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Navigational Bronchoscopy: Overview of Technology and Practical Considerations—New Current Procedural Terminology Codes Effective 2010 FREE TO VIEW

Eric Edell, MD, FCCP; Diane Krier-Morrow, MBA, MPH, CCS-P
Author and Funding Information

From the Department of Pulmonary and Critical Care Medicine (Dr Edell), Mayo Clinic, Rochester, MN; and Diane Krier-Morrow and Associates, Inc. (Ms Krier-Morrow), Evanston, IL.

Correspondence to: Eric S. Edell, MD, FCCP, Mayo Clinic, 20 First Street Southwest, Gonda 18S, Rochester, MN 55905; e-mail: edell.eric@mayo.edu


Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal.org/site/misc/reprints.xhtml).


© 2010 American College of Chest Physicians


Chest. 2010;137(2):450-454. doi:10.1378/chest.09-2003
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Navigational bronchoscopy provides a three-dimensional virtual “roadmap” that enables a physician to maneuver through multiple branches of the bronchial tree to reach targeted lesions in distal regions of the lung. It is designed to be used with a standard bronchoscope to facilitate obtaining tissue samples and for placing radiosurgical or dye markers. This article overviews this technology and the Current Procedural Terminology codes that have been created for its use.

Lung nodules are common in clinical practice and can be challenging to manage. The identification of malignant nodules is important because they represent a potentially curable form of lung cancer. Evidence-based clinical practice guidelines have been developed for management of the solitary pulmonary nodule.1 These guidelines conclude that patients with solitary pulmonary nodules “should be evaluated by review of old films, estimation of the probability of malignancy, performance of imaging tests to characterize the nodule better, evaluation of the risks associated with various management alternatives, and elicitation of patient preferences for treatment.”

The first step in the management of suspected lung lesion is often “watchful waiting,” which involves a course of repeat CT scans over 2 years. There are situations in which this strategy may not be appropriate.

Bronchoscopic lung biopsy is a minimally invasive and common method for obtaining biopsies. Its diagnostic yield ranges from 19% to 86%, depending on lesion size and location.25 Bronchoscopic lung biopsy is unreliable in biopsies of small peripheral lesions. A diagnostic yield of 14% has been reported for peripheral lesions ≤ 2 cm.2

Another option is transthoracic needle aspiration (TTNA), or CT-guided fine-needle aspiration. The reports of diagnostic yield for CT-guided fine-needle aspiration vary from 36% to 84%.1 The greatest disadvantage of TTNA is pneumothorax, which occurs in 30% to 50% of procedures.2,4,6 The risk of pneumothorax is directly related to lesion size, distance from the pleura, number of passes, and patient’s condition (ie, emphysema).7,8 Thus, TTNA may not be an option for patients with compromised lung function or for patients with a lesion that is unreachable.

The final option is surgical resection. This may be an appropriate option if the pretest probability of malignancy is high and the patient is a surgical candidate. Nontherapeutic surgical biopsies have been reported to be between 20% and 49%, meaning many patients with benign nodules have been subjected to an invasive surgical biopsy procedure.9

Because of the limitations of the above-described approaches, there is need for a procedure that will offer a minimally invasive approach to reach peripheral areas of lung currently inaccessible by standard bronchoscopy. Being able to obtain diagnostic specimens from lesions in the periphery of the lung via bronchoscopy could prevent the occurrence of complications associated with more invasive methods and possibly reduce the number of surgical interventions on benign lesions.

Navigational systems, including the electromagnetic navigation bronchoscopy (ENB) system (inReach System; superDimension Inc.; Minneapolis, MN), appear to meet the above-stated needs. These minimally invasive technologies enable navigation to distal regions of the lungs and enable physicians to perform biopsy of suspicious lesions.

ENB was cleared by the US Food and Drug Administration in 2008 to “display images of the tracheobronchial tree to aid the physician in guiding endoscopic tools or catheters in the pulmonary tract and to enable marker placement within soft lung tissue. It does not make a diagnosis and is not an endoscopic tool.” The ENB procedure can be performed under moderate (conscious) sedation and uses three technologies:

  •  Planning software that converts DICOM images from a CT scan into three-dimensional reconstruction and virtual bronchoscopy of the airways;

  •  Steerable sensor probe designed with the ability to navigate turns in the endobronchial tree; and

  •  Electromagnetic navigation board, a field generator connected to a computer containing the planning data.

Planning

The physician loads the previously acquired chest CT scans of the lungs into the planning laptop. Navigational bronchoscopy software generates a three-dimensional image of the patient’s chest. Critical anatomic landmarks are identified in the intrathoracic airways using the virtual image of the patient’s lung anatomy (eg, main carina, left and right upper lobe carina, and so forth) and marked as “registration points.” The virtual and CT images are used to plan the guide catheter (extended working channel) and the steerable navigation catheter (locatable guide) pathway through the tracheobronchial tree to the lesion(s). The lesions of interest are marked to identify the target center. The patient’s virtual plan is saved and exported to a flash drive.

Navigation

The patient’s navigational plan is downloaded into the navigational computer. A standard adult therapeutic flexible video bronchoscope is introduced, and an airway examination is performed. The ENB steerable navigation catheter (locatable guide [LG]) and the guide catheter (extended working channel catheter [EWC]) are placed through the working channel of the conventional bronchoscope.

Once registration is complete, the ENB System software is switched to navigation mode. Using the patient’s CT images, the LG navigates toward the target lesion via three perpendicular views, achieving a three-dimensional effect. The system displays an additional view, which provides steering directions. From this point on, the real-time location of the tip of the LG is displayed graphically onto the CT images as the physician guides the tip toward the target lesion. The effects of the patient’s movements are compensated by way of reference sensors placed on the patient’s chest.

When the LG reaches the target, the EWC catheter is locked in place and the LG is retracted. At this point, navigation is complete and any standard endoscopic tool is inserted through the EWC to obtain a tissue sample. Brushings (report Current Procedural Terminology [CPT] code 31623), transbronchial lung biopsies (report CPT code 31628), or transbronchial needle aspirations (report CPT code 31629) of the target lesions are performed.

Placement of Fiducial Markers

ENB technology can also be used to place fiducial markers within the lung parenchyma to guide stereotactic radiotherapy. The bronchoscopist navigates to the desired target tumor(s) as described above. Radiopaque markers are placed to guide external beam radiation or dye markers are placed to guide video-assisted thoracoscopic surgery.

A number of clinical studies have been conducted and reported in peer-reviewed journals, assessing effectiveness and safety parameters associated with the ENB system. The studies include diagnostic yield, navigational accuracy, procedure time, pneumothorax rate, and other characteristics. The following summarized clinical data include the experience of using the ENB system on a total of about 600 patients.

ENB System for the Diagnosis of Lung Lesions

The first study was published by Becker at al.10 Twenty-nine patients with peripheral lung lesions located were enrolled. The size of the lesions ranged from 1.2 to 10.6 cm. They achieved a diagnostic yield of 69% (20/29), with 25% (5/20) having confirmed benign lesions. On average, the ENB procedure added 12.3 min to the total procedure time. One biopsy-related pneumothorax (3.4%) and three occurrences of minor bleeding were reported.

Gildea et al2 enrolled patients (n = 56) unsuitable for CT-guided biopsy or standard bronchoscopy. The average size of the lesion was 2.28 cm (SD = 1.26). The lesions’ diagnostic yield was shown to be 74% (40/54) and independent of lesion size. For lesions < 2 cm the yield was 66.6%. The procedure added on average 10 min to the total bronchoscopy time of 51 min. Two patients suffered pneumothorax (3.5%; 2/56). No device-related adverse events were reported.

Eberhardt et al3 conducted a multicenter prospective, randomized, controlled trial of 118 patients. Randomization was to one of three study arms: endobronchial ultrasound (EBUS) (n = 39), ENB (n = 39), or EBUS combined with ENB system (n = 40). In the third group (EBUS and ENB), navigation to the lesion was first performed via the ENB system. When the lesion was located, the ENB sensor probe was removed and the EBUS probe was inserted to confirm visualization of the target. The overall diagnostic yield rate via bronchoscopic biopsy was 72% (85/118). There was no difference between EBUS-only (69%; 27/39) vs ENB-only (59%; 23/39). The diagnostic yield of combined EBUS with ENB was 88% (35/40). This was significantly better than either EBUS or ENB alone. The mean overall lesion size was 2.6 cm; ENB-only mean size 2.8 cm, EBUS-only mean size 2.5 cm, and EBUS with ENB mean size 2.4. Benign lesions were confirmed in 69% (59/85) of the biopsies. Surgical biopsy (ie, nondiagnostic rate) was required in 28% (33/118) of patients.

In a second study by the same authors the ENB yield, obtained from 89 patients with 92 peripheral lung lesions, was 67% (62/92).11 The mean lesion size was 2.4 cm, and diagnostic yields were independent of lesion size. The pneumothorax rate was 2.2% (2/89).

In a retrospective analysis the ENB diagnostic yield showed comparable results. Wilson and Bartlett12 conducted a single-center, retrospective study of 248 patients, with 279 peripheral lung lesions to measure ENB diagnostic yield per patient on the day of the procedure. All procedures were done in conjunction with rapid on-site cytology evaluation. The majority of the lesions (51%) were located in the upper lobes. The mean lesion size was 2.1 cm (SD = 1.4). The system reached 95% of the lesions and the overall yield rate was 65% on the day of procedure (161/248). The limitation of this study is that not all inconclusive cases were further confirmed by additional diagnostic procedures, and thus it was difficult to establish the exact final diagnostic yield, which ranged from 70% to 97% with an average of 86%. Pneumothorax occurred in three patients (1.2%) with an overall complication rate of 3.2% (8/248).

ENB System for Placement of Fiducial Markers

Kupelian et al6 performed a study describing 23 cases of marker placement. Fifteen patients had fiducial markers placed transcutaneously under CT or fluoroscopy guidance, and eight patients had markers placed via ENB guidance. The mean lesion size was 2.6 cm, and at least one marker was successfully placed in all patients. Markers were stable throughout treatment regardless of the implantation technique. The pneumothorax rate in patients who underwent transcutaneous marker placement was 53% (8/15). None of the patients who received markers via ENB guidance suffered a pneumothorax.

Anantham et al13 conducted an open-label feasibility study of nine patients with peripheral lung lesions to assess fiducial marker placement using the ENB system. A successful procedure was defined as at least three fiducial markers placed close enough to the lesion center to proceed with stereotactic radiosurgery. A procedure failure was defined as a need for alternative or additional marker placement. Mean lesion size was 3.6 cm. Thirty-nine fiducial markers (mean of 4.9 markers placed per patient) were successfully placed in 89% (8/9) of patients. The mean procedure time was 26.9 min. Ninety percent (35/39) of markers remained stable 1 week after placement. No pneumothoraces were reported, compared with an historical pneumothorax rate of 13% in fiducial markers placed via a transthoracic approach.14

Practical Consideration, Costs, and Coverage

The list price of the ENB system is $150,000 or more with varying other charges. As a new technology, ENB was reported with unlisted codes prior to 2010. CPT 76499 “unlisted diagnostic radiographic procedure” was for the planning phase, a bronchoscopy code (31622-31633, 31641, 31643) for the surgical intervention, and an unlisted code 31899 (“unlisted procedure of the bronchi or trachea”) for the navigation phase. For the placement of radiosurgical markers, an unlisted procedure code for lungs and pleura, CPT code 32999, was reported along with both CPT codes 76499 (planning) and 31899 (navigation).

For Medicare Part B coverage, Noridian was the first Medicare contractor to write coverage policy for ENB. If the procedure is performed in the office, place of service (POS 11) should be reported. Fiducial markers and the disposable probe will be paid for separately. If it is performed in a facility (ie, outpatient hospital) the fiducials and probe are not separately paid. National Government Services released a Local Coverage Determination for ENB, and coverage bulletins posted for Trailblazer and Palmetto GBA.

The New 2010 CPT Codes

The three phases of navigational bronchoscopy—planning, navigation and fiducial markers placement—are captured in two new CPT codes for use on January 1, 201015:

CPT 31626 bronchoscopy, rigid or flexible, including fluoroscopic guidance, when performed; with placement of fiducial markers, single or multiple. (Report supply of device separately.) CPT 31626 is a stand-alone code that includes the 31622 base bronchoscopy code.

CPT 31627 with computer-assisted, image-guided navigation. (List separately in addition to code for primary procedure[s].) CPT 31627 includes three-dimensional reconstruction. Do not report 31627 in conjunction with 76376, 76377. (Use 31627 in conjunction with 31615, 31622-31631, 31635, 31636, 31638-31643.) CPT 31627, an add-on code, is for the planning and navigation phases of navigational bronchoscopy.

Additional bronchoscopy codes may also be reported in varying combinations on the same patient, same session, same day. CPT codes 31622 to 31643 include fluoroscopic guidance, when performed. In addition, 31620 EBUS may be used to sample another area as a guidance tool to assist in the placement of fiducial markers and also can be reported with any of the bronchoscopy codes, including these two new codes. All CPT codes are reported with appropriate International Classification of Diseases, 9th ed., diagnosis codes, such as malignant bronchial neoplasm codes 162.2 through 162.9.

The procedures reported with these codes are typically performed in hospital outpatient departments or ambulatory surgical centers (Table 1). If an evaluation and management (E/M) service is provided on the same day as a bronchoscopy code, it is imperative to append a modifier 25 to the E/M code, which indicates that a separately identifiable service was provided on the same calendar day by the same physician providing the bronchoscopic procedure. It is important to write a separate note for E/M documentation to support the level of E/M code reported. If the 25 modifier is not applied to the E/M service, only the visit or the procedure will be reimbursed.

Table Graphic Jump Location
Table 1 —Procedure Codes

CPT = current procedural terminology; RVU = relative value unit.

Other Navigational Systems are or have been developed and will use these new CPT codes.16 These systems may or may not involve the use of a proprietary catheter. If there is a separate Healthcare Common Procedure Coding System (HCPCS) code for the catheter, the work of planning and execution of the navigational bronchoscopy is similar. However, if the catheter is bundled into the practice expense of the code (as in the 2010 Medicare Fee Schedule, for example), the physician in the office setting would at least need to use a reduced services modifier 52 for the new virtual technique to reflect the lower direct practice expense. In the facility setting, where the physician payment does not include the direct practice expense, the CPT 31627 code would apply.

Multiple Endoscopy Rule

CPT code 31626 is just like other bronchoscopy 0-day global period codes that can be billed together with the multiple endoscopy rule being applied during claims processing. Under this rule, total bronchoscopy reimbursement for physicians is calculated as the full reimbursement for the most complex bronchoscopic procedure (highest relative value) and the sum of the differences in reimbursement between each of the less complex codes and the base bronchoscopy code for a single patient. Simply, the multiple endoscopy rule means that other than the first reported highest relative value unit (RVU) bronchoscopy code reported (eg, 31628 or 31629), each additional bronchoscopy code reported has 3.92 total facility RVUs subtracted when performed in a hospital outpatient or ambulatory surgical center setting.17

The multiple endoscopy rule does not affect ZZZ add-on codes. Therefore, CPT 31620 and 31627 are paid in full when reported and documented appropriately with other bronchoscopy codes.

The multiple procedure rule (modifier 51) does not apply to endoscopy/bronchoscopy procedures. Modifier 51 should not be appended to bronchoscopy codes unless instructed to do so by a third-party insurance carrier. Additional information is published in chapter 9 of the Coding for Chest Medicine 2010 book, which is updated annually and available at www.chestnet.org.

This article provides an overview of the technology and the new CPT codes to report for navigational bronchoscopy. The technology has potential to improve the diagnostic yield of transbronchial biopsies, and may be useful in the early diagnosis of lung cancer. In review of the literature, the ENB system is safe with an average pneumothorax rate of <3%. It appears effective in a specific patient cohort, that is, those patients in whom lesion size and location (peripheral lung lesions) are beyond the usefulness of conventional flexible bronchoscopy, patients who are not surgical candidates or who are not medically suitable for more invasive methods (eg, TTNA or surgery) because of clinical presentation and comorbidities, and patients for whom previous methods were nondiagnostic. Unfortunately there are no studies comparing ENB directly to conventional techniques and published data represent selected case series. Without this comparative data we are unable to estimate the overall impact of this new technology.

To summarize how to report navigational bronchoscopy, the proceduralists would report all appropriate bronchoscopy codes performed. For example, CPT 31628, 31627, the add-on code for the planning and navigation phases, and if fiducial markers are placed, CPT 31626 would be reported as a stand-alone code, which includes relative values for the base bronchoscopy procedure, 31622. Any additional bronchoscopy procedures provided would be reported in addition to that. The multiple endoscopy rule would apply for reimbursement of these procedures.

Financial/nonfinancial disclosures: The authors have reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Other contributions: Physician’s Current Procedural Terminology (CPT) codes, descriptions, and numeric modifiers are copyrighted by the American Medical Association. All rights reserved.

CPT

current procedural terminology

EBUS

endobronchial ultrasound

E/M

evaluation and management

ENB

electromagnetic navigation bronchoscopy

EWC

extended working channel catheter

LG

locatable guide

RVU

relative value unit

TTNA

transthoracic needle aspiration

Gould MK, Fletcher J, Iannettoni MD, et al. American College of Chest Physicians Evaluation of patients with pulmonary nodules: when is it lung cancer? ACCP evidence-based clinical practice guidelines (2nd edition). Chest. 2007;1323suppl:108S-130S. [CrossRef] [PubMed]
 
Gildea TR, Mazzone PJ, Karnak D, Meziane M, Mehta AC. Electromagnetic navigation diagnostic bronchoscopy: a prospective study. Am J Respir Crit Care Med. 2006;1749:982-989. [CrossRef] [PubMed]
 
Eberhardt R, Anantham D, Ernst A, Feller-Kopman D, Herth F. Multimodality bronchoscopic diagnosis of peripheral lung lesions: a randomized controlled trial. Am J Respir Crit Care Med. 2007;1761:36-41. [CrossRef] [PubMed]
 
Makris D, Scherpereel A, Leroy S, et al. Electromagnetic navigation diagnostic bronchoscopy for small peripheral lung lesions. Eur Respir J. 2007;296:1187-1192. [CrossRef] [PubMed]
 
Shulman L, Ost D. Advances in bronchoscopic diagnosis of lung cancer. Curr Opin Pulm Med. 2007;134:271-277. [CrossRef] [PubMed]
 
Kupelian PA, Forbes A, Willoughby TR, et al. Implantation and stability of metallic fiducials within pulmonary lesions. Int J Radiat Oncol Biol Phys. 2007;693:777-785. [CrossRef] [PubMed]
 
Cox JE, Chiles C, McManus CM, Aquino SL, Choplin RH. Transthoracic needle aspiration biopsy: variables that affect risk of pneumothorax. Radiology. 1999;2121:165-168. [PubMed]
 
Baaklini WA, Reinoso MA, Gorin AB, Sharafkaneh A, Manian P. Diagnostic yield of fiberoptic bronchoscopy in evaluating solitary pulmonary nodules. Chest. 2000;1174:1049-1054. [CrossRef] [PubMed]
 
Bernard A. The Thorax Group Resection of pulmonary nodules using video-assisted thoracic surgery. Ann Thorac Surg. 1996;611:202-205. [CrossRef] [PubMed]
 
Becker HD, Herth F, Ernst A, et al. Bronchoscopic biopsy of peripheral lung lesions under electromagnetic guidance: a pilot study. Journal of Bronchoogyl. 2005;121:9-13. [CrossRef]
 
Eberhardt R, Anantham D, Herth F, Feller-Kopman D, Ernst A. Electromagnetic navigation diagnostic bronchoscopy in peripheral lung lesions. Chest. 2007;1316:1800-1805. [CrossRef] [PubMed]
 
Wilson DS, Bartlett RJ. Improved diagnostic yield of bronchoscopy in a community practice: combination of electromagnetic navigation system and rapid on-site evaluation. Journal of Bronchology. 2007;144:227-232. [CrossRef]
 
Anantham D, Feller-Kopman D, Shanmugham LN, et al. Electromagnetic navigation bronchoscopy-guided fiducial placement for robotic stereotactic radiosurgery of lung tumors: a feasibility study. Chest. 2007;1323:930-935. [CrossRef] [PubMed]
 
Whyte RI, Crownover R, Murphy MJ, et al. Stereotactic radiosurgery for lung tumors: preliminary report of a phase I trial. Ann Thorac Surg. 2003;754:1097-1101. [CrossRef] [PubMed]
 
 Current Procedural Terminology CPT 2010 Changes: An Insider’s View. 2009; Chicago American Medical Association
 
Merritt SA, Gibbs JD, Yu KC, et al. Image-guided bronchoscopy for peripheral lung lesions: a phantom study. Chest. 2008;1345:1017-1026. [CrossRef] [PubMed]
 
Manaker S, Krier-Morrow D, Pohlig C. Northbrook: American College of Chest Physicians; Coding for Chest Medicine 2010. 2009;14th edChapter 9
 

Figures

Tables

Table Graphic Jump Location
Table 1 —Procedure Codes

CPT = current procedural terminology; RVU = relative value unit.

References

Gould MK, Fletcher J, Iannettoni MD, et al. American College of Chest Physicians Evaluation of patients with pulmonary nodules: when is it lung cancer? ACCP evidence-based clinical practice guidelines (2nd edition). Chest. 2007;1323suppl:108S-130S. [CrossRef] [PubMed]
 
Gildea TR, Mazzone PJ, Karnak D, Meziane M, Mehta AC. Electromagnetic navigation diagnostic bronchoscopy: a prospective study. Am J Respir Crit Care Med. 2006;1749:982-989. [CrossRef] [PubMed]
 
Eberhardt R, Anantham D, Ernst A, Feller-Kopman D, Herth F. Multimodality bronchoscopic diagnosis of peripheral lung lesions: a randomized controlled trial. Am J Respir Crit Care Med. 2007;1761:36-41. [CrossRef] [PubMed]
 
Makris D, Scherpereel A, Leroy S, et al. Electromagnetic navigation diagnostic bronchoscopy for small peripheral lung lesions. Eur Respir J. 2007;296:1187-1192. [CrossRef] [PubMed]
 
Shulman L, Ost D. Advances in bronchoscopic diagnosis of lung cancer. Curr Opin Pulm Med. 2007;134:271-277. [CrossRef] [PubMed]
 
Kupelian PA, Forbes A, Willoughby TR, et al. Implantation and stability of metallic fiducials within pulmonary lesions. Int J Radiat Oncol Biol Phys. 2007;693:777-785. [CrossRef] [PubMed]
 
Cox JE, Chiles C, McManus CM, Aquino SL, Choplin RH. Transthoracic needle aspiration biopsy: variables that affect risk of pneumothorax. Radiology. 1999;2121:165-168. [PubMed]
 
Baaklini WA, Reinoso MA, Gorin AB, Sharafkaneh A, Manian P. Diagnostic yield of fiberoptic bronchoscopy in evaluating solitary pulmonary nodules. Chest. 2000;1174:1049-1054. [CrossRef] [PubMed]
 
Bernard A. The Thorax Group Resection of pulmonary nodules using video-assisted thoracic surgery. Ann Thorac Surg. 1996;611:202-205. [CrossRef] [PubMed]
 
Becker HD, Herth F, Ernst A, et al. Bronchoscopic biopsy of peripheral lung lesions under electromagnetic guidance: a pilot study. Journal of Bronchoogyl. 2005;121:9-13. [CrossRef]
 
Eberhardt R, Anantham D, Herth F, Feller-Kopman D, Ernst A. Electromagnetic navigation diagnostic bronchoscopy in peripheral lung lesions. Chest. 2007;1316:1800-1805. [CrossRef] [PubMed]
 
Wilson DS, Bartlett RJ. Improved diagnostic yield of bronchoscopy in a community practice: combination of electromagnetic navigation system and rapid on-site evaluation. Journal of Bronchology. 2007;144:227-232. [CrossRef]
 
Anantham D, Feller-Kopman D, Shanmugham LN, et al. Electromagnetic navigation bronchoscopy-guided fiducial placement for robotic stereotactic radiosurgery of lung tumors: a feasibility study. Chest. 2007;1323:930-935. [CrossRef] [PubMed]
 
Whyte RI, Crownover R, Murphy MJ, et al. Stereotactic radiosurgery for lung tumors: preliminary report of a phase I trial. Ann Thorac Surg. 2003;754:1097-1101. [CrossRef] [PubMed]
 
 Current Procedural Terminology CPT 2010 Changes: An Insider’s View. 2009; Chicago American Medical Association
 
Merritt SA, Gibbs JD, Yu KC, et al. Image-guided bronchoscopy for peripheral lung lesions: a phantom study. Chest. 2008;1345:1017-1026. [CrossRef] [PubMed]
 
Manaker S, Krier-Morrow D, Pohlig C. Northbrook: American College of Chest Physicians; Coding for Chest Medicine 2010. 2009;14th edChapter 9
 
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