This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for TRACER RGD-K5 Carotid Plaque Imaging Study (NCT01968226), a na phase 2 study. The primary outcome is Target to Background Ratio (TBR).
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT01968226 |
| Phase | Phase 2 |
| Condition | Carotid Artery Disease, Carotid Stenosis |
| Allocation | Not applicable (single group) |
| Design model | Single Group |
| Masking | None (open label) |
| Enrollment | 3 |
| Arms in the primary outcome | n/a |
| Lead sponsor | The Cleveland Clinic |
| Results posted | Yes |
2. Clinical Question
Population
Participants with carotid artery stenosis being considered for carotid endarterectomy. The record describes the study group as people with carotid artery stenosis and frames the imaging assessment as occurring before surgery. It does not report a subject analysis, so the number of participants represented in the primary outcome is not reported in the registry record.
Intervention
Intravenous administration of the radiolabeled tracer [F-18] RGD-K5, followed by PET/CT imaging to measure uptake in carotid plaque. The record describes the imaging procedure and tracer exposure; it does not report an analyzed uptake value.
Comparator
There is no separate comparator group. The study is described as single-group and non-randomized, and the registry record does not identify a control arm or a like-for-like comparison.
Primary question
Can plaque uptake of [F-18] RGD-K5 be assessed with PET/CT before carotid endarterectomy, using the target-to-background ratio of the standard uptake value as a surrogate marker of plaque inflammation? The record also describes an intended comparison with histological study of plaque samples collected during planned surgery, but reports no analysis of imaging or histology.
3. Trial Design
This is a Phase II, exploratory, open-label, single-center, non-randomized, single-group study. The registry lists an enrollment of 3 and a status of terminated. The listed study dates are start in 2013-11 and primary completion in 2016-06. The reason for termination is not reported in the registry record.
The study group is described as participants with carotid artery stenosis. The stated purpose was to examine [F-18] RGD-K5 uptake in carotid plaque using PET imaging in people being considered for carotid endarterectomy. The tracer is described as being administered intravenously, with plaque uptake observed by PET. The primary outcome is specified at baseline, before carotid endarterectomy.
Although the intervention is categorized as a drug, the described study question concerns tracer uptake measured during imaging. The record characterizes the study as observational in its group description: all participants have carotid artery stenosis, and the observation is plaque uptake after tracer administration. The record does not describe a randomized treatment assignment or a control group. Thus, it does not support a treatment-versus-control estimate.
The stated purpose also includes confirming imaging findings through histological studies of plaque samples collected during planned surgery. However, the registry record reports no subject analysis for the primary outcome and no analysis count. It does not report whether the planned histological assessments were completed or how imaging and histology were to be compared. Those details, along with the reason the study was terminated, are not reported in the registry record.
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
| Stage | PET Imaging With [F-18] RDG-K5 |
|---|---|
| STARTED | 3 |
| COMPLETED | 1 |
| NOT COMPLETED | 2 |
Reasons for not completing this period:
| Reason | PET Imaging With [F-18] RDG-K5 |
|---|---|
| [F-18] RDG-K5 was not available | 2 |
Analysis population for the primary outcome, as defined in the registry: no subject analysis done
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: Due to trial termination, no subject analysis was completed
| Characteristic | Unit | PET Imaging With [F-18] RDG-K5 |
|---|---|---|
| Participants analysed | 3 | |
| Age, Categorical: <=18 years | Participants | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 0 |
| Age, Categorical: >=65 years | Participants | 0 |
| Sex: Female, Male: Female | Participants | 1 |
| Sex: Female, Male: Male | Participants | 2 |
| Ethnicity (NIH/OMB): Hispanic or Latino | Participants | 0 |
| Ethnicity (NIH/OMB): Not Hispanic or Latino | Participants | 3 |
| Ethnicity (NIH/OMB): Unknown or Not Reported | Participants | 0 |
| Race (NIH/OMB): American Indian or Alaska Native | Participants | 0 |
| Race (NIH/OMB): Asian | Participants | 0 |
| Race (NIH/OMB): Native Hawaiian or Other Pacific Islander | Participants | 0 |
| Race (NIH/OMB): Black or African American | Participants | 0 |
| Race (NIH/OMB): White | Participants | 3 |
| Race (NIH/OMB): More than one race | Participants | 0 |
| Race (NIH/OMB): Unknown or Not Reported | Participants | 0 |
6. Primary Endpoint
The registry lists the primary outcome as Target to Background Ratio (TBR), measured over Baseline.
| Element | Registry entry |
|---|---|
| Result type | N/A |
| Measure of spread | not applicable |
| Unit | not stated |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint is the target-to-background ratio (TBR) of the standard uptake value (SUV) for [F-18] RGD-K5 in carotid plaque, assessed with PET/CT at baseline. In general, a target-to-background ratio expresses a signal measured in a target region relative to a reference or background signal. It is intended to make the target signal interpretable in relation to surrounding or reference activity, rather than as an isolated uptake measurement.
The registry record identifies plaque TBR as a surrogate marker of plaque inflammation in participants being considered for carotid endarterectomy. A surrogate is a measured feature used as an indicator of a biological process or clinical feature; it is not itself the clinical outcome of interest. The study’s stated purpose was to investigate whether tracer uptake could identify regions of unstable atherosclerotic plaque and to examine that ability using histological studies of surgical plaque samples.
The endpoint is specified for baseline, before surgery. No unit, numerical TBR result, summary statistic, or analysis is reported in the registry record. The record also reports no subject analysis, so it does not establish whether the planned measure was obtained or how it related to histological findings.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record identifies a planned primary measure—baseline plaque TBR from [F-18] RGD-K5 PET/CT—but gives no analyzed value for that measure. It explicitly states that no subject analysis was done. Therefore, there is no posted estimate of plaque tracer uptake to interpret, and no estimate of precision such as a confidence interval. The record does not report an analysis of whether the imaging measure corresponds to plaque inflammation or to histological findings.
The enrollment listed in the record is 3, but enrollment is not the same as an analyzed endpoint sample. Because the record says no subject analysis was done, it is not possible to infer how many participants contributed usable imaging data, whether any measurements were missing, or whether the planned surgery and tissue collection occurred. Such details are not reported in the registry record.
The design also limits the kind of conclusion the study could support. It is a single-group, non-randomized study without a separate comparator. Its stated purpose is exploratory assessment of tracer uptake, not estimation of a randomized contrast between interventions. The record therefore does not provide a comparison that could separate imaging findings from differences between treatment groups. No such comparison is reported.
The listed endpoint is a surrogate marker, not a clinical event or a direct measure of patient benefit. Even if a TBR value had been reported, interpretation would depend on how the value was measured and summarized, its variability, and whether it was assessed against an appropriate reference such as histology. Those results are not reported in the registry record. The endpoint’s intended role as a marker does not by itself establish that it identifies unstable plaque.
The status is terminated, but the registry record does not report why the study ended or whether termination was related to enrollment, feasibility, safety, or another reason. It is not appropriate to infer a cause from the status alone. The safety record lists one participant at risk for serious adverse events and zero affected, and one participant at risk for other adverse events and zero affected. These limited entries do not provide a complete account of safety experience; deaths are not reported in the registry record.
Overall, the record documents an imaging question and an intended endpoint, but not analyzed imaging findings. It therefore supports description of the study’s aim and design, not a conclusion about tracer performance, plaque inflammation, histological agreement, or clinical benefit.
9. Statistical Methods Explained
The record describes a single-group, non-randomized study. In general, a single-group design observes participants who receive or undergo the same study procedure, without a separate concurrent control group. It can describe measurements within that group, but it does not create a randomized comparison between groups. Here, the stated observation is carotid plaque uptake after intravenous [F-18] RGD-K5 and PET imaging. The registry record does not report an analyzed uptake result.
What does randomization contribute?
In general, randomization assigns participants to study groups by chance. When a study compares groups, random assignment can help balance known and unknown participant characteristics, making differences in outcomes easier to interpret as related to the assigned intervention. This study is listed as non-randomized and single-group, with no separate comparator. It therefore does not estimate a randomized between-group effect. The record’s allocation field is listed as not applicable, consistent with the absence of a randomized allocation.
The study is open-label, meaning the record does not describe masking. In general, masking can reduce the influence of knowledge about a study procedure on measurement, interpretation, or reporting. The registry record does not describe any masking or give details about how PET images or histological samples were assessed. Those procedures are not reported in the registry record.
How should the endpoint be understood?
The primary endpoint is TBR of SUV in carotid plaque at baseline. In general, a ratio places one measurement in relation to another and can be useful when the target signal needs context from a background or reference signal. The ratio also has statistical considerations: its behavior can depend on both the target and reference measurements, and uncertainty in either can affect the resulting ratio. This is a general explanation, not a description of an analysis reported for this study.
In general, a statistical summary of an endpoint might include a point estimate, a measure of variability, and an interval expressing uncertainty. A confidence interval gives a range of values compatible with the observed data under the chosen statistical model; it does not guarantee that the true value lies within that interval. No endpoint estimate, variability measure, confidence interval, or statistical test is reported in the registry record. No subject analysis was done.
Variability matters because participants may differ in their underlying plaque characteristics and because imaging measurements can vary. In general, over-dispersion occurs when the observed variability is greater than a statistical model expects. If a model fails to account for over-dispersion, uncertainty may be understated. The registry record does not report a statistical model or an assessment of dispersion for this endpoint; this general issue should not be mistaken for a finding from the study.
What do the planning assumptions mean?
The planning illustration is described as using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It is based on a stated fraction of an observed effect. In general, a two-sided significance level sets a threshold for assessing evidence against a null hypothesis in either direction; it is not the probability that a conclusion is correct. Equal allocation describes a planning setup in which groups are assigned the same planned size. A normal approximation uses a normal distribution to represent the behavior of a statistic under specified assumptions.
These assumptions do not describe the registered study design, which is single-group and has no comparator arm. The registry record does not report an observed effect for this study, so the effect to be used in an illustration is not reported in the registry record. A planning calculation is not observed power and does not establish that the study could detect an effect. Any sample-size values should be read as planning illustrations under their stated assumptions, not as results from participants in this study.
The record notes that time-to-event planning tables use a total number of events, while other planning tables use participants per arm. In general, event-based planning focuses on how many outcome events are observed, whereas group-based planning expresses a planned participant count for each arm. Neither form should be interpreted as an observed count or as an estimate of this study’s outcome, particularly because the registered design has one group and reports no subject analysis.
The record does not report a statistical analysis plan, a primary hypothesis test, adjustment for covariates, handling of repeated measurements, criteria for image quality, or a method for comparing imaging with histology. It also does not report interim analyses. These items are not reported in the registry record, so a specific inferential method cannot be attributed to the study.
10. Multiplicity, Missing Data and Analysis Populations
The registry record lists one primary outcome measure: baseline TBR of SUV for [F-18] RGD-K5 in carotid plaque. It reports no analysis for that measure and no analysis count. The intended histological assessment is described in the study purpose, but the registry record does not list an analyzed histological outcome or explain how multiple measurements or comparisons would be handled.
Multiplicity arises in general when several outcomes, time points, subgroups, or statistical tests are examined. Without a prespecified analysis plan, repeated testing can increase the chance of findings that appear notable by chance. The registry record does not report a multiplicity strategy, a hierarchy of outcomes, or a statistical analysis plan. It is therefore not possible to determine whether any adjustment or other multiplicity approach was planned.
The record states that no subject analysis was done. It does not report participant-level endpoint availability, reasons for missing imaging or histology, exclusions, or an analysis population. These details are not reported in the registry record. Enrollment of 3 does not establish how many participants had analyzable PET measurements or surgical tissue available.
In general, missing-data methods depend on why observations are missing and on the analysis being conducted. The registry record does not describe a missing-data method or provide enough information to assess missingness. It also does not report whether any participants withdrew or whether any measurements were unusable. No assumptions about complete follow-up or missing outcomes can be made from the available record.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| PET Imaging With [F-18] RDG-K5 | 0 | 1 | 0.0% |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| PET Imaging With [F-18] RDG-K5 | 0 of 1 |
The safety entries list one participant at risk for serious adverse events and zero affected. For other adverse events, the record also lists one participant at risk and zero affected. These are the counts recorded in the registry entry; they do not constitute a detailed description of events or a full analysis of safety.
The record does not list serious adverse event terms, and it does not report event timing, severity details, relatedness to the tracer or imaging procedure, or a broader narrative of safety monitoring. These details are not reported in the registry record. The deaths field is null, which means a death count is not reported in the registry record; it should not be interpreted as a reported zero.
The listed number at risk is limited and should be read as a denominator attached to the registry safety entry, not as evidence that all enrolled participants were assessed for every safety outcome. The record does not explain how the safety population was defined. In general, safety counts describe recorded events within a defined group and period; they do not by themselves show whether an intervention caused an event. No causal safety conclusion can be drawn from these entries.
12. What the Result Does, and Does Not, Mean
The record establishes that an exploratory Phase II study was registered to assess carotid plaque uptake of [F-18] RGD-K5 using PET/CT. Its primary measure was baseline TBR of SUV, intended as a surrogate marker of plaque inflammation before carotid endarterectomy. The study’s stated purpose also included histological assessment of plaque samples collected during planned surgery.
The record does not establish what the imaging found. It reports no subject analysis and gives no numerical TBR result, uncertainty estimate, or analysis comparing imaging with histology. It therefore does not show whether tracer uptake identified unstable plaque, whether the imaging measure agreed with histological findings, or how reproducible the measure was.
The design is single-group and non-randomized, without a separate comparator. Even with a reported measurement, this design would describe observations in the study group rather than provide a randomized comparison between interventions. The listed endpoint is a surrogate marker; a surrogate measurement is not equivalent to evidence about a clinical outcome.
The registry lists enrollment of 3 and a terminated status. It does not report the reason for termination or explain whether the planned assessments were completed. The safety entries list zero affected for the recorded serious and other adverse event categories, but the risk counts are limited and deaths are not reported in the registry record. These entries should not be treated as a complete safety account.
Accordingly, the record is informative about the study question and intended design, but it does not provide analyzed findings from which to judge tracer performance, clinical value, or safety comprehensively. No conclusion that the tracer works or does not work is supported by the registry record.
13. Why This Trial Matters Statistically
This study illustrates a distinction between a clearly described research question and an interpretable statistical result. The registry identifies a specific imaging measure—plaque TBR of SUV—and states why it was of interest: to assess tracer uptake as a surrogate marker of plaque inflammation. Yet the record reports no subject analysis. Without an analyzed measurement, the endpoint cannot answer the stated imaging question.
It also highlights how design determines the scope of inference. A single-group, non-randomized study can be exploratory and can characterize measurements in its study group, but it does not supply a randomized comparator. In this record, no endpoint estimate is reported either, so even a descriptive account of uptake is unavailable. The study’s intended comparison with histology would require reported measurements and a clear account of how they were related; those results are not reported in the registry record.
The mismatch between the single-group design and the two-arm assumptions described for planning illustrations is also statistically important. Planning assumptions belong to a calculation framework, not necessarily to the design that was ultimately registered. They should not be mistaken for evidence that the study enrolled or compared two arms, or for proof that a particular effect could be detected.
Finally, the record shows why status and enrollment alone cannot substitute for outcome reporting. A terminated status does not explain what happened to the study, and an enrollment figure does not identify how many participants contributed analyzable imaging or histology. Clear reporting of analysis populations, missing data, methods, estimates, and uncertainty is necessary to interpret a clinical study’s findings.
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 main limitation for statistical interpretation is that the primary endpoint has no reported subject analysis. There is no TBR estimate, variability measure, confidence interval, or statistical test in the registry record. Consequently, the record cannot describe the observed distribution of tracer uptake or its precision.
The registered design is single-group and non-randomized, with no separate comparator. That limits the study’s ability to support a comparative inference. The record describes the planned use of histological studies to confirm imaging ability, but does not report whether those studies were completed or how imaging and tissue findings were analyzed.
The registry lists enrollment of 3, but does not report the primary endpoint analysis population, image availability, missing measurements, withdrawals, or exclusions. Enrollment cannot be substituted for the number of participants with usable outcome data. The reason for the terminated status is also not reported in the registry record.
Other methodological details are not reported in the registry record, including the statistical analysis plan, image-reading procedures, blinding of assessors, handling of multiple measurements, missing-data methods, and any interim analyses. Without those details, the planned or completed inferential procedures cannot be evaluated.
Safety information is limited to the listed at-risk and affected counts. Event descriptions and deaths are not reported in the registry record. These limitations mean that the available record supports description of the study’s aim and design, but not a substantive assessment of efficacy, imaging validity, histological agreement, or comprehensive safety.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: TRACER RGD-K5 Carotid Plaque Imaging Study — NCT01968226.
- Registry record last updated 2017-09-12; status last verified 2017-08.
- Results first posted 2017-08-10.
- 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.
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18. Record Summary
The registry record describes TRACER RGD-K5 as an exploratory, open-label, single-center, non-randomized Phase II study in participants with carotid artery stenosis being considered for carotid endarterectomy. The study was designed to assess carotid plaque uptake of intravenously administered [F-18] RGD-K5 using PET/CT, with baseline TBR of SUV listed as the primary outcome.
The record lists enrollment of 3, a start in 2013-11, primary completion in 2016-06, and a status of terminated. It reports no subject analysis for the primary outcome and no analysis count. The reason for termination, analyzed imaging results, histological findings, and a statistical analysis plan are not reported in the registry record.
Safety entries list one at risk and zero affected for both serious and other adverse events. Deaths are not reported in the registry record. The entry therefore describes the intended study and limited registry results, but does not provide an analyzed estimate of tracer uptake or its relationship to plaque inflammation.