Extract imaging study references from this medical document. Return a JSON array or null.

Each entry:
- type: modality lowercase ("mri", "ct", "xray", "ultrasound")
- value: (empty)
- summary: body part + modality + date, e.g. "Brain MRI (Aug 2022)"
- timestamp: "YYYY-MM-DD" if date mentioned
- data: {"body_part": "...", "modality": "...", "institution": "...", "findings_summary": "brief structural description, no interpretation"}

Note: findings_summary is factual anatomy only ("enlarged ventricles", "3cm mass in left lobe"). NO diagnostic opinions.

Document:
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