AJR 2005; 184:S40-S42
© American Roentgen Ray Society
Radiographic Appearance of a Catheter-Free Wireless Esophageal pH Probe
Charles T. Lau1,
Warren B. Gefter1 and
David C. Metz2
1 Division of Thoracic Imaging, Department of Radiology, Hospital of the
University of Pennsylvania, 3400 Spruce St., 1 Silverstein, Philadelphia, PA
19104.
2 Division of Gastroenterology, Hospital of the University of Pennsylvania,
Philadelphia, PA 19104.
Received March 5, 2004;
accepted after revision May 13, 2004.
Address correspondence to W. B. Gefter
(gefter{at}rad.upenn.edu).
Introduction
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
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. 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.
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Discussion
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.
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.
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.
Acknowledgments
We thank Robin Obelmejias for her help in acquiring the Bravo pH
measurement probe used for this manuscript.
References
- Heidelbaugh JJ, Nostrant TT, Kim C, VanHarrison R. Management of
gastroesophageal reflux disease. Am Fam Physician2003; 68:1311
-1318[Medline]
- 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
- 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[Medline]
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Introduction
Case Report
