In our study 22 patients aged 44 to 76 years (mean age 61 years) with histologically proven clear cell renal cell carcinoma (ccRCC) were examined between February 2018 and October 2018.
Male to female=2:1.
All of themwere underwent renal CT perfusion imaging before surgical resection and pathological analysis in P.
Hertsen Moscow Oncology Research Institute.
Exclusion criteria were significant respiratory artifacts which couldn’t be reduced with post processing and previous antiangiogenic treatment.
All patients were examined with 80-sliced and 64-sliced СТ scanners.
Patients were required to breathe slightly to minimize respiratory artifacts.
In addition a compression band was placed across the abdomen to reduce abdominal wall movement.
An unenhanced CT scan of abdomen was performed to locate the renal mass. The supervising radiologist identified the tumor and placed the predefined scan volume of 4 cm to cover the lesion for the perfusion study.
If the tumor was more than 4 cm and/or contained areas with necrosis the scan was selected in such a way to avoid the necrosis area as much as possible.
22 patients were divided into two groups depending on used scanning technique and mathematic modeling.
11 patients included to the first group were examined on 80-sliced CT scanner,
perfusion was determined using compartmental model.
Compartmental analysis is based on single compartment or two-compartment model.
The foundation of single-compartmental method is the Fick principle.
It assumes that the intravascular and extravascular spaces are a single compartment and estimates tissue perfusion using the maximal slope or the peak height of the tissue concentration curve normalized to the arterial input function.
A major disadvantage of this method is that the assumption of no venous outflow at the time of the maximum initial slope of the tissue timedensity curve is not always true.
Patlak plotting (two-compartment model) is a kinetic model that divides intravascular and extravascular components,
the exchange between them is estimated (Fig 1).
If this method of post-processing is used the following parameters are evaluated: blood flow (BF),
blood volume (BV) and clearance.
The followed scanning parameters were used: scanning field of view 40 mm,
100 kV,
60-90 mA (depending on patient weight),
0.5 s gantry revolution time,
512x512 pixel,
examination time 90 seconds.
For perfusion imaging nonionic iodine contrast agent (volume 0.5 mL/kg of body weight,
concentration 370 mg/mL) was injected in cubital vein at a flow rate 5.5-8 ml/sec followed by saline solution at the same volume and flow rate.
The total duration of injection was 6-7 seconds.
11 patients included to the second group were examined on 64-sliced CT scanner,
perfusion was determined using deconvolution method.
Deconvolution analysis is based on the use of arterial and tissue time-concentration curves to calculate the impulse residue function,
which represents the fraction of contrast medium that remains in the tissue as time evolves after a bolus injection into the arterial input.
Deconvolution-based method assumes that the concentration of contrast agent in the tissue is linearly depended on the arterial input and it is considered that BF is constant.
In post-processing it is possible to estimate more than 10 quantitative characteristics,
but usually only 4 mean parameters are measured: BV,
BF,
mean transit time (MTT) and permeability surface area product (PS).
PS= clearance/unit volume.
The followed scanning parameters were used: scanning field of view 40 mm,
100 kV,
70-160mA (depending on patient weight),
2s gantry rotation time,
512x512 pixel,
examination time 173 seconds.
For perfusion imaging 60 ml of nonionic iodine contrast medium (concentration 350 mg/mL) was administrated intravenously at a flow rate 5ml/sec followed by 30 ml of saline solution at the similar flow rate.
Effective radiation dose was calculated in both groups.
Computed tomography perfusion parameters were measured by 2 independent radiologists (with 5 years of experience) who were blinded to the histopathological results.
In the first group the following parameters were measured and analyzed: BF,
BV and clearance of tumor and normal renal cortex.
At that BF was measured by using maximal slope method (it takes about 2-3 minutes) and BV and clearance were measured by Patlak plotting (it takes 10-15 minutes depending on examination).
In the second group BF,
BV,
MTT and PS of the tumor and normal renal cortex were measured and analyzed,
it took about 5-8 minutes.