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Effect of Obesity on Image Quality: Fifteen-year Longitudinal Study for Evaluation of Dictated Radiology Reports¹

¹ From the Department of Radiology, Division of Abdominal Imaging and Interventional Radiology, Massachusetts General Hospital, Harvard Medical School, 55 Fruit St; White 270, Boston, MA 02114 (R.N.U., D.V.S., P.F.H., P.R.M.); and Department of Radiology, Emory Healthcare, Emory University School of Medicine, Atlanta, Ga (M.K.K., S.S.S.). Received July 1, 2005; revision requested August 26; revision received October 7; final version accepted November 4. Address correspondence to R.N.U. (e-mail: ruppot{at}partners.org).

	ABSTRACT

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Purpose: To retrospectively assess the effect of obesity on image quality, as determined from dictated radiology reports filed between 1989 and 2003.

Materials and Methods: Institutional review board approval was obtained for this HIPAA-compliant study; informed consent was not required. Electronic records were searched for radiology reports with the phrase "limited due to body habitus" (hereafter, "habitus limited") filed between 1989 and 2003; reports were retrospectively reviewed. Habitus limited was qualified as the search phrase by auditing radiologic images and patient weights. Trends in the number of habitus-limited reports were calculated for each year, and linear regression analysis was performed. The number of habitus-limited reports was also compared between modalities within a year and within each modality across 15 years. The trend was correlated with the prevalence of obesity in Massachusetts by using the Pearson correlation coefficient.

Results: There was a significant difference (P < .001) between the weight of patients with habitus-limited reports and the weight of patients with reports that were not habitus limited. Overall, 7778 (0.15%) of 5 253 014 reports were habitus limited. Between 1989 and 2003, there was a linear increase of 0.010% per year (95% confidence interval: 0.007%, 0.013%; P < .001). There was a positive correlation between the increased number of habitus-limited reports and the increased prevalence of obese individuals in Massachusetts between 1991 and 2001. The modality most commonly associated with habitus-limited reports was abdominal ultrasonography.

Conclusion: There was a small but progressive increase in the number of habitus-limited radiology reports between 1989 and 2003.

© RSNA, 2006

	INTRODUCTION

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Obesity is a growing health problem in the United States. An estimated 64.5% of Americans older than 20 years are overweight, obese, or morbidly obese according to body mass index measurements (1). Obesity directly affects health and health care, with an increased incidence of diabetes, cardiovascular disease, and cancer in obese individuals (1).

There is a growing awareness of the indirect effects of obesity on health care. An article in the Wall Street Journal (2) described the strain that obese patients place on hospitals. Hospitals now require larger wheelchairs and beds, and standard operating tables and imaging equipment are not suited for large patients.

Obesity also affects medical imaging. Members of radiology departments are responsible for transporting obese patients to the imaging department, accommodating them on imaging equipment, and obtaining diagnostic-quality images despite a patient's size. Difficulties in obtaining diagnostic-quality images in obese patients have been documented for various modalities, including chest computed tomography (CT) for evaluation of pulmonary embolism (3), mammography (4), and combined positron emission tomography and CT (5).

The purpose of our study was to retrospectively assess the effect of obesity on image quality, as determined from dictated radiology reports filed between 1989 and 2003.

	MATERIALS AND METHODS

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Database Search and Audit
When radiologists are faced with images of limited quality due to factors related to a patient's habitus, they often qualify their reports with the phrase "These images are limited due to body habitus." The consistent use of the terms limited and habitus (hereafter, habitus limited) by radiologists in their dictated reports has allowed us to assess the longitudinal effect of obesity on image quality. A retrospective review of dictated radiology reports that included the phrase "habitus limited" and that were filed over 15 years was performed with use of electronic medical records.

The Massachusetts General Hospital Partners Human Research Committee approved this study and did not require informed consent to be obtained from patients. Our study complied with the Health Insurance Portability and Accountability Act.

A preliminary audit (R.N.U., P.F.H.) was performed with various terms, including unsatisfactory, incomplete, habitus, and limited, to identify which terms were best suited for use in the identification of reports in which obesity affected image quality. Thereafter, all dictated reports filed between 1989 and 2003 and identified in the electronic databases of the radiology department of Massachusetts General Hospital were searched (R.N.U.) for concurrent use of the terms habitus and limited. This search was performed with an electronic database search engine (Folio Views for Windows, version 4.2; Open Market, Burlington, Mass), and it was conducted on the basis of each report rather than on the basis of each billing unit. For example, abdominal CT scans that were acquired and reported in association with pelvic CT scans were considered a single report.

The terms habitus and limited were chosen because they appeared to be the most commonly used terms in reports in which image quality was limited due to obesity. The database search engine was used to identify 30 reports with the phrase "habitus limited." These reports were audited before the study began, and the corresponding diagnostic images were reviewed by two radiologists (R.N.U., D.V.S., with 8 and 12 years of experience, respectively) to confirm that limitations in image quality were due to patients' habitus. The following limitations were noted: (a) inadequate image contrast due to underpenetration of x-rays, (b) motion artifacts, (c) inability to distinguish normal anatomy and anatomic landmarks because of excessive ultrasound beam attenuation, (d) area of interest was outside the field of view because surface area coverage was inadequate, and (e) beam-hardening or near-field artifacts were caused by physical contact between the patient's body and the imager bore or gantry. Medical records confirmed that a patient had a history of obesity (if his or her weight was unavailable) or that a patient weighed more than 200 lbs (90 kg).

Data Collected and Statistical Analysis
To qualify the phrase habitus limited as associated with obese patients, 200 patients were randomly selected from the pool of patients with habitus-limited reports filed in 2003. Two authors (R.N.U., P.F.H.) compared the weights of these patients with the weights of 200 randomly selected age- and sex-matched control patients from the same pool of patients whose reports did not include the phrase habitus limited. An independent-samples t test was performed with statistical software (StatView II, version 1.03 for Macintosh; Abacus Concepts, Berkeley, Calif) to compare the average weight of the patient groups. A P value of less than .001 was considered to indicate a significant difference.

To identify trends in habitus-limited reports during the study period, the percentage of habitus-limited reports was calculated (R.N.U.) for each year. The number of habitus-limited reports for a given year was divided by the total number of reports in our database for that year.

We sought to identify a significant relationship between the number of habitus-limited reports per year and the prevalence of obesity in Massachusetts, as defined by statistics published by the Centers for Disease Control and Prevention (1). Simple linear regression analysis was performed (P.F.H.), and the Pearson correlation coefficient was calculated with statistical software.

To identify the radiologic modality and anatomic location in which image quality was most limited by obesity, each modality coded in our database (chest and abdominal radiography, abdominal and pelvic ultrasonography [US], abdominal and chest CT, and abdominal magnetic resonance [MR] imaging) was searched and cross-referenced with the phrase habitus limited (R.N.U.). Both the total number and the percentage of habitus-limited reports per modality per year were identified. Percentages were compared not only between modalities within a year but also within each modality across the study period.

	RESULTS

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Overall, 7778 (0.15%) of 5 253 014 reports identified between 1989 and 2003 were classified as habitus limited. The average age of patients with habitus-limited reports was 57.1 years (age range, 3 months to 101 years). A total of 5073 (65.2%) reports were classified as habitus limited in female patients, and 2705 (34.8%) reports were classified as habitus limited in male patients.

Qualification of the Search Process
The average weight of the 200 randomly selected patients with habitus-limited reports was 239 lbs (108 kg). The average weight of the 200 randomly selected control subjects was 162 lbs (73 kg). An independent-samples t test showed a significant difference (P < .001) between the weights of patients in the two groups; therefore, use of the phrase habitus limited in the identification of heavier patients was qualified.

Trends
The number of habitus-limited reports steadily increased between 1989 and 2003. In 1989, 292 (0.10%) of 286 384 radiology reports filed at our institution were classified as habitus limited. This number rose to 444 (0.14%) of 319 959 reports by 1995 and 910 (0.19%) of 473 568 reports by 2003 (Fig 1a). The simple linear regression line for habitus-limited studies as a percentage of all studies was calculated as follows: y = 0.010x – 19.55, where x represents the year from 1989 to 2003. Linear regression analysis indicates that the number of habitus-limited reports has increased by an average of 0.010% per year (95% confidence interval: 0.007%, 0.013%; P < .001).

View larger version (24K): [in this window] [in a new window] [Download PPT slide]   Figure 1a: Graphs show (a) the percentage of habitus-limited reports between 1989 and 2003 and (b) the prevalence of obesity in Massachusetts between 1991 and 2001. There is a significant correlation between the increase in the number of habitus-limited reports and the increase in the prevalence of obesity in Massachusetts (MA).

View larger version (21K): [in this window] [in a new window] [Download PPT slide]   Figure 1b: Graphs show (a) the percentage of habitus-limited reports between 1989 and 2003 and (b) the prevalence of obesity in Massachusetts between 1991 and 2001. There is a significant correlation between the increase in the number of habitus-limited reports and the increase in the prevalence of obesity in Massachusetts (MA).

View larger version (24K): [in this window] [in a new window] [Download PPT slide]   Figure 2: Graph shows abdominal US (U/S) and chest radiography (CXR) have the fastest rate increase corresponding to the modalities with the greatest limitations due to patient habitus. ABD = abdominal radiography, C/T (abd) = abdominal CT.

Overall, 1435 (0.08%) of 1 794 075 chest radiographic reports were classified as habitus limited. In 1989, 94 (0.08%) of 108 173 reports were classified as habitus limited. By 2003, 244 (0.19%) of 131 037 reports were classified as habitus limited. Between 1989 and 2003, the percentage of habitus-limited reports increased at a rate of 0.007% per year (95% confidence interval: 0.0008%, 0.013%; P < .05).

	DISCUSSION

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Advances in imaging technology between 1989 and 2003 have focused on improving image quality; however, there has been a small but progressively increasing number of radiology reports described as "limited by body habitus." We found that obesity has a growing effect on image quality; however, our study had some limitations.

In this retrospective study, we examined the subjective assessments of numerous radiologists during a 15-year period. This method did not account for radiologists' biases, technologists' abilities, or equipment variations. In particular, technological improvements, such as more powerful x-ray tubes and digital radiographic techniques, may have reduced the effect of obesity on image quality in our practice.

Another limitation was our assumption that the phrase habitus limited was universally used by radiologists to identify reports in which image quality was limited by obesity. We performed a preliminary audit of various phrases that could be used, and the terms limited and habitus resulted in the most accurate hits and minimized the number of reports limited due to factors other than obesity. Although other terms, such as unsatisfactory and incomplete, could have been used, our preliminary search audit showed that the greatest uniform criteria in identifying reports affected by obesity were the terms limited and habitus. Also, in 2003, there was a significant difference (P < .001) between the weight of patients with habitus-limited reports and the weight of patients with radiology reports that were not classified as habitus limited.

Statistical analysis was limited because the linear regression, P values, associated correlation of the percentage of habitus-limited reports per year, and prevalence of obesity in Massachusetts were based on the assumption that the percentages apply to all points in that time period. As a result, the P values were not exact. However, if there were overall trends for the occurrence of habitus-limited reports per year and the prevalence of obesity in Massachusetts, those trends would also apply within each time period.

Another limitation was that we did not correlate our findings with patients' actual body mass index. Thus, some patients who had habitus-limited reports may have been large but not necessarily obese. It was interesting, however, that the increased number of habitus-limited reports correlated strongly with the increased prevalence of obesity in Massachusetts (defined by the Centers for Disease Control as a body mass index of 30 or greater).

The modalities most affected by obesity were US and chest radiography. The minimal effect of obesity on CT and MR imaging in our study was understandable, as there was some selection bias. If a patient met the table weight and gantry size criteria, he or she could undergo the imaging examination. Current imaging protocols for people who can fit in an imager are, for the most part, not limited by obesity. Increases in tube current and voltage can allow images of diagnostic quality to be obtained; however, the attendant increase in radiation dose in larger patients undergoing CT should be understood.

The percentage of habitus-limited reports was small, as evidenced by the fact that only 1.5% of abdominal US reports were classified as habitus limited; however, radiologists are increasingly faced with issues related to an inability to fit patients on CT or MR imaging tables or to obtain quality images in large patients. An example of this problem is the increasing subset of patients who are admitted to the hospital for gastric bypass surgery. At our institution, all of these patients undergo postoperative contrast material–enhanced (Isovue 300; Bracco Diagnostics, Princeton, NJ) imaging to ensure there are no anastomotic leaks. The weight of these patients can exceed the weight limit of the fluoroscopy table. In this case, the examination is limited to obtaining poor-quality serial chest and abdominal conventional radiographs, thus resulting in an insufficient examination. Occasionally, however, a patient will exceed the weight limit of the fluoroscopy table but will not exceed the diameter of the opening of the image intensifier; in these cases, if the patient is ambulatory, he or she can be imaged in an erect position. Evaluation for clinically suspected complications of gastric bypass surgery, such as an anastomotic leak or an intraabdominal abscess, is nearly impossible if the patient exceeds the CT table weight limit.

Images of limited quality obtained in obese patients can have an economic effect on health care. Images of limited quality may be insufficient for diagnostic purposes, and they can lead to further tests and increased hospitalization. In addition, patients who did not undergo imaging because they were too large can experience the economic and social effects of obesity in the form of resultant costs for further diagnostic work-up, increased hospital stays, and consequences of misdiagnosis or failure to make a diagnosis. Additional effects of obesity that were not addressed in this investigation include acute and chronic injuries to technologists and support personnel from attempting to move or image obese patients and stress placed on imaging equipment (such as use of higher tube current and voltage settings, thus leading to more rapid burnout of x-ray tubes) when examining obese patients. Approximately 83% of technologists have reported some pain when moving obese patients (6).

Radiologists should be aware of the limitations of current imaging equipment and be knowledgeable in the optimization of imaging protocols and equipment settings when examining large patients. Future prospective studies performed to establish a correlation between body mass index and image quality for each modality could help manufacturers and radiologists achieve their goal of improving image quality in an increasing population of obese Americans.

	ADVANCES IN KNOWLEDGE

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• Patients with habitus-limited radiology reports weighed significantly (P < .001) more than age- and sex-matched control subjects whose reports were not classified as habitus limited.
  
• There was a small but progressive increase in the number of habitus-limited radiology reports between 1989 and 2003.
  
• The increase in the number of habitus-limited radiology reports correlates with the increase in the prevalence of obesity in Massachusetts.
  
• Abdominal US examinations are most frequently classified as habitus limited.
  

	ACKNOWLEDGMENTS

 
We thank Elkan Halpern, PhD, chief statistician, Radiology Institute for Technology Assessment, Massachusetts General Hospital, for his help with addressing inquiries during the statistical review of this article.

	FOOTNOTES

 
Authors stated no financial relationship to disclose.

Author contributions: Guarantors of integrity of entire study, all authors; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, R.N.U.; clinical studies, R.N.U.; statistical analysis, R.N.U., P.F.H.; and manuscript editing, all authors

	References

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1. Centers for Disease Control and Prevention. Overweight and obesity: obesity trends—1991–2001. Prevalence of obesity among U.S. adults by state. Department of Health and Human Services Web site. http://www.cdc.gov/nccdphp/dnpa/obesity/trend/prev_reg.htm. Accessed May 22, 2006.
2. Rundle RL. U.S.'s obesity woes put a strain on hospitals in unexpected ways. Wall Street Journal Online Edition. May 1, 2002. online.wsj.com/article/0,,SB1020194636122710680.djm,00.html. Accessed July 1, 2005.
3. Wittmer MH, Duszak R, Lewis ER, Wagner BJ. Does obesity degrade image quality of helical CT for suspected pulmonary embolism? [abstr]. AJR Am J Roentgenol 2004;182(4):113.
4. Elmore JG, Carney PA, Abraham LA, et al. The association between obesity and screening mammography accuracy. Arch Intern Med 2004;164(10):1140–1147.[Abstract/Free Full Text]
5. Halpern BS, Dahlbom M, Quon A, et al. Impact of patient weight and emission scan duration on PET/CT image quality and lesion detectability. J Nucl Med 2004;45(5):797–801.[Abstract/Free Full Text]
6. Kumar S, Moro L, Narayan Y. Perceived physical stress at work and musculoskeletal discomfort in x-ray technologists. Ergonomics 2004;47(2):189–201.[Medline]

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This Article Abstract Figures Only Full Text (PDF) All Versions of this Article: 2402051110v1 240/2/435    most recent Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted 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 Uppot, R. N. Articles by Mueller, P. R. Search for Related Content PubMed PubMed Citation Articles by Uppot, R. N. Articles by Mueller, P. R.