Purpose: Due to the lack of standardized manufacturer guidelines for pillow height in nuclear medicine, clinical practices often rely on empirical experience. This study evaluates the effect of head elevation on image quality and lesion distortion using an ACR (American College of Radiology) phantom to establish the optimal standardized height for maintaining diagnostic accuracy. Materials and Methods: Images were acquired using a Siemens Symbia E gamma camera equipped with a LEHR (Low-Energy HighResolution) collimator. To simulate intracranial lesions, the hot cylinders of an ACR phantom(25, 16, 12, and 8 mm) were utilized with a target to background radioactivity ratio of 10:1. The phantom was elevated from the table in 2 cm increments (0, 2, 4, and 6 cm, with 5-minute static images acquired at each height. Quantitative analysis of total counts, length, area, and FWHM (full width at half maximum) was performed under three ROI (Region of Interest) conditions: (1) Auto ROI with an 80% threshold, (2) Fixed-size ROI, and (3) Modified ROI defined by isolating the high-intensity red spectrum within a Rainbow color scale. All results were expressed as percentage reductions relative to the baseline values at 0 cm. Results: Three analytical parameters (total counts, area, and length) exhibited a downward trend as height increased from the 0 cm baseline, while the FWHM demonstrated a corresponding upward trend. In the Auto ROI analysis, total counts at 6 cm decreased by 26% (8 mm), 34.4% (12 mm), and 14% (16 mm and 25 mm) compared to 0 cm. The most rapid decline in counts occurred at different intervals depending on cylinders size: 0–2 cm for the 8 mm lesion, 2–4 cm for the 12 mm lesion, and 4–6 cm for both 16 mm and 25 mm lesions. Furthermore, compared to the baseline at 0 cm, the FWHM values at a height of 6 cm increased by 24.9% for the 8 mm cylinder, 24.2% for the 12 mm cylinder, 14.7% for the 16 mm cylinder, and 10.1% for the 25 mm cylinder. Conclusion: Head elevation significantly induces lesion distortion and degrades image quality, with small lesions (≤12 mm) exhibiting higher sensitivity to minor distance changes. While larger lesions show prominent distortion beyond 2 cm, smaller lesions are affected immediately. To minimize diagnostic inaccuracy, it is recommended that the height of the pillow or headgear be maintained below 2 cm and must not exceed 4 cm.