Assessment of cerebrovascular reserve capacity with Acetazolamide Challenge Test (ACT): a systematic review of imaging methods of ACT
- Introduction: In patients with chronic steno-occlusive disease, the ability to maintain normal cerebral blood flow by reducing vascular resistance secondary to autoregulatory vasodilation is compromised. To assess impairment of the cerebrovascular autoregulation, it is necessary to evaluate hemodynamic parameters both in the resting state & under conditions of external stimulation. The use of the different techniques in the evaluation of CVR is still under investigation; few studies have been performed to assess the comparability of different techniques. The current modalities vary in their accuracy & use different parameters to determine CVR capacity. To compare techniques, there is also a need to definite a gold standard.
- Methods: This systematic literature review evaluated the clinical performance & reliability of different published imaging techniques, as well as the comparability of their results. Inclusion criteria included: ACT-challenge test for at least one imaging method; comparison between two or more different imaging methods; comparison of different radiotracers was not considered appropriate for comparison for the purpose of this review; MR methods which assess different physiological parameters were appropriate for inclusion as different imaging techniques; human studies only; case studies & reviews were excluded; studies published between 1989 and 2010 because of the rapid advances in imaging technology in the recent two decades; language restriction: 6 Japanese papers and one Hungarian paper could not be included due to lack of available translation facilities; & validity of results: Studies were evaluated according to QUADAS-Criteria.
- Results: 793 references were found using Medline & 1256 references using Embase, 2049 in total, of which 662 were duplicates. The remaining 1387 references were manually screened for relevance firstly by title alone (1028 excluded), then by abstract (274 eliminated). The remaining 85 references were assessed by reading the full text, of which 19 were animal studies, 13 case reports & 12 reviews. Of remaining 41 comparison studies evaluated by QUADAS-criteria, 36 were determined not valid, mainly due to review bias because both tests (index & reference test) were not interpreted independently from each others’ results.
- Discussion: There was large heterogeneity of comparison studies. One main drawback of most comparison studies was the lack of independent and blinded interpretation of test results. Neither standard technique for clinical practice nor any consistent reference standard for comparison of the different imaging techniques had been established since a similar review in 1999. Additional parameters and new measurement methods have been developed during the last 11 years but the problem remains: the different parameters that can be assessed to determine cerebrovascular autoregulation relate to different underlying pathophysiological pathways whose degree of dependence remains unclear. Impaired cerebrovascular reserve capacity detected by one method does not necessarily stand for abnormal results of another measurement technique.
- Conclusion: There is a need for randomized control studies for each of the parameters to assess its value as independent risk factor for stroke. Before implementation of new imaging techniques there is still need for establishing a gold standard to be used for valid comparison studies that provide independent and blinded interpretation of results as well as determination of clinically relevant thresholds for the parameters.
- Systematic review
|Application / disease keywords:
- Chronic steno-occlusive disease