Gadobutrol Enhanced MRA of the Renal Arteries: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Gadobutrol Enhanced MRA of the Renal Arteries (NCT01344460), a non-randomized phase 3 study. The primary outcome is Percentage of Assessable Vascular Segments Using Gadobutrol-Enhanced MRA and Unenhanced MRA.

2. Clinical Question

This is an imaging-evaluation question, not a comparison of clinical outcomes between treatment groups. All participants were in a single study group, and the record describes no randomized control arm. The comparison of interest is between imaging approaches applied to participants in the study, with independent blinded readers evaluating the images. The CTA reference helps contextualize the imaging assessments, but the primary endpoint itself concerns whether segments are assessable on the two MRA image sets.

The registry record identifies six segments per participant—three in each renal artery—and notes that participants with a renal transplant could have up to nine segments assessed. The number of segments may therefore differ across participants. The posted results do not report the endpoint percentages or the underlying evaluable counts, so the registry record does not establish the observed degree of assessability or the size of any difference between imaging approaches.

3. Trial Design

NCT01344460 was a Phase 3, multicenter, open-label study sponsored by Bayer. It was nonrandomized and used a single-group model, with no masking listed. The registry reports 317 enrolled participants. The study started in 2011-05, had primary completion in 2012-07, and is listed as completed.

Participants with known or suspected renal artery disease were recruited from those referred for routine CTA or MRA. The study involved a single injection of gadobutrol at 0.1 mmol/kg. MRA images were taken before and after the injection. The registry describes a study duration of between 2 and 12 days for each participant and two to three visits to the study doctor.

The diagnostic imaging assessment included gadobutrol-enhanced MRA, unenhanced MRA, and CTA. CTA images could come from an examination performed up to 60 days before enrollment; if no qualifying CTA had been performed, one was required for the study. MRA and CTA images were collected for independent review by blinded readers. The primary endpoint description names three independent blinded readers, alongside on-site investigators, and defines a majority-reader result as one determined by at least two blinded readers.

These design features distinguish the imaging comparison from a randomized treatment comparison. The registry lists one study group rather than separate randomized arms, and the record does not describe an untreated or placebo group. The readers’ blinding applies to image review as described in the record; the study itself is listed as open-label with no masking. The specific procedures used to preserve reader blinding are not reported in the registry record.

The record does not report a protocol-level justification for the enrollment target, a formal hypothesis-testing plan, or a prespecified analysis hierarchy. It also does not report the exact statistical model used for the primary endpoint. Those omissions mean that design details beyond the listed study structure and endpoint definition cannot be inferred from the registry entry.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Before assignment: A total of 338 participants were screened, of which 317 were enrolled and 315 received the study drug. The 23 participants who did not receive the study drug included 9 screen failures and 12 premature discontinuations (10 participants withdrew consent and 2 participants for other reasons) and 2 participants never received the study drug.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: FAS; in below table, "n/n" signifies the number of participants/segments that were evaluable in specified category for both groups.

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Percentage of Assessable Vascular Segments Using Gadobutrol-Enhanced MRA and Unenhanced MRA, measured over Images were taken pre-injection and post-injection.

The primary endpoint is the percentage of vascular segments assessed as assessable on gadobutrol-enhanced MRA and unenhanced MRA. It concerns whether the image allows a segment to be evaluated, rather than directly measuring the presence or severity of disease. Under the registry definition, a segment is assessable when it is visualized along its entire length and any region of stenosis can be measured reliably.

Assessability matters because an image that does not show the full segment, or does not allow a narrowing to be measured reliably, cannot support the same evaluation as a fully interpretable image. In general, reporting assessability helps distinguish image interpretability from diagnostic correctness. A high assessability percentage alone would not establish that a stenosis was classified accurately; that would require diagnostic-performance results against a reference standard.

The endpoint was evaluated for each modality by on-site investigators, three independent blinded readers, and a majority-reader assessment. The majority-reader result was defined as a determination made by at least two of the blinded readers. The analysis population is identified as FAS, but the registry does not expand that label or provide the endpoint results. The record describes six segments per participant, with up to nine for participants with renal transplant, so the segment-level observations are clustered within participants rather than necessarily representing independent individuals.

The registry record does not report the percentages, evaluable counts, uncertainty intervals, or a statistical comparison for this endpoint. Therefore, it supports an explanation of what was intended to be measured, but not a conclusion about how assessability differed between the MRA approaches.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The study’s main statistical challenge is that its primary measure is a percentage of assessable vascular segments, while each participant can contribute several segments and several reader assessments. The registry record defines the endpoint and reader groups but does not report the statistical method used to analyze it. The concepts below explain how such data are generally interpreted; they are not claims about an unreported analysis in this study.

What a segment-level percentage describes

General statistical explanation: a percentage of assessable segments describes the proportion of evaluated segments that meet a prespecified interpretability rule. Here, the rule requires visualization along the entire segment and reliable measurement of any stenosis. A percentage summarizes the observed segment assessments, but its denominator matters: it is the number of evaluable segments included in that reader and modality assessment, not automatically the number of enrolled participants.

The endpoint description notes six segments per participant, and up to nine for participants with renal transplant. If some segments cannot be evaluated or some image assessments are unavailable, denominators can vary. The primary endpoint definition says that the result is reported as a percentage of segments; the registry does not provide the actual numerator and denominator values. The population is labeled FAS, but what that analysis population includes is not reported in the registry record.

Repeated segments within a participant

General statistical explanation: observations from the same participant may be correlated. For example, image quality or anatomy shared by one participant can influence more than one segment assessment. Treating all segments as independent can make uncertainty appear smaller than it is. Methods for clustered data can account for within-participant dependence, or an analysis can summarize information at participant level. The registry record does not state which approach was used for the primary endpoint.

The same issue can arise across readers. The three independent blinded readers evaluated the images, and the record also describes a majority-reader outcome based on agreement by at least two readers. Reader-specific assessments and a combined majority assessment are related views of the same underlying images, not necessarily independent datasets. The analysis plan for handling reader variation is not reported in the registry record.

Paired imaging assessments

General statistical explanation: when two imaging approaches are assessed in the same participants, a paired comparison can account for the fact that each participant serves as their own context for comparison. Paired methods focus on within-participant differences rather than treating the groups as unrelated. The record describes pre-injection and post-injection images and comparisons of enhanced and unenhanced MRA, but it does not report whether a paired statistical test or model was used, or how missing paired assessments were handled.

CTA has a separate role in the design: it is described as the standard of reference, whereas unenhanced MRA is an imaging comparator for enhanced MRA. In general, a reference standard allows diagnostic classification to be compared with another test, but an assessability endpoint is not itself an accuracy statistic. The registry does not report diagnostic accuracy estimates or the methods used to derive them.

Uncertainty and interpretation

General statistical explanation: a confidence interval describes a range of values compatible with the observed data under a specified statistical method. It communicates precision as well as an estimate. A percentage without its denominator and uncertainty interval can be difficult to interpret, especially when observations are clustered or denominators differ. No primary endpoint estimates or confidence intervals are reported in the registry record, so precision cannot be assessed from the posted results described in the record.

General statistical explanation: a significance test addresses compatibility with a specified null hypothesis under its assumptions; it does not describe the clinical importance of an effect. The registry record does not report a primary hypothesis test, p-value, confidence interval, or prespecified decision threshold. No conclusion about statistical significance can therefore be drawn from the endpoint description alone.

Planning illustrations

The planning illustration uses a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It is computed from an observed effect, with the effect to detect expressed as a stated fraction of that observed effect. The illustration is not the trial’s own design: this study is listed as nonrandomized and single-group. The illustrative outputs are planning quantities, not observed power, and do not establish what enrollment was chosen for in the original protocol. The registry record does not report the effect values underlying the illustration or the trial’s sample-size justification.

General statistical explanation: a sample-size calculation depends on the assumed effect, variability, analysis method, allocation, and error-rate target. Changing those assumptions changes the planned sample size. An illustration based on an observed effect is especially dependent on that effect estimate and should not be interpreted as proof that the study had a particular probability of detecting an effect. No numerical planning estimates are reported in the registry record.

Multiplicity and model assumptions

The registry lists 22 outcome measures and 29 analyses. General statistical explanation: when many outcomes, readers, or comparisons are examined, the chance of at least one apparently unusual result can increase if each is assessed separately. A prespecified testing hierarchy or multiplicity adjustment can address some of this issue, but the registry record does not describe whether either was used. The existence of multiple listed measures alone does not show that any particular adjustment was required or applied.

General statistical explanation: binary assessability outcomes can be summarized with proportions, while models may be used to account for clustering, reader, modality, or other design features. The appropriate method depends on the analysis question and data structure. Because the record does not report the model, missing-data procedures, or endpoint results, no specific model-based estimate can be reconstructed or attributed to this study.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists 22 outcome measures and 29 analyses. The primary endpoint description includes assessments by on-site investigators, three independent blinded readers, and a majority-reader outcome. Secondary outcomes cover additional image characteristics, including vessel length and diameter, stenosis location, and artifacts. This range of outcomes and reader assessments creates multiple opportunities for analysis.

General statistical explanation: multiplicity matters when several hypotheses or comparisons are assessed, because interpreting each result separately can make chance findings harder to distinguish from robust signals. Common strategies include prespecifying a primary comparison, defining a testing order, or adjusting significance thresholds. The registry record does not report whether a multiplicity strategy was prespecified or used. It also does not give a complete statistical analysis plan, so no hierarchy or adjustment should be inferred.

The primary analysis population is labeled FAS. Its definition, exclusions, and handling of participants without evaluable images are not reported in the registry record. The primary endpoint description says that the population is FAS and describes evaluability at the segment level, but it does not provide missing-data counts or explain whether missing segments were excluded, classified as non-assessable, or handled another way.

General statistical explanation: missing observations can affect an estimated percentage if the chance of being missing is related to image quality or participant characteristics. Reporting the number and reasons for missing assessments, together with the analysis rule, helps readers judge whether the reported result represents the intended population. Those details are not reported in the registry record. There are also no endpoint denominators or estimates with which to assess the impact of missingness.

Consequently, neither the control of multiplicity nor the sensitivity of the primary result to missing data can be evaluated from the registry record. The record’s endpoint description alone does not establish how the analyses were prioritized or which observations contributed to each reported result.

11. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 1% reporting threshold.

Most frequent non-serious adverse event terms

The safety entry lists 315 participants at risk for serious adverse events and 0 participants affected by serious adverse events. It lists 315 at risk for other adverse events and 14 participants affected. No serious adverse-event terms are listed. The number of deaths is not reported in the registry record.

These are descriptive counts in the registry, not estimates from a randomized safety comparison. The study is listed as nonrandomized and single-group, so there is no randomized control group in the record against which to compare event frequencies. The counts also do not, by themselves, establish whether an event was caused by gadobutrol. The registry record does not provide event narratives, timing, severity details for the other adverse events, or a causal attribution summary.

General statistical explanation: an adverse-event count describes what was recorded in a defined group over the study observation period. Interpretation depends on the population, duration of observation, event definitions, and completeness of reporting. The record says participants were involved for between 2 and 12 days, but it does not give individual follow-up durations for safety or further details about event ascertainment. The listed safety counts should therefore be read as registry-reported observations, not as a complete estimate of risk beyond the study setting.

12. What the Result Does, and Does Not, Mean

The registry record establishes that the study was designed to evaluate renal artery images acquired with gadobutrol-enhanced MRA and unenhanced MRA, with CTA serving as the stated standard of reference. Its primary endpoint asks whether vascular segments were sufficiently visualized for reliable assessment. This is an interpretable image-quality question, distinct from whether a diagnosis was correct or whether an imaging finding changed care.

The record does not report the primary endpoint percentages, reader-specific values, majority-reader values, or uncertainty estimates. It therefore does not show the observed level of assessability or how precisely that level was estimated. The listed secondary measures also have no results in the registry record. No conclusion about diagnostic performance or relative imaging performance can be drawn from the endpoint definitions alone.

The study’s single-group, nonrandomized design is also important. It does not provide a randomized comparison between participant groups assigned to different imaging strategies. The imaging assessments are described within the same study, but the record does not provide enough information to characterize every analysis as paired, determine how incomplete image sets were handled, or evaluate a formal statistical contrast.

General statistical explanation: an endpoint can be measured precisely yet remain limited in what it answers. Assessability indicates whether images can be interpreted according to the stated rule; it does not, by itself, quantify sensitivity, specificity, agreement with CTA, or clinical benefit. Those questions require their own defined outcomes and reported analyses.

The safety entry records no serious adverse events among 315 participants at risk, 14 participants with other adverse events among 315 at risk, and no reported death count. These observations do not establish causation or comparative safety. Overall, the registry supplies design and endpoint definitions but not the outcome data needed to quantify the imaging findings. The scope of interpretation is therefore limited to what the study set out to measure and how it was structured.

13. Why This Trial Matters Statistically

This study illustrates a statistical distinction that matters in imaging research: whether a feature is assessable is not the same question as whether it is classified correctly. A segment may meet the registry’s visualization and measurement rule without that result alone establishing diagnostic accuracy. Keeping those endpoints separate helps prevent an image-quality measure from being interpreted as a clinical-performance measure.

The design also highlights the structure of imaging data. Multiple vascular segments can be assessed within one participant, and the same images can be read by multiple readers. General statistical explanation: these repeated assessments may be related. Analyses that account for participant clustering and reader variation can give a more appropriate account of uncertainty than methods that treat every segment or reader assessment as independent. The registry record does not say how these features were handled, making the missing analysis details consequential for interpretation.

The comparison has more than one reference point. Enhanced MRA is assessed against unenhanced MRA, while CTA is described as the standard of reference. Distinguishing comparator from reference standard clarifies what an analysis can establish. A comparison of assessability between MRA image sets is not interchangeable with an accuracy comparison against CTA.

The registry also lists many outcome measures and analyses. General statistical explanation: a broad analysis program makes prespecification and transparent reporting important, because readers need to know which outcomes were primary and how multiple comparisons were addressed. The record identifies a primary endpoint but does not report the analysis plan, multiplicity approach, or results.

Finally, the absence of endpoint estimates is itself an interpretive constraint. Study design details can explain the intended question, but they cannot substitute for effect estimates, denominators, and uncertainty. This record is therefore useful for understanding the measurement framework and its limitations, while leaving the central empirical result unresolved.

14. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The primary limitation for interpretation is that the registry record describes the endpoint but does not report its values. No percentage of assessable segments, evaluable denominator, reader-specific estimate, majority-reader estimate, or uncertainty interval is reported. The corresponding results for the listed secondary outcomes are also not reported in the registry record.

The analysis population is identified as FAS, but the acronym is not defined in the record. There is no account of exclusions, unavailable images, missing segments, or how incomplete assessments were handled. Because the endpoint is segment-based and participants can contribute different numbers of segments, the actual contribution of each participant to the reported analysis cannot be determined from the record.

The statistical methods are not described in enough detail to assess whether the analysis accounted for clustering of segments within participants or variation across readers. The record defines a majority-reader result but does not report reader agreement, reader-specific results, or the treatment of disagreements beyond that definition. It also does not report a hypothesis-testing plan or a method for handling multiple outcomes and analyses.

The study is open-label, nonrandomized, and single-group. Independent blinded image review is described, but procedures ensuring reader blinding are not reported. CTA could have been performed up to 60 days before enrollment or required for the study; the record does not report the distribution of these timing situations or discuss how differences in timing were handled in analyses.

Enrollment was 317, while safety entries list 315 participants at risk. The record does not explain this difference. It reports no serious adverse events, 14 participants affected by other adverse events, and no death count. Details needed to assess event timing, follow-up completeness, and causal attribution are not reported. These limitations prevent reconstruction of the endpoint findings or a comprehensive assessment of safety from the registry record alone.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Gadobutrol Enhanced MRA of the Renal Arteries — NCT01344460.
• Registry record last updated 2015-08-26; status last verified 2015-07.
• Results first posted 2015-08-26.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

18. Record Summary

NCT01344460, titled Gadobutrol Enhanced MRA of the Renal Arteries, is listed as a completed Phase 3, multicenter, open-label, nonrandomized, single-group study sponsored by Bayer. It enrolled 317 participants with known or suspected renal artery disease. The study started in 2011-05, and primary completion was in 2012-07.

Participants received a single injection of gadobutrol at 0.1 mmol/kg. The primary endpoint was the percentage of vascular segments assessable on enhanced and unenhanced MRA, with CTA described as the standard of reference. Assessability required full-length visualization and reliable measurement of any stenosis. Three independent blinded readers and a majority-reader assessment were described.

The registry lists 22 outcome measures and 29 analyses. It reports 0 participants with serious adverse events among 315 at risk and 14 participants affected by other adverse events among 315 at risk. The death count is not reported in the registry record. Primary and secondary outcome results, statistical analysis details, and missing-data procedures are not reported in the registry record.