# Application of Wavelet Transform and Fractal Analysis for
### GERD Diagnostics with MII-pH Measurement  
The diagnosis of gastroesophageal reflux disease can be carried out using invasive methods (such as 24-h pH-metry with/without impedance, esophageal endoscopy, esophageal manometry, balloon mucosal impedance, or double-contrast radiography) and non-invasive methods (real-time MRI, IPP test, or swallowing sound analysis) [2; 15; 16; 17; 18; 19]. There are even attempts to combine traditional pH-metry with other diagnostic techniques, such as the simultaneous measurement of pH in the esophagus and larynx [20; 21]. According to current guidelines, the gold standard among invasive diagnostic methods for GERD is MII-pH (multichannel intraluminal impedance-pH). Numerous studies have shown that this method has a number of advantages over other methods, which translates into high effectiveness in diagnosing GERD [2; 15; 22; 23; 24; 25; 26; 27; 28; 29], and thus, this method proves to be one of the most informative tests that could be performed in patients with suspected GERD, particularly in those patients with atypical symptoms, or to assess the response to therapy. A particular advantage of this method is also the possibility of using it in both adults and children (including infants) [30]. However, the method has its limitations--the difficulty in interpreting the test results requires the assessment of a specialist with extensive experience. Another limitation is the price of the MII-pH apparatus: not every diagnostic centre is able to purchase this equipment, which makes it necessary to use other, less effective, diagnostic methods. This is seen especially in the less prosperous parts of countries that are particularly in need of a good GERD diagnosis. Therefore, taking this into account, further research is focused solely on the pH monitoring method only. Thanks to this approach, the test results can be applied to more common devices, which increases the probability of detecting GERD in a wider population. With the use of esophageal 24-h pH-metry, the gastroenterologist can determine the pH of the contents inside the esophageal lumen. With the standard 24-h pH-metry alone, the patient had one or two pH probes attached to the esophageal wall (one near the lower esophageal sphincter and, if there was a need for a second probe, one near the pharynx). The research shows that stomach content that has a pH value lower than 4 is harmful to the tissues of the esophagus. The test is performed during a 24-h period, in which the pH data are measured and stored on a special device/Holter. The patient is encouraged to act casually, as if he was performing his normal daily routine. After the exam is over the gastroenterologist has to read the pH course and determine whether the pattern is physiological or pathological. The analysis of the pH courses involves using a method described by [PERSON] [7; 31]. It allows the more or less objective description of each pH course and the reduction of the analysis to numbers, which can be then compared to the standards for a healthy/sick patient. Therefore, the specialist must find the parameters which are characteristic to GERD, which are shown in Table 1, and sum them up to calculate the total DeMeester count. Subsequently, this value is then compared with a reference value of 14.71. If the value of the total DeMeester count is higher than the above-mentioned reference value, then the patient is diagnosed as sick. Using the DeMeester method has major advantages. Every pH course can be assessed in the same way and can therefore be compared objectively, no matter what measuring device was used. Moreover, modern pH analysis programs calculate this value automatically; so, the physician can only glance through the pH course and confirm or reject the calculation, based on his own experience. Unfortunately, pH-metry has its limitations--the method only allows the detection of pH changes in the esophagus and gives no information about the state of the content passing through the esophagus (whether it is solid, liquid, or gas).