March 2005, VOLUME 184
NUMBER 3_supplement

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Volume 184, Number 3_supplement

Chest Imaging

Case Report

Radiographic Appearance of a Catheter-Free Wireless Esophageal pH Probe

+ Affiliations:
1Division of Thoracic Imaging, Department of Radiology, Hospital of the University of Pennsylvania, 3400 Spruce St., 1 Silverstein, Philadelphia, PA 19104.

2Division of Gastroenterology, Hospital of the University of Pennsylvania, Philadelphia, PA 19104.

Citation: American Journal of Roentgenology. 2005;184: S40-S42. 10.2214/ajr.184.3_supplement.01840s40

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Catheter-based continuous esophageal pH monitoring has been a traditional means of detecting and diagnosing gastroesophageal reflux disease. However, many gastroenterologists have started to use a catheter-free, wireless pH monitoring system free of many limitations associated with traditional catheter-based monitoring. The wireless esophageal pH probe used in this system has a characteristic appearance on conventional radiography that, to our knowledge, has not been previously described. Familiarity with the appearance of these wireless pH probes is important, particularly during the radiographic evaluation of an atypical esophageal foreign body.

Case Report
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A 54-year-old man with chest pain presented to our department for a chest radiographic examination, which revealed a small, intricate metallic object in the retrocardiac region of the middle mediastinum on the lateral film (Figs. 1A and 1B). No other foreign body was identified. Initially, the appearance and location of the object led us to suspect that the patient had ingested a foreign body, possibly an earring, which was now lodged in the middle segment of the esophagus. After discussion with the referring physician, however, it was discovered that a catheter-free, wireless esophageal pH probe was present in the patient's esophagus, accounting for the finding on the chest radiographs.

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Fig. 1A. 54-year-old man with chest pain. Lateral chest radiograph reveals metallic object situated in retrocardiac region in middle mediastinum, probably within middle segment of esophagus.

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Fig. 1B. 54-year-old man with chest pain. Magnification of lateral chest radiograph reveals intricate metallic object with paired round objects at one end. A swallowed earring was initially suspected.

Discussion
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A number of tests exist for the detection and diagnosis of gastroesophageal reflux disease. Among these tests, prolonged (24 hr) ambulatory monitoring of esophageal pH is still considered the gold standard [1]. Traditionally, the lower esophageal sphincter (LES) region is first identified manometrically, and a thin nasogastric catheter containing precalibrated pH-sensitive antimony electrodes is advanced into the gastric lumen, with the primary reference electrode positioned 5 cm proximal to the upper border of the LES [2]. The pH-sensitive electrode within the catheter relays pH measurements at 4-sec intervals to an ambulatory recorder worn on the patient's belt or carried on a shoulder strap during normal daily activities. At the conclusion of the study, the catheter is removed and the data are uploaded into a computer for analysis.

A number of drawbacks exist with the traditional catheter-based method of continuous esophageal pH monitoring. Many patients find the catheter-based system uncomfortable and unappealing. In addition, because of the discomfort and social stigma associated with wearing the catheter for a prolonged period, patients often alter their normal daily activities, which results in false-negative testing up to 10% of the time. Other limitations inherent in the catheter-based pH monitoring system include the potential for catheter migration and probe displacement relative to the LES during respiratory excursion.

As a result, many gastroenterologists have begun to use a catheter-free, wireless pH monitoring system that recently received U.S. Food and Drug Administration approval (Bravo pH Measurement System, Medtronic). This system, available from only a single vendor, consists of a small, wireless probe (Fig. 2) attached to the esophageal mucosa (Fig. 3) by a small metallic retaining bar. The usual technique requires endoscopic visualization of the gastroesophageal junction with careful measurement of its distance from the incisors. The probe is then placed blindly 6 cm above the gastroesophageal junction using a transoral placement catheter. Deployment is achieved with suction that pulls esophageal mucosa into a small well on the side of the probe, after which the metallic retaining bar is triggered to pierce the suctioned tissue and the placement catheter is withdrawn. Most gastroenterologists reendoscope the patient to confirm an adequate attachment.

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Fig. 2. Wireless pH probe. pH sensor, small circuit board, two disk batteries, retaining bar, and antenna are encapsulated inside object not much longer than the width of a penny.

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Fig. 3. Endoscopic image within esophageal lumen. Wireless pH probe is attached to esophagus wall.

The wireless probe continuously transmits pH data to a pager-sized device worn on the patient's hip, and, because of better tolerability, studies of 48 hr in duration are now used to improve the accuracy of diagnosis [3]. The probe spontaneously detaches from the esophageal wall within 15 days and is eliminated via the gastrointestinal tract. Because no clinical or preclinical studies evaluating the effect of MRI on a wireless pH probe within the body exist, it is not known how serious or trivial this effect may be. The device's vendor generally instructs patients to not undergo MRI scanning for up to 1 month after placement. This provides a conservative amount of time for the probe to detach from the esophagus and pass through the digestive system. In an emergent situation requiring MRI within this 1-month window, the authors would consider scout radiographs of the chest, abdomen, and pelvis to document passage of the probe. Wireless ambulatory pH monitoring is contraindicated in individuals with implantable electronic devices because of concerns relating to electrical interference. They also cannot be placed in persons who previously have undergone bowel resections or have known bowel strictures because of the possibility of impaction after detachment. A small percentage of patients develop chest pain during monitoring, and occasionally a repeat upper endoscopy is required to manually detach the probe, which can either be removed transorally with a snare or left in the stomach to pass naturally.

The wireless probe is slightly longer than the width of a penny and encapsulates a pH sensor, small circuit board, two disk batteries, retaining bar, and antenna, resulting in a distinctive appearance on radiography (Figs. 4A, 4B, 4C). A linear radioopaque structure and two radiopaque discs are always visualized at one end of this object, corresponding to the probe's retaining bar and disk batteries. Intricate metal structures present in the remainder of this object on radiography correspond to the probe's small circuit board and antenna.

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Fig. 4A. Wireless pH probe. Wireless pH probe mounted on its delivery device.

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Fig. 4B. Wireless pH probe. Lateral fluoroscopic image of wireless pH probe mounted on its delivery device reveals appearance identical to object identified in lateral chest radiograph in Figs. 1A and 1B.

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Fig. 4C. Wireless pH probe. Frontal fluoroscopic image of wireless pH probe mounted on its delivery device shows another appearance wireless probe may have on radiography.

As wireless pH measurement systems become increasingly popular, familiarity with the appearance of wireless pH probes on radiography will be necessary, particularly when an atypical esophageal foreign body is encountered in an active thoracic imaging or general radiology practice.

Address correspondence to W. B. Gefter ().

We thank Robin Obelmejias for her help in acquiring the Bravo pH measurement probe used for this manuscript.

References
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1. Heidelbaugh JJ, Nostrant TT, Kim C, VanHarrison R. Management of gastroesophageal reflux disease. Am Fam Physician 2003; 68:1311-1318 [Google Scholar]
2. Carty H. pH probe. The encyclopedia of medical imaging, volume VII. Available at: www.amershamhealth.com/medcyclopaedia/Volume%20VII/PH%20PROBE.asp. Accessed February 6, 2004 [Google Scholar]
3. Pandolfino J, Richter JE, Ours T, Guardino JM, Chapman J, Kahrilas PJ. Ambulatory pH monitoring using a wireless system. Am J Gastroenterol 2003; 98:740-749 [Google Scholar]

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