**2. Wireless Capsule Endoscopy (WCE)**

In gastroenterology, the most common and established technique to visually inspect the GI tract and diagnose its diseases is endoscopy. The traditional endoscopic examinations applied for diagnosis in the upper and lower part of the GI tract, including esophagus, stomach, duodenum, terminal ileum and colon, are highly invasive causing discomfort to the patients. The visual inspection of the entire small intestine, in particular, has posed a challenge to gastroenterologists due to the strain of physically reaching it. Its important length and numerous windings make the examination extremely difficult, painful and not always possible, since usually there is a dead space in the middle part. Some imaging techniques used for the small intestine inspection include enteroclisis, small bowel follow through, push, sonde, and double balloon enteroscopy. Nevertheless, they are deeply inconvenient for the patients and require highly experienced gastroenterologists.

In 2000, advances in high integration and miniaturization allowed the researchers of Given Imaging to draw the attention of the GI community by unveiling what is now called endoscopic capsule. Wireless capsule endoscopy (WCE) (Iddan *et al.*, 2000) is a novel medical procedure, which has revolutionized endoscopy, as it has enabled, for the first time, a painless and effective diagnosis inside the GI tract. A WCE system consists of the capsule endoscope, a data recorder system and computer software for WCE data processing. The capsule endoscope is a disposable, pill-shaped device which consists of a CMOS camera, four light sources, two batteries and a radio transmitter. The patient shallows the capsule which captures images of the GI tract at a speed of two frames per second (fps). These images are compressed with JPEG algorithm and transmitted wirelessly to a special recorder attached to the patient's waist. The entire process lasts approximately 8 hours until the batteries exhaust. Finally, the images stored in the recorder are downloaded to a computer and the physicians, with the aid of the special software, can review the images and analyse potential sources of various GI diseases. The capsule travels along the digestive tract with the physiological peristalsis, without the need for air insufflation and sedation. Thus, the examination of the entire small intestine has become the most comfortable endoscopic examination for the patient to undergo. In this way WCE is suitable even for children and elderly.

WCE has proven invaluable in evaluating various diseases of the small bowel (Friedman, 2004; Pennazio, 2005), such as obscure bleeding (Mylonaki *et al., 2003*), polyps and neoplasm, Crohn's disease, celiac disease and mucosal ulcers (Aronott & Lo, 2004). Ulcer is one of the most common lesions of the GI tract that affects approximately 10% of the people. The most usual causes are Helicobacter pylori bacteria and use of nonsteroidal antiinflammatory drugs (NSAID). Ulcer is a chronic inflammatory sore or erosion on the internal mucous membranes that arises in small intestine, especially in duodenum (the upper part of the small intestine) and in stomach. Some serious diseases are associated with ulcer, like Crohn's disease and ulcerative colitis. Although ulcer by itself is not lethal, complications are capable of causing death. That is the reason why early diagnosis and treatment is extremely essential.

#### **2.1 Side effects**

188 New Advances in the Basic and Clinical Gastroenterology

introducing new feature vectors (FVs). In particular, this chapter describes the use of innovative computer vision approaches towards the evaluation of ulcer-related content of WCE images. These approaches are similar to those employed by physicians in clinical practice to reach a diagnosis, i.e., the concept of color-texture characteristics. More specifically, they include sophisticated image processing tools with robust mathematical background, drawn from the field of Multi-Resolution Analysis, resulting in discrimination between ulcer and healthy regions. Additionally, innovative feature extraction algorithms, structured in both space and space-frequency domains, are presented, along with their application to real WCE data, collected from patients with ulcerous diseases. The chapter concludes by pointing out the potential of the proposed approaches towards efficient automated ulcer detection systems that will moderate the labour of the gastroenterologist

In gastroenterology, the most common and established technique to visually inspect the GI tract and diagnose its diseases is endoscopy. The traditional endoscopic examinations applied for diagnosis in the upper and lower part of the GI tract, including esophagus, stomach, duodenum, terminal ileum and colon, are highly invasive causing discomfort to the patients. The visual inspection of the entire small intestine, in particular, has posed a challenge to gastroenterologists due to the strain of physically reaching it. Its important length and numerous windings make the examination extremely difficult, painful and not always possible, since usually there is a dead space in the middle part. Some imaging techniques used for the small intestine inspection include enteroclisis, small bowel follow through, push, sonde, and double balloon enteroscopy. Nevertheless, they are deeply

In 2000, advances in high integration and miniaturization allowed the researchers of Given Imaging to draw the attention of the GI community by unveiling what is now called endoscopic capsule. Wireless capsule endoscopy (WCE) (Iddan *et al.*, 2000) is a novel medical procedure, which has revolutionized endoscopy, as it has enabled, for the first time, a painless and effective diagnosis inside the GI tract. A WCE system consists of the capsule endoscope, a data recorder system and computer software for WCE data processing. The capsule endoscope is a disposable, pill-shaped device which consists of a CMOS camera, four light sources, two batteries and a radio transmitter. The patient shallows the capsule which captures images of the GI tract at a speed of two frames per second (fps). These images are compressed with JPEG algorithm and transmitted wirelessly to a special recorder attached to the patient's waist. The entire process lasts approximately 8 hours until the batteries exhaust. Finally, the images stored in the recorder are downloaded to a computer and the physicians, with the aid of the special software, can review the images and analyse potential sources of various GI diseases. The capsule travels along the digestive tract with the physiological peristalsis, without the need for air insufflation and sedation. Thus, the examination of the entire small intestine has become the most comfortable endoscopic examination for the patient to undergo. In this way

WCE has proven invaluable in evaluating various diseases of the small bowel (Friedman, 2004; Pennazio, 2005), such as obscure bleeding (Mylonaki *et al., 2003*), polyps and neoplasm, Crohn's disease, celiac disease and mucosal ulcers (Aronott & Lo, 2004). Ulcer is

inconvenient for the patients and require highly experienced gastroenterologists.

and, consequently, the cost of the WCE examination.

**2. Wireless Capsule Endoscopy (WCE)** 

WCE is suitable even for children and elderly.

WCE is a well-tolerated and safe procedure with very few and rare complications. The main risk of WCE is capsule retention. Despite the small diameter of the capsule, a narrowing of the small bowel may cause it to become retained at a site of stricture. However, retention is estimated to occur in less than 1% of cases (Liao *et al.,* 2010). The 2005 International Conference on Capsule Endoscopy reached a consensus stating that a capsule would be deemed to have been retained if it could be shown to be remaining in the GI tract more than two weeks, without symptoms, after it had been ingested. The causes of capsule retention are bowel obstructions narrower than the size of the capsule (11mm diameter). Small bowel strictures are a frequent complication of Crohn's disease (Cheifetz *et al.*, 2006) and prolonged use of NSAID (Meredith *et al.*, 2009). The risk of capsule retention is also high for patients with a history of bowel obstruction or a previous gastrointestinal surgery. In case of retention, the removal of the capsule is most commonly performed by surgery (Barkin & Friedman, 2002), often resecting the obstructing lesion at the same time. However, there are cases where the removal is possible with traditional endoscopic techniques.

In order to reduce the risk of retaining the capsule, a barium small bowel examination should be performed or a biodegradable patency capsule (Fig. 2) (Riccioni *et al.*, 2003) should be digested prior to WCE. However, two studies (Meredith *et al.*, 2009) indicated that small bowel follow through radiography (SBFT) investigations were not effective at excluding patients at risk of retention. Additionally, patients with abnormal SBFT can have successful WCE. The patency capsule is exactly the same size as the capsule endoscope but it is made from lactose, with 10% barium sulphate to make it radiopaque, and surrounded by

Fig. 2. Schematic drawing of a biodegradable patency capsule.

Enhanced Ulcer Recognition from Capsule Endoscopic Images Using Texture Analysis 191

raises the transmission rate. Additionally, the recorder identifies if the capsule is in motion or stationary. If the capsule is moving the camera captures up to 35 images per second. Last but not least, the recorder has the intelligence to notify the patient with a sound signal and a vibration to ingest a prokinetic agent if the capsule resides in stomach for over an hour. This new design and technical achievements are very impressive. Yet the critical question to be addessed is whether this new capsule endoscope leads to improved diagnostic performance compared to traditional colonoscopy. Studies (Adler & Metzger, 2011) indicate that the

Currently, researchers intensely strive to unravel the issue of limited energy store inside the capsule by developing external wireless power transmission systems (Carta *et al.*, 2010). These approaches are based on magnetic fields and three-dimensional (3D) coils through a process that is known as inductive coupling. According to this phenomenon, an alternating magnetic field induces electrical voltage and electrical current to a coil that resides inside the field. Thus, the concept is to create a magnetic field around the human body that will transmit power to the capsule. To accomplish this, the capsule is equipped with windings of very thin copper wires (Fig. 3) around a ferrite core towards all three directions (3D coil). Ferrite is a lightweight material with efficient electromagnetic characteristics that support the formation of magnetic field. The existence of a ferrite core inside a coil has the effect of locally intensifying the magnetic field; hence, increasing the amount of collected power. On the contrary, the absence of the ferrite core would necessitate a larger coil for the same amount of received power. External power transmission systems seem promising and safe. Over 300mW usable power can be delivered while the maximum specific adsorption rate (SAR) does not exceed 0,329 W/Kg (Xin *et al.*, 2010), under the basic restrictions of the International Commission on Nonionizing Radiation Protection (ICNIRP). However, there are major issues to deal with. The orientation of the capsule inside the body highly affects the stability of the received power. The amount of received power may drop over 55% for specific orientations which affects the proper operation of the capsule. Moreover, there is extensive power loss (over 70mW) in the electronic circuit that accompanies the coil inside the capsule. Another, equally important, problem is the stability of the external magnetic field which is altered by the human body. Despite the aforementioned issues, great steps forward have been made and it is likely, in the

The development of imaging technology and miniaturization resulted in size reduction of the image sensors and expansion of the camera angle of view. A wider viewing angle means

Fig. 3. 3D coil inside capsule endoscope for wireless power transmission (Carta *et al.*,2010).

diagnostic yield of WCE in colon has increased but still cannot surpass colonoscopy.

near future, an externally powered capsule endoscope to be realized.

a cellophane coating. It has a timer plug which is slowly dissolved by gastric fluids, giving a disintegration time of 40-100 hours post ingestion, and contains a very small radiofrequency identification tag (RFID) which can be used to tract its location in the small bowel without the use of ionizing radiation. The patency capsule remaining in one area for a large period of time can suggest retention. Early experience with this biodegradable capsule indicates that it allows accurate and objective evaluation of potentially obstructing small bowel lesions prior to WCE (Belvin *et al.*, 2003; Cauendo *et al.*, 2003). Although the patency capsule is mostly soluble, there needs to be further research to determine whether its use will reduce the risk of the patient, requiring surgery to remove there is a pathological stricture present. Successful passing of this patency capsule intact and without pain can provide evidence that a capsule endoscope will have a similar successful journey.

To conclude, the retention of a capsule endoscope can be a significant complication procedure, requiring corrective surgery. Whilst the overall risk of retention is low, factors that increase this risk include known or suspected Crohn's disease, a history of NSAID use and previous small bowel surgery. Taking a careful medical history can identify those patients at higher risk of retention, and for those identified, the administration of a patency capsule allows the assessment of the patient's risks from swallowing a small bowel WCE.

#### **2.2 Advances in wireless capsule endoscopy**

WCE is still an under development technology, which may change endoscopy forever. However, there are technical limitations that raise some serious questions. Will capsule endoscopy replace traditional upper gastrointestinal endoscopy and colonoscopy? Will capsule endoscopy be able to deliver therapy? The answer is probably yes, but, there are major challenges that the capsule technology needs to overcome, to compete with probe gastroscopy and colonoscopy. As mentioned before, WCE is especially recommended for exploration of the small bowel, while it exhibits poorer diagnostic efficacy for the examination of esophagus, stomach and colon (Van Gossum *et al.*, 2009). The limitations/challenges include: power management, camera speed and image quality, controllable manoeuvring, and interventional capabilities (Swain, 2008).

The first endoscopic capsule, due to limited power supply, ceased image capturing before crossing the entire GI tract. It was even possible that transmission stopped before the end of ileum, in case of extended residence in stomach. Consequently, visualization of colon was impossible. In this context, researches were directed towards a more energy efficient capsule, capable of exploring the entire digestive tract. Technological advances allowed researchers to make radical changes in WCE design and energy supply (Moglia *et al.*, 2009). In particular, two breakthroughs took place. Firstly, the advent of more efficient battery materials (i.e., carbon nanotubes and buckytubes) led to batteries smaller in size with better electrical conductivity leaving room for a third battery in the capsule with a slight increase in size. Secondly, an intelligent power management system was introduced in the data recorder that saves energy by regulating the image transmission rate and applying a sleep mode to the capsule. The recorder recognizes the location of the capsule inside the GI tract and adjusts the transmission rate accordingly. The capturing of images starts half an hour after ingestion to allow travelling to the target area (sleep mode). When the capsule arrives in stomach, the recorder recognizes it and maintains a slow transmission rate of six images per minute. The recorder is also able to detect when the capsule enters small intestine and

a cellophane coating. It has a timer plug which is slowly dissolved by gastric fluids, giving a disintegration time of 40-100 hours post ingestion, and contains a very small radiofrequency identification tag (RFID) which can be used to tract its location in the small bowel without the use of ionizing radiation. The patency capsule remaining in one area for a large period of time can suggest retention. Early experience with this biodegradable capsule indicates that it allows accurate and objective evaluation of potentially obstructing small bowel lesions prior to WCE (Belvin *et al.*, 2003; Cauendo *et al.*, 2003). Although the patency capsule is mostly soluble, there needs to be further research to determine whether its use will reduce the risk of the patient, requiring surgery to remove there is a pathological stricture present. Successful passing of this patency capsule intact and without pain can provide evidence that

To conclude, the retention of a capsule endoscope can be a significant complication procedure, requiring corrective surgery. Whilst the overall risk of retention is low, factors that increase this risk include known or suspected Crohn's disease, a history of NSAID use and previous small bowel surgery. Taking a careful medical history can identify those patients at higher risk of retention, and for those identified, the administration of a patency capsule allows the assessment of the patient's risks from swallowing a small bowel WCE.

WCE is still an under development technology, which may change endoscopy forever. However, there are technical limitations that raise some serious questions. Will capsule endoscopy replace traditional upper gastrointestinal endoscopy and colonoscopy? Will capsule endoscopy be able to deliver therapy? The answer is probably yes, but, there are major challenges that the capsule technology needs to overcome, to compete with probe gastroscopy and colonoscopy. As mentioned before, WCE is especially recommended for exploration of the small bowel, while it exhibits poorer diagnostic efficacy for the examination of esophagus, stomach and colon (Van Gossum *et al.*, 2009). The limitations/challenges include: power management, camera speed and image quality,

The first endoscopic capsule, due to limited power supply, ceased image capturing before crossing the entire GI tract. It was even possible that transmission stopped before the end of ileum, in case of extended residence in stomach. Consequently, visualization of colon was impossible. In this context, researches were directed towards a more energy efficient capsule, capable of exploring the entire digestive tract. Technological advances allowed researchers to make radical changes in WCE design and energy supply (Moglia *et al.*, 2009). In particular, two breakthroughs took place. Firstly, the advent of more efficient battery materials (i.e., carbon nanotubes and buckytubes) led to batteries smaller in size with better electrical conductivity leaving room for a third battery in the capsule with a slight increase in size. Secondly, an intelligent power management system was introduced in the data recorder that saves energy by regulating the image transmission rate and applying a sleep mode to the capsule. The recorder recognizes the location of the capsule inside the GI tract and adjusts the transmission rate accordingly. The capturing of images starts half an hour after ingestion to allow travelling to the target area (sleep mode). When the capsule arrives in stomach, the recorder recognizes it and maintains a slow transmission rate of six images per minute. The recorder is also able to detect when the capsule enters small intestine and

controllable manoeuvring, and interventional capabilities (Swain, 2008).

a capsule endoscope will have a similar successful journey.

**2.2 Advances in wireless capsule endoscopy** 

raises the transmission rate. Additionally, the recorder identifies if the capsule is in motion or stationary. If the capsule is moving the camera captures up to 35 images per second. Last but not least, the recorder has the intelligence to notify the patient with a sound signal and a vibration to ingest a prokinetic agent if the capsule resides in stomach for over an hour. This new design and technical achievements are very impressive. Yet the critical question to be addessed is whether this new capsule endoscope leads to improved diagnostic performance compared to traditional colonoscopy. Studies (Adler & Metzger, 2011) indicate that the diagnostic yield of WCE in colon has increased but still cannot surpass colonoscopy.

Currently, researchers intensely strive to unravel the issue of limited energy store inside the capsule by developing external wireless power transmission systems (Carta *et al.*, 2010). These approaches are based on magnetic fields and three-dimensional (3D) coils through a process that is known as inductive coupling. According to this phenomenon, an alternating magnetic field induces electrical voltage and electrical current to a coil that resides inside the field. Thus, the concept is to create a magnetic field around the human body that will transmit power to the capsule. To accomplish this, the capsule is equipped with windings of very thin copper wires (Fig. 3) around a ferrite core towards all three directions (3D coil). Ferrite is a lightweight material with efficient electromagnetic characteristics that support the formation of magnetic field. The existence of a ferrite core inside a coil has the effect of locally intensifying the magnetic field; hence, increasing the amount of collected power. On the contrary, the absence of the ferrite core would necessitate a larger coil for the same amount of received power. External power transmission systems seem promising and safe. Over 300mW usable power can be delivered while the maximum specific adsorption rate (SAR) does not exceed 0,329 W/Kg (Xin *et al.*, 2010), under the basic restrictions of the International Commission on Nonionizing Radiation Protection (ICNIRP). However, there are major issues to deal with. The orientation of the capsule inside the body highly affects the stability of the received power. The amount of received power may drop over 55% for specific orientations which affects the proper operation of the capsule. Moreover, there is extensive power loss (over 70mW) in the electronic circuit that accompanies the coil inside the capsule. Another, equally important, problem is the stability of the external magnetic field which is altered by the human body. Despite the aforementioned issues, great steps forward have been made and it is likely, in the near future, an externally powered capsule endoscope to be realized.

The development of imaging technology and miniaturization resulted in size reduction of the image sensors and expansion of the camera angle of view. A wider viewing angle means

Fig. 3. 3D coil inside capsule endoscope for wireless power transmission (Carta *et al.*,2010).

Enhanced Ulcer Recognition from Capsule Endoscopic Images Using Texture Analysis 193

release space that could be used for other interactive functions, and maximize power supply. New engineering methods for constructing tiny moving parts, miniature actuators and even motors into capsule endoscopes are being developed. However, these moving components require considerable amounts of power. Another limitation to therapeutic capsule endoscopy is the low mass of the capsule endoscope (approximately 4 grams). A force exerted on tissue, for example, by biopsy forceps may push the capsule away from the tissue. Opening small biopsy forceps to grasp tissue and pull it free will require different solutions to those used at conventional endoscopy. All these interventional capabilities seem to be something of a pipe dream at present but the huge technological leaps pave the way

The ideal WCE of the gastroenterologist's imagination should be remote controlled and capable of performing an ordinary biopsy as well as stop bleeding using adrenaline injection or a heat probe. The ultimate capsule would include special detectors for white blood cells and be able to measure various cytokines, pH, temperature and pressure, in addition to delivering drugs. Finally, the optimal WCE needs to contain a computerized system for automatic detection of pathologies, such as ulcer and polyps, in order to overcome the drawback of time-consuming viewing the video (Fireman, 2010). Technology for improving the capability of the future generation capsule is almost within grasp and it would not be

Automated knowledge extraction from medical images is a fast growing field of interest for the researchers. The attainment of this objective requires image decomposition to its components that will disclose the inherent structural characteristics of the image. In this context, this section presents Bidimensional Ensemble Empirical Mode Decomposition, a

In 1998, Huang *et al.* introduced a novel, intuitive and alternative signal decomposition technique for time-frequency analysis, namely Empirical Mode Decomposition (EMD) (Huang *et al.*, 1998). The major characteristic of EMD that renders it superior to traditional analysis methods, such as Fourier and Wavelets, is its adaptive nature. The decomposition does not require the use of *a priori* basis function. On the contrary, it is totally data driven. The concept that lies behind EMD is the existence of oscillations in every signal, at a very local level. Therefore, its target is to seek and reveal these inherent oscillatory modes, called Intrinsic Mode Functions (IMFs). EMD is designed to estimate IMFs of a signal so that, no matter how complicated the signal is, it embeds. A given signal x(t) can be decomposed into

> x�t�=�ci(t) n

> > i=1

where ��(t) is ith IMF (IMF i) and rn(t) is the low frequency trend of x(t) (residue). The highest frequency component of x(t) corresponds to the lowest value of index *i*, i.e., ��(t) (IMF 1).

+rn(t), (1)

surprising to witness the realization of these giant steps within the coming decade.

for an active therapeutic capsule.

novel tool for image analysis.

*n* IMFs as:

**3. The concept of image decomposition** 

**3.1 Empirical Mode Decomposition (EMD)** 

more panoramic images. Smaller cameras contributed to increased free space inside the capsule, and as a result, the inclusion of a second camera. The twin camera capsule with a wider angle of view combined with the increased transmission frame rate enabled esophageal WCE (Waterman & Granlnek, 2009) with promising diagnostic efficiency. The size reduction of image sensors is, also, expected to result in increasing number of pixels and solve the problem of low resolution WCE images. New and more efficient image compression algorithms will, additionally, assist towards quality and color enhancement. Image compression is essential in WCE in order to significantly reduce the size of the image and, consequently, the storage space and transmission time required. However, the compression procedure lowers image quality by smoothing the razor-sharp details.

Gastroenterologists eagerly look forward the day that they will be able to control and steer the capsule endoscope as they do in standard endoscopy. This would give them control in maintaining the capsule steady in selected areas and hold the view in order to examine carefully the opposite wall of the bowel. To solve this problem, magnetic manoeuvring has recently become a thrust research area. The proposed approaches rely on a magnetic field applied to the capsule from the exterior of the patient, exploiting the principle that a magnet inside a magnetic field aligns with the direction of the field. The magnetic field can be used to control the movement trajectory, the position and the orientation of the endoscopic capsule. By changing the direction of the magnetic field, the direction of the capsule also changes. For this purpose, various techniques have been proposed in order to make an endoscopic capsule responsive to an external magnetic field. These include either magnetic parts and induction coils to be arranged inside the capsule, or magnetic shells to be reversibly applied to the capsule externally (Capri *et al.*, 2007) (Fig. 4). Capsule motions can readily be induced with hand-held/hand-guided magnets, as demonstrated even in the esophagus and stomach of a volunteer (Swain, 2010). This system is only available for research purposes. Nevertheless, the main issue related to the development of a clinically applicable technique is the generation and precise control of a stable magnetic field, really capable of guaranteeing accurate and reliable manoeuvrings of an endoscopic capsule. Such techniques start to emerge (Capri *et al.*, 2011; Gao *et al.*, 2010) and the realization of a selfpropelled capsule is close.

Fig. 4. Capsule with magnetic shield for controllable maneuvering (Capri *et al.*, 2011).

At present, WCE remains just a diagnostic tool that has yet to prove its potential. The endoscopic capsule is passive and cannot obtain biopsies, aspirate fluid, deliver drugs or brush lesions for cytology. The main pressure is to reduce the capsule size, which will release space that could be used for other interactive functions, and maximize power supply. New engineering methods for constructing tiny moving parts, miniature actuators and even motors into capsule endoscopes are being developed. However, these moving components require considerable amounts of power. Another limitation to therapeutic capsule endoscopy is the low mass of the capsule endoscope (approximately 4 grams). A force exerted on tissue, for example, by biopsy forceps may push the capsule away from the tissue. Opening small biopsy forceps to grasp tissue and pull it free will require different solutions to those used at conventional endoscopy. All these interventional capabilities seem to be something of a pipe dream at present but the huge technological leaps pave the way for an active therapeutic capsule.

The ideal WCE of the gastroenterologist's imagination should be remote controlled and capable of performing an ordinary biopsy as well as stop bleeding using adrenaline injection or a heat probe. The ultimate capsule would include special detectors for white blood cells and be able to measure various cytokines, pH, temperature and pressure, in addition to delivering drugs. Finally, the optimal WCE needs to contain a computerized system for automatic detection of pathologies, such as ulcer and polyps, in order to overcome the drawback of time-consuming viewing the video (Fireman, 2010). Technology for improving the capability of the future generation capsule is almost within grasp and it would not be surprising to witness the realization of these giant steps within the coming decade.

#### **3. The concept of image decomposition**

192 New Advances in the Basic and Clinical Gastroenterology

more panoramic images. Smaller cameras contributed to increased free space inside the capsule, and as a result, the inclusion of a second camera. The twin camera capsule with a wider angle of view combined with the increased transmission frame rate enabled esophageal WCE (Waterman & Granlnek, 2009) with promising diagnostic efficiency. The size reduction of image sensors is, also, expected to result in increasing number of pixels and solve the problem of low resolution WCE images. New and more efficient image compression algorithms will, additionally, assist towards quality and color enhancement. Image compression is essential in WCE in order to significantly reduce the size of the image and, consequently, the storage space and transmission time required. However, the

compression procedure lowers image quality by smoothing the razor-sharp details.

Fig. 4. Capsule with magnetic shield for controllable maneuvering (Capri *et al.*, 2011).

At present, WCE remains just a diagnostic tool that has yet to prove its potential. The endoscopic capsule is passive and cannot obtain biopsies, aspirate fluid, deliver drugs or brush lesions for cytology. The main pressure is to reduce the capsule size, which will

propelled capsule is close.

Gastroenterologists eagerly look forward the day that they will be able to control and steer the capsule endoscope as they do in standard endoscopy. This would give them control in maintaining the capsule steady in selected areas and hold the view in order to examine carefully the opposite wall of the bowel. To solve this problem, magnetic manoeuvring has recently become a thrust research area. The proposed approaches rely on a magnetic field applied to the capsule from the exterior of the patient, exploiting the principle that a magnet inside a magnetic field aligns with the direction of the field. The magnetic field can be used to control the movement trajectory, the position and the orientation of the endoscopic capsule. By changing the direction of the magnetic field, the direction of the capsule also changes. For this purpose, various techniques have been proposed in order to make an endoscopic capsule responsive to an external magnetic field. These include either magnetic parts and induction coils to be arranged inside the capsule, or magnetic shells to be reversibly applied to the capsule externally (Capri *et al.*, 2007) (Fig. 4). Capsule motions can readily be induced with hand-held/hand-guided magnets, as demonstrated even in the esophagus and stomach of a volunteer (Swain, 2010). This system is only available for research purposes. Nevertheless, the main issue related to the development of a clinically applicable technique is the generation and precise control of a stable magnetic field, really capable of guaranteeing accurate and reliable manoeuvrings of an endoscopic capsule. Such techniques start to emerge (Capri *et al.*, 2011; Gao *et al.*, 2010) and the realization of a self-

Automated knowledge extraction from medical images is a fast growing field of interest for the researchers. The attainment of this objective requires image decomposition to its components that will disclose the inherent structural characteristics of the image. In this context, this section presents Bidimensional Ensemble Empirical Mode Decomposition, a novel tool for image analysis.

#### **3.1 Empirical Mode Decomposition (EMD)**

In 1998, Huang *et al.* introduced a novel, intuitive and alternative signal decomposition technique for time-frequency analysis, namely Empirical Mode Decomposition (EMD) (Huang *et al.*, 1998). The major characteristic of EMD that renders it superior to traditional analysis methods, such as Fourier and Wavelets, is its adaptive nature. The decomposition does not require the use of *a priori* basis function. On the contrary, it is totally data driven. The concept that lies behind EMD is the existence of oscillations in every signal, at a very local level. Therefore, its target is to seek and reveal these inherent oscillatory modes, called Intrinsic Mode Functions (IMFs). EMD is designed to estimate IMFs of a signal so that, no matter how complicated the signal is, it embeds. A given signal x(t) can be decomposed into *n* IMFs as:

$$\mathbf{x}(\mathbf{t}) = \sum\_{i=1}^{n} \mathbf{c}\_{i}(\mathbf{t}) + \mathbf{r}\_{n}(\mathbf{t}),\tag{1}$$

where ��(t) is ith IMF (IMF i) and rn(t) is the low frequency trend of x(t) (residue). The highest frequency component of x(t) corresponds to the lowest value of index *i*, i.e., ��(t) (IMF 1).

Enhanced Ulcer Recognition from Capsule Endoscopic Images Using Texture Analysis 195

scales. The IMFs of each ensemble member are noisy but the final average IMFs are noisefree, since white noise cancels itself for a large number of ensemble members. Figure 5c presents the correct decomposition (using EEMD) of the signal in Fig. 5b. IMFs 1-3 include only the high frequency components while IMF5 contains the sinusoidal oscillation of the

A multidimensional approach of EMD is required in case of a multidimensional signal. The extension of EMD in two dimensions (2D), namely Bidimensional EMD (BEMD), is an alternative multi-resolution analysis technique for image analysis and pattern discrimination. BEMD decomposes a 2D signal in 2D IMFs in the same way as eq. (1) demonstrates. However, there are two approaches for the realization of 2D extension. The first approach treats 2D data (images) as a collection of 1D slices (rows/columns) and applies 1D EMD on each row/column of the image (pseudo-BEMD). The second approach directly transplants the idea of 1D EMD algorithm in 2D data (genuine BEMD) after applying the appropriate changes (for example, fitting surfaces replace fitting curves). The first approach has the advantage of higher speed, while the latter exhibits improved performance, since the correlation among rows/columns of the image is taken into account.

Texture is a major property of any image that is useful in machine vision applications, especially for medical purpose. There are many approaches for texture analysis proposed in the literature. This paragraph describes the concept of Differential Lacunarity, an efficient

Lacunarity (Lac) was introduced by Mandelbrot (Mandelbrot, 1993) as a fractal property, counterpart to fractal dimension (Mandelbrot, 1982), that describes the texture of a fractal. *Fractal dimension* is a measure of how much space is filled without consideration about the space-filling characteristics of data. In other words, two datasets with identical fractal dimensions can have distinct patterns with great differences in appearance. The introduction of Lac addressed this issue. Lac analyzes *how space is filled and consequently, can discriminate textures and natural surfaces that share the same fractal dimension*. In this direction, Lac has been used as a general technique to analyze patterns of spatial dispersion (Plotnick *et al.,* 1996). The term "lacunarity" has been used to evaluate and describe the distribution of gap sizes along datasets. A set with gaps of widely disparate sizes is considered heterogeneous and is characterized by high Lac, while a homogeneous set, with uniform gap sizes, exhibits lower Lac. It should be highlighted that homogeneous sets at large scales can be quite heterogeneous when examined at smaller scales and vice versa. From this perspective, Lac can be considered as a scale dependent tool to measure the heterogeneity or

Various algorithms have been proposed to calculate and quantify Lac, but the most popular are based on the "gliding box algorithm" (GBA) (Allain & Coitre, 1991) that is

Bidimensional EEMD is the extension of EEMD in 2D (Wu *et al.*, 2009).

tool for texture features extraction and identification.

initial signal.

**3.3 Bidimensional EEMD (BEEMD)** 

**4. Texture extraction** 

**4.1 Lacunarity Analysis (Lac)** 

texture of an object (Gefen *et al.*, 1983).

While the value of *i* increases, lower frequency components are obtained. An example is given in Fig. 5a, where the signal is decomposed into five IMFs plus residue. The process to calculate each ܿ(t) is called sifting process. The local extrema are defined and interpolated, resulting in two fitting curves, one for the maxima and one for the minima. Then, the mean curve is calculated and subtracted from the signal. This procedure continues until a stopping criterion is satisfied. The signal that remains after the last subtraction is ܿଵ(t). Next, ܿଵ(t) is subtracted from the initial signal and the remainder constitutes the new initial signal on which the above procedure is applied in order to extract the following IMFs until the desired number is obtained.

#### **3.2 Ensemble EMD (EEMD)**

Despite the great advantage of EMD, deficiency arises when the extrema of the original signal are unevenly distributed. In such a case, the IMFs are incorrectly calculated, since either a single IMF contains signals of widely disparate scales or a single mode of oscillations resides in two or more IMFs. This phenomenon is called *mode mixing* and an example is depicted in Fig. 5b. It is clear that the first two IMFs, apart from the high frequency component of the signal, incorrectly include a low frequency oscillation. To overcome this issue, Huang *et al.* proposed a noise-assisted version of EMD, namely ensemble EMD (EEMD) (Wu & Huang, 2009). EEMD requires the generation of an ensemble that contains multiple copies of the original signal that are distorted by white Gaussian noise, different for each copy, of finite amplitude. EMD is applied on every member of the ensemble and the final IMFs of the initial signal are derived by averaging the corresponding IMFs of each member of the ensemble. The concept of EEMD is grounded on the intuitive characteristics of white noise. White noise populates the whole time-frequency space uniformly and, as a result, establishes proper reference scales for the IMFs. The inherent modes of the signal are triggered by the noise and are projected accurately on the correct

Fig. 5. (a) EMD analysis, (b) mode mixing phenomenon, (c) ensemble EMD analysis.

scales. The IMFs of each ensemble member are noisy but the final average IMFs are noisefree, since white noise cancels itself for a large number of ensemble members. Figure 5c presents the correct decomposition (using EEMD) of the signal in Fig. 5b. IMFs 1-3 include only the high frequency components while IMF5 contains the sinusoidal oscillation of the initial signal.
