[Paper](Review)Time domain functional NIRS imaging for human brain mapping
Time domain functionalNIRS imaging for human brain mapping
期刊/年分：NeuroImage/2014
重點
•我們提供了最新的時域型功能性NIRS關鍵性調查報告。
•時域型功能性NIRS 的穿透深度取決於光子飛行時間，而非光源與接收器之間距。
•時域型功能性NIRS 能夠區分出大腦內、外訊號(具有深度選擇性)。
•與連續型功能性NIRS 進行於光學假體以及活體實驗中的比較。
•系統之性能評估以及標準化相關問題的協定。
Highlights
•We provide a critical up-to-date review on time domain (TD) functional NIRS (fNIRS).
•TD fNIRS penetration depth depends on photon time-of-flight, not on optode distance.
•TD fNIRS discriminates intra- and extra-cerebral signals (depth selectivity).
•A comparison on phantoms and in vivo with continuous wave (CW) fNIRS is included.
•Protocols for performance assessment and standardization issues are presented.
摘要
此篇文獻回顧文章旨在呈現最先進的時域型 (TD) 功能性近紅外光譜術 (fNIRS)。一開始，我們會介紹其物理原理，包括建模以及數據分析。接下來，時域型fNIRS系統中會使用到的基本硬體元件 (光源、感測技術、訊號傳輸以及收集系統) 也會做逐一的說明。還會將從古到今，以及下一代新型的時域型fNIRS做完整的系統介紹，也會與連續型fNIRS做比較。根據於光學假體或活體中進行的實驗結果，嚴謹地檢查諸如血液動力學、穿透深度、深度選擇性、空間分辨率和對比度 - 噪聲比的量化問題。最後我們將介紹一些能夠使時域型fNIRS 於神經影像學領域中更加泛用的相關技術。
Abstract
This review is aimed an presenting the state-of-the-art of time domain (TD) functional near-infrared spectroscopy (fNIRS). We first introduce the physical principles, the basics of modeling and data analysis. Basic instrumentation components (light sources, detection techniques, and delivery and collection systems) of a TD fNIRS system are described. A survey of past, existing and next generation TD fNIRS are highlighted, also in comparison with continuous wave (CW) fNIRS, Issues like quantification of the hemodynamic response, penetration depth, depth selectivity, spatial resolution and contrast-to-noise ratio are critically examined, with the help of experimental results performed on phantoms or in vivo. Finally we give an account on the technological developments that would pave the way for a broader use of TD fNIRS in the neuroimaging community.
介紹
Introduction
此篇文獻回顧文章旨在呈現最先進的時域型 (TD) 功能性近紅外光譜術 (fNIRS)。如同其他相關文獻所述，TD-fNIRS的歷史最早可以追述到1996年代，第一篇有關單通道的TD-fNIRS文章被發表刊登，而在之後的幾年內，也就是 1998-2000 年間第一篇多通道的TD-fNIRS也被刊載於期刊上。值得注意的是，若以物理、技術的角度來看，TD-fNIRS的起源是在1980 年代，當時研究人員開始探索在擴散光子在隨機介質中的迷人行為模式。幾年後，有些研究便開始針對「利用脈衝雷射得到擴散光子影像、光譜」以及「皮秒 (picosecond) 等級的光感測技術」這兩個領域進行發展。
This review is aimed at presenting the state-of-the-art of time domain (TD) functional near-infrared spectroscopy (fNIRS). As described in a recent review on the history of fNIRS, while fNIRS dates back about 20 years ago, we have to wait till 1996 for the first single-channel TD fNIRS study to appear in the literature, and only some years later, in 1998-2000, the first papers describing multi-channel TD fNIRS instruments were published. Noticeably, from the physical and technological point of view the origin of TD fNIRS can be traced back to the 1980s, when researchers started exploring the fascinating field of diffusing photons in random media. A few years later, several studies were focused on diffuse optical imaging and spectroscopy with pulsed laser and photo-detection techniques with picosecond resolution.
距離第一篇研究三十年的現在，市面上只有一台雙通道的TD-fNIRS系統有在販售，而且還指現在日本國內，海外無法購買。而有少數實驗室所製作的原型機則是被應用在學術或公共研究中心內。在某種程度上來說，這可以說TD fNIRS系統在生醫光子學中是一失敗的系統。(否則怎麼會如此稀少，廣度又少呢?)事實上，與市售的連續式(CW)NIRS相比，TD-fNIRS 或是相關的時間解析系統，實在是過於笨重、龐大且昂貴。在寫這篇文章的時候，我們不能忽略CW和TD-fNIRS技術之間存在著所有這些缺陷和差距仍然。 然而，我們處在一個新時代的最前沿，其中光子技術的最新進展可能允許TD fNIRS彌合差距並可能超越CW fNIRS。在這次文章中，我們試圖通過敘述TD-fNIRS相關技術已達到成熟階段並在生物醫學和神經影像學領域傳播的關鍵物理和技術方面來證實這一遠見。
Nowadays, about thirty years after the first studies, there is only one dual-channel TD fNIRS commercial system not sold outside Japan, while there are no commercial TD fNIRS imagers available. A few laboratory prototypes have been developed by research groups located in academic or public research centers. To some extent this situation could be interpreted as the failure of the TD approach within biomedical optics. Indeed, in part of the scientific community TD fNIRS (and TD techniques in general) had the reputation of being cumbersome, bulky and very expensive as compared to commercial continuous wave (CW) fNIRS systems. At the time of writing we cannot ignore all these pitfalls and a gap still exists between CW and TD fNIRS technology. However, we are at the forefront of a new era where recent advances in photonic technologies might allow TD fNIRS to bridge the gap and potentially to overtake CW fNIRS, In this review we try to substantiate this foresight by outlining the key physical and technological aspects that will allow TD fNIRS to reach a maturity stage and to spread in the biomedical and neuroimaging community.
在接下來的段落中，我們一開始會先介紹TD-fNIRS背後的原理以及該系統的基本硬體架構。接下來將介紹相比於CW系統，TD-fNIRS的強項以及弱勢在哪。更進一步地，我們將提到TD-fNIRS的數據分析以及相關應用。最後，我們將介紹未來前景和技術發展，以期神經影像學相關研究領域能夠更廣泛地使用TD-fNIRS系統。
In the following sections we first describe the principle behind TD fNIRS and the basic of TD fNIRS instrumentation. We then highlight the main strengths and weakness of TD fNIRS, notably in comparison with CW fNIRS. A concise survey of TD fNIRS data analysis and applications is further reported. Finally we give an account on future perspectives and technological developments that pave the way for a broader use of TD fNIRS in the neuroimaging community.
Principles of TD fNIRS
Basics of NIRS
To properly understand the principles of TD fNIRS it is useful to briefly recall the basics of near-infrared spectroscopy (NIRS). NIRS is a powerful spectroscopic technique used in several fields (e.g. food and agriculture, chemical industry. life sciences, medical and pharmaceutical, textiles) to nondestructively test samples like liquids (e.g. in the food sector: oil, wine, and milk), powders (e.g. pharmaceutical tablets and pills, and wheat flour), and bulk objects (e.g. in the food sector: fruits and vegetables, meat, and cheese), allowing for their analytical and chemical characterization.
In the biomedical field NIRS makes use of light to noninvasively monitor tissue hemodynamics and oxidative metabolism. In the 600-1000 nm spectral range, light attenuation by the main tissue constituents (i.e. water, lipid, and hemoglobin ) is in fact relatively low and allows for penetration through several centimeters of tissue. Moreover, the difference in the absorption spectra of oxygenated and deoxygenated hemoglobin allows the the separate measurement of the concentration of these two species (O2Hb and HHb, respectively), and the derivation of physiologically relevant parameters like total hemoglobin concentration (tHb = HHb + O2Hb) and blood oxygen saturation (SO2 = O2Hb / tHb). The term fNIRS is then used to specifically address NIRS applications in the neuroimaging field aiming at mapping and understanding the functioning of the human brain cortex.
In NIRS a weak (a few mW) light signal is injected in the tissue and the emitted signal which carries information on tissue constituents is measured. As a result of the microscopic discontinuities in the refractive index of biological tissues, NIR light is highly scattered, therefore it is the complex interplay between light absorption and light scattering that determines the overall light attenuation. Proper physical models for photon migration (e.g. diffusion, random walk, Monte Carlo) should be used to correctly interpret NIRS signals unraveling the absorption from the diffusive contribution.
此篇文獻回顧文章旨在呈現最先進的時域型 (TD) 功能性近紅外光譜術 (fNIRS)。如同其他相關文獻所述，TD-fNIRS的歷史最早可以追述到1996年代，第一篇有關單通道的TD-fNIRS文章被發表刊登，而在之後的幾年內，也就是 1998-2000 年間第一篇多通道的TD-fNIRS也被刊載於期刊上。值得注意的是，若以物理、技術的角度來看，TD-fNIRS的起源是在1980 年代，當時研究人員開始探索在擴散光子在隨機介質中的迷人行為模式。幾年後，有些研究便開始針對「利用脈衝雷射得到擴散光子影像、光譜」以及「皮秒 (picosecond) 等級的光感測技術」這兩個領域進行發展。
This review is aimed at presenting the state-of-the-art of time domain (TD) functional near-infrared spectroscopy (fNIRS). As described in a recent review on the history of fNIRS, while fNIRS dates back about 20 years ago, we have to wait till 1996 for the first single-channel TD fNIRS study to appear in the literature, and only some years later, in 1998-2000, the first papers describing multi-channel TD fNIRS instruments were published. Noticeably, from the physical and technological point of view the origin of TD fNIRS can be traced back to the 1980s, when researchers started exploring the fascinating field of diffusing photons in random media. A few years later, several studies were focused on diffuse optical imaging and spectroscopy with pulsed laser and photo-detection techniques with picosecond resolution.
距離第一篇研究三十年的現在，市面上只有一台雙通道的TD-fNIRS系統有在販售，而且還指現在日本國內，海外無法購買。而有少數實驗室所製作的原型機則是被應用在學術或公共研究中心內。在某種程度上來說，這可以說TD fNIRS系統在生醫光子學中是一失敗的系統。(否則怎麼會如此稀少，廣度又少呢?)事實上，與市售的連續式(CW)NIRS相比，TD-fNIRS 或是相關的時間解析系統，實在是過於笨重、龐大且昂貴。在寫這篇文章的時候，我們不能忽略CW和TD-fNIRS技術之間存在著所有這些缺陷和差距仍然。 然而，我們處在一個新時代的最前沿，其中光子技術的最新進展可能允許TD fNIRS彌合差距並可能超越CW fNIRS。在這次文章中，我們試圖通過敘述TD-fNIRS相關技術已達到成熟階段並在生物醫學和神經影像學領域傳播的關鍵物理和技術方面來證實這一遠見。
距離第一篇研究三十年的現在，市面上只有一台雙通道的TD-fNIRS系統有在販售，而且還指現在日本國內，海外無法購買。而有少數實驗室所製作的原型機則是被應用在學術或公共研究中心內。在某種程度上來說，這可以說TD fNIRS系統在生醫光子學中是一失敗的系統。(否則怎麼會如此稀少，廣度又少呢?)事實上，與市售的連續式(CW)NIRS相比，TD-fNIRS 或是相關的時間解析系統，實在是過於笨重、龐大且昂貴。在寫這篇文章的時候，我們不能忽略CW和TD-fNIRS技術之間存在著所有這些缺陷和差距仍然。 然而，我們處在一個新時代的最前沿，其中光子技術的最新進展可能允許TD fNIRS彌合差距並可能超越CW fNIRS。在這次文章中，我們試圖通過敘述TD-fNIRS相關技術已達到成熟階段並在生物醫學和神經影像學領域傳播的關鍵物理和技術方面來證實這一遠見。
Nowadays, about thirty years after the first studies, there is only one dual-channel TD fNIRS commercial system not sold outside Japan, while there are no commercial TD fNIRS imagers available. A few laboratory prototypes have been developed by research groups located in academic or public research centers. To some extent this situation could be interpreted as the failure of the TD approach within biomedical optics. Indeed, in part of the scientific community TD fNIRS (and TD techniques in general) had the reputation of being cumbersome, bulky and very expensive as compared to commercial continuous wave (CW) fNIRS systems. At the time of writing we cannot ignore all these pitfalls and a gap still exists between CW and TD fNIRS technology. However, we are at the forefront of a new era where recent advances in photonic technologies might allow TD fNIRS to bridge the gap and potentially to overtake CW fNIRS, In this review we try to substantiate this foresight by outlining the key physical and technological aspects that will allow TD fNIRS to reach a maturity stage and to spread in the biomedical and neuroimaging community.
在接下來的段落中，我們一開始會先介紹TD-fNIRS背後的原理以及該系統的基本硬體架構。接下來將介紹相比於CW系統，TD-fNIRS的強項以及弱勢在哪。更進一步地，我們將提到TD-fNIRS的數據分析以及相關應用。最後，我們將介紹未來前景和技術發展，以期神經影像學相關研究領域能夠更廣泛地使用TD-fNIRS系統。
在接下來的段落中，我們一開始會先介紹TD-fNIRS背後的原理以及該系統的基本硬體架構。接下來將介紹相比於CW系統，TD-fNIRS的強項以及弱勢在哪。更進一步地，我們將提到TD-fNIRS的數據分析以及相關應用。最後，我們將介紹未來前景和技術發展，以期神經影像學相關研究領域能夠更廣泛地使用TD-fNIRS系統。
In the following sections we first describe the principle behind TD fNIRS and the basic of TD fNIRS instrumentation. We then highlight the main strengths and weakness of TD fNIRS, notably in comparison with CW fNIRS. A concise survey of TD fNIRS data analysis and applications is further reported. Finally we give an account on future perspectives and technological developments that pave the way for a broader use of TD fNIRS in the neuroimaging community.
Principles of TD fNIRS
Basics of NIRS
To properly understand the principles of TD fNIRS it is useful to briefly recall the basics of near-infrared spectroscopy (NIRS). NIRS is a powerful spectroscopic technique used in several fields (e.g. food and agriculture, chemical industry. life sciences, medical and pharmaceutical, textiles) to nondestructively test samples like liquids (e.g. in the food sector: oil, wine, and milk), powders (e.g. pharmaceutical tablets and pills, and wheat flour), and bulk objects (e.g. in the food sector: fruits and vegetables, meat, and cheese), allowing for their analytical and chemical characterization.
In the biomedical field NIRS makes use of light to noninvasively monitor tissue hemodynamics and oxidative metabolism. In the 600-1000 nm spectral range, light attenuation by the main tissue constituents (i.e. water, lipid, and hemoglobin ) is in fact relatively low and allows for penetration through several centimeters of tissue. Moreover, the difference in the absorption spectra of oxygenated and deoxygenated hemoglobin allows the the separate measurement of the concentration of these two species (O2Hb and HHb, respectively), and the derivation of physiologically relevant parameters like total hemoglobin concentration (tHb = HHb + O2Hb) and blood oxygen saturation (SO2 = O2Hb / tHb). The term fNIRS is then used to specifically address NIRS applications in the neuroimaging field aiming at mapping and understanding the functioning of the human brain cortex.
In NIRS a weak (a few mW) light signal is injected in the tissue and the emitted signal which carries information on tissue constituents is measured. As a result of the microscopic discontinuities in the refractive index of biological tissues, NIR light is highly scattered, therefore it is the complex interplay between light absorption and light scattering that determines the overall light attenuation. Proper physical models for photon migration (e.g. diffusion, random walk, Monte Carlo) should be used to correctly interpret NIRS signals unraveling the absorption from the diffusive contribution.
留言
張貼留言