Correlation of whole body fluorescence imaging and ultrasound imaging for assessment of tumor size in mice with orthotopic implants of fluorescently-labeled pancreatic tumor cells. Mice harboring tumors of varying sizes (n = 30) were imaged using both fluorescence and ultrasound imaging to assess tumor size. The resulting measurements (cross-sectional area in mm2, determined as previously explained) for each tumor were graphed to determine how well the imaging modalities correlated for assessment of tumor size over a range of tumor sizes. We assessed tumor sizes at two exposure times, 67 msec and 120 msec, that gave clear visual images which were neither under-exposed nor over-saturated and analyzed these images to measure tumor size. A-B. Determination of tumor size from fluorescence images taken with either a 67-millisecond exposure time (panel A) or a 120-millisecond exposure time (panel B). There is a strong correlation between fluorescence and ultrasound imaging modalities for assessment of tumor size over a range of tumor sizes at both exposure times. Both exposure times (67 msec and 120 msec) yielded similar values for R2 and P.