Correlation Of Abdominal Fat Ratio With Hepatic CT Enhancement

Objective1. Analysis the statistical significance of age on hepatic CT enhancement extent.2. Analysis the influence of abdominal fat to liver CT enhancement degree, try to findout the contrast agent dosage in hepatic CT scan of obese patients.MethodsPatientsInstitutional review committee approved this study and patient written informed consentwas waived. We searched an electronic database from June2008to June2012to identify allpatients who underwent a test bolus CT scan as part of their routine abdominal CT imaging.We included patients who had undergone abdominal CT imaging for various reasons, withnegative results or only slight abnormalities such as small angioneoplasms, hepatic cysts oradrenal adenomas, which were considered to have no or little influence on hepaticenhancement. We also included patients who had no evidence of alcohol abuse, viral hepatitis,liver cirrhosis or other hepatic/biliary diseases on history taking, physical examination,laboratory test, or Doppler sonography of liver.Contrast Material Injection and Scan ProtocolsPatients who had fasted overnight lay supine on a table for the test bolus CT scan with a64-row multi-detector CT scanner (Sensation64, Siemens AG, Muenchen, Germany). Beforethe scan, patients underwent an abdominal scan without contrast medium during a breath hold at the end of expiration (120kV,250mA,5-mm slice thickness,1-s cycle time and standardreconstruction algorithm). We selected a slice near the level of the hepatic hilus. Then,15mLcontrast material (Iohexol,300mg I/mL, Changfujiejing Pharmaceutical Co., Shandong,China) was given at2.3mL/s via a20-gauge intravenous catheter in the antecubital vein witha power injector (Stellant, Medrad Inc., Indianola, PA, USA). To record the hepaticenhancement change over time, the test bolus scans involved multiple-slice dynamicsequences lasting96s at the selected level taken10s after injection of the contrast material.The test bolus protocol involved24low-dose serial scans, for96images (120kVp,40mA,10-mm slice thickness,0.36-s scan time and4-s circle time). The patients breathed normallyduring the test bolus scan. Diagnostic scans were then performed according to the hepaticenhancement characteristics acquired from test bolus scans.Quantitative Image AnalysisAfter image acquisition, the data were transferred to an image processing workstation(SyngoMMWP, Siemens AG, Muenchen, Germany). A5-mm-thick slice at the umbilicallevel on the unenhanced transverse series was selected, and the software Volume integratedwith the workstation was used to measure the volume of total abdomen and adipose tissue bya semi-automatic segmentation technique, as previously described and validated [9]. Afreehand region of interest (ROI) was manually traced outside the abdominal wall. Abdominaladipose tissue and total volume was defined as pixels within a window of-190to-30and-190to1000Hounsfield units (HU), respectively. Abdominal adipose tissue volume dividedby total abdominal volume (AFR) was used as a marker of body fat.The software DynEva integrated with the workstation was used to assess features ofhepatic enhancement with the test bolus series. One circular ROI was set on the hepaticparenchyma, avoiding blood vessels, liver margins and possible lesions. The time-densitycurve of the ROI was then automatically generated, and the maximal hepatic enhancement(MHE, peak CT numbers in HU subtracted by those on an unenhanced image) was calculated(Fig.1). The mean of3measurements was calculated. Images with serious artifacts wereexcluded from assessment. We analyzed the adjusted MHE (aMHE; MHE divided by the ofiodine in grams divided by BW in kilograms) by patient age and AFR.Statistical Analysis All data analyses were conducted separately for men and women. Data are expressed asmean±SD. Pearson correlation coefficient was used to assess the association of patient ageand AFR with aMHE. The association of AFR and aMHE was evaluated by linear regressionanalysis. p <0.05was considered statistically significant. Data analysis involved use of SPSSv16.0(SPSS Inc., Chicago, IL, USA).ResultsPatient informationWe included87patients:47men (age55.09±13.27, range34-78years),40women (age60.43±11.29, range37-77years).Correlation of patient age and AFR with aMHEThe mean AFR, BW and aMHE was40.26%±7.45(range26.00-54.09%),63.64Kg±10.90(range42.90-94.70Kg) and97.88HU±10.75(range81.07-119.48HU),respectively, for men and38.97%±9.80(range20.50-60.40%),60.60Kg±8.79(range41.50-74.80Kg) and100.76HU±13.34(range83.11-124.97HU), respectively, for women.aMHE was positively correlated with AFR for men (r=0.48, p<0.01; relational expressionaMHE=70.25+0.69×AFR) and women (r=0.46, p<0.01; relational expressionaMHE=76.26+0.63×AFR)(Fig.2) but not patient age for men or women (r=-0.09and-0.14,respectively, both p>0.05).Conclusion1. The contrast agent dosage select principle of CT enhanced scan is reduce the contrastagent dosage as far as possible on the premise of ensure the imaging quality.2. abdominal fat is a sensitive measure of obesity, the use of spiral CT to measure theabdominal fat has important clinical value, abdominal fat ratio (AFR) can be used as themeasuring index, AFR=abdominal fat volume/total abdominal volume x100%.3. aMHE and AFR of patients were positively correlated (r=0.48/0.46, both P <0.01),abdominal fat content can affect liver CT enhancement degree, high abdominal fat patientscan get the same liver enhancement degree by less contrast medium dosage in comparison ofless abdominal fat patients. 4. There’s no significant correlation between aMHE and the age of patients (r=-0.09/-0.14,both P>0.05), suggesting that age does not affect hepatic CT enhancementdegree.