The electronic databases used for the systematic search from databases inception to 12 April 2024, included PubMed, Embase, Cochrane Database of Systematic Reviews (CDSR), Cochrane Controlled Trials Register (CENTRAL), China National Knowledge Infrastructure (CNKI), Chinese BioMedical Literature Database (CBM), Chonqing VIP (CQVIP), and Wanfang. Detailed search strategies are provided in Supplementary file S1.

The inclusion criteria were: (1) Study types: This review included clinical studies on acupuncture for stroke, limited to journal articles. (2) Participants: Study participants were diagnosed with stroke based on various diagnostic criteria. The study subjects underwent two MRI scans before or after acupuncture or one MRI scan during acupuncture. (3) Intervention types: The experimental group received acupuncture therapy alone or in combination with other conventional therapies. (4) Type of control: The control group evaluated the effects of acupuncture, with participants receiving sham acupuncture (SA), placebo acupuncture, no treatment, drugs, Chinese medicine, rehabilitation therapy, or other therapies. (5) Types of outcome: At least one MRI technique was used, resulting in MRI outcome measures. The exclusion criteria were: (1) Animal experiments, reviews, case studies, experience reports, or protocols; (2) Duplicate studies or data; (3) Studies where contacting the author via email did not resolve missing data or yield the necessary information.

Two authors (Chao Ke and Wenying Shi) independently screened and examined the features of all articles identified using the PICOS (population, interventions, comparators, outcomes, study design) selection criteria, and extracted the data for further evaluation. Subsequently, a cross-check was performed, and any disagreements were resolved through arbitration by a third author (Wei Zhang). Data extraction included the following: general study information (title, author, country, journal, journal level, year of publication, registration, and funding source); patient demographics (lesion location, first-episode, functional disorder category, stroke type, and disease stage); trial design (study type, total sample size, trial design, control design, and neuroimaging design); and outcome evaluation (MRI type and outcomes).

The results were presented in a preferred reporting item for systematic reviews and meta-analyses (PRISMA) flow diagram using a combination of textual descriptions and charts, and visual representations were created using Microsoft Excel 2003, Original, and chiPlot website (https://www.chiplot.online/) for data analysis and synthesis. The presentation also included bubble plots, a fold line diagram, three-line table.

MRI studies on acupuncture for stroke began in 2,000, with 158 studies published between 2000 and April 2024. Results showed an increasing trend in research in recent years, peaking in 2023. The annual distribution of the literature is shown (Figure 2). A total of 158 studies were published across 96 distinct journals. Approximately 25.31% of the selected papers were published in the Science Citation Index Journal (SCI), 59.49% in core journals such as the Chinese Core Journal Criterion of Peking University (CSCD) and the China Core Periodicals of Science and Technology (CSTPCD), and the remaining 15.19% in other journals. Most studies received project funding (130/158, 82.28%), such as the Natural Science Foundation of China and 973 projects; very few studies reported registration status (13/158, 8.23%). Most studies were authored by Chinese authors, with only Germany and Boston contributing a single study each (Table 1).

Ischemic stroke accounts for approximately 87% of all stroke cases in the United States (Feigin et al., 2013) and 80% of all stroke cases in China (Barthels and Das, 2020). The review of the evidence in previous literature suggests that the primary subtype of stroke is ischemic stroke, aligning with epidemiological trends (GBD Parkinson’s Disease Collaborators, 2016). Additionally, MRI studies of acupuncture for stroke address multiple post-stroke dysfunctions, such as motor, speech, cognitive, swallowing, and sensory impairments, with a significant emphasis on motor impairments. Our results similarly support this conclusion. Post-stroke motor impairment is a common complication, with over 70% of stroke survivors experiencing motor dysfunctions (Wang et al., 2017). These studies make the functional abnormalities and reorganization between brain regions or networks observable.

Several commonly used experimental design methods are described as follows: (1) Single-group, single-session design: A group of patients with stroke participated in the study and received a single intervention and single-signal acquisition to observe immediate brain activity. (2) Single-group pre-post control design: A group of patients with stroke participated in the study and received a period of intervention, with signal acquisition conducted before and after the intervention to observe brain activity over time. (3) Two-group single-session design: Two groups of patients with stroke participated in the study, each receiving different interventions and undergoing single-signal acquisition after randomization, allowing the observation of immediate brain activity. (4) Two-group pre-post control design: Two groups of patients with stroke participated in the study, with different interventions administered after randomization. Signal-acquisition was performed before and after the intervention to observe brain activity over time. Healthy controls could/could not be included in this study.

Additionally, two other studies focused on natural recovery state design (Zhao et al., 2017; Stinear et al., 2020). These studies compared brain activity in patients with stroke under natural recovery conditions and observed brain activity changes over time. During this period, no acupuncture intervention was performed, although the acupuncture BLOCK intervention was used to stimulate brain activity at each visiting viewpoint. Five studies employed two-group cross-over control designs (Chang et al., 2003; Zhang et al., 2014; Chen et al., 2015; Liao et al., 2016; Chen C. et al., 2024; Chen T. et al., 2024), which involved two groups of single-session designs with another intervention after the washout period to create two groups of cross-control studies. Consequently, immediate brain activity was observed. This design was mostly used in the group design of acupuncture and SA acupuncture controls. Two studies used a single-group, multi-control design (Si et al., 2013; Chen et al., 2014), where a group of patients with stroke received several different interventions in sequence, separated by a washout period. In the two-group crossover control and single-group multi-control designs, each patient received two different interventions, reducing the sample size and eliminating individual differences.

Resting-state (rs)-fMRI and task-state fMRI are the two primary paradigms for fMRI studies.

Our results showed that the most frequently observed patterns were the resting-state, classical BLOCK, non-repeated event-related (NRER), and MIX-BLOCK paradigms. Each research paradigm has different objectives and purposes.

Our findings indicate that the control design of acupuncture in stroke MRI studies primarily addresses two major research objectives: the mechanism of acupuncture and its efficacy. The investigation of mechanisms includes comparisons such as VA / VA combined with other therapies, VA versus HC, VA versus SA, self-control before and after, and VA 1 versus VA 2. The purpose of SA is to prove that the positive effects of acupuncture treatment are due to the placebo effect. Of the included studies, 18 used the following three types of SA: (1) acupuncture treatment at non-acupoints, with two studies emphasizing that non-meridian points should be avoided De-qi (Zhang J. et al., 2023; Zhang J. S. et al., 2023; Zhang Y. et al., 2023; Chen C. et al., 2024; Chen T. et al., 2024); (2) mild stimulation such as superficial acupuncture (Chen et al., 2014; Wang et al., 2023); and (3) tactile stimulation (Chen et al., 2015), use of non-penetrating and flexible needles (Huang et al., 2013), and application of no-current electric stimulators (Schaechter et al., 2007). SA plays a critical role in understanding and analysing the effects of acupuncture; however, the overall quality of reporting is suboptimal. SA reports are recommended based on the guidelines outlined in the fake needle report list (Jiang et al., 2017). The purpose of the healthy population is to demonstrate the functional specificity of acupuncture, suggesting that acupuncture exerts a significant effect under pathological conditions. The therapeutic efficacy of acupuncture is attained by restoring the internal environmental balance. Imaging studies conducted in healthy subjects may reflect pre-intervention brain homeostasis in patients, thereby providing a more comprehensive understanding of the mechanisms underlying the efficacy of acupuncture.

Several potential factors were considered regarding efficacy, including needle timing, needle retention time, Deqi and non-Deqi, and different acupoints. A study investigating the differential activation responses of the brains of patients with stroke in the morning and afternoon revealed a stronger activation effect in the morning than in the afternoon (Ma et al., 2023). Another study categorized participants into groups based on needle retention times of 1, 2, and 3 min, utilizing a consistent acupoint prescription across groups. These findings indicate that varying the retention time of acupuncture treatment results in distinct neural effects in patients with stroke, with the volume of the activated voxel cluster showing a positive correlation with the duration of acupuncture (Gao et al., 2015). Several studies have demonstrated that the Deqi group exhibits significant activation in relevant brain regions compared with the non-Deqi group (Zhou et al., 2023). Additionally, researchers have compared the effects of cardiac and pericardial meridian acupoints on disease and brain mechanisms, with results showing a better effect of pericardial meridian acupoints than that of cardiac meridian acupoints (Li et al., 2015). Furthermore, the central effect of the Baihui acupoint is more potent than that of Yanglingquan in ameliorating memory impairment post-stroke, potentially due to the enhanced functional connectivity of the hippocampus and the brain network between the frontal and parietal lobes (Zhang et al., 2019). These studies provide neuroimaging evidence supporting the underlying mechanisms in acupuncture.

MRI is an emerging neuroimaging method for exploring the central mechanism of acupuncture in patients with stroke. Our review indicates that multimodal MRI technologies are increasingly attracting research attention.

In neuroimaging, fMRI is widely used to explore brain function, behavior, perception, and emotions. Our findings indicate that these trends are significantly expanding both transversely and longitudinally. Researchers’ observation index has broadened from initially focusing on local neural activity within specific brain regions to including the effects on different regions within the ipsilateral and contralateral hemispheres, extending to the overall brain network. Magnetic resonance spectroscopy imaging (MRS/1H-MRS) is primarily employed to quantify the concentration of specific metabolites in the brain or other tissues and is frequently used to investigate the metabolic state and pathological lesions of the brain. Different lesion areas can be selected for detection based on stroke complications. Additionally, dynamic, non-invasive monitoring of critical brain metabolites can be conducted, thereby providing robust evidence supporting molecular imaging in the acupuncture treatment of stroke. Diffusion magnetic resonance imaging (DWI/DTI) is predominantly used to delineate the structural architecture and white matter pathways within the brain and investigate acupuncture as a treatment modality for motor dysfunction following stroke. This imaging technique enables quantitative analysis of nerve fiber damage and motor dysfunction, which is crucial for understanding acupunctures’ efficacy in motor function rehabilitation. DTI is often combined with fMRI to explore the interrelationships between the brain structure and function. Magnetic resonance perfusion imaging, including arterial spin labelling (ASL) and perfusion-weighted imaging (PWI), offers a rapid assessment of haemodynamic alterations in the brain tissue. ASL perfusion imaging is a common technique for measuring cerebral blood flow (CBF). In patients with stroke, variations in infarct location correspond to differences in cerebral blood flow signals. Alterations in local cerebral blood flow within specific brain regions may constitute a critical neural mechanism underlying functional impairment. Additionally, acupuncture may facilitate neural repair by augmenting the local cerebral blood flow. Structural magnetic resonance imaging (sMRI) provides high-resolution images of the brain and other anatomical structures, facilitating the detailed observation of anatomical features. This modality is extensively utilized for diagnostic purposes, disease monitoring, and investigating structural changes in the brain.

Thus, fMRI focuses on brain activity and function, MRS/1H-MRS on chemical and metabolic states, DWI/DTI on white matter structure and function, sMRI on anatomical structures, and ASL/PWI on cerebral blood flow. Collectively, these neuroimaging techniques provide robust scientific and quantitative evidence supporting the efficacy of acupuncture in stroke treatment by addressing various dimensions, such as functional activity, metabolic processes, structural integrity, and cerebral perfusion. This multifaceted approach highlights the comprehensive therapeutic potential of acupuncture for stroke rehabilitation.

This review presents the first systematic review using evidence map to illustrate the current state of neuroimaging research on the acupuncture treatment of stroke. It provides a significant reference for future scholarly research, offering imaging evidence that elucidates the brain network mechanism of acupuncture interventions in stroke. However, the current study has certain limitations, including a predominance of single-center studies with small sample sizes and a lack of long-term follow-up. Future research should consider the implementation of multicenter, large-sample, clinical randomized controlled studies to further investigate the clinical efficacy of acupuncture and the potential brain network mechanisms that could enhance stroke recovery.