Inclusion Criteria:
* Meets the DSM-5 criteria for opioid use disorder or amphetamine use disorder, with a severity level of severe, and does not currently meet the criteria for in sustained remission;
* Within 7 days prior to the screening assessment, the participant must have been receiving a stable dose of medication treatment, such as methadone, buprenorphine/naloxone, or naltrexone;
* Within 7 days prior to the screening assessment, the participant must have abstained from illicit substances and alcohol, and must have a negative urine drug test;
* The bilateral nucleus accumbens must be clearly identifiable on magnetic resonance imaging (MRI), such that they are sufficient for treatment targeting and for indirect measurement from other anatomical structures;
* The participant must be able to communicate effectively and express their feelings and experiences during the study procedures;
* The participant must be willing to comply with the study requirements, including adherence to prescribed medications and cooperation with study visits and assessments.
(The participant must have the capacity to make independent medical decisions, as determined by the clinical team.)
Exclusion Criteria:
* Presence of neurological disorders or major psychiatric disorders, such as acute-phase schizophrenia spectrum disorder, acute-phase bipolar disorder, acute-phase major depressive disorder, severe cognitive impairment, or recent suicidal ideation or plan;
* Antisocial personality disorder;
* Occurrence of major physical health problems within 6 months prior to the trial, including: Cardiovascular or hemodynamic abnormalities, such as heart failure, arrhythmia, tachycardia or bradycardia (\>100 bpm or \<60 bpm), abnormal systolic blood pressure (\>180 mmHg or \<90 mmHg), or abnormal diastolic blood pressure (\>180 mmHg); Platelet or coagulation abnormalities (INR \> 1.5) or current use of medications that may cause anticoagulation, such as warfarin or Avastin; Renal dysfunction (eGFR \< 30 mL/min/1.73 m²) or ongoing hemodialysis; Severe infection; Immunocompromised status; History of intracranial hemorrhage, intracranial aneurysm, cerebrovascular events within the past 6 months, or brain tumor; Neurological diseases, such as stroke, epilepsy, Parkinson's disease, dementia, or related disorders; Any other physical illness that, based on clinical evaluation, may pose a significant risk to physical function or life during treatment.
* Participants who, upon evaluation, are deemed unsuitable for MR-guided focused ultrasound treatment, including those with a low skull density ratio (\<0.4), intracranial implants, or energy-absorbing structures or sensitive tissues along the ultrasound beam path that cannot be avoided (such as prior ventriculoperitoneal shunt sites, surgical metal clips, significant calcifications, extensive scarring, or any rigid implants). During the pre-treatment evaluation, a head CT scan will be performed to determine whether the skull density ratio is suitable for focused ultrasound treatment. Based on prior theoretical evidence, an excessively low skull density ratio may reduce the efficiency of MR-guided focused ultrasound and increase the risk of adverse effects, and therefore such participants are considered unsuitable for focused ultrasound treatment.
* Structural abnormality of either side of the nucleus accumbens;
* Contraindications to MRI, such as claustrophobia, allergy to MRI contrast agents, or the presence of metallic implants incompatible with MRI;
* Contraindications to PET imaging, such as allergy to radiopharmaceutical contrast agents;
* Inability to comply with trial-related instructions, lack of legal/behavioral capacity, or lack of motivation to receive treatment;
* Pregnancy or breastfeeding;
* Scalp atrophy or poor wound healing of the scalp;
* Any other condition that, in the physician's judgment, makes the participant unsuitable for enrollment in the clinical trial.
