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Establishment and Results of a Magnetic Resonance Quality Assurance Program for the Pediatric Brain Tumor Consortium

Posted Aug 31, 2008 Updated Apr 7, 2023
By Robert V. Mulkern PhD , Peter Forbes MA , Kevin Dewey MEd , Stravoula Osganian MD ScD , Maureen Clark MS , Sharon Wong BS , Uma Ramamurthy PhD , Larry Kun MD , Tina Young Poussaint MD
10 min read

Rationale and Objectives

Magnetic resonance (MR) imaging is used to assess brain tumor response to therapies, and a MR quality assurance (QA) program is necessary for multicenter clinical trials employing imaging. This study was performed to determine overall variability of quantitative imaging metrics measured with the American College of Radiology (ACR) phantom among 11 sites participating in the Pediatric Brain Tumor Consortium (PBTC) Neuroimaging Center (NIC) MR QA program.

Materials and Methods

An MR QA program was implemented among 11 participating PBTC sites and quarterly evaluations of scanner performance for seven imaging metrics defined by the ACR were sought and subject to statistical evaluation over a 4.5-year period. Overall compliance with the QA program, means, standard deviations, and coefficients of variation (CV) for the quantitative imaging metrics were evaluated.

Results

Quantitative measures of the seven imaging metrics were generally within ACR recommended guidelines for all sites. Compliance improved as the study progressed. Intersite variabilities, as gauged by CV for slice thickness and geometric accuracy, imaging parameters that influence size or positioning measurements in tumor studies, were on the order of 10% and 1%, respectively.

Conclusions

Although challenging to establish, MR QA programs within the context of PBTC multisite clinical trials when based on the ACR MR phantom program can indicate sites performing below acceptable image quality levels and establish levels of precision through instrumental variabilities that are relevant to quantitative image analyses (eg, tumor volume changes).

Among children ages 0–19 years, the incidence rate for pediatric brain tumors was 29.1 cases/1,000,000 between 1996 and 2003 ( ). Given these statistics, efforts to accrue sufficient numbers of patients for investigating more effective treatment strategies must hinge largely on multicenter trials, a defining feature of the National Institutes of Health–funded Pediatric Brain Tumor Consortium (PBTC), established in 1999. Comprising 10 major pediatric brain tumor research centers and the neuro-oncology branch of the National Cancer Institute, the PBTC broadened its mission in 2003 with the addition of the Neuroimaging Center (NIC) whose mission is three-fold to: 1) coordinate imaging research; 2) provide imaging support for novel therapeutic trials; and 3) develop a framework by which correlative imaging data are codified and uniformly applied to PBTC multicenter trials.

Equipped with relatively sophisticated neuroimaging capabilities and a commitment to neuroimaging research, the NIC is intensively engaged in facilitating quality assurance (QA) and promoting clinically relevant imaging research. Specifically, imaging acquisition protocols aimed primarily at positron emission tomography and magnetic resonance (MR) must be continuously analyzed, modified, updated, and uniformly applied across institutions and within relevant trials. The importance of standardizing acquisition protocols among sites cannot be understated. After protocols are standardized, tumor volume measurements, for example, typically calculated during most trials, can be compared reliably to those taken during similar or equivalent trials within the PBTC. In addition to standardizing imaging protocols, the NIC is assessing the variability of basic imaging metrics among the various PBTC instruments, gauging whether statistically significant differences exist, and determining whether these differences affect or skew findings within representative PBTC cohorts. An assessment of variability measures is an essential feature of any comprehensive QA program ( ), and nowhere is this more evident than in the context of MR, in general, and in the efforts of the NIC, in particular.

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Materials and methods

Overview of Data Collection Guidelines

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Table 1

Results from the Geometric Accuracy Test from T1-weighted Images

Length (mm) n Mean Standard Deviation Min Max Coefficient Variation P1 148 259 146.91 1.27 140.00 149.50 0.87 P2 190 260 189.84 1.06 182.00 192.00 0.56 P3 190 260 189.94 0.78 186.00 192.00 0.41 P4 190 260 189.92 0.91 185.00 192.00 0.48 P5 190 260 189.85 1.05 180.10 193.00 0.55 P6 190 260 189.71 0.93 186.40 192.40 0.49 P7 190 260 189.78 0.83 186.90 192.00 0.44

Max, maximum; Min, minimum; P, phantom lengths.

The American College of Radiology specifies that lengths should be within ±2 mm of actual length shown in first column.

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Figure 1, A T1-weighted spin echo image of axial slice 1 of the American College of Radiology phantom from which three of the seven imaging tests are performed. Top arrow : Slice position test; middle arrow : slice thickness test; bottom arrow : high-contrast spatial resolution grids.

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E-mail Notification System for Submission of MR QA Reports

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Imaging Test Analysis

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Results

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Figure 2, Percentage of compliance for each site as based on a perfect score of 12 scans per magnetic resonance imaging scanner over the 4.5-year period.

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Table 2

High-contrast Spatial Resolution Results from the T1- and T2-weighted Images from the Lower Right (LR) and Upper Left (UL) Grids at the Three Separate Spatial Resolutions 1.1, 1.0, and 0.9 mm provided in the American College of Radiology Phantom

Scores T1 Percent Test Success T2 Percent Test Success LR (1.1) 100 100 UL (1.1) 100 100 LR (1.0) 97 94 UL (1.0) 98 98 RL (0.9) 58 38 UL (0.9) 54 39

The American College of Radiology specifies that a 1-mm resolution should be regularly achieved with the settings employed for this test.

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Figure 3, Results from the slice thickness accuracy test as measured from all 11 sites with a 5-mm thickness being the perfect score. Box plots are used to summarize the observed data for this test and the other tests described in Figures 4–7 . The boxes show the 25th, 50th, and 75th percentiles of the distribution of scores. Box plot whiskers extend from each end of the box (ie, from the 25th and 75th percentiles) to the most extreme observed values within 1.5× the box length. Observations beyond these limits may be outliers; each of these is displayed individually with dots. The box plots include reference lines for plus and minus two standard deviations (Std. Dev.) from the overall mean. These lines indicate the range over which the vast majority of observations appeared.

Table 3

MR QA Summary Statistics for the Remaining 5 Imaging Tests

Measure n Mean (95% CI) Standard Deviation Coefficient Variation Median Min Max ACR Specs Slice thickness accuracy 261 5.07 (5.00–5.13) 0.52 10.34 5.05 3.83 7.97 5 ± 0.7 mm Slice 1 position accuracy 262 1.98 (1.69–2.28) 2.40 121.00 2.00 −5.00 9.00 <5 mm Slice 11 position accuracy 263 1.69 (1.42–1.95) 2.17 128.81 1.60 −6.00 8.00 <5 mm T1 percent integral uniformity 261 94.60 (94.22–94.98) 3.09 3.27 95.20 70.32 99.95 >87.5% T2 percent integral uniformity 259 94.28 (93.94–94.62) 2.77 2.94 94.80 70.37 99.80 >87.5% T1 signal ghosting ratio 260 0.0024 (0.0021–0.0028) 0.0030 125.39 0.0014 −0.0018 0.0240 <0.025 T2 signal ghosting ratio 256 0.0054 (0.0046–0.0063) 0.0068 125.85 0.0036 −0.0067 0.0500 <0.025 T1 low-contrast detectability 263 36.62 (36.19–37.05) 3.53 9.65 37.00 13.00 40.00 >9 T2 low-contrast detectability 260 33.68 (32.98–34.38) 5.75 17.08 35.00 1.00 40.00 >9

CI, confidence interval; Max, maximum; Min, minimum.

The American College of Radiology (ACR) recommended specifications for the various test values are provided in the last column.

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Figure 4, Results from the slice position accuracy test for ( a ) slice 1 position accuracy and ( b ) slice 11 position accuracy from all 11 sites as summarized by box plots described in Figure 3 . The actual score measured in this case is twice the actual slice position offset in millimeters, and a perfect score for this test is 0 mm. Measurements were made from the T1-weighted images only. Std. Dev, standard deviation.

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Figure 5, Results from the percent image uniformity for ( a ) T1-weighted images and ( b ) T2-weighted images from all 11 sites as summarized by box plots described in Figure 3 . The score here is a dimensionless quantity that reflects how uniform the signal over a large field of view is with 100% being the perfect score. Std. Dev, standard deviation.

Figure 6, Results from ghosting ratio test for ( a ) T1-weighted images and ( b ) T2-weighted images from all 11 sites as summarized by box plots described in Figure 3 . The score here is a dimensionless quantity reflecting the difference between phase and frequency-encoded ghosting or signal bleed along those directions with a perfect score being 0. Std. Dev, standard deviation.

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Figure 7, Results from the low-contrast detectability tests for ( a ) for T1-weighted images and ( b ) T2-weighted images from all 11 sites as summarized by box plots described in Figure 3 . The score reflects the number of complete spokes out of 40 possible, which have been clearly identified. Std. Dev, standard deviation.

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Discussion

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Compliance

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Geometric Accuracy

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High Contrast

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Slice Thickness

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Slice Position Accuracy

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Image Intensity Uniformity

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Ghosting Ratios

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Low-contrast Detectability

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Conclusion

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Acknowledgments

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Appendix

Pediatric Brain Tumor Consortium Neuroimaging Center MR Quality Assurance Form 2

Section A: General Information

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Section B: Results of Test 1—Geometric Accuracy

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Section C: Results of Test 2—High-contrast Spatial Resolution

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Section D: Results of Test 3—Slice Thickness Accuracy

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Section E: Results of Test 4—Slice Position Accuracy

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Section F: Results of Test 5—Image Intensity Uniformity

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Section G: Results of Test 6—Signal Ghosting Ratio

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Section H: Results of Test 7—Low-contrast Object Detectability

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Academic Radiology, Volume 15, Issue 9
Journals General Radiology
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