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Functional MR Imaging versus Wada Test for Evaluation of Language Lateralization: Cost Analysis¹

¹ From the Division of Neuroradiology and Health Outcomes, Policy and Economics (HOPE) Center, Department of Radiology, Miami Children’s Hospital, 3100 SW 62 Ave, Miami, FL 33155 (L.S.M., E.A., B.B., N.R.A.). Received August 30, 2002; revision requested October 28; final revision received March 24, 2003; accepted May 8, 2003. Address correspondence to L.S.M. (e-mail: santiago.medina@mch.com).

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
PURPOSE: To compare the total direct costs (fixed and variable costs) of functional magnetic resonance (MR) imaging and of the Wada test for evaluation of language lateralization.

MATERIALS AND METHODS: The direct fixed and variable costs of functional MR imaging (performed in 21 patients with mean age ± SD of 15.5 years ± 8.9) and of the Wada test (performed in 18 patients aged 19.2 years ± 5.4) were determined prospectively with time and motion analyses. The labor of all personnel involved in evaluations of language lateralization was tracked, and involvement times were recorded to the nearest minute. All material items used in the studies were recorded. Costs of labor and of materials were determined from personnel reimbursement data and from vendor pricing, respectively. Direct fixed costs were determined from hospital accounting department records. Means (± SDs) were calculated for all direct fixed and variable costs. Total direct costs were determined for each procedure and compared by using the Student t test.

RESULTS: The total direct costs of the Wada test ($1,130.01 ± $138.40) and of functional MR imaging ($301.82 ± $10.65) were significantly different (P < .001). The cost of the Wada test was 3.7 times higher than that of functional MR imaging.

CONCLUSION: Substantial savings are achievable with the use of functional MR imaging instead of the Wada test to evaluate language lateralization.

© RSNA, 2004

Index terms: Brain, function • Cost-effectiveness • Electroencephalography (EEG), 10.122 • Magnetic resonance (MR), functional imaging, 10.12146

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
The localization of language-eloquent areas in the brain is important before surgery is performed for seizure disorders or neoplasm resection (1). The procedure most often used to assess language lateralization is the Wada test, which involves intracarotid injection of amobarbital sodium (1), conventional angiography performed with iodinated contrast material, and imaging with ionizing radiation—all of which incur risks to the patient. The Wada test also requires the participation of a large medical team with both an angiography component (radiologist, radiologic technologists and nurses) and a neuroscience component (neurologist or neurophysiologist, neuropsychologists, and electroencephalographic [EEG] technologists). The Wada procedure is time consuming: It usually involves 1–2 hours of testing and 4–6 hours of patient recovery time.

Functional magnetic resonance (MR) imaging, which does not require the use of exogenous contrast material or catheterization, is a noninvasive alternative method for evaluating language lateralization. Functional MR imaging is less time consuming than the Wada test: It usually requires 30–60 minutes of procedural time and no postprocedural recovery time. Many studies have been reported in which the results of functional MR imaging for language lateralization have been compared with those of the Wada test or electrocortical stimulation. These results are summarized in Table 1. Overall, excellent agreement has been found between the results obtained with these procedures (1–10).

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
The inclusion of patients in this prospective study was based on the following criteria: history of seizures, consideration for surgical treatment, and resultant need for evaluation of language lateralization. Between August 1995 and December 2000, 38 patients were recruited and evaluated with the Wada test or with functional MR imaging for language lateralization. A total of 39 evaluations were performed: Eighteen patients underwent the Wada test, and 21 underwent functional MR imaging. Twenty-nine patients were evaluated at Miami Children’s Hospital and nine were evaluated at Cincinnati Children’s Hospital Medical Center. The mean ages (± SDs) of the patients who underwent evaluation were 19.2 years ± 5.4 for the Wada test group and 15.5 years ± 8.9 for the functional MR imaging group (Table 2). In the Wada test group, nine patients were male (mean age, 19.4 years ± 5.3) and nine were female (mean age, 19 years ± 5.8). In the functional MR imaging group, 10 patients were male (mean age, 15.2 years ± 8.7) and 11 were female (mean age, 15.8 years ± 9.5).

Wada Test
A flowchart of the procedure used in the Wada test is shown in Figure 1. After the test was explained to the patient and guardian, the patient was transferred to the angiography suite and was positioned on the angiography table. Local skin analgesia was achieved with lidocaine 1% (Xylocaine 1%; AstraZeneca, Wilmington, Del), and no sedative or general anesthetic was administered. Standard sterile technique was applied throughout the study. The femoral artery was accessed, and selective catheter placement in the carotid artery was performed with fluoroscopic guidance. Anteroposterior and/or lateral images were acquired (Maximus M100, Philips Medical Systems, Best, the Netherlands; and Advantax DX, GE Medical Systems, Milwaukee, Wis) after intraarterial administration of a nonionic contrast material—either iohexol (Omnipaque 300; Nycomed, Princeton, NJ) or ioversol (Optiray 350; Mallinckrodt, St Louis, Mo)—at a dose of 1–3 mL per kilogram of body weight. Additional views were acquired at the discretion of the attending radiologist. Ten patients (56%) underwent single carotid angiography, and eight (44%) underwent bilateral carotid angiography.

View larger version (39K): [in this window] [in a new window] [Download PPT slide]   Figure 1. Flowchart of the Wada test procedure.

After the Wada test was completed, the EEG equipment was removed by the neuroscience team. At the same time, the catheter was removed and hemostasis was achieved by applying direct pressure to the puncture site. The mean duration (± SD) of the Wada procedure was 92 minutes ± 23. From entries in the departmental logbook, the mean daily use of the angiography suite was determined to be 8 hours.

Subsequently, the patient was transported to the recovery area and remained there for 4–6 hours until discharge by a radiologist. After the completion of the Wada test, the radiologist interpreted the angiograms and the neuroscience team interpreted the results of EEG and neuropsychologic tests. Interpretation time, including the time needed for notification of or discussion with the referring physician, was included in the analysis. Teaching time spent by the medical team was not included in the analysis.

Functional MR Imaging
A flowchart of the procedure used in functional MR imaging is shown in Figure 2. After the procedure was explained to the patient and guardian, the patient was positioned in a 1.5-T MR imager (LX MRI, GE Medical Systems) and the audiovisual system was tested. No sedative or general anesthetic was administered. Anatomic landmark images of the entire head were obtained with a three-dimensional spoiled gradient-recalled sequence. Functional MR imaging sequences based on the blood oxygenation level–dependent contrast effect and having the following parameters were applied: repetition time msec/echo time msec, 3,750/60; flip angle, 90°. Ten transverse sections were obtained, each with a thickness of 6 mm, with a gap of 2 mm between sections. In each functional MR imaging evaluation, images were obtained while the patient performed three language-related tasks that involved passive listening to a story, demonstration of semantic fluency, and verb generation. During the ON epoch, the patient listened to three story fragments, each of which lasted 30 seconds. In the test of semantic fluency, the patient had to think of as many nouns as possible in each of three categories (animals, vegetables, and fruits). In the verb generation task, the patient had to generate one or more verbs related to a list of nouns that was orally presented. The paradigm for each linguistic task included three ON and three OFF conditions distributed at 48 time points. The patient was briefly trained and tested with similar exercises before the procedure to ensure comprehension and good performance of the tasks. Subsequent image data were analyzed for motion, spatially smoothed, and signal normalized by using software (MEDx version 3.4.1; Sensor Systems, Sterling, Va). Parametric statistical (z-score) maps were obtained by using an unpaired Student t test. z-Score maps were registered and fused with the three-dimensional image volumes.

View larger version (29K): [in this window] [in a new window] [Download PPT slide]   Figure 2. Flowchart of functional MR imaging procedure.

Definition of Costs
Costs were categorized as direct or indirect. Direct costs were those directly associated with the performance of the examination and included fixed and variable costs (12), according to the system of classification used by the U.S. Panel on Cost Effectiveness in Health and Medicine (11) and by our medical centers’ cost accounting departments. Fixed costs were those that did not change with the procedure, such as costs of equipment purchase and depreciation (12). Variable costs were those that depended on the procedure, such as costs of labor (by physicians, nurses, and technologists) and supplies (eg, contrast material, catheters, guide wires, angiography tray, and media for image creation and storage) (12).

Indirect costs are those incurred independently of the procedure, including expenses for grounds (eg, walkways, parking areas, and landscaping) and general administration, human resources, utilities, housekeeping, general maintenance, and depreciation (15). Because indirect costs are incurred regardless of the procedure performed, they were excluded from the statistical analysis.

In this study, fixed direct costs included the costs of equipment purchase, depreciation, maintenance, and service. Variable direct costs included the costs of labor and materials directly attributable to the performance of the procedures. Cost analysis was performed from a medical center perspective. All costs were adjusted to year 2000 U.S. dollars.

Measurement of Costs
Fixed direct costs.—All fixed direct costs were determined from accounting records of the medical centers. The fixed direct costs of each patient examination were based on utilization calculations and on total costs incurred during the measurement period, as reported in the management departmental logbooks (12). Fixed costs of equipment were calculated on the basis of assumed 5-year linear depreciation, in accordance with guidelines of the American Hospital Association Health Data and Coding Standards Group (16).

Variable direct costs.—Variable direct costs were tracked by a technologist using a standardized form for all patients studied. All materials used during the procedures were recorded, and their costs were assigned on the basis of the actual prices paid by the medical center’s purchasing department.

Labor costs were measured with time and motion analysis. The amount of time spent by personnel involved in patient examinations and postprocedural care was recorded to the nearest minute and entered into the time and motion analysis model. Laborers included physicians, technologists, nurses, and assistants. For salaried workers, labor cost calculations were based on total annual compensation, including benefits and salary, divided by the estimated number of billable labor hours per year (15). The time spent by radiologists in image interpretation also was measured. All images were interpreted and reported by the attending radiologist or neuroscientist. Teaching time was not included as part of the analysis.

Statistical Analysis
Total direct costs were tabulated for each examination by two of the authors (L.S.M., E.A.) and classified as either fixed or variable costs (17). Variable direct costs were further subdivided into variable costs of labor, supplies, and contrast material. Table 3 shows the unit cost estimates used in the analysis.

	RESULTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
The direct fixed and variable costs of examination with the Wada test and with functional MR imaging are shown in Table 4 and Figure 3. The mean total direct cost of the Wada test was $1,130.01 ± $138.40 (95% CI: $1,066.07, $1,193.95), and the mean total direct cost of functional MR imaging was $301.82 ± $10.65 (95% CI: $297.27, $306.38). There was a statistically significant difference in mean total direct cost between the Wada test and functional MR imaging (P < .001). The mean total cost of the Wada test relative to that of functional MR imaging was 3.74 (95% CI: 3.30, 4.25).

View larger version (23K): [in this window] [in a new window] [Download PPT slide]   Figure 3. Bar graph shows direct (fixed and variable) costs of functional MR imaging versus the Wada test (P < .001).

The mean direct variable cost of the Wada test was $830.82 ± $105.83 (95% CI: $781.93, $879.71), and the mean direct variable cost of functional MR imaging was $176.99 ± $9.40 (95% CI: $172.97, $181.01). The mean variable cost of the Wada test relative to that of functional MR imaging was 4.7 (95% CI: 3.99, 5.52).

The cost of physician personnel (a subcategory of variable labor) for the Wada test was 2.99 (95% CI: 2.48, 3.60) times higher than that for functional MR imaging because of longer procedural time, the need for a neurologist or neurophysiologist to perform the EEG and neuropsychologic evaluation, and the need for a second radiologist or other staff member to assist the primary radiologist in performing the angiographic component of the Wada test. The cost of nonphysician medical personnel (a subcategory of variable labor) for the Wada test was 6.60 (95% CI: 4.43, 9.81) times higher than that for functional MR imaging because of longer procedural time, the need for EEG technologists and for nursing assistance during angiography and postprocedural recovery, and the extended use of the radiologic technologist. The cost of supplies for the Wada test was 163.62 (95% CI: 28.19, 949.51) times higher than that for functional MR imaging because of the angiographic tray, catheters, guide wires, intravascular contrast material, and EEG materials required for the Wada test.

Sensitivity Analyses
The results of sensitivity analysis of fixed costs per examination with functional MR imaging and with the Wada test at five different daily use levels are shown in Figure 4. Mean daily hours of operation of the angiography suite for the Wada test were 8, for a mean fixed cost of $299.19. When angiography suite hours of operation increased to 16, the fixed cost decreased to $179.00 and the total Wada test cost decreased to $1,009.82.

View larger version (20K): [in this window] [in a new window] [Download PPT slide]   Figure 4. Graph shows results of sensitivity analysis of fixed costs per examination with functional MR imaging and with the Wada test at five different daily use levels.

In summary, the results of the sensitivity analyses indicate that if the hours of operation were increased to 16 and if variable costs were decreased by using a registered nurse as radiology assistant, the fixed and variable costs of the Wada test would be $179.00 and $239.41, respectively. With the incorporation of these two changes into the calculations, the total direct cost of the Wada test decreases from a mean of $1,130.01 to $925.21.

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
The results of this study indicate that the cost of functional MR imaging for language lateralization is substantially lower than that of the Wada test. The Wada test incurs a higher total direct cost than does functional MR imaging because of higher fixed and variable costs. The higher fixed and variable costs of the Wada test in our study resulted from the higher cost per patient examination with the angiography suite and from the higher cost of labor (both physician and nonphysician) and supplies (ionic contrast media, angiographic tray and materials, and EEG supplies), respectively.

The mean physician labor cost of the Wada test relative to that of functional MR imaging was 2.99 (95% CI: 2.48, 3.60). This difference is attributable mainly to the increased physician labor required to perform the angiographic component (primary operator and assistant) and the neuropsychologic component (neurologist or neurophysiologist and neuropsychologist) of the Wada test.

The results of cost-effectiveness and cost-benefit analyses are published with increasing frequency in the medical literature, but the investigative methods used in many analyses of imaging modalities and procedures have not been sufficiently rigorous (21). We performed a cost-identification analysis in which equivalent outcomes of the diagnostic strategies were assumed for the evaluation of language lateralization (1). We chose to define costs from the perspective of the medical center (22,23) because managed health care and discounted fee for service have become the predominant models of health care expense reimbursement in the United States. With capitation, health care providers bear the burden of actual costs and have no possibility of reimbursement for expenses that exceed prepaid premiums (15). To maintain appropriate net revenue, health care providers must know the costs of each procedure (15). Our time and motion analyses of direct fixed and variable costs enabled rigorous quantification and eliminated the assumptions inherent in estimated cost measurement (24–27), charge-based analyses (28–32), analyses based on ratio of costs to charges (24,33–38), and relative value unit–based analyses (15,33,39,40).

Our results, however, may not be generalizable to all medical institutions and centers. First, the data used in this study were collected from two institutions rather than from multiple medical centers with different physician and patient constituencies. Furthermore, because all costs, particularly those of labor, are based on regional standards, the absolute costs reported in this study may diverge from absolute costs incurred in other regions. The relative costs, however, should be generalizable to most institutions in the United States (15).

In conclusion, the direct cost of assessment of language lateralization in our study was 3.74 times higher with the Wada test than with functional MR imaging. Given that functional MR imaging is noninvasive, does not require use of intravascular contrast material, and provides results that are in excellent agreement with those of the Wada test, the substantial cost reduction achieved with functional MR imaging should provide further justification for its use in language lateralization.

	ACKNOWLEDGMENTS

 
We are indebted to the radiologists, angiography and MR imaging technologists, nurses, assistants, and other personnel in the Department of Radiology and to the neurologists, neurophysiologists, neuropsychologists, and EEG technologists in the Department of Neurology at Miami Children’s Hospital and Cincinnati Children’s Hospital Medical Center. We are indebted also to Marelis Rodriguez and Milton Sanchez for their substantial help with manuscript and table preparation.

	FOOTNOTES

 
Abbreviation: EEG = electroencephalography

Author contributions: Guarantor of integrity of entire study, L.S.M.; study concepts and design, all authors; literature research, L.S.M., E.A., B.B.; clinical studies, L.S.M., E.A., B.B.; data acquisition and analysis/interpretation, L.S.M., E.A., B.B.; statistical analysis, L.S.M., E.A.; manuscript preparation, L.S.M., E.A.; manuscript definition of intellectual content, editing, and revision/review, all authors; manuscript final version approval, L.S.M., N.R.A.

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This Article Abstract Figures Only Full Text (PDF) Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Medina, L. S. Articles by Altman, N. R. Search for Related Content PubMed PubMed Citation Articles by Medina, L. S. Articles by Altman, N. R.