Effect of Positioning of the Region of Interest on Bone Density of the Hip.

BACKGROUND: Large changes in positioning of the global region of interest (ROI) influence the measurement of bone mineral density (BMD) in the hip and forearm regions. However, it is unknown whether minor shifts in the positioning of the bottom of the global hip ROI affect the measurement of total hip BMD. METHODS: The hip BMDs of 40 clinical densitometry patients were analyzed at baseline with the bottom of the global hip ROI positioned as usual, 10 mm distal to the base of the lesser trochanter (position 0). Then the hip was reanalyzed by shifting the bottom of the global hip ROI 1 mm proximally 10 times (positions +1 through +10) and then by shifting the bottom of the global hip ROI 1 mm distally 10 times (positions -1 through -10). The significance of the differences between mean values at the various distances from baseline was assessed using a Wilcoxon signed-rank test. RESULTS: The mean total hip area, bone mineral content and BMD decreased as the bottom of the global hip ROI was shifted proximally; the decrease was significant when shifted by even 1 mm (p < 0.001). The mean total hip area, bone mineral content and BMD increased as the bottom of the global hip ROI was shifted distally; the increase was significant when shifted by even 1 mm (p < 0.001). The change in BMD with each 1 mm shift was uniform across the range studied from positions +10 through -10, and was approx 0.54%/mm. When the least significant change was based on 40 pairs of measurements, where each pair was comprised of the baseline scan and the same scan at -1 position, the least significant change was 0.01 g/cm2. CONCLUSIONS: The BMD of the total hip is sensitive to even minor changes in the positioning of the bottom of the global hip ROI. Although a 1 mm change in the bottom of the global hip ROI positioning would make little difference in the reported T-score, it could easily affect the determination of significance in changes in BMD over time.

Effect of Positioning of the ROI on BMD of the Forearm and Its Subregions.

Inconsistent positioning of patients and region of interest (ROI) is known to influence the precision of bone mineral density (BMD) measurements in the spine and hip. However, it is unknown whether minor shifts in the positioning of the ROI along the shaft of the radius affect the measurement of forearm BMD and its subregions. The ultradistal (UD-), mid-, one-third, and total radius BMDs of 50 consecutive clinical densitometry patients were acquired. At baseline the distal end of the ROI was placed at the tip of the ulnar styloid as usual, and then the forearm was reanalyzed 10 more times, each time shifting the ROI 1 mm proximally. No corrections for multiple comparisons were necessary since the differences that were significant were significant at p < 0.001. The UD-radius BMD increased as the ROI was shifted proximally; the increase was significant when shifted even 1 mm proximally (p < 0.001). These same findings held true for the mid- and total radius bone density, though the percent increase with moving proximally was significantly greater for the UD radius than for the other subregions. However, there was no significant change in the one-third radius BMD when shifted proximally 1-10 mm. Minor proximal shifts of the forearm ROI substantially affect the BMD of the UD-, mid- and total radius, while having no effect on the one-third radius BMD. Since the one-third radius is the only forearm region usually reported, minor proximal shifts of the ROI should not influence forearm BMD results significantly.

Enhanced Precision of the New Hologic Horizon Model Compared With the Old Discovery Model Is Less Evident When Fewer Vertebrae Are Included in the Analysis.

The International Society for Clinical Densitometry guidelines recommend using locally derived precision data for spine bone mineral densities (BMDs), but do not specify whether data derived from L1-L4 spines correctly reflect the precision for spines reporting fewer than 4 vertebrae. Our experience suggested that the decrease in precision with successively fewer vertebrae is progressive as more vertebrae are excluded and that the precision for the newer Horizon Hologic model might be better than that for the previous model, and we sought to quantify. Precision studies were performed on Hologic densitometers by acquiring spine BMD in fast array mode twice on 30 patients, according to International Society for Clinical Densitometry guidelines. This was done 10 different times on various Discovery densitometers, and once on a Horizon densitometer. When 1 vertebral body was excluded from analysis, there was no significant deterioration in precision. When 2 vertebrae were excluded, there was a nonsignificant trend to poorer precision, and when 3 vertebrae were excluded, there was significantly worse precision. When 3 or 4 vertebrae were reported, the precision of the spine BMD measurement was significantly better on the Hologic Horizon than on the Discovery, but the difference in precision between densitometers narrowed and was no longer significant when 1 or 2 vertebrae were reported. The results suggest that (1) the measurement of in vivo spine BMD on the new Hologic Horizon densitometer is significantly more precise than on the older Discovery model; (2) the difference in precision between the Horizon and Discovery models decreases as fewer vertebrae are included; (3) the measurement of spine BMD is less precise as more vertebrae are excluded, but still quite reasonable even when only 1 vertebral body is included; and (4) when 3 vertebrae are reported, L1-L4 precision data can reasonably be used to report significance of changes in BMD. When 1 or 2 vertebrae are reported, precision data for 1 or 2 vertebrae, respectively, should be used, because the exclusion of 2-3 vertebrae significantly worsens precision.

Direct Comparison of the Precision of the New Hologic Horizon Model With the Old Discovery Model.

Previous publications suggested that the precision of the new Hologic Horizon densitometer might be better than that of the previous Discovery model, but these observations were confounded by not using the same participants and technologists on both densitometers. We sought to study this issue methodically by measuring in vivo precision in both densitometers using the same patients and technologists. Precision studies for the Horizon and Discovery models were done by acquiring spine, hip, and forearm bone mineral density twice on 30 participants. The set of 4 scans on each participant (2 on the Discovery, 2 on the Horizon) was acquired by the same technologist using the same scanning mode. The pairs of data were used to calculate the least significant change according to the International Society for Clinical Densitometry guidelines. The significance of the difference between least significant changes was assessed using a Wilcoxon signed-rank test of the difference between the mean square error of the absolute value of the differences between paired measurements on the Discovery (Δ-Discovery) and the mean square error of the absolute value of the differences between paired measurements on the Horizon (Δ-Horizon). At virtually all anatomic sites, there was a nonsignificant trend for the precision to be better for the Horizon than for the Discovery. As more vertebrae were excluded from analysis, the precision deteriorated on both densitometers. The precision between densitometers was almost identical when reporting only 1 vertebral body. (1) There was a nonsignificant trend for greater precision on the new Hologic Horizon compared with the older Discovery model. (2) The difference in precision of the spine bone mineral density between the Horizon and the Discovery models decreases as fewer vertebrae are included. (3) These findings are substantially similar to previously published results which had not controlled as well for confounding from using different subjects and technologists.

Effect of Clothing on Measurement of Bone Mineral Density.

It is unknown whether allowing patients to have BMD (bone mineral density) studies acquired while wearing radiolucent clothing adlib contributes appreciably to the measurement error seen. To examine this question, a spine phantom was scanned 30 times without any clothing, while draped with a gown, and while draped with heavy winter clothing. The effect on mean BMD and on SD (standard deviation) was assessed. The effect of clothing on mean or SD of the area was not significant. The effect of clothing on mean and SD for BMD was small but significant and was around 1.6% for the mean. However, the effect on BMD precision was much more clinically important. Without clothing the spine phantom had an least significant change of 0.0077 gm/cm(2), while when introducing variability of clothing the least significant change rose as high as 0.0305 gm/cm(2). We conclude that, adding clothing to the spine phantom had a small but statistically significant effect on the mean BMD and on variance of the measurement. It is unlikely that the effect on mean BMD has any clinical significance, but the effect on the reproducibility (precision) of the result is likely clinically significant.

Utility of Reviewing Radiology Studies in Electronic Medical Records When Preparing Bone Mineral Density Reports.

We quantitated how often review of recent radiology studies provides information useful to the densitometrist. While preparing bone mineral density (BMD) reports on 1012 consecutive patients, radiology reports in electronic medical records (EMRs) for the previous 5 years at potentially relevant sites (lumbar spine X-rays, abdominal computed tomography (CT) scans, and so forth) were reviewed. When a study was found, it received a grade according to how relevant findings were to the BMD report: "1" for studies that were irrelevant, "2" for those that confirmed the impression formed from review of the BMD images, "3" for those that clarified the impression that was unclear after reviewing the BMD images, and "4" for those that revealed new relevant data when no abnormality was noted on review of the BMD images. A total of 562 patients (55.5%) had a radiologic study at a site of potential interest within the past 5 years. Fifty-three patients (5.2% of all patients) had a grade 4 study, 88 patients (8.7% of all patients) had a grade 3 study, and 185 patients (18.3% of all patients) had a grade 2 study. Two hundred sixty-four patients (25.8%) had a grade 2 or 3 study, and 299 (29.5%) had a grade 2-4 study. The radiographic study that was most likely to be found in patients' EMR was chest X-ray (34.7% of all patients), but it was also the one that was least likely to have any relevance to the reader; only 10.5% of the total chest X-rays were graded 2-4. The next most likely studies to be found in patients' EMR were abdominal CT scans (18.0% of all patients) and lumbar spine X-rays (14.4% of all patients), but these studies were much more likely to be useful to the reader, as 62.6% of abdominal CT scans and 78.1% of lumbar spine X-rays were graded 2-4. The likelihood of a patient having radiologic examinations in the EMR at sites potentially relevant to the BMD reader is high, but the likelihood that these clarify abnormalities noted on BMD is only moderate. Review of the EMR is unlikely to be relevant when the dual-energy X-ray absorptiometry images are normal.

Inconsistency in filling in the bottom of the spine bone map affects reported spine bone mineral density.

OBJECTIVE: We hypothesized that variability from year to year in how much of the bone map was filled in at the bottom of the spine region of interest (ROI) contributes substantially to variability in measurement of spine bone mineral density (BMD). METHODS: A total of 110 spine BMDs with defects in the bone mapping at the bottom were reanalyzed, with the only change being manually drawing a straight line across the bottom of the ROI and filling in the bone map. RESULTS: The mean (SD) change in area, bone mineral content, and BMD for total spine when the bottom of the bone map was filled in was 0.919 (0.411) cm2, 0.201 (0.121) g, and -0.0098 (0.0043) g/cm2, respectively, and all changes were significant (P<.0001). The largest individual change in total spine BMD with reanalysis was 0.0238 g/cm2, close to the least significant change (LSC) of 0.026 g/cm2 in our center. To quantify variability due to this change in analysis, we calculated an LSC(fill), in which the pairs of scans consisted of the same scan before and after filling in the bottom of the spine bone map, without any other change. The LSC(fill) attributable just to the reanalysis of missing bone map at the bottom of the spine was 0.021 g/cm2, suggesting substantial variance due to variability in mapping the bottom of the spine. CONCLUSION: When there is a noticeable defect in the bottom of the spine bone map, filling this defect in consistently eliminates a significant source of variability in analysis of spine BMDs and might allow us to achieve smaller LSCs.

Lifting Disabled Patients onto the Densitometer with a Ceiling Lift: Effect of the Sling on Measurement of BMD.

OBJECTIVE: Lifting disabled patients onto a densitometer manually is dangerous for both the patient and the densitometry staff; using a ceiling lift is the preferred method of transfer. This system requires the use of a sling underneath the patient. Unless extra time is taken for its removal, the sling remains underneath the patient as bone mineral density (BMD) is measured. The aim of this study was to determine whether leaving this sling in place during scan acquisition affects the BMD measurement. METHODS: Measurements were taken of a spine phantom 30 times by itself, 30 times with a standard sling underneath the spine phantom, and 16 times with a disposable sling underneath the spine phantom. RESULTS: We found that mean BMD was significantly different versus the phantom alone when a sling was used, due to differences in area, bone mineral content, or both. The disposable sling affected the mean BMD to a much greater extent than did the standard sling (+1.9% vs. -0.41%; P for the difference between slings <.001). The standard sling did not increase the variance in the BMD measurement compared with the spine phantom alone, whereas the disposable sling did increase the variance in the BMD measurements. CONCLUSION: Commercially available ceiling-lift slings affect BMD measurements of spine phantoms. This effect is expected to persist when BMD is measured in patients and suggests that when lifting a patient onto the densitometer using these slings, it is best to take the time to remove the sling from under the patient after transfer and before scanning.

Effect of implementing a computerized system for bone mineral density storage and report preparation on result turnaround time and savings in cost, time, and space.

OBJECTIVE: To evaluate whether introduction of a densitometry workflow, data-storage, and reporting software system would result in streamlined workflow with fewer expenses and quicker result turnaround time. METHODS: BoneStation was implemented March 30, 2009, in a large, urban, tertiary referral center performing more than 6000 bone mineral density studies annually at 3 different geographic sites. The times of scan acquisition, report preparation, and final signature in the online medical record were recorded, and the delays from scan to report and from scan to final signature in the online medical record were calculated for each patient during 2 representative weeks before (n = 274) and 2 weeks after (n = 235) implementation of BoneStation. RESULTS: Use of BoneStation reduced time from scan to report from 2.11 +/- 0.16 days to 0.46 +/- 0.05 days (P<.001). BoneStation saved our practice $8.94 per scan, while costing only $3 per scan, resulting in net savings. Considering that the total reimbursement from Medicare in 2010 for dual-energy x-ray absorptiometry is projected to be $55.44, this constitutes cost savings of 10.7% of the total reimbursement. CONCLUSION: The introduction of a specialized electronic medical system for data storage and reporting reduced costs and improved result turnaround time in a densitometry practice.