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 Compare Technegas Ventilation-Perfusion SPECT and Xenon Ventilation-Perfusion Planar Imaging for Pulmonary Embolism (NCT01458639), a non-randomized phase 3 study. The primary outcome is Sensitivity of Technegas V/Q SPECT for the Diagnosis of PE.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT01458639 |
| Phase | Phase 3 |
| Condition | Pulmonary Embolism |
| Allocation | Non-Randomized |
| Design model | Crossover |
| Masking | Single |
| Enrollment | 18 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Cyclomedica Australia PTY Limited |
| Results posted | Yes |
2. Clinical Question
Population
People being evaluated for pulmonary embolism were the intended study population. The registry lists pulmonary embolism as the condition and an enrollment of 18. The primary outcome description refers to a final diagnosis based on clinical information at 30 days of follow-up. It also describes adjudication by an Independent Adjudication Committee, but the record notes that the trial was terminated and its description of adjudication ends mid-sentence. Whether adjudication was completed for participants is not reported in the registry record.
Intervention
The investigational imaging approach was Technegas ventilation-perfusion SPECT. The arm description specifies Technegas V SPECT imaging with technetium-99m labeled carbon particles and says the results were compared with those of a Xenon-133 ventilation scan. The brief summary also mentions technetium-99m macro-aggregated albumin perfusion imaging. The registry presents these as components of the diagnostic imaging comparison, not as treatment for pulmonary embolism.
Comparator
The comparator was Xenon-133 ventilation planar imaging, described alongside technetium-99m macroaggregate of albumin perfusion imaging in the brief summary. The record identifies a non-randomized crossover design, so the comparison was intended to be within-subject rather than a randomized comparison of separate treatment groups. It does not report the order in which imaging methods were performed or whether that order varied.
Primary question
The primary outcome asked about the sensitivity of Technegas V/Q SPECT for diagnosing pulmonary embolism compared with the sensitivity of Xenon V/Q planar imaging. The reference for the diagnosis was described as blinded reader assessments of V/Q SPECT images compared with a final diagnosis based on clinical information at 30 days. A numerical sensitivity estimate or direct comparison is not reported in the registry record, so the primary question cannot be answered from the posted results.
3. Trial Design
This was a Phase 3, non-randomized, single-masked crossover trial of imaging methods for people being evaluated for pulmonary embolism. The registry lists enrollment as 18. Its brief summary describes a within-subject comparison of Technegas V/Q SPECT with Xenon-133 V/Q planar imaging, with technetium-99m macro-aggregated albumin perfusion imaging included in each approach. In a crossover design, participants are assessed using more than one study condition, allowing comparisons to be made within individuals. That design feature does not make the allocation randomized: the registry explicitly identifies allocation as non-randomized.
The study start is listed as 2012-08 and primary completion as 2015-06. Its status is terminated. The record does not explain why the trial was terminated, when the termination occurred, or how termination affected the number of participants with completed imaging or follow-up. It lists single masking but does not identify who was masked. The outcome description separately calls for blinded readings of the imaging examinations; the record does not give further operational details about masking or reader procedures.
The primary outcome was sensitivity of Technegas V/Q SPECT for pulmonary embolism, compared with sensitivity of Xenon V/Q planar imaging. The stated timeframe was prospective follow-up over 30 days. The description refers to blinded image readings and a final diagnosis based on clinical information, with an Independent Adjudication Committee intended to determine pulmonary embolism status for primary and secondary outcomes. Because the record's text about adjudication is incomplete, the extent to which this process was carried out is not reported in the registry record.
The registry also lists secondary outcomes concerning diagnostic accuracy, positive and negative predictive values, likelihood ratio, and Technegas safety. It records seven outcome measures and zero analyses. These entries show the breadth of the planned outcome assessment, but do not provide numerical results for the primary comparison. The protocol, detailed statistical analysis plan, sample-size justification, interim-analysis plan, imaging sequence, and reasons for termination are not reported in the registry record. The non-randomized allocation also means this should not be read as a like-for-like randomized control comparison.
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: Subjects suspected of PE to have Xe-133 ventilation/Tc-99m macroaggregated albumin (MAA) perfusion (VQ) scan. Must have at least one within 72 hours before imaging: D-dimer, Doppler ultrasound for deep vein thrombosis (DVT) or computed tomography angiography (CTA) for PE. Not have therapeutic dose blood thinner for \> than 72 hrs prior to imaging.
Overall Study
| Stage | Overall Study |
|---|---|
| STARTED | 18 |
| COMPLETED | 12 |
| NOT COMPLETED | 6 |
Reasons for not completing this period:
| Reason | Overall Study |
|---|---|
| Physician Decision | 4 |
| Equipment issue | 1 |
| Inability to obtain subject blood sample | 1 |
Analysis population for the primary outcome, as defined in the registry: Pulmonary embolism adjudication was to be determined by an Independent Adjudication Committee for primary and secondary outcome data and blinded readings of Xe-133 and Technegas Ventilation and Tc-99m MAA Perfusion images were required for primary outcome data. Due to trial termination PE adjudication and blinded readings of images were not 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: All subjects enrolled in the trial.
| Characteristic | Unit | Overall Study |
|---|---|---|
| Participants analysed | 18 | |
| Age, Categorical: <=18 years | Participants | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 12 |
| Age, Categorical: >=65 years | Participants | 6 |
| Age, Continuous | years | 59.5 (34 to 81) |
| Sex: Female, Male: Female | Participants | 7 |
| Sex: Female, Male: Male | Participants | 11 |
| Ethnicity (NIH/OMB): Hispanic or Latino | Participants | 8 |
| Ethnicity (NIH/OMB): Not Hispanic or Latino | Participants | 10 |
| 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 | 8 |
| Race (NIH/OMB): White | Participants | 10 |
| Race (NIH/OMB): More than one race | Participants | 0 |
| Race (NIH/OMB): Unknown or Not Reported | Participants | 0 |
| Region of Enrollment: United States | participants | 18 |
6. Primary Endpoint
The registry lists the primary outcome as Sensitivity of Technegas V/Q SPECT for the Diagnosis of PE, measured over Prospective, 30 days follow-up.
| 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 was the sensitivity of Technegas V/Q SPECT for the diagnosis of pulmonary embolism, compared with the sensitivity of Xenon V/Q planar imaging. Sensitivity is a diagnostic-accuracy measure: in general, it describes how often an imaging method identifies the condition among people classified as having it by a reference standard. It addresses recognition of cases under that reference definition; it does not by itself describe how often a positive imaging result is correct or how often people without the condition receive a negative result.
The registry describes the reference diagnosis as a final diagnosis derived from clinical information at 30 days of follow-up. It also states that blinded reader assessments of V/Q SPECT images were compared with that final diagnosis, and that an Independent Adjudication Committee was to determine pulmonary embolism status for primary and secondary outcomes. The record's description of the adjudication process is cut off after noting trial termination, so completion and implementation details are not reported in the registry record.
Sensitivity is used in diagnostic studies because it focuses on detection among reference-standard cases. A comparison between imaging methods can therefore address whether their case-detection results differ, provided the reference standard and analysis are sufficiently defined. In a crossover study, measurements from the same participant are related rather than independent, a feature that should be accounted for when estimating uncertainty. These are general statistical considerations, not confirmation of the analysis used in this trial.
No numerical sensitivity estimate, between-method contrast, confidence interval, or significance test for the primary endpoint is reported in the registry record. Without those results, the size and precision of any difference between imaging methods cannot be assessed.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record identifies a clinically focused diagnostic comparison: Technegas V/Q SPECT and Xenon V/Q planar imaging in people being evaluated for pulmonary embolism. Its primary question concerns sensitivity, with a final diagnosis based on clinical information at 30 days described as the reference. However, the record does not report a numerical primary sensitivity estimate for either method or a numerical comparison between them. It therefore does not establish from posted results whether the observed sensitivities were similar or different, nor how large any difference may have been.
The design matters for interpreting any comparison. The study is identified as non-randomized and crossover, and its brief summary describes a within-subject comparison. Measurements from the same person are generally correlated. General statistical practice for such a design is to retain that pairing in the analysis and uncertainty estimates; treating the observations as unrelated can misstate precision. The registry does not report the statistical method used, so it is not possible to determine whether or how this dependence was handled.
The record lists single masking and describes blinded readings of imaging examinations. It does not identify who was masked or provide details about how reader assessments were conducted. It also refers to an Independent Adjudication Committee for pulmonary embolism determinations. Because the primary outcome description is incomplete after a statement about trial termination, the record does not establish whether adjudication and follow-up were completed for all participants.
The study status is terminated, and the registry lists enrollment as 18. The reason for termination and its effect on available data are not reported. In general, early termination can leave a study with less information than intended, but the record does not give enough detail to determine whether that occurred or to quantify its consequences. There are seven listed outcome measures and zero analyses recorded. The absence of a posted analysis means that the diagnostic accuracy, predictive values, likelihood ratio, and primary sensitivity comparison cannot be evaluated from this record.
Consequently, statistical significance and precision cannot be assessed. No confidence interval is reported, so the range of effects compatible with the posted data is unavailable. A confidence interval, in general, expresses uncertainty around an estimate; it helps distinguish a precise estimate from one that remains compatible with a broad range of values. No p-value or equivalent test result is reported either. These omissions do not demonstrate that the imaging methods are equivalent or that one is superior. They mean that the registry record does not contain the numerical analysis needed to make those statistical judgments.
The safety listing records zero participants affected by serious adverse events among 12 at risk in the overall study group, and one participant affected by other adverse events among 12 at risk. These counts should be read as registry entries, not as a complete safety comparison between imaging approaches: the displayed adverse-event grouping is overall, and separate method-specific counts are not reported. The death field is null, so deaths are not reported in the registry record.
9. Statistical Methods Explained
Diagnostic sensitivity is the primary statistical concept in this trial. In general, sensitivity is the proportion of people with the condition according to a chosen reference standard who are identified as positive by the test being evaluated. It addresses detection among reference-standard cases. It is distinct from specificity, positive predictive value, and negative predictive value, which address other aspects of diagnostic performance. The registry lists accuracy, positive predictive value, negative predictive value, and likelihood ratio among secondary outcomes, but it does not report numerical analyses for those outcomes.
A diagnostic study needs a reference standard against which test classifications can be judged. The primary outcome description identifies a final diagnosis based on clinical information at 30 days of follow-up and refers to blinded reader assessments of V/Q SPECT images. It also says that an Independent Adjudication Committee was to determine pulmonary embolism status for primary and secondary outcome data. These details indicate the intended basis for judging diagnostic status, but the record's description ends mid-sentence after mentioning trial termination. The completed adjudication procedures, final diagnostic classifications, and handling of uncertain diagnoses are not reported in the registry record.
The trial is listed as crossover and non-randomized, and its brief summary calls it a within-subject comparison. General methods for crossover studies recognize that observations from the same participant are related. An analysis can account for this pairing, while an analysis that assumes independent observations may give inappropriate uncertainty estimates. The record does not identify the statistical model, estimator, or variance method used, so it is not possible to verify how the paired structure was treated. It also does not report the sequence of imaging procedures or whether order effects were assessed.
The registry lists single masking and specifies blinded readings for primary outcome data. Masking can reduce the influence of knowledge about other information on image interpretation, but its role depends on who is masked and how the process is implemented. The record does not identify the masked parties, describe reader training or disagreement resolution, or state whether image readings were independent. Those operational details are not reported in the registry record.
A confidence interval is, in general, a way to express uncertainty around an estimated quantity. For a diagnostic comparison, intervals around each sensitivity or around a paired difference would help show how precisely performance was estimated. No sensitivity estimates, comparative estimate, or confidence interval are reported in the registry record. A p-value or other hypothesis-test result is also not reported. Accordingly, no inferential conclusion about the primary contrast can be drawn from the posted results.
Enrollment is listed as 18, but the record does not state how many participants contributed usable images, complete follow-up, or evaluable reference diagnoses. The distinction matters because the number enrolled need not equal the number analyzed for every outcome. The record lists zero analyses, and does not give analysis populations, exclusions, missing-data counts, or a missing-data method. These details are important for assessing whether the available participants and diagnostic classifications could have affected the reported estimates.
Planning calculations are a different matter from an observed trial result. The record's planning illustration is described as using a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and an effect set as a stated fraction of the observed effect. For time-to-event outcomes, it uses the total number of events under a Schoenfeld approach; other illustrations are expressed as participants per arm. These are general planning assumptions, not a report of the trial's own sample-size justification or observed power. The actual sample-size justification and statistical analysis plan are not reported in the registry record. No planning illustration can substitute for estimates and uncertainty from the completed study.
Over-dispersion is a general issue for count outcomes when variability exceeds what a simple model assumes. It can require a model that allows greater variability to avoid misleading standard errors. The primary outcome is diagnostic sensitivity, not a count outcome as described in the record, and no over-dispersion analysis is reported. This concept therefore should not be read as a method used in this trial. More broadly, no statistical model or analysis specification for the primary endpoint is reported in the registry record.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists seven outcome measures and zero analyses. Among the named secondary outcomes are diagnostic accuracy, positive predictive value, negative predictive value, likelihood ratio, and Technegas safety. The primary outcome is sensitivity of Technegas V/Q SPECT compared with Xenon V/Q planar imaging. Multiple outcomes create a general multiplicity issue: when many hypotheses are assessed, the chance of at least one apparently unusual result can increase unless the analysis plan addresses that issue. The registry does not report a multiplicity adjustment, hierarchy of outcomes, or other strategy for interpreting multiple tests.
The protocol and detailed statistical analysis plan are not reported in the registry record. It is therefore not possible to determine which outcomes were prespecified for formal testing, how outcome definitions were operationalized, or which analyses were intended as primary, secondary, or exploratory. Nor does the record report interim analyses or stopping rules. The trial status is terminated, but the reason and its relationship to planned analyses are not reported.
Missing-data information is also absent. The record lists enrollment as 18 but does not report the number with completed imaging, reference diagnoses, or 30-day follow-up, or the number included in each analysis. It does not describe exclusions, missingness by imaging method, or any method for handling missing observations. These omissions limit assessment of whether the participants with evaluable data represent the enrolled group.
The analysis populations are not reported in the registry record. In general, diagnostic comparisons can depend on which participants have results for both methods and an adequate reference diagnosis. The record does not say whether all enrolled participants, only complete cases, or another defined group contributed to the primary comparison. No adjustment for multiple outcomes or missing data can be inferred from the registry entries.
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 |
|---|---|---|---|
| Overall Study | 0 | 12 | 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 |
|---|---|
| Overall Study | 1 of 12 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Overall Study |
|---|---|---|
| Systolic blood pressure increase | Investigations | 1 of 12 |
The registry's overall study group lists 12 participants at risk for serious adverse events and 0 affected. For other adverse events, it lists 12 at risk and 1 affected. These are separate registry counts and should be interpreted as recorded, not as evidence that the imaging approaches were compared on safety. The adverse-event information is grouped for the overall study, rather than reported separately for Technegas and Xenon imaging.
The listed serious adverse event terms contain no entries. This means no serious adverse-event terms are listed in the registry record; the record does not provide event descriptions or further detail to interpret the absence of listed terms. The death field is null, so deaths are not reported in the registry record. A null entry is not a numerical count and should not be read as a recorded count of zero.
Technegas safety was named as a secondary outcome, but the overall adverse-event listing does not provide a method-specific comparison or explain how events were attributed to an imaging procedure. The registry also does not report event timing, severity definitions, follow-up completeness, or a detailed safety analysis. The counts should therefore be treated as limited descriptive reporting, not as a comprehensive safety assessment.
12. What the Result Does, and Does Not, Mean
This trial record describes a Phase 3, non-randomized crossover comparison of Technegas V/Q SPECT and Xenon V/Q planar imaging for pulmonary embolism evaluation. Its primary question is diagnostic sensitivity, with a final diagnosis based on clinical information at 30 days described as the reference. That design and endpoint make the study relevant to how different ventilation-perfusion imaging approaches were intended to be compared.
The posted record does not report a numerical sensitivity estimate for either method or a numerical contrast between them. It also does not report confidence intervals or hypothesis-test results. As a result, the statistical evidence does not establish whether sensitivity differed, how large any difference was, or how precisely it was estimated. The lack of a reported comparison is not evidence that the methods are equivalent, and it is not evidence that one method is better.
The non-randomized crossover design should also be kept distinct from a randomized comparison between separate groups. Within-subject comparisons can be useful because each participant contributes information under more than one imaging approach, but the paired data structure needs suitable analysis. The statistical method is not reported, so the record does not show how that structure was incorporated. The single-masking designation and the statement about blinded readings do not provide enough detail to judge the full conduct of masking.
Termination is recorded, but its reason and impact on available data are not reported. The registry lists enrollment as 18, yet does not give the number with complete imaging, adjudication, or follow-up. It also records seven outcome measures and zero analyses. Consequently, the secondary diagnostic measures and the safety outcome cannot be evaluated numerically from the registry record.
The overall adverse-event entry lists 0 affected by serious adverse events among 12 at risk and 1 affected by other adverse events among 12 at risk. These counts are not separated by imaging method, and the death field is null. They provide limited descriptive information rather than a complete comparative safety analysis. In general, conclusions depend not only on the stated design but also on complete outcome data, clearly specified analysis methods, and estimates with uncertainty. Those elements are not reported sufficiently to support a statistical conclusion about diagnostic performance or comparative safety.
13. Why This Trial Matters Statistically
The study raises a statistical question that is common in diagnostic research: how to compare two imaging approaches when participants are assessed using both. A within-subject design can make each participant serve as a reference point for comparing methods, but the resulting observations are paired. The correct interpretation depends on preserving that relationship in the analysis and describing how the reference diagnosis was established.
This record identifies the intended comparison, primary endpoint, follow-up timeframe, and broad reference-standard process. It also identifies the study as non-randomized and crossover, rather than inviting interpretation as a randomized comparison of separate groups. Those details are valuable because design labels influence which statistical assumptions are appropriate. The stated blinded readings and planned Independent Adjudication Committee further point to the importance of limiting bias in both image interpretation and outcome classification.
At the same time, the registry status is terminated, and the posted record does not include a numerical primary analysis. That gap illustrates why a stated endpoint is not itself evidence of an observed effect. Without estimates and uncertainty, readers cannot assess the magnitude or precision of the diagnostic comparison. The reasons for termination, analysis populations, missing-data handling, and statistical plan are also not reported, leaving important context unavailable.
The record therefore matters as an example of the distinction between a study question and a statistical result. It shows the comparison the trial was designed to address, while the posted analyses do not permit that question to be answered quantitatively. This distinction is especially important for crossover diagnostic studies, where design, reference standards, paired analysis, and completeness of follow-up all contribute to interpretation.
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 most direct limitation is that the registry record does not report a numerical result for the primary sensitivity comparison. No estimate, confidence interval, or significance test is posted, and the record lists zero analyses. It is therefore not possible to assess the direction, magnitude, or precision of the primary comparison from the registry record.
The trial is marked terminated, but the reason for termination and its effect on data collection are not reported. Although enrollment is listed as 18, the record does not state how many participants completed both imaging procedures, had an adjudicated diagnosis, or completed 30 days of follow-up. It does not report missing observations, exclusions, or analysis populations. The outcome description refers to adjudication but is incomplete after noting trial termination, so the extent of completed adjudication is unclear.
The design is non-randomized and crossover. The brief summary describes a within-subject comparison, but the registry does not report imaging order or whether sequence effects were considered. The statistical analysis method is not reported, so it is not possible to determine how paired observations were analyzed. The masking designation is single, and blinded image readings are described, but the identity of the masked parties and details of reading procedures are not reported.
The record also does not provide the protocol, statistical analysis plan, sample-size justification, interim-analysis plan, or multiplicity strategy. The safety counts are grouped overall rather than by imaging approach, and the death field is null. These limitations are specific to the information available in the registry record and constrain interpretation of diagnostic and safety outcomes.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Compare Technegas Ventilation-Perfusion SPECT and Xenon Ventilation-Perfusion Planar Imaging for Pulmonary Embolism — NCT01458639.
- Registry record last updated 2015-11-10; status last verified 2015-10.
- Results first posted 2015-11-10.
- 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
NCT01458639 is a Phase 3, non-randomized, single-masked crossover study comparing Technegas V/Q SPECT with Xenon-133 V/Q planar imaging in people being evaluated for pulmonary embolism. The registry lists enrollment as 18, a start of 2012-08, primary completion of 2015-06, and status as terminated.
The primary outcome was sensitivity of Technegas V/Q SPECT compared with Xenon V/Q planar imaging, using a final diagnosis based on clinical information at 30 days as the stated reference. The record also lists secondary diagnostic outcomes and Technegas safety. It records seven outcome measures and zero analyses. No numerical primary sensitivity result or comparative estimate is reported in the registry record.
The reason for termination, completed analysis populations, missing-data methods, and detailed statistical plan are not reported. Overall safety entries list 0 affected by serious adverse events among 12 at risk and 1 affected by other adverse events among 12 at risk; deaths are not reported in the registry record.