This prospective study was performed through 1 year. It included 50 patients, 30 males (60%) and 20 females (40%), with mean age 58.3 ± 15.7 years. All the patients underwent double time-point 18F-FDG PET/CT with informed consent before enrollment. 18F-FDG PET CT imaging was performed using a dedicated whole-body PET/CT scanner (Philips Ingenuity PET/CT system).
Patients’ selection
The selection process included identifying those patients who fulfilled the criteria given below and approved by the ethical committee.
Inclusion criteria
Exclusion criteria
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Patients who underwent aortic angioplasty or stenting.
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Patient who underwent surgery including major vascular intervention.
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Patients with recently diagnosed malignant tumors known to be associated with vascular invasion or receiving prior chemotherapy or radiotherapy.
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Patient who were on atherosclerotic therapy.
Medical data
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Personal history: gender, age, smoking, height, weight and body mass index. History of diabetes mellitus, hypertension, or administration of anti-atherosclerotic medication should be documented.
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Present illness:
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Previous investigation related to aorta.
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Previous treatment: e.g., drugs for dyslipidemia.
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General examination:
Weight, height, body mass index, pulse rate, blood pressure, and random blood sugar.
Image protocol
PET images were acquired from mid-skull to mid-thigh in 3D mode and reconstructed in transverse, coronal, and sagittal planes using a 64-row multidetector hybrid system (Philips—Ingenuity PET/CT system) and (GE Healthcare 16-slice system), with an axial field of view (FOV) of 216 mm and a PET sensitivity of 7.6 counts per second /kBq.
Patient preparation
Patients are instructed fasting for at least 6 h and were asked to avoid strenuous exercise for previous 24 h. Blood glucose was checked in all patients prior to FDG injection. Serum blood glucose levels were determined by finger stick measurement before administration of the radiotracer to ensure a serum glucose level below 200 mg/dl.
All patients were kept in warm and calm environment then received ~ 5.2 MBq of 18F-FDG per kilogram of body weight intravenously. Each patient underwent multiple time-point 18F-FDG PET CT imaging at ~ 60 and 180 min after the administration of 18F-FDG. At 60 min, the acquisition time per bed position was 2 min. To compensate for radioactive decay of the tracer, the acquisition time per bed position was extended to 4 min for the 3-h scan. A low-dose CT-scan for attenuation correction and anatomical orientation as well as to detect aortic calcification was performed at a speed of 0.42 s per rotation and a section thickness of 5.0 mm. The window level in non-enhanced images was zero Hounsfield Units (HU) settled in water. For detection of aortic intimal changes, a bolus intravenous injection of contrast was given to differentiate the aortic wall from the intra-luminal blood. An adequate concentration of contrast medium was obtained at a flow rate of 0.4 ml/s using a power injector. Enhanced images from the aortic arch to the bifurcation were obtained by injecting a total volume of 50–60 ml of contrast medium.
Image analysis
The obtained data were interpreted and analyzed both quantitatively and qualitatively as will be mentioned. All images were viewed on a workstation, which showed multiplanar and 3D reconstructions of the PET and CT images as well as quantitative and semi-quantitative measurements. The entire aorta, starting at the ascending aorta and ending at the aortic bifurcation, was assessed. Blinded for time points and patient characteristics, each PET scan was reviewed and quantitatively assessed for the degree of global arterial 18 F-FDG uptake (Figs. 1, 2, and 3) as follows.
PET findings
For each patient, for each time point, the global 18F-FDG uptake in the aorta was determined by manually drawing regions of interest (ROIs) around the outer part of the arterial wall on every slice of the attenuation-corrected transverse PET CT images. The blood pool 18F-FDG activity was determined in the inferior vena cava lumen as a representative of blood pool activity. Per-patient, per-time-point, per-vessel, and per-ROI radiotracer decay-corrected and body weight-corrected standard uptake values (SUVs) were calculated, resulting in a single mean value of maximum SUV for the aorta and inferior vena cava. The blood pool FDG activity as well as the aortic wall FDG uptake were measured in both early and delayed images and expressed on terms of SUVmax. Then retention index percentage of the blood pool as well as of the aorta was measured. The retention index percentage was calculated by subtracting the SUVmax in early images from the SUVmax in delayed images and dividing by SUVmax in early images.
$$ \frac{\left(\mathrm{SUVmax}\kern0.17em \mathrm{in}\ \mathrm{delayed}\ \mathrm{images}-\mathrm{SUVmax}\ \mathrm{in}\ \mathrm{early}\ \mathrm{images}\right)}{\mathrm{SUVmax}\kern0.17em \mathrm{in}\kern0.17em \mathrm{early}\kern0.17em \mathrm{images}} $$
The FDG uptake by the aortic arterial wall in the delayed images was graded as follows:
Grade 1 when arterial FDG activity is equal or less than the blood pool FDG activity.
Grade 2 when arterial FDG activity is higher than the blood pool FDG activity but less than that of liver.
Grade 3 when arterial FDG activity is higher than blood pool but equal to the liver FDG activity.
Grade 4 when arterial FDG activity is higher than blood pool and slightly higher to the liver FDG activity.
CT findings
Aortic arterial wall were assessed at four parts of the aorta, including ascending aorta, aortic arch, descending thoracic aorta, and descending abdominal aorta. Within each part intimal HU mean, maximum intimal thickness, degree of intimal changes, degree of aortic calcification, and intra-luminal diameter.
Intimal HU mean were measured in non-enhanced images by multiple drawing regions of interest including the aortic wall measuring HU mean in each drawing. Then the mean of all readings were calculated for each part.
The intimal thickness were measured in the contrast enhancing images to differentiate the enhanced luminal blood from the relative less enhancing aortic wall. The degree of intimal changes was shown by a percentage of thickenings of the circumference of the aortic wall for each segment. The intimal changes were evaluated qualitatively including outline irregularity with or without calcific changes. Regarding intra-luminal diameter, the internal luminal diameter measured in the largest cross-section of the aortic diameter except in aortic arch where the shortest axis is used. The ratio of the aortic diameter to body surface area was used to correct for differences in individual body build. The degree of aortic calcification was measured in non-enhanced CT images. It was expressed in the form of percentage of the longitudinal dimensions of each length.
Statistical methods
Data were statistically described in terms of mean ± standard deviation (± SD), median and range, or frequencies (number of cases) and percentages when appropriate. Stepwise multivariate regression analysis was performed to examine the potential interactions among the entered covariates. The Student t test was used for comparison of paired data; P values less than 0.05 was considered statistically significant. Comparison of numerical variables between the study groups was done using Kruskal-Wallis test with post-hoc multiple 2-group comparisons. Spearman’s correlation coefficient (Rs) was used to measure of the strength of the relationship. − 1 ≤ Rs ≤ 1. The absolute value of RS
0.00–0.19 “very weak”
0.20–0.39 “weak”
0.40–0.59 “moderate”
0.60–0.79 “strong”
0.80–1.0 “very strong”
While the sign indicate the direction of the correlation either directly proportion (positive) or inversely proportion (negative). Correlation between various variables was done using Spearman rank correlation equation for non-normal variables/non-linear monotonic relation. All statistical calculations were done using computer program IBM SPSS (Statistical Package for the Social Science; IBM Corp, Armonk, NY, USA) for Microsoft Windows.