies for multi-resolution analysis of phase extraction. The proposed method was studied using simulated images and patients' MR images. Both single tagged images (SPAMM) and subtracted tagged images (CSPAMM) were generated using our simulation method, and their results calculated using AWHARP and HARP methods were compared. Normal and pathological tagged MR images were also processed to evaluate the performance of our method.
Our experimental results show that the accuracies of phase and strain images calculated using the AWHARP method are higher than that calculated using the HARP method especially for large tag line deformation. The improvement in accuracies can be up to 3.2 strain (E1) and 17.3 calculation from MR images reveals that the cardiac strain in the end-systolic state is significantly reduced for patients with hypertrophic cardiomyopathy (HCM) compared to that of healthy subjects.
The proposed AWHARP is an accurate and efficient method for cardiac strain estimation from MR images. This new algorithm can help clinicians to detect left ventricle dysfunctions and myocardial diseases with accurate cardiac strain analysis.
从标记的磁共振（MR）图像计算出的心脏应变可为临床医生提供有关患者心脏壁运动异常的信息。开发一种准确、高效的方法来确定心脏应变非常重要。本文提出了一种用于计算心脏应变的自适应窗口谐相位（AWHARP）方法。
AWHARP 基于自适应窗口傅里叶变换（AWFT）和二维 Gabor 小波变换（2D-GWT）。AWFT 提供了信号频谱的空间变化表示，从而可以高精度地提取谐相位（HARP）图像。使用 2D-GWT 计算瞬时空间频率，并根据瞬时空间频率确定自适应窗口的宽度，以进行相位提取的多分辨率分析。使用模拟图像和患者的 MR 图像对所提出的方法进行了研究。使用我们的模拟方法生成了单标记图像（SPAMM）和减影标记图像（CSPAMM），并比较了使用 AWHARP 和 HARP 方法计算的结果。还处理了正常和病理标记的 MR 图像，以评估我们方法的性能。
我们的实验结果表明，使用 AWHARP 方法计算的相位和应变图像的精度高于使用 HARP 方法计算的精度，尤其是在大标记线变形的情况下。精度的提高最高可达 3.2 倍（E1）。从 MR 图像计算得出的结果表明，与健康受试者相比，肥厚型心肌病（HCM）患者的收缩末期心脏应变明显降低。
提出的 AWHARP 是一种从 MR 图像估计心脏应变的准确、高效方法。这种新算法可以帮助临床医生通过准确的心脏应变分析来检测左心室功能障碍和心肌疾病。
