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Registration of Emission and Transmission Whole-Body Scintillation-Camera Images

Department of Radiation Physics, Jubileum Institute, University Hospital, Lund University, Lund, Sweden; and Institute of Nuclear Medicine, Middlesex Hospital, London, United Kingdom

View larger version (32K): [in a new window]   FIGURE 1. Definition of regions for attenuation factor image. Bounding box, marked as rectangle surrounding patient, is determined from threshold image. Coordinates xmidline, yhead, yupper, and ylegs are calculated using Equation 1 and are used to define head region (x[0, xend-of-matrix], y[0, yhead]) (1), upper body (x[0, xend-of-matrix], y[0, yupper]) (2), pelvic region (x[0, xend-of-matrix], y[yupper, ylegs]) (3), right leg region (x[0, xmidline], y[ylegs, yend-of-matrix]) (4), and left leg region (x[xmidline, xend-of-matrix], y[ylegs, yend-of-matrix]) (5).

View larger version (90K): [in a new window]   FIGURE 2. Test transformation of mass-density image. (A) Original image. (B) Transformed image. (C) Absolute difference between transformed image and original image. (D) Transformation applied to regular grid, shown for illustration. Coefficients used were p00 = -7, q00 = -7, p01 = 1.02, q01 = 1.02, = -4, ß = 5, p10L = -0.05, p10R = 0.07, and q02U = 0.0005. Euclidian distance is illustrated in A and B, where center of mass of evaluation regions for original image are marked as squares and as crosses for transformed image. Values are head region, 33 mm; trunk, 25 mm; right leg, 41 mm; and left leg, 9 mm, yielding average of 27 mm. Summation of counts in C yields value of SAD of 40%.

View larger version (124K): [in a new window]   FIGURE 3. (A–C) Three noise realizations for simulated WB images. Image total counts are 104, 105, and 106 for A, B, and C, respectively, corresponding to SNRs of approximately 1, 4, and 12, respectively. (D) Patient image. In this patient, uptake in heart was higher than that used in simulation, and kidney uptake was lower. Source distribution was estimated from several patient images, and, as illustrated, individual variations occur.

View larger version (103K): [in a new window]   FIGURE 4. WB attenuation factor images: simulated image (A) and patient image (B). Main differences between images occur at jaw because of amalgam fillings, in right lung because of portal catheter, and at hip because of implant at neck of femur. No negative effects on registration accuracy were seen because of such patient-related details. Noise level is generally low for clinical images; therefore, no separate noise simulations were performed for attenuation factor images.

View larger version (14K): [in a new window]   FIGURE 5. Euclidian distances obtained for registration of posteroanterior images (A) and attenuation factor to geometric mean images (B). Results are displayed as function of total number of counts in images. Results, including preprocessing, with associated error bars (mean ± SD) (). (A) Error bars for 106, 2.5 . 106, and 5 . 106 counts cannot be seen on scale but were within ±1 mm for all 3 points. (B) SDs for 5 . 105, 106, 2.5 . 106, and 5 . 106 counts were within ±1 mm. Results for unprocessed images, where error bars have been omitted for clarity (•).