Multi-detector row CT of the kidney: optimizing scan delays for bolus tracking techniques of arterial, corticomedullary, and nephrographic phases.
OBJECTIVE
To determine optimal scan delays for renal arterial-, corticomedullary-, and nephrographic-phase imaging with multi-detector row computed tomography (MDCT) of the kidney using a bolus-tracking technique.


METHODS
One hundred and twenty-eight patients underwent three-phase CT scan of the kidney with eight-row MDCT after receiving 2 mL/kg of 300 mgI/mL contrast medium at 4 mL/s. Patients were prospectively randomized into three groups with different scan delays for the three scan phases (arterial, corticomedullary, and nephrographic) after bolus-tracking triggered at 50 HU of aortic contrast enhancement: group 1 (5, 20, 45 s); group 2 (10, 25, 50s); and group 3 (15, 30, 55 s). Mean CT values (HU) of the abdominal aorta, renal artery, renal vein, renal cortex, and renal medulla were measured; increases in CT values pre- to post-contrast were assessed as contrast enhancement. Renal artery-to-vein and renal cortex-to-medulla contrast differences were also assessed. Qualitative analysis was also performed.


RESULTS
Mean renal artery enhancement was 240-288 HU at 5-15s after the trigger and peaked at 10s (P<.001). Mean renal cortical enhancement was 195-217 HU at 10-30s and peaked at 25s (P<.01). Contrast enhancement in the renal medulla increased gradually and reached mean 145 HU at 55 s. Cortex-to-medulla contrast difference was high (110-140 HU) at 5-30s and decreased below 30 HU at 45 s after the trigger. Renal artery-to-vein contrast difference was high (121-125 HU) at 5-10s. Qualitative results correlated well with quantitative results.


CONCLUSIONS
For the injection protocol used in this study, optimal scan delays after the bolus-tracking trigger were 5-10 s for renal arterial, 15-25 s for corticomedullary, and 50-55 s for nephrographic phases.
Goshima
Satoshi
S
Department of Radiology, Gifu University School of Medicine, 1-1 Yanagido, Gifu 501-1193, Japan.
Kanematsu
Masayuki
M
Nishibori
Hironori
H
Kondo
Hiroshi
H
Tsuge
Yusuke
Y
Yokoyama
Ryujiro
R
Miyoshi
Toshiharu
T
Onozuka
Minoru
M
Shiratori
Yoshimune
Y
Moriyama
Noriyuki
N
Bae
Kyongtae T
KT
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D003287:Contrast Media / Q000493:pharmacokinetics*; D005260:Female; D006801:Humans; D007472:Iohexol / Q000493:pharmacokinetics*; D007668:Kidney / Q000098:blood supply / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D011857:Radiographic Image Interpretation, Computer-Assisted; D012079:Renal Circulation; D018709:Statistics, Nonparametric; D013997:Time Factors; D036542:Tomography, Spiral Computed / Q000379:methods*
D003287:Contrast Media; D007472:Iohexol