Comparison of 18F FDG PET/CT TO PET MRI: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Comparison of 18F FDG PET/CT TO PET MRI (NCT01986985), a na na study. The primary outcome is PET/MR Images Clinical Usefulness.

2. Clinical Question

The central question is about the clinical usefulness of images obtained with the PET/MRI system, rather than a randomized comparison of imaging strategies. The record says the study aimed to gather images and associated data to test MR attenuation correction of PET data, and to support regulatory submission and future product development and marketing. It does not describe a specific disease-focused research question or a comparison of diagnostic decisions between imaging methods.

The broad eligibility description covers any condition with a clinical indication for PET/CT exam. It does not specify which conditions, clinical settings, or participant characteristics were represented. The primary outcome population is limited to people whose images were successfully collected using PET/MR. Whether this population included all enrolled participants is not reported in the registry record. The registry record also does not report a primary endpoint result, so it cannot establish how often clinically relevant images were obtained.

3. Trial Design

NCT01986985 is listed as completed, with a single-group model and an enrollment of 58 participants. The recorded study start is 2014-01 and the primary completion date is 2014-06. The sponsor is GE Healthcare. The phase and allocation are listed as NA, and masking is listed as NONE. These design details describe a non-randomized evaluation rather than an allocation of participants between competing study arms.

The sole listed arm is a single-arm PET MRI group, described as a single-group evaluation of PET/MRI system scans for diagnostic quality of image. The intervention is the PET/MRI system, categorized as a device. No separate PET/CT arm, usual-care arm, or other control group is listed. Accordingly, the title's reference to PET/CT and PET MRI should not be read as evidence that the registry describes a controlled, like-for-like comparison. The record specifically flags that the study is not a randomized comparison and that its arms are not a like-for-like control comparison.

The objective in the study summary is to gather image and associated data for a pre-market PET/MRI scanner. The summary identifies testing MR attenuation correction of PET data as a reason for collecting clinical data, and also mentions regulatory submission and future product development and marketing. It says these aims require a clinical study. It does not give further details about the scanning protocol, image-reading process, criteria for diagnostic quality, or how clinical relevance was judged; these details are not reported in the registry record.

Completion status and enrollment describe the study's administrative and recruitment record, not the primary outcome result. The registry record lists one outcome measure but no analyses. It does not report a sample-size justification, a planned control comparison, or additional design details that would support a comparative efficacy interpretation.

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.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Subjects with images successfully collected using PET/ MR

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.

Population: Intent to treat

6. Primary Endpoint

The registry lists the primary outcome as PET/MR Images Clinical Usefulness, measured over 1 day.

The primary outcome, titled PET/MR Images Clinical Usefulness, is a participant count. It is defined as the number of participants for whom clinically relevant images are obtained. The stated timeframe is 1 day, and the outcome population is subjects with images successfully collected using PET/MR.

This type of endpoint can describe whether an imaging session yielded images that meet a clinical-usefulness criterion. It focuses on image acquisition and assessment, rather than on a change in a participant's health or on a direct comparison of diagnostic accuracy between two imaging systems. The registry record does not provide the operational definition of clinically relevant, the assessment criteria, or who made the assessment. It also does not report how disagreements between assessors, if any, were handled.

The population wording matters for interpretation: the outcome is defined among participants with successfully collected images. If participants without successfully collected images were excluded from the endpoint denominator, the count would not describe image usefulness among every enrolled participant. The registry record does not state the number of participants with successfully collected images or explain whether unsuccessful collection was incorporated into the endpoint.

No primary outcome count or other result for this endpoint is reported in the registry record. Therefore, the endpoint definition explains what the study intended to measure, but the record does not support a numerical estimate of how often clinically relevant images were obtained.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registered primary outcome is binary in nature: each participant either has clinically relevant images obtained or does not, according to the study's assessment. The outcome is expressed as a number of participants rather than as a continuous measurement. The record gives the outcome title, the count parameter, its timeframe of 1 day, and the population description, but does not provide an operational rule for classifying images as clinically relevant.

What does a participant count tell the reader?

For a binary endpoint, the observed count describes how many participants meet the stated criterion. To understand the frequency, readers also need the relevant denominator. A proportion can be calculated only when the number meeting the criterion and the population included in that calculation are known. Neither a primary outcome count nor the endpoint denominator is reported in the registry record. No proportion should therefore be inferred from enrollment alone, especially because the endpoint population is specified as subjects with images successfully collected.

General statistical explanation: uncertainty around a binary outcome estimate is commonly described with a confidence interval. Such an interval gives a range of values consistent with the observed data under a chosen method and assumptions. Its interpretation depends on the data, denominator, and method; it is not a guarantee that a particular value is correct. The registry record does not report an estimate or confidence interval for the primary outcome, so neither the level of observed usefulness nor its precision can be assessed.

Why does the single-group design matter?

The record lists a single PET MRI group, with no separate comparator group. A single-group design can describe observations made in that group, if outcome data are reported. It does not by itself distinguish the effect of the imaging system from other explanations for observed differences, and it does not provide a randomized comparison with PET/CT. Here, the primary outcome result is also absent, so even a descriptive estimate of the group outcome is unavailable in the registry record.

General statistical explanation: random allocation can help balance known and unknown participant characteristics between groups, while a control group provides a reference for interpreting outcomes. Neither feature is described for this study. The record lists allocation as NA and masking as NONE. These entries should be read as registry design descriptors, not as evidence about the quality of an unreported image assessment.

What do the analysis and sample-size details establish?

The registry record lists zero analyses. It does not report an analysis method for the primary endpoint, a hypothesis test, an adjusted model, or a precision estimate. A lack of an analysis entry does not establish what analyses may have been conducted outside the registry record; it means those details are not reported in the registry record.

The record does not report a trial-specific sample-size justification. Any sample-size illustrations associated with this study are planning illustrations, not the design basis of the trial and not observed power. The stated illustration assumptions are a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with the effect to detect specified as a fraction of the observed effect. The record notes that time-to-event illustrations give total events, while other illustrations give participants per arm. Those are planning conventions, not findings from this single-group study, and should not be treated as evidence that the trial was planned or conducted as a two-arm comparison.

General statistical explanation: power calculations are prospective planning tools that depend on assumptions about the effect, variability or event frequency, significance level, and design. They do not measure the probability that a particular result is true after data collection. Observed power is not an appropriate substitute for an effect estimate and its uncertainty. Since no primary outcome estimate is reported, the registry record does not permit an assessment of the observed effect or its precision.

Why are denominator and missingness rules important?

The endpoint population is limited to participants whose images were successfully collected. The record does not say how many participants met that description, whether all enrolled participants had images collected, or what happened to images that were missing, incomplete, or not assessable. Different denominator rules can answer different questions: an analysis among successfully imaged participants describes that selected group, while an analysis including all enrolled participants can also reflect whether image collection succeeded. The registry record does not specify which approach was used for the posted endpoint, and no endpoint count is reported.

General statistical explanation: missing data can affect both the denominator and the interpretation of an estimate. If missingness is related to participant characteristics or the outcome, results among observed cases may differ from results for the full enrolled group. Clear reporting usually states how missing observations were handled and identifies the analysis population. Neither a missing-data method nor a defined analysis population beyond the endpoint's image-success wording is reported in the registry record.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Single Arm PET MRI")
n      <- c(58)
events <- c(51)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Single Arm PET MRI  58  51  87.9  76.7  95.0  77.1  94.0  77.1  94.0

11. Multiplicity, Missing Data and Analysis Populations

The registry record lists one primary outcome measure: the number of participants for whom clinically relevant PET/MR images are obtained. It lists zero analyses. No additional primary or secondary outcome analyses, statistical testing strategy, or adjustment for multiple comparisons is reported in the registry record. Although a single listed endpoint reduces ambiguity about which registered measure is primary, it does not establish that no other analyses were planned or performed outside the record.

General statistical explanation: multiplicity arises when several outcomes, comparisons, time points, or subgroups are tested. Repeated testing can increase the chance of a false-positive result if each test is interpreted without regard to the others. Methods such as prespecifying a primary outcome or adjusting inference can address particular multiplicity concerns. The registry record does not describe such methods, and no inferential result is reported for the primary outcome.

The endpoint population is described as subjects with images successfully collected using PET/MR. The record does not report how many enrolled participants had successfully collected images, whether all enrolled participants were included in the endpoint population, or how participants with missing or unusable images were handled. It also does not describe imputation, exclusions, or a sensitivity analysis. These missing details matter because the outcome count could be interpreted differently depending on whether unsuccessful image collection is excluded or counted as failure to obtain clinically relevant images.

No named analysis population, such as an intention-to-treat or per-protocol population, is reported in the registry record. With a single-group design and no primary outcome result, it is not possible to determine which participants contributed to an analysis or whether the analytic set differed from the 58 enrolled participants. The safety entries report their own at-risk counts, but these do not define the analysis population for the image-usefulness endpoint.

12. 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 0% reporting threshold.

Most frequent non-serious adverse event terms

The registry record lists 58 participants at risk for serious adverse events and reports 0 participants affected. It also lists 58 participants at risk for other adverse events and reports 5 participants affected. These are participant counts in the safety record; they should not be confused with the primary outcome, which concerns clinically relevant images.

The record does not list specific serious adverse event terms. The deaths field is not reported in the registry record. The safety entries do not provide event descriptions, timing, severity details beyond the serious-versus-other categorization, or information about attribution to the imaging system. The counts alone cannot establish whether an event was caused by the device or by another factor.

General statistical explanation: an observed count is descriptive. Its interpretation depends on how events were collected, how long participants were followed, and how events were classified. The primary outcome timeframe is listed as 1 day, but the safety follow-up duration is not reported in the registry record. The counts therefore should be read as the registry's reported safety figures, not as a complete account of risk over a known period or as a comparison with another group.

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

The registry record establishes that NCT01986985 was a completed, single-group evaluation of a PET/MRI system, with 58 participants enrolled. It describes an intended primary assessment of whether clinically relevant images were obtained and gives the endpoint timeframe as 1 day. The record also explains that the study aimed to gather image and associated data to test MR attenuation correction of PET data, with regulatory submission and future product development and marketing among the stated purposes.

What the posted record does not establish is the primary outcome result. No count of participants with clinically relevant images is reported, and the endpoint denominator is not given. Therefore, the record does not show how often the criterion was met or how precise an estimate would be. The status COMPLETED and the enrollment count do not serve as substitutes for those missing results.

The title refers to PET/CT and PET MRI, but the registered design lists one PET MRI group and no comparator arm. Consequently, the record does not provide a like-for-like estimate of differences between the imaging methods. It also does not report comparative diagnostic accuracy, effects on clinical decisions, or patient outcomes. These questions should not be answered by inference from the study title or objective.

The safety record reports 0 participants affected by serious adverse events among 58 at risk and 5 participants affected by other adverse events among 58 at risk. These figures are descriptive and are not accompanied by serious event terms or a reported follow-up duration. They do not provide a comparison with another group or establish attribution.

General statistical explanation: study objectives, design, and results are distinct. An objective states what investigators sought to assess; a design describes how the evaluation was organized; results show what was observed. The registry record supplies the first two for this evaluation but does not report the primary endpoint finding. A careful reading should retain that distinction and avoid interpreting an unreported result as either favorable or unfavorable.

14. Why This Trial Matters Statistically

This study is statistically notable because its title suggests a comparison, while its registered model is single group. That distinction illustrates why design details matter: a reader should identify the groups actually registered before interpreting a study as a controlled comparison. The record lists one PET MRI arm and explicitly notes that it is not a randomized comparison and that the arms are not a like-for-like control comparison.

The primary outcome also illustrates the importance of defining the analysis population. It is a participant count among subjects with images successfully collected using PET/MR, rather than an explicitly stated count among all enrolled participants. Without the number of successful image collections and the outcome count, neither the endpoint frequency nor the relationship between image collection and image usefulness can be evaluated from the registry record.

The study objective concerns a technical imaging question: collecting clinical data to test MR attenuation correction of PET data. Such a purpose makes image acquisition and the clinical usability of resulting images relevant outcomes. Yet a clear outcome definition, transparent assessment procedure, and reported result are needed for readers to evaluate what was observed. The registry record does not report the criteria used to classify images as clinically relevant or the primary result.

Finally, the record demonstrates that enrollment and completion status are not outcome summaries. The study is listed as completed with an enrollment of 58, but those administrative details do not reveal the primary endpoint count or its precision. For statistical interpretation, readers need the observed endpoint data, denominator, analysis population, and methods—not just the design description and objective.

15. 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.

Several limitations specific to this registry record constrain interpretation. First, the primary outcome result is not reported. The record defines clinically relevant images as the outcome but gives no number of participants meeting that definition and no endpoint denominator. This leaves the main study question unanswered by the posted results.

Second, the listed endpoint population includes only subjects with images successfully collected using PET/MR. The number of successful collections, the handling of unsuccessful scans, and the inclusion or exclusion of participants without usable images are not reported in the registry record. This prevents readers from determining whether the endpoint describes all enrolled participants or a subset selected by successful acquisition.

Third, the record describes one PET MRI group rather than a separate PET/CT comparison group. Despite the title, the design does not provide a registered like-for-like control comparison. The record also does not report the image acquisition protocol, assessment criteria for clinical relevance, assessor qualifications, or procedures for resolving differing assessments.

Fourth, statistical methods are sparse in the record. It lists zero analyses and does not report an analysis plan, sample-size justification, confidence interval, or method for handling missing data. These details are not reported in the registry record, so the statistical precision and robustness of any endpoint finding cannot be assessed.

Finally, the safety entries lack reported serious event terms and a stated follow-up duration; deaths are not reported in the registry record. The available safety counts therefore offer limited context and should not be treated as a complete characterization of safety or as a comparison against another imaging method.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Comparison of 18F FDG PET/CT TO PET MRI — NCT01986985.
• Registry record last updated 2016-03-07; status last verified 2016-02.
• Results first posted 2015-05-04.
• 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.

19. Record Summary

NCT01986985 is listed as a completed single-group evaluation of a PET/MRI system, sponsored by GE Healthcare. Enrollment was 58, with a study start of 2014-01 and primary completion of 2014-06. The record lists the condition as any condition with a clinical indication for PET/CT exam and describes the objective as collecting image and associated data for a pre-market PET/MRI scanner, including testing MR attenuation correction of PET data.

The sole primary outcome is PET/MR Images Clinical Usefulness: the number of participants for whom clinically relevant images are obtained, among subjects with images successfully collected, with a timeframe of 1 day. The primary outcome result and its denominator are not reported in the registry record. The listed design has no separate comparator group, and the record lists zero analyses.

Safety entries report 0 participants affected by serious adverse events among 58 at risk and 5 affected by other adverse events among 58 at risk. Serious event terms and deaths are not reported in the registry record. The design and outcome definitions are available, but the primary finding needed to evaluate image usefulness is absent.