| introductionAt present,people pay more attention to the damage induced by iodinated contrast medium and the influence of the X-ray radiation.The concept of "double low",that is,low contrast medium dose and low radiation dose,has been deeply rooted in the hearts of the people.CT angiography is very common in clinical practice and plays an important role in the assessment of renal artery stenosis,renal transplantation donors,reanl vascular hypertention,renal vascular malformation and kidney surgery planning,especially for the laparoscopic partial nephrectomy,which can effectively avoid the vessel damages and severe operative complications.Currently,there are few studies about the optimal delay time for renal CT enhancement,especially for the assessment of renal artery and vein simultaneously.CT angiography of renal arteries and veins is obtained in the arterial and parenchymal phase,respectively.The most commonly used contrast agent is of low osmolality and high concentration(350 mg I/m L or 370 mg I/m L)with a dosage of 100 to 150 m L.However,repeated scanning in both arterial and parenchymal phases brings a high radiation dose,and the effective radiation dose will reach as high as 25-35 m Sv in the CT urography(CTU)examination including four phases(plain,arterial,parenchymal and excretory phases).In patients with renal diseases and probably associated impaired renal function,the higher concentration,osmotic pressure and dosage of contrast medium has,the greater damage to the kidney it makes.Therefore,the issue of how to reduce the contrast medium concentration(iodine content),the osmotic pressure,as well as the radiation dose on the premise of equal or even superior image quality is of great importance in clinical practice.The renal vein angiography can be acquired within a short time after the arterial phase due to the specific microvasclular structures of the kidney.With the application of spectral CT image,this narrow time window could be widened,which makes it possible to evaluate renal arteries and veins simultaneously at the sole late arterial phase.There are few studies on the CT enhancement effect of two different concentration contrast agents,especially 320 mg I/ml and 270 mg I/ml with the same iso-osmotic pressure,and less application of gemstone CT spectroscopy in this field.The comfortability and safety of isotonic iodixanol(270 mg I/m L and 320 mg I/m L)have been verified in CT scanning.The enhancement degrees of aorta,liver and portal vein by using isotonic contrast medium were higher than those by low-osmolar contrast agent with the same concentration,due to the difference of their diffusion effects.The iodine concentration is one of the most important factors affecting the enhancement degree,and the image quality of CT angiography will be compromised as the iodine concentration of the contrast agent decreases.To improve the contrast ratio of the vessels,a low tube voltage can be used according to the attenuation characteristics of iodine,yet with noise increased accordingly.By using spectral imaging,the monochromatic image with the highest contrast to noise ratio(CNR)could be selected to optimizethe demonstration of target vessels even using contrast agent with low iodine concentration.Image quality of spectral CT angiography of abdominal aorta,superior mesenteric and renal arteries with iohexol 270 mg I/m L was better than that of conventional CT angiography with low-osmolar iohexol 350 mg I/m L,while the radiation dose showed no significant difference between them.However,the difference of renal spectral CT angiography between iodixanol 270 mg I/m L and 320 mg I/m L has never been reported previously,and their difference in the effects on renal function remained undocumented.So,the purpose of this study was to evaluate both renal artery and vein simultaneously with dual-energy spectral CT angiography in the sole late arterial phase with isotonic contrast agent with two iodine concentrations(iodixanol 270 mg I/m L and 320 mg I/m L)and to compare the image quality and the renal toxicity between them.Part I : Comparison of Visipaque 270 mg I/ml with Spectral Imaging and Omnipaque 350 mg I/ml with Conventional 120 k Vp in Renal Artery Computed Tomography AnigographyPurpose:To compare the enhancement effects,image quality and radiation dose of Visipaque 270 mg I/ml(iso-osmolar)with spectral imaging and Omnipaque 350 mg I/ml(low-osmolar)with conventional 120 k Vp in renal arterial computed tomography angiography(CTA).Methods:72 patients underwent renal arterial CTA using bolus tracking technique after receiving contrast agent(1.0ml/kg,injection rate 3.5ml/s).42 patients receiving Visipaque 270 mg I/ml underwent spectral CT scanning(abdorminal GSI-15 scan mode,640 m A,0.6s/rotation,large field of view 40 mm,and reconstruction thickness 0.625mm).Optimal monochromatic images for abdominal aorta,bilateral renal arteries and renal cortex were adopted respectively.30 patients receiving Omnipaque 350 mg I/ml underwent automatic tube current modulation scanning(noise index 8,pitch 1.375:1,120 k Vp,0.6s/ rotation,reconstruction thickness 0.625mm).CT values,noise and contrast to noise ratio(CNR),the radiation dose and the discomfort reaction rate were compared between the two groups.Results The radiation dose of conventional scanning group was significantly higher than that of spectral scanning group(CTDIvol,18.87±3.81 vs.15.64 m Gy,t=2.68,p<0.05).The optimal kev of abdominal aorta,bilateral renal arteries and cortex ranged from 48 ke V to 58 ke V,with the most frequency at 53 ke V.CT values and CNRs of the abdomen aorta,bilateral renal arteries and cortex in Visipaque 270 mg I/ml with low ke V imaging were 1.4~1.9 and 1.3~1.5 times higher than those in Omnipaque 350 mg I/ml with 120 k Vp scanning(p<0.001).And the noise of Visipaque 270 mg I/ml at 53 ke V was significantly lower than that of Omnipaque 350 mg I/ml with 120 k Vp scanning(18.37±0.21 vs.24.83±7.21 HU,p<0.01).The discomfort reaction rate of Visipaque 270 mg I/ml was significantly lower than that of Omnipaque 350 mg I/ml(p<0.05).Conclusion Visipaque 270 mg I/ml with 53 ke V imaging can provide better image quality,lower contrast agent and radiation dose than Omnipaque 350 mg I/ml with conventional 120 k Vp in renal artery computed tomography angiography.Part II : Comparison of 270 mg I/m L versus 320 mg I/m L iodixanol in one-stop assessment of both renal arteries and veins with dual-energy spectral CT in late arterial phasePurpose : To compare the image quality of renal arteries and veins with dual-energy spectral CT imaging in late arterial phase using 270 mg I/m L and 320 mg I/m L iodixanol.Materials and Methods: A total of 1062 cases(547 males,515 females)with a mean age of 55.1 ± 12.3 years(range,15-86)were enrolled prospectively and consecutively.Patients were divided into group 1(iodixanol 270 mg I/m L,n = 540)and group 2(iodixanol 320 mg I/m L,n = 522)according to a random number table and all the CT scans were performed with a 64-slice multidetector CT scanner(HD750 Discovery,GE,US)with a total dose of 1.0 m L/kg at a rate of 3.5 m L/s.Images in the late arterial phase were obtained with a dual-energy scan protocol while images in plain,parenchymal and excretory phases were obtained with low radiation dose protocol.The CT value,contrast to noise ratio(CNR)and signal to noise ratio(SNR)of bilateral renal arteries and veins as well as their subjective score based on volume rendering(VR)images were compared between the two groups.Results: group 270 mg I/ml: CT value(HU),SNR and CNR of left / right renal artery were 451.11±104.68/454.48 ± 110.00,25.66 ±7.27/25.54 ± 7.75 and 32.23±7.95/32.20 ±9.31;left / right renal vein were 222.81 ± 68.80/226.76 ± 68.15,13.13 ±5.02/12.85 ±4.67 and 19.81± 6.39/19.50 ±6.17.group 320 mg I/ml CT value(HU),SNR and CNR of left / right renal artery were 481.44 ± 115.00/480.52±117.11,27.44 ±9.18/26.38 ±848 and 34.4 ± 10.36/33.25± 9.57;left / right renal vein were 228.33± 88.15/234.63 ± 86.03,13.01 ±6.29/13.29 ± 5.75 and 19.72±7.90/20.28 ±7.31,there was no significant difference between the two groups(P >0.05).The subjective score of renal artery and vein ranged from 3-5 and 2-3 respectively without significant differences between the two groups(all P > 0.05).Conclusions: The renal arteries and veins can be fully assessed in late arterial phase with isotonic and low concentration iodixanol(270 mg I/m L)using dual-energy spectral CT scan.And the clinical popularization and application of it are of great value in reducing one phase radiation dose.Part III : A comparative study on the influence on renal function injecting isotonic contrast medium iodixanol 270 mg I/ml and 320 mg I/ml with dual-energy spectral CT in later arterial phasePurpose : To compare the influence on renal function with dual-energy spectral CT imaging in late arterial phase using 270 mg I/m L and 320 mg I/m L iodixanol.Materials and Methods: A total of 1062 cases(547 males,515 females)with a mean age of 55.1 ± 12.3 years(range,15-86)were enrolled prospectively and consecutively.Patients were divided into group 1(iodixanol 270 mg I/m L,n = 540)and group 2(iodixanol 320 mg I/m L,n = 522)according to a random number table and all the CT scans were performed with a 64-slice multidetector CT scanner(HD750 Discovery,GE,US)with a total dose of 1.0 m L/kg at a rate of 3.5 m L/s.Images in the late arterial phase were obtained with a dual-energy scan protocol while images in plain,parenchymal and excretory phases were obtained with low radiation dose protocol.Patients were divided into two subgroups according to their renal function: normal(estimated glomerular filtration rate(e GFR)> 90 m L · min-1 · 1.73 m-2)and abnormal(e GFR < 90 m L · min-1 · 1.73 m-2)groups and the influence of the two contrast agents on renal function and the incidence of contrast induced nephropathy(CIN)were compared.Results: The CIN incidence in the subgroup with abnormal renal function using 320 mg I/m L was significantly higher than that using 270 mg I/m L(P =0.043).But there was no significant difference of CIN incidence between the two groups and subgroups with normal renal function(P > 0.05),The incidence of CIN in the subgroup with abnormal baseline renal function was significantly higher than that with normal renal function using 320 mg I/m L(P = 0.002),while there was no significant difference using 270 mg I/m L(P = 0.079).Conclusions: the Isotonic and low concentration contrast medium iodixanol 270 mg I/ml is helpful to reduce the damage of renal function in late arterial phase using dual-energy spectral CT scan... |
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