Figure 15. Importance of adjusting threshold in case of inadequate mixing of the contrast and urine. (a) Source CT image shows a fluid–fluid level (arrows) due to adequate mixing of the contrast and urine. (b) Virtual cystoscopy image with threshold of 190 HU shows artefact in the anterior wall of the bladder. (c) On virtual cystoscopy image with threshold of 100 HU, the artefact disappears and a small nodule (arrow), confirmed as transitional cell carcinoma, is noted.