chial epithelial abnormalities include: autofuorescence bronchoscopy (AFB) and narrow band imaging (NBI). More precise airway inspection especially for the depth of tumor invasion to the bronchial layer can be obtained with radial probe endobronchial ultrasound (EBUS) and optical coherence tomography (OCT) [4]. Confocal laser endomicroscopy (CLE) using fexible probe-­ based system is another useful technique, allowing in vivo microscopic assessment of the airway basement membrane and alveolar components [12]. Endocytoscopy bronchoscopy system has allowed in vivo microscopic imaging of bronchial mucosa [13]. However, confocal laser ­endomicroscopy and endocytoscopy system are still under investigational use.

In this chapter, the advanced bronchoscopic imaging techniques of the airway will be reviewed and their roles in the early diagnosis of lung cancer will be shown.

History and Historical Perspective

Autofuorescence Bronchoscopy (AFB)

AFB combined with white light observation improves sensitivity for detection of preinvasive lesions in the central airways [10]. It is a technique of advanced mucosal airway examination taking advantage of the property of the normal, pre-neoplastic and neoplastic tissues to change appearance when illuminated with different wavelengths of light depending on differential epithelial thickness, tissue blood fow, and fuorophore concentration. Preinvasive and neoplastic tissues express diminished red and subsequently green autofuorescence compared with normal tissues when illuminated with blue-light (440– 480 nm wavelength) [14]. Natural tissue chromophores (elastin, collagen, favins, nicotinamide adenine dinucleotide, nicotinamide adenine dinucleotide hydrogen [NADH]) emit light when their electrons return to ground level after being excited with light of speci c wavelength. The low level of tissue autofuorescence cannot be

picked up with WLB given the “noise” from high degree background refected and backscattered light. However, AFB selectively picks up the subtle changes in natural tissue autofuorescence patterns. Tissue metaplasia, dysplasia, and neoplasia reduce natural concentration of airway chromophores (diminished expression of ribofavin, favin, and NADH due to increased anaerobic metabolism and lactic acid production) [15]. Higher neoplastic tissue blood fow increases light absorption by the hemoglobin. Malignant tissue proliferation even if only microscopic atrst results in higher degree of light scattering by tissue hyperplasia. These changes overall result in diminished tissue green autofuorescence with the abnormal tissue assuming a red-brown color [16]. These initially subtle mucosal changes are identi able by WBL in only less than 30% of cases, even by experienced bronchoscopists. Different AFB imaging systems have been developed all with slightly different sensitivity for detection of the mucosal abnormalities. Continuous improvement of AFB devices allows for increased speci city. In the SAFE 1000 system (Pentax, Asahi Optical, Tokyo, Japan), xenon lamp replaced used in the light-induced fuorescence endoscopy (LIFE) device laser light. AFB is highly sensitive for detection of pre-neoplastic and neoplastic lesions, however, lacks speci city for detection of pre-invasive lesions. It often cannot differentiate between the areas of high blood fow and metabolism occurring in chronic infammatory states like bronchitis. To overcome this limitation, video-autofuorescence systems such as SAFE-3000 and AFI has been developed [17] (Fig. 21.1).

Narrow Band Imaging (NBI)

Narrow band imaging (NBI) is an optical image technology classi ed as an image enhancement endoscopy using special blue and green light wavelengths allowing for enhanced visualization of microvascular structures in the mucosal and submucosal layers [18–20]. NBI utilizes wavelengths at 415 nm (blue light) and 540 nm (green

Fig. 21.1  Autofuorescence bronchoscopy (AFB) image using AFI system. Representative case of carcinoma in situ. (a) White light bronchoscopy showed thickening of the bifurcation and partially covered with white coat. (b)

Corresponding AFB image using AFI system (Olympus). The cancerous area was visualized as a magenta lesion with a clear border to normal mucosa

light). Narrow bandwidths reduce the mucosal light scattering and enable enhanced visualization of endobronchial microvasculature structure. The 415 nm blue light is absorbed by the super - cial capillary vessels whereas the 540 nm wavelength is absorbed by the hemoglobin in the deeper, submucosal vessels. Fine blood vessels appear brown and the deeper vessels cyan.

Beside molecular changes allowing autonomous progression of cell cycle that imparts metastatic potential, cancer cells must also develop extended angiogenic capabilities allowing for rapid growth and invasion. Multi-step angiogenesis process has been described in epithelial tumors [21, 22]. To ful ll high metabolic demands of rapidly dividing tumor, neoplastic cells have to develop enhanced angiogenic capabilities. Animal and human invasive neoplasia pathogenesis studies suggest that so-called “angiogenic switch” is thought to occur in preinvasive lesions prior to invasive tumor formation [23, 24]. Since squamous cell cancer is thought to progress through developmental staged from

squamous cell metaplasia to dysplasia and CIS, detection of each of these stages could have a signi cant impact on therapeutic interventions and prognosis (Fig. 21.2).

High Magni cation

Bronchovideoscope (HMB)

High magni cation bronchovideoscope (HMB) is a system that was developed to enhance detailed white light observation of bronchial dysplasia. Increased thickening of the bronchial epithelium and increased vessel growth are thought to be related to the appearance of areas of abnormal fuorescence, suggesting roles for neovascularization or increased mucosal microvascular growth in bronchial dysplasia. However, the only abnormality seen on WLB in dysplasia is swelling and redness at the bronchial bifurcations. HMB is a direct viewing WLB system that has an outer diameter of 6 mm and can easily be inserted into the tracheobronchial tree. HMB combines

a

b

c

Fig. 21.2  Narrow band imaging (NBI). Representative case of carcinoma in situ (same as Fig. 21.1). (a) White light bronchoscopy using high de nition bronchovideoscope. (b) Narrow band imaging (NBI) of the same area. (c) Close view of NBI identi ed dotted vessel and spiral/screw type vessels which was typically observed for carcinoma in situ

two systems—a video observation system for high magni cation observation and a ber observation system for orientation of the bronchoscope tip. For the video observation system an objective optical system, in xed focus mode rather than zoom mode, was used to give an outer diameter of about 6 mm to allow for the bronchoscope and the observation depth of 1–3 mm. Magni cation is about fourfold higher than that of the regular bronchovideoscope. The bronchial mucosa is observed minutely on a 14-inch TV monitor at a high magni cation of 110 times at the nearest point [25].

HMB has enabled observation of vascular networks within the bronchial mucosa in patients with respiratory disease such as asthma, chronic bronchitis, sarcoidosis, and lung cancer. Areas of increased vessel growth and complex networks of tortuous vessels in the bronchial mucosa that are detected using HMB at sites of abnormal fuorescence may allow clinicians to differentiate between bronchitis and dysplasia. In areas of abnormal fuorescence on AFB, HMB can detect dysplasia more accurately than AFB alone with a sensitivity of 70% and speci city of 90% [25]. HMB observation in patients with asthma showed that the vessel area density and vessel length density are signi cantly increased compared to control subjects [26] (Fig. 21.3).

Dual Red Imaging (DRI)

DRI is a novel image enhanced endoscopy technology that enables to visualization of relatively deeper blood vessels in the tissue by using two different wavelength lights, 600 nm and 630 nm, in the red band [27]. This technology is used primarily in the gastrointestinal eld because RDI images easily nd the blood vessels in deeper tissue. DRI increased the visibility of esophageal varices [28] and was applied to evaluate the severity of ulcerative colitis [29]. DRI is also valid for endoscopic treatment in the gastrointestinal eld, such as endoscopic mucosal resection. DRI quickly detects the blood vessels in the deeper mucosal layer and the bleeding point during the procedure [27]. The utility of

Fig. 21.3  Several bronchoscopic imaging techniques of the airway. Representative case of micro-invasive squamous cell carcinoma. (a) White light bronchoscopy. (b) AFB using AFI system. (c) White-light bronchoscopy

using high de nition bronchovideoscope. (d) Narrow band imaging. (e, f) Endocytoscopy images using methylene blue staining of the mucosa