Sparse multispectral processing for accelerated EPR oximetry in three dimensions

描述（由申请人提供）：电子顺磁共振（EPR）光谱能够对生物样品中的自由基进行无创测量。EPR可以用来测量氧的分压，通过观察氧诱导的线形增宽引入顺磁探针。在肿瘤中，氧浓度对于确定对不同治疗方案的反应是有用的。同样，氧的存在在缺血和随后的再灌注期间心肌损伤的病理生理中起着关键作用。因此，EPR随时间测量氧气的能力可以提供表征疾病状态进展的重要信息，并确定不同治疗方案的疗效。不幸的是，较长的数据采集时间限制了EPR在这些应用程序中的使用。本提案的目的是开发和验证处理方法，减少使用EPR成像在三维中绘制氧气分压的采集时间。研究计划中的两个目标提出了一种策略，可以将颗粒自旋探针成像时的采集时间减少80倍。提出的改进采集时间的机会是由颗粒顺磁探针的最新发展创造的。在第一个目标中，该方法通过联合处理吸收分量和色散分量的多重谐波，充分利用了共振信号中的所有能量。通过多光谱处理，我们获得的信号能量大约是单次谐波吸收光谱中信号能量的四倍。在第二个目标中，我们结合了粒子探针呈现的稀疏但非结构化的自旋分布。这两个目标提供了处理增益，导致更少的投影，更窄的扫描宽度和更快的扫描速率，以实现所需的图像分辨率。初步结果证明了假设的大幅度减少获取时间的可行性。首先，我们的团队开发了能够感知和报告细胞和组织pO2的颗粒自旋探针，具有卓越的氧敏感性（优于0.1 Torr），可重复性，生物稳定性和窄线宽。其次，对于二维光谱空间成像，我们已经证明，通过直接估计洛伦兹线参数，而不是首先对光谱空间对象进行成像，可以将采集时间提高38:1。第三，我们利用粒子自旋探针的稀疏分布演示了三维氧映射，将投影数量从1024个减少到32个。因此，初步结果对从小时到分钟、从分钟到秒的转变持乐观态度。公共卫生相关性：电子顺磁共振（EPR）血氧仪提供了一种直接的、微创的氧浓度测量方法。血氧测定在预测肿瘤对不同治疗方案的反应和了解心血管疾病损伤后心脏恢复的病理生理学方面是有用的。然而，微弱的信号强度和较长的数据采集时间禁止广泛使用EPR血氧仪。本提案的目标是开发加速数据采集的信号处理方法。该方法充分利用了射频共振信号中所有可观测信号能量，并利用了新开发的粒子自旋探针固有的稀疏性。初步结果表明，将采集时间从几十分钟缩短到几十秒是可行的。

DESCRIPTION (provided by applicant): Electron paramagnetic resonance (EPR) spectroscopy enables noninvasive measurement of free radicals in biological samples. EPR can be used to measure the partial pressure of oxygen by observing oxygen-induced broadening in the lineshape of an introduced paramagnetic probe. In tumors, the oxygen concentration is useful in determining the response to different treatment options. Likewise, the presence of oxygen plays a critical role in the pathophysiology of myocardial injury during both ischemia and subsequent reperfusion. Therefore, the ability of EPR to measure oxygen over time can provide vital information to characterize the progression of a disease state and to determine the efficacy of different treatment options. Unfortunately, long data acquisition times have limited the use of EPR for these applications. The objective of this proposal is to develop and verify processing methods that reduce acquisition time for mapping partial pressure of oxygen in three dimensions using EPR imaging. The two aims in the research plan present a strategy for reducing by a factor of 80 the acquisition time when imaging with particulate spin probes. The opportunity for the proposed improvement in acquisition time is created by the recent development of particulate paramagnetic probes. In the first aim, the proposed approach fully utilizes all energy in the resonance signal by jointly processing multiple harmonics of both the absorption and dispersion components. With multi-spectral processing, we access approximately four times more signal energy than is present in the first harmonic absorption spectrum alone. In the second aim, we incorporate the sparse, but unstructured, distribution of spins presented by particulate probes. These two aims provide processing gains that result in fewer projections, narrower sweep widths and faster sweep rates for achieving a desired image resolution. Preliminary results demonstrate feasibility of the hypothesized ambitious reductions in acquisition time. First, our team has developed particulate spin probes capable of sensing and reporting cellular and tissue pO2 with remarkable oxygen sensitivity (better than 0.1 Torr), repeatability, bio-stability, and narrow line width. Second, for two dimensional spectral-spatial imaging we have demonstrated a 38:1 improvement in acquisition time by directly estimating Lorentzian line parameters, rather than first imaging a spectral-spatial object. Third, we have demonstrated oxygen mapping in three dimensions using sparse distribution of particulate spin probes to reduce the number of projections from 1024 to 32. Thus, preliminary results give optimism for turning hours to minutes and minutes to seconds. PUBLIC HEALTH RELEVANCE: Electron paramagnetic resonance (EPR) oximetry provides a direct, minimally invasive measure of oxygen concentration. Oximetry is useful in predicting the response of tumors to different treatment options and in understanding the pathophysiology of cardiac recovery following injury due to cardiovascular disease. However, weak signal strength and long data acquisition times prohibit widespread use of EPR oximetry. The objective of this proposal is to develop signal processing methods that accelerate data acquisition. The approach fully accesses all observable signal energy in the radio frequency resonance signal and exploits the inherent sparseness of newly developed particulate spin probes. Preliminary results demonstrate the feasibility of reducing acquisition time from tens of minutes to tens of seconds.