DTI-ALPS index reduced in traumatic brain injury, meta-analysis findsBrain imaging shows how head injuries affect fluid drainage

AJNR. American journal of neuroradiology Published August 16, 2026 Study authors: Broomand Lomer Nima, Ahmadzadeh Amir Mahmoud, Ashoobi Mohammad Amin, Diaz-Arrastia Ramon, Verma Ragi… PubMed ↗ DOI ↗ Editorial oversight: Dr. Lars van Dijk, PhD · Surgical, Procedural & Diagnostic

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Key Takeaway

Consider DTI-ALPS as a research biomarker for glymphatic impairment in TBI, but not yet for clinical use.

This meta-analysis pooled data from studies comparing DTI-ALPS index values between patients with traumatic brain injury (TBI) and healthy controls (HCs). The analysis included 694 patients with TBI and 503 HCs. The primary outcome was DTI-ALPS values, a proposed biomarker of glymphatic system function.

The main finding was a significant reduction in DTI-ALPS values in patients with TBI compared with HCs, with a large pooled effect size (Hedges g = -0.77; 95% CI, -1.38 to -0.15). However, heterogeneity was substantial (I² = 93%), indicating considerable variability across studies. Secondary analyses found no significant correlation between DTI-ALPS and age or Glasgow Coma Scale scores. Notably, a meta-regression suggested a larger decrease in DTI-ALPS values over time in TBI patients (beta = -0.01, p =.03), hinting at time-dependent deterioration.

The authors acknowledge important limitations, including substantial heterogeneity and a small number of included studies. These factors limit the certainty of the findings. The results suggest an association between TBI and reduced DTI-ALPS values, but causality cannot be inferred from this meta-analysis.

For clinicians, DTI-ALPS shows potential as a biomarker of glymphatic impairment in TBI, but its clinical utility is not yet established due to methodological heterogeneity. Further research with standardized protocols is needed before considering it in practice.

How this fits prior evidence

This meta-analysis extends prior coverage on TBI by introducing a novel imaging biomarker, DTI-ALPS, to assess glymphatic function. It complements earlier findings on early enteral nutrition and tranexamic acid by focusing on a diagnostic tool rather than a therapeutic intervention. The reduced DTI-ALPS values in TBI patients align with the evolving understanding of secondary injury mechanisms, such as the brain-lung-immune-microbiome axis, by providing evidence of glymphatic impairment. However, the substantial heterogeneity and small number of studies limit direct comparison with prior evidence on functional outcomes.

When someone suffers a traumatic brain injury, the body's ability to clear waste and fluids from the brain can be compromised. This process is vital for health, but it is hard to see on standard scans. Researchers looked at a specific measurement called DTI-ALPS to see if it could act as a marker for this drainage problem.

The study compared 694 patients with brain injuries to over 500 healthy people. They found that those with injuries had significantly lower DTI-ALPS values. This suggests that the brain's waste clearance system, known as the glymphatic system, may be impaired after a head injury. Interestingly, these levels seemed to drop even further as time passed following the injury.

While this finding is promising for identifying how injuries affect the brain, there are hurdles to clear. The data came from a small number of studies and showed a lot of variation between different reports. Because of this, doctors cannot use it as a standard clinical tool just yet, but it offers a new way to study how the brain heals.

What this means for you:

Lower DTI-ALPS values in brain scans may signal impaired fluid drainage after a traumatic brain injury.

Common questions

What does the DTI-ALPS measurement tell doctors?

The DTI-ALPS index is used as a way to look at the glymphatic system, which is how the brain clears out waste and fluids. In this study, patients with traumatic brain injuries had significantly lower values than healthy people. This suggests the scan can help identify when this drainage system is not working correctly after an injury.

Does the condition get worse over time?

The data shows that DTI-ALPS values actually decreased more as time passed for patients with traumatic brain injuries. This suggests a decline in the drainage system over time, though researchers note that the evidence is still limited by the small number of studies and high variation between results.

Can this be used to treat patients immediately?

Not yet. While the DTI-ALPS index shows a clear link to brain injury, it is not currently established as a standard clinical tool. Because the study had many variations and only included a small number of reports, doctors need more consistent data before using it for routine patient care.

Study Details

Study typeMeta analysis

Sample sizen = 694

EvidenceLevel 1

PublishedAug 2026

PMID41667226

View Original Abstract ↓

BACKGROUND: The glymphatic system, essential for metabolic waste clearance and brain homeostasis, is vulnerable to disruption following traumatic brain injury (TBI). There is a pressing need for practical and robust methods to assess glymphatic function after TBI, as well as for other neurologic disorders. DTI along the perivascular space (DTI-ALPS) might have value in quantifying glymphatic dysfunction. PURPOSE: Our aim was to consolidate existing evidence to determine differences in DTI-ALPS values between patients with TBI and healthy controls (HCs). DATA SOURCES: All studies using the DTI-ALPS index and reporting its mean and SD in both patients with TBI and HCs were identified through searches of PubMed, EMBASE, Scopus, and the Web of Science from inception to August 8, 2025. STUDY SELECTION: Eleven studies comprising 694 patients with TBI and 503 HCs were included. DATA ANALYSIS: Meta-analysis was conducted using a random-effects model. Standardized mean differences (Hedges g) were used as the effect size measure. Pooled correlations between DTI-ALPS indices and demographic variables were evaluated. Heterogeneity was assessed using the Higgins I statistic. Subgroup analyses, meta-regression, and sensitivity analyses were performed to identify potential sources of heterogeneity, and publication bias was examined using funnel plots and the Begg test. DATA SYNTHESIS: DTI-ALPS values were found to be significantly reduced in patients with TBI compared with HCs (Hedges g = -0.77; 95% CI, -1.38 to -0.15; I = 93%). DTI-ALPS showed no significant correlation with age or Glasgow Coma Scale scores. Subgroup analyses revealed larger effect sizes in single-shell studies and those with higher methodologic rigor. Meta-regression showed a larger decrease in DTI-ALPS values in patients with TBI with time (β = -0.01, = .03). No substantial publication bias was detected ( = .12). LIMITATIONS: Our meta-analysis is limited by substantial heterogeneity and the small number of included studies. CONCLUSIONS: TBI is associated with significantly reduced DTI-ALPS values, with more prominent deteriorations over the long term, supporting its potential as a biomarker of glymphatic impairment. However, methodologic heterogeneity emphasizes the need for standardized protocols and longitudinal studies to establish clinical utility.

DTI-ALPS index reduced in traumatic brain injury, meta-analysis findsBrain imaging shows how head injuries affect fluid drainage

How this fits prior evidence

Common questions

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DTI-ALPS index reduced in traumatic brain injury, meta-analysis findsBrain imaging shows how head injuries affect fluid drainage

How this fits prior evidence

Common questions

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