Tradução e Resumo

Original Article Image quality in abdominal CT using an iodine contrast reduction algorithm employing patient size and weight and low kV CT technique Veena R Iyer1 Eric C Ehman1 Ashish Khandelwal1 Michael L Wells1 Yong S Lee1 Nikkole M Weber1 Matthew P Johnson2 Lifeng Yu1 Cynthia H McCollough1 and Joel G Fletcher1 Acta Radiologica 00 110 The Foundation Acta Radiologica 2020 Article reuse guidelines sagepubcomjournalspermissions DOI 1011770284185119898655 journalssagepubcomhomeacr Abstract Background Low tube potentialhigh tube current computed tomography CT imaging allows reduction in iodinebased contrast dose and may extend the benefit of routine contrastenhanced CT exams to patients at risk of nephrotoxicity Purpose To determine the ability of an iodine contrast reduction algorithm to maintain diagnostic image quality for contrastenhanced abdominal CT Material and Methods CT exams with iodine contrast reduction were prescribed for patients at risk for renal dysfunction The iodine contrast reduction algorithm combines weightbased contrast volume reduction with patient widthbased low tube potential selection and bolustracking Control exams with routine iodine dose were selected based on weight width and scan protocol Three radiologists evaluated image quality and diagnostic confidence using a 4point scale 2 acceptable Another radiologist assessed contrast reduction indications and measured portal vein and liver contrasttonoise ratios Results Fortysix contrast reduction algorithm and control exams were compared mean creatinine 16 vs 12 mgdL P 00001 Thirtynine contrast reduction patients had an eGFR 60 mLmin173m2 and 15 had single or transplanted kidney Mean iodine contrast dose was lower in the contrast reduction group 209 vs 394 gmL P 00001 Diagnostic confidence was rated as acceptable in 95 131138 of contrast reduction and 100 of control exams 118128 vs 102113 respectively P 006 Liver attenuation and contrasttonoise ratio CNR were similar P 008 but portal vein attenuation and CNR were lower with contrastreduction mean 176 vs 198 HU P 002 13 vs 16 P 00002 Conclusion This sizebased contrast reduction algorithm using low kV and bolus tracking reduced iodine contrast dose by 50 while achieving acceptable image quality in 95 of exams Keywords Iodine renal insufficiency Xray computed tomography Date received 3 September 2019 accepted 18 November 2019 Introduction The role of intravenous iodinebased contrast used for diagnostic computed tomography CT in the development of nephrotoxicity is debated in literature 15 Although there is emerging evidence that renal injury after radiocontrast is lower than previously estimated 34 this counters longstanding beliefs about 1Department of Radiology Mayo Clinic Rochester MN USA 2Biomedical Statistics and Informatics Mayo Clinic Rochester MN USA Corresponding author Joel G Fletcher 200 First Street SW Rochester MN 55905 USA Email fletcherjoelmayoedu the risk of renal toxicity of iodinebased contrast Concern for postcontrast acute kidney injury PC AKI is higher in patients with preexisting chronic kidney disease acute renal failure and diabetes melli tus 1 In this highrisk patient population the American College of Radiology and European Society of Urogenital Radiology 67 recommends restricted contrast use These patients are frequently evaluated with a noncontrast CT examination which often cannot provide sufficient contrast discrimination to answer the diagnostic question With this in mind some researchers have evaluated the benefit of CT exams predominantly CT angiography exams with reduced iodinated contrast 813 to assess if such a strategy can extend the benefit of contrastenhanced exams to patients with perceived risk for PCAKI Tubepotential selection tools are commercially available on CT systems and used in routine CT exami nations Their primary goal is reducing radiation dose by utilizing lower tube energy Lower tube voltage increases iodine signal and can improve lesion conspi cuity since Xrays produced at lower tube energy such as 80 kVp instead of 120 kVp are closer to the kedge of iodine of 33 keV 1415 If the same principles are applied but routine radiation doses are maintained then iodinebased contrast dose can be reduced while maintaining image quality and iodine contrasttonoise CNR ratios 16 Applying this concept studies on CT angiography of the chest abdomen and pelvis with reduced iodine based contrast dose have shown that image quality is acceptable with lower contrast volumes 8111719 In CT angiography the primary imaging task involves detection of abnormalities with a high contrast differ ence eg the completely opacified vascular tree com pared to surrounding retroperitoneal fat However the primary task in CT examinations of the abdomen nearly always involves detection of lesions with low contrast differences Few studies have addressed the feasibility and image quality of reducedcontrast dose CT examinations of the abdomen for evaluation of hepatocellular carcinoma 142021 and lymphoma 16 and their results are encouraging The purpose of our study is to determine the ability of an iodine con trast reduction CR algorithm to maintain diagnostic image quality for single or multiphase contrast enhanced abdominal CT exams Material and Methods Patient selection and protocol This Institutional Review Board IRBapproved HIPAAcompliant retrospective casecontrol study was performed at an academic tertiarycare 2059bed hospital Only patients who gave permission for their health records to be used for research pur posed were included as required by state law The requirement for written informed consent was waived by the IRB The study included 46 patients who underwent clin ically indicated CT scans of the abdomen between April 2014 and October 2017 using a CR algorithm developed to reduce the dose of iodinebased contrast integrating patient weight and size In this method a reduced contrast dose is injected based on patient weight and a lower tube potential is selected based on patient width at the level of the liver To compensate for the reduced amount of contrast patients were scanned on a CT system equipped with automatic tube potential selection an expanded number of tube potential choices ie 70150 kV in increments of 10 and a newly designed CT Xray tube Somatom Force Siemens Healthineers 22 Due to its higher power reserves this system allows for high tube current gen eration to compensate for increased noise with low tube potential keeping the focal spot small at the low tube potentials employed 22 The CR algorithm was prescribed during routine clinical work by the radiolo gist based on the patients renal function and presence of a single or transplanted kidney Such patients were triaged to the CT scanner capable of performing the examination Fifteen singlephase portalvenous phase abdominal CT scans two singlephase CT enterogra phies and 29 multiphase abdominal CT scans were included 11 of the kidneys eight of the pancreas seven of the liver and three of the small bowel Sizematched controls within 10 kg of weight and within 5 cm of lateral width who underwent the same type of CT protocol were selected from other patients in our practice consecutively from CT scanner logs Due to more tube potential options on the CT system used for the CR algorithm radiation dose could not be controlled between cases and controls However control exams had identical reference tube potential and automatic exposure control settings All control exams utilized vendorsupplied automatic tube potential selection program Care kV Siemens Healthineers Malvern PA USA A radiologist who was not a reader in image quality evaluation noted patient age sex weight renal func tion single or transplant kidney and serum creatinine within 30 days of the exam exam indication intrave nous contrast type and volume and whether patients scanned using the CR algorithm had previously under gone abdominal CT without contrast for the same indi cation from medical records CT acquisition tube potential and CT dose index CTDIvol were recorded 2 Acta Radiologica 00 Image acquisition All CR algorithm examinations were performed on a dualsource 192multidetector CT MDCT system Somatom Force Siemens Healthineers with a detector collimation of 96 06 mm Using zflying focal spot technique 192 slices were simultaneously acquired Other parameters for spiral acquisition include TR05 s collimation192 06 and pitch06 Control examinations were performed either on a 128MDCT or 192MDCT single or dual source system Somatom Definition AS Somatom Definition Edge Somatom Definition Flash or Somatom Definition Force Siemens Healthineers For cases and controls reference tube potential was set at 120 kV and vendor supplied automatic tube potential selection software CARE kV Siemens Healthineers was used with the slider bar set to 8 except for CT enterography where it was 10 Automatic exposure control software was used for all examinations and was not changed for this study On the CT systems employed in the control arm automatic exposure control settings for single phase routine abdominal CTs CT enterography and multiphase renal exams was 200 quality reference mAs with 280 and 240 quality reference mAs used for multiphase pancreas and liver CTs respectively On the CT system used for CR algorithm scans automatic exposure control settings for singlephase routine abdominal CTs and multiphase renal exams was 180 quality reference mAs 120 quality reference mAs for CT enterography and 280 and 240 quality reference mAs for multiphase pancreas and liver CTs respectively CR algorithm scans were acquired using a tube potential of 80 kV if patient width at the liver was 45 cm and at 90 kV if the width was 45 cm Contrast volumes for cases with the low iodine CR algorithm and controls ie routine scans were injected based on patient weight and empirically set based on patient weight as summarized in Table 1 Owing to the reduced amount of iodine in the CR algorithm bolustracking was utilized Monitoring was performed in the descending thoracic aorta 2 cm above the starting point of the scan and triggered at an enhancement threshold of 125 HU on a 120kV monitoring scan with fixed delays to obtain the appropriate phase of enhancement Delays after trigger before image acquisition were 19 s for corticomedullary pancreatic or late arterial phases 35 s for enteric or portal phase exams 55 s for nephrographic phase and 180 s for other phases For multiphase exams the time between completing the first phase of enhancement and the image acquisition for the second phase was calculated as Time between first and second phaseDelayafter threshold of second phase acquisition only Delayafter threshold for first phase Scan timefirst phase For example if the first phase required 5 s of scan time and it was a pancreatic phase and the second phase was a portal phase exam the delay between the two phases would be Time between pancreatic and portal phases Delayafter threshold of portal phase acquisition only 35 s Delayafter threshold for first pancreatic phase 19 s Scan timepancreatic phase 5 s 11 s Control CTs were performed using our standard protocols which generally used fixed time delays single phase CT enterography60 s portal venous phase70 s corticomedullarypancreatic phase3545 s nephrographic phase90 s and delayed phase180 s Late arterial phase scans for hepatocellular carcinoma used bolustracking with a 19s delay Injection rates were weightbased per routine clinical protocols For CR algorithm the same injection rates Table 1 Iodinated contrast volumes used in renalsparing protocol and standard protocol for abdominal CT examinations Patient body weight kg Contrast volume and type for controls 100140 kV Contrast volume and type for contrast reduction algorithm 80 or 90 kV 64 100 mL of Iohexol 300 60 mL of Iohexol 350 or 64109 140 mL of Iohexol 300 70 mL of Iohexol 300 depending on injection rate 110136 200 mL of Iohexol 300 80 mL of Iohexol 350 or 136 200 mL of Iohexol 350 100 mL of Iohexol 300 depending on injection rate Examinations were performed with use of either Iohexol 300 or Iohexol 350 Omnipaque 300 or Omnipaque 350 GE Healthcare followed by 50 mL of saline flush For injection rates of 23 mLs the lower contrast dose was used for injection rates of 45 mLs the higher contrast dose was used CT computed tomography were used as routine exams as if the full dose of contrast was utilized Images were reconstructed using a medium sharp kernel with iterative reconstruction SAFIRE Siemens Healthineers Multiplanar reconstructions were made with axial images reconstructed at 5mm slice thickness and increments of 5 mm for routine portalphase abdominopelvic exams 3 mm for CT enterography multiphase renal and hepatic CT examinations and 2 mm for multiphase pancreatic CT examinations All exams had coronal images reconstructed using a slice thickness of 2 or 3 mm Reconstruction field of view was adapted to patient size Routine clinical exams used an iterative reconstruction strength of 2 SAFIRE or ADMIRE depending on the CT system Siemens Healthineers except for liver and pancreas scans which utilized an iterative reconstruction strength of 3 Image quality evaluation Images were evaluated both qualitatively and quantitatively For qualitative evaluation three abdominal radiologists with six eight and nine years of experience as staff radiologists blinded to contrast volume and scan acquisition parameters evaluated contrast reduction and control CTs Modified European guidelines on quality criteria for CT Table 2 1223 were used for scoring Scans were presented in a randomized order and studies were read in two sessions Image sharpness and noise were evaluated on a 3point scale paying specific attention to small structures like mesenteric vessels and common bile duct Table 2 Artifacts visualization of critical structures and diagnostic confidence were evaluated on a 4point scale Table 2 A score of 2 was considered to be acceptable for diagnostic confidence and all image quality criteria For quantitative assessment two round or oval regions of interest ROIs were placed in the mid liver avoiding hepatic vessels and in the main portal vein at its bifurcation and mean CT numbers were recorded Noise was measured by placement of ROIs in the subcutaneous fat of the anterior abdominal wall and recording the standard deviation of attenuation All ROIs were approximately 100 mm2 in size this size was not so small as to be affected by pixel variability and not so large as to include surrounding structures Visible vessels and bile ducts were excluded from the ROI in the liver parenchyma Iodine CNR was calculated for the liver and portal vein according to the formula iodine CNR CT number liver or portal vein HUnoise subcutaneous fat HU 12 Statistical analysis Patient characteristics were compared between cases and controls by paired ttest or Wilcoxon signedrank test based on normality for continuous variables and by McNemars test for categorical variables Iodine contrast dose contrast volume radiation dose overall noise and portal vein and liver attenuation and CNR were also compared by paired ttest or Wilcoxon signedrank test to account for the 11 paired nature of the data Mean image quality scores for each of the three readers were compared with the same tests All statistical analyses were conducted using SAS version 94 SAS Institute Inc Cary NC USA Table 4 Image quality as reported by three abdominal radiologists blinded to amount of iodinebased contrast Measure and readers Iodine CR algorithm CT examinations n46 Sizematched CT n46 Mean image quality score Evaluation with acceptable image quality score n138 Mean image quality score Evaluation with acceptable image quality score n138 P value Image sharpness Reader 1 12 133 964 122 138 100 100 Reader 2 100 100 NV Reader 3 143 12 003 Noise Reader 1 189 131 949 207 131 949 010 Reader 2 173 172 100 Reader 3 167 128 001 Visualization of critical structures Reader 1 130 131 949 111 138 100 006 Reader 2 117 100 003 Reader 3 130 113 011 Artifacts Reader 1 126 133 964 126 136 986 100 Reader 2 107 100 025 Reader 3 120 104 014 Diagnostic confidence Reader 1 128 131 949 113 138 100 014 Reader 2 118 102 006 Reader 3 126 107 006 A score of 2 was considered acceptable for diagnosis Compared with CT exams performed with contrast reduction algorithm Image sharpness scale 1very sharp 2questionable but adequate for diagnosis 3noticeable blur Statistically significant Noise scale 1less than usual 2optimal 3noise affects interpretation Visualization of critical structures scale 1no artifacts high confidence 2mild artifacts not affecting visualization 3major artifacts affecting the visualization of normal structures 4severe artifacts confidence degraded diagnosis questionable Artifacts scale 1no artifacts high confidence in diagnostic capability 2mild artifacts not affecting the visualization of any structure 3major artifacts affecting the visualization of normal structures 4severe artifacts confidence degraded diagnosis questionable Diagnostic confidence scale 1fully confident 2probably confident 3confident under limited conditions for visualization 4unacceptable CR contrast reduction CT computed tomography NV no variation patients this clinical concern was previously being addressed using a less optimal noncontrast CT technique This algorithm thus extends the benefit of a contrastenhanced CT to patients with tenuous renal function and those with single kidneys and renal allografts We did not find a significant difference in hepatic CNR between patients scanned at lowiodine dose and those scanned with our normal contrast dose protocols and good parenchymal opacification of the liver was of crucial value in most of the indications in our group of patients Although one reader found significantly poorer mean image sharpness scores and greater mean noise scores in the CR algorithm group this did not result in a significantly worse mean scoring of diagnostic confidence Our results agree with studies showing 2540 contrast reductions could be achieved without image degradation for hepatic dynamic contrast examinations using 80 kVp and high tube current 14212425 Similar studies have shown no reduction in CNR of hepatic tumors during the hepatic arterial phase using lower contrast dose at 80 kVp 20 Our results are congruent with work on combined use of lowiodineload bolustracking and lowtubevoltage scanning for renal parenchymal assessment without adverse effect on image quality 26 We also demonstrate feasibility of lowiodinedose CT enterography exams which have not yet been studied The present study has some limitations It was performed in a small cohort Investigation with a larger cohort will be necessary to confirm our findings In this retrospective study the lower contrast dose was prescribed at the discretion of the radiologist at the time of the examination and hence there was no uniformity for protocol selection All patients in our cohort weighed 136 kg most were much lighter Body fat distribution and contour were not uniform between cases and sizematched controls The low contrastdose CT was performed on a CT system with expanded number of tube potential steps an automatic kilovoltage selection system and a large generator Hence our study technique is difficult to directly apply to CT systems without these capabili ties Finally we did not followup patients to evaluate accuracy of the diagnosis made with lowcontrast CT Fig 2 A 65yearold man with a renal and pancreas transplants undergoing lowiodine CTusing the described CR algorithm admitted for suspected allograft pancreatitis to rule out intraabdominal abscess Hospital providers initially ordered a noncontrast CTexam but after discussion with radiologist the transplant team elected to proceed with CTusing the contrast reduction algorithm Axial CT images from the contrast reduction algorithm CT a b permitted confident visualization of a multiloculated abscess white arrows and enhancement of the pancreas transplant open arrow which would be difficult without intravenous contrast After CT the abscess was drained percutaneously and the patient was discharged from the hospital the next day Two radiologists rated diagnostic confidence as fully confident and one rated diagnostic confidence as probably confident Fig 1 Diagnostic confidence ratings for contrastenhanced CTexams in patients undergoing the iodine contrast reduction algorithm and size and weightmatched patients undergoing the same CT exams Scale for diagnostic confidence was 1 ¼ fully confident 2 ¼ probably confident 3 ¼ confident under limited conditions for visualization and 4 ¼ unacceptable Iyer et al 7 Fig 3 A 54yearold man underwent routine contrastenhanced CT which discovered a papillary renal cell carcinoma a arrow which was treated with right nephrectomy with a small indeterminate left renal mass also noted a open arrow Followup contrast enhanced CT obtained one year later was performed using the CR algorithm and demonstrates increasing size of small enhancing mass in left kidney b open arrow The mass was biopsied confirmed to be a papillary renal cell carcinoma and was subsequently cryoablated All three abdominal radiologists rated diagnostic confidence for this exam as fully confident Fig 4 A 51yearold man undergoing contrastenhanced CT using contrast reduction algorithm with low image quality rating suboptimal image noise and sharpness This patient was referred for gastrointestinal bleeding and small bowel ulcerations of undetermined etiology and underwent low iodine CT enterography with iodine contrast reduction due to stage 3 chronic kidney disease and a congenital solitary kidney However image quality was sufficient for clinical radiologist to diagnose sinistral hypertension due to splenic vein occlusion a open arrow resulting in multiple short gastric varices and pancreaticoduodenal varices All three abdominal radiologists rated diagnostic confidence as probably confident for image quality but two out of three rated noise as increased and affecting interpretation 8 Acta Radiologica 00 but instead focused our study on image quality evaluation In conclusion the developed low iodine contrast prescription algorithm can preserve image quality while extending the benefit of contrastenhanced abdominal CT exams to patients with perceived risk of PCAKI Declaration of conflicting interests The authors declared no potential conflicts of interest with respect to the research authorship andor publication of this article Drs McCollough and Fletcher receive industry grant support from Siemens Healthcare which is provided to Mayo Clinic Funding The authors received no financial support for the research authorship andor publication of this article ORCID iD Joel G Fletcher httpsorcidorg0000000289415434 References 1 Do C Intravenous contrast friend or foe A review on contrastinduced nephropathy Adv Chronic Kidney Dis 201724147149 2 Luk L Steinman J Newhouse JH Intravenous contrast induced nephropathythe rise and fall of a threatening idea Adv Chronic Kidney Dis 201724169175 3 McDonald RJ McDonald JS Carter RE et al Intravenous contrast material exposure is not an indepen dent risk factor for dialysis or mortality Radiology 2014273714725 4 WilhelmLeen E MontezRath ME Chertow G Estimating the risk of radiocontrastassociated nephrop athy J Am Soc Nephrol 201728653659 5 Nash K Hafeez A Hou S Hospitalacquired renal insuf ficiency Am J Kidney Dis 200239930936 6 ACR Manual on Contrast Media Version 9 Available at httpwwwacrorgqualitysafetyresourcescontrast manual Fig 5 Top row shows box and whisker plots showing CT number for liver and portal vein and image noise in subcutaneous fat for cases using the iodine contrast reduction algorithm and size and weightmatched control patients undergoing the same contrast enhanced exams Bottom row shows portal vein and liver CNR Note that despite using approximately half the iodine of the control exams CT exams with the CR algorithm had similar CT number and CNR in the liver Small differences in the portal vein were statistically significant Box represents the 25th and 75th percentiles with the median shown as the junction of the gray boxes Upper and lower hash marks represent maximum and minimum respectively Iyer et al 9 7 Stacul F van der Molen AJ Reimer P et al Contrast induced nephropathy updated ESUR Contrast Media Safety Committee guidelines European Radiology 20112125272541 8 Vasconcelos R Vrtiska TJ Foley TA et al Reducing iodine contrast volume in CT angiography of the abdom inal aorta using integrated tube potential selection and weightbased method without compromising image qual ity AJR Am J Roentgenol 2017208552563 9 Durmus T Rogalla P Lembcke A et al Lowdose triple ruleout using 320rowdetector volume MDCTless con trast medium and lower radiation exposure Eur Radiol 20112114161423 10 Nijhof WH Baltussen EJ Kant IM et al Lowdose CT angiography of the abdominal aorta and reduced con trast medium volume Assessment of image quality and radiation dose Clin Radiol 2016716473 11 Wichmann JL Hu XH Kerl JM et al 70 kVp computed tomography pulmonary angiography potential for reduc tion of iodine load and radiation dose Journal of Thoracic Imaging 2015306976 12 Hough DM Fletcher JG Grant KL et al Lowering kilovoltage to reduce radiation dose in contrastenhanced abdominal CT initial assessment of a prototype auto mated kilovoltage selection tool AJR Am J Roentgenol 201219910701077 13 Shen YQ Hu XM Zou XL et al Did low tube voltage CT combined with low contrast media burden protocols accomplish the goal of double low for patients An overview of applications in vessels and abdominal paren chymal organs over the past 5 years Int J Clin Pract 201670B5B15 14 Nakaura T Awai K Maruyama N et al Abdominal dynamic CT in patients with renal dysfunction contrast agent dose reduction with low tube voltage and high tube currenttime product settings at 256detector row CT Radiology 2011261467476 15 Aschoff AJ Catalano C Kirchin MA et al Low radia tion dose in computed tomography the role of iodine Br J Radiol 20179020170079 16 Hough DM Yu L Shiung MM et al Individualization of abdominopelvic CT protocols with lower tube voltage to reduce iv contrast dose or radiation dose AJR Am J Roentgenol 2013201147153 17 Hunsaker AR Oliva IB Cai T et al Contrast opacifica tion using a reduced volume of iodinated contrast mate rial and low peak kilovoltage in pulmonary CT angiography Objective and subjective evaluation AJR Am J Roentgenol 2010195W118124 18 Nakayama Y Awai K Funama Y et al Lower tube voltage reduces contrast material and radiation doses on 16MDCT aortography AJR Am J Roentgenol 2006187W490497 19 Utsunomiya D Oda S Funama Y et al Comparison of standard and lowtube voltage MDCT angiography in patients with peripheral arterial disease Eur Radiol 20102027582765 20 Yanaga Y Awai K Nakaura T et al Hepatocellular carcinoma in patients weighing 70 kg or less initial trial of compactbolus dynamic CT with lowdose contrast material at 80 kVp AJR Am J Roentgenol 201119613241331 21 Nakaura T Nakamura S Maruyama N et al Low con trast agent and radiation dose protocol for hepatic dynamic CT of thin adults at 256detector row CT effect of low tube voltage and hybrid iterative reconstruc tion algorithm on image quality Radiology 2012264445454 22 Meinel FG Canstein C Schoepf UJ et al Image quality and radiation dose of low tube voltage 3rd generation dualsource coronary CT angiography in obese patients a phantom study Eur Radiol 20142416431650 23 Froemming AT Kawashima A Takahashi N et al Individualized kV selection and tube current reduction in excretory phase computed tomography urography potential for radiation dose reduction and the contribu tion of iterative reconstruction to image quality J Comput Assist Tomogr 201337551559 24 Namimoto T Oda S Utsunomiya D et al Improvement of image quality at lowradiation dose and lowcontrast material dose abdominal CT in patients with cirrhosis intraindividual comparison of low tube voltage with iter ative reconstruction algorithm and standard tube voltage J Comput Assist Tomogr 201236495501 25 Noda Y Kanematsu M Goshima S et al Reducing iodine load in hepatic CT for patients with chronic liver disease with a combination of lowtubevoltage and adaptive statistical iterative reconstruction Eur J Radiol 2015841118 26 Kanematsu M Goshima S Kawai N et al Lowiodine load and lowtubevoltage CT angiographic imaging of the kidney by using bolus tracking with saline flushing Radiology 2015275832840 10 Acta Radiologica 00 Iyer VR Ehman EC Khandelwal A et al Image quality in abdominal CT using an iodine contrast reduction algorithm employing patient size and weight and low kV CT technique Acta Radiologica 202061911861195 doi1011770284185119898655 Tradução literal Qualidade de imagem em TC abdominal usando algoritmo de redução de contraste de iodo empregando tamanho de paciente e peso e técnica CT com baixo kV O papel do contraste intravenoso à base de iodo utilizado para tomografia computadorizada diagnóstica CT no desenvolvimento de nefrotoxicidade é debatido na literatura 15 Mesmo que existam evidências emergentes de que lesões renais após radiocontrastes é mais baixo do que estimado anteriormente 34 isso contradiz crenças de longa data sobre o risco da toxicidade renal de contrastes à base de iodo Preocupações para lesões agudas póscontraste PCAKI é maior em pacientes com doenças renais crônicas préexistentes falência renal aguda e diabetes mellitus 1 Nessa população de pacientes de alto risco a American College of Radiology e a European Society of Urogenital Radiology 67 recomendam o uso restrito de contraste Esses pacientes são frequentemente avaliados com examinação CT sem contraste e que frequentemente não conseguem prover discriminação de contraste suficiente para responder as questões de diagnóstico Com isso em mente alguns pesquisadores têm avaliado o benefício de exames CT predominantemente exames CT de angiografia com contraste iodado reduzido para investigar se essa estratégia pode estender o benefício de exames aprimorados com contraste em pacientes com riscos de PCAKI Ferramentas de seleção de potencial de tubo estão comercialmente disponíveis em sistemas CT e são utilizados na rotina de exames CT O objetivo primário é reduzir a dose de radiação utilizando um tubo com energia mais baixa Tensão de tubo mais baixa aumenta o sinal de iodo e pode melhorar a visibilidade de lesões já que os raios X produzidos em tubos de energia menor como 80 kVp em vez de 120 kVp são mais próximos da bordak do iodeto de 33 keV 1415 Se os mesmos princípios forem aplicados porém a dose de rotina de radiação for mantida então a dose do contraste a base de iodo pode ser reduzida enquanto mantém a qualidade da imagem e da razão contrasteruído CNR Aplicando esse conceito estudos em CT angiografia do peito abdômen e pélvis com dose reduzida de contraste a base de iodo tem mostrado que a qualidade da imagem é aceitável com volumes menores de contraste 811 1719 Na CT angiografia a geração primária de imagens envolve a detecção de anormalidades com grandes diferenças de contraste por exemplo a arvore vascular completamente opacificada em comparação com a gordura retroperitoneal circundante Porém a tarefa primária em exames CT do abdômen quase sempre envolve a detecção de lesões com baixas diferenças de contraste Alguns estudos tem abordado a viabilidade e a qualidade de imagem de exames de dose reduzida de contraste a base de iodo para o abdômen na avaliação do carcinoma hepatocelular 142021 e linfoma 16 e seus resultados são encorajadores O objetivo do nosso estudo é determinar a capacidade de um algoritmo de redução de contraste de iodo CR de manter a qualidade da imagem diagnóstica para exames de TC abdominal com contraste monofásico ou multifásico Table 3 Demographic description of case patients undergoing contrast reduction algorithm and control CT exams matched within 5 kg weight and undergoing matched CT protocol Variable Cases Controls P value Age n46 662149 598144 0043 Gender n46 1000 Male 27 5870 27 5870 Female 19 4130 19 4130 Weight kg n46 7961940 7831855 0080 S creatinine mgdL n43 164071 116141 00001 eGFR n44 43951871 76412582 00001 Values are given as meanSD or n CT computed tomography eGFR estimated glomerular filtration rate CTs 13255 mGy cases vs 13064 mGy controls P073 Qualitative image analysis Table 4 shows image quality data for the three readers For the three readers diagnostic confidence with CR algorithm CT was similar to controls There was a tendency for a small nonsignificant improvement in image quality scores for each reader with controls P006 mean improvement in image quality being 017 better for controls Figs 13 For image sharpness 5138 cases in 3 65 patients were graded a score of 3 for noise 7138 exams in 7 15 patients were graded as 3 and for artifacts 5138 in 2 43 patients were graded 2 None of the patients undergoing CR algorithm CT examination received a nondiagnostic rating for image quality rank of 4 but 2 43 patients had a rank of 3 indicating confident under limited conditions by two of three abdominal radiologists Figs 3 and 4 Quantitative image analysis Mean portal vein attenuation mean176 HU vs 198 HU P002 and CNR 13 vs 16 P00002 was significantly higher in the controls Liver attenuation 113 HU vs 114 HU P088 and liver CNR 8 vs 9 P008 was not significantly different Overall noise 15 HU vs 13 HU P002 was significantly higher in the cases Results are summarized in Fig 5 Discussion Our results indicate that the contrast prescription algorithm used in this study reduces iodine dose by 50 while achieving acceptable image quality in 95 of exams This is not at the expense of significantly increased radiation dose Modern CT scanner systems permit scanning at low tube potentials one of the benefits of which is increased conspicuity of iodinated contrast The value of lowiodine lowtube potential scanning has been demonstrated in CT angiographic studies and few studies evaluating abdominal solid organs 13 Our scans were obtained on CT systems capable of producing high tube currents This along with the routine use of iterative reconstruction offsets the impact of increase in image noise at low tube potentials The lowiodine protocol was prescribed in a variety of clinical situations encountered in clinical practice and diagnostic accuracy was not adversely affected in a majority of the examinations In particular it was useful in oncological evaluation for initial characterization of masses in the liver kidneys and pancreas and posttreatment followup In a small subset of the Resumo Diante da problemática trazida por pacientes de alto risco na utilização de altas doses de contraste de iodo o trabalho visa estudar um algoritmo de redução de contraste de iodo mantendo a qualidade da imagem para exames de TC abdominal A introdução também traz algumas referências para mostrar que esse tipo de trabalho envolvendo a redução do contraste de iodo já vem sendo estudado e que parecem promissores como exemplo o uso de ferramentas de seleção de potencial de tubo reduzindo a dose de radiação com um tubo de energia mais baixa Também cita que as técnicas envolvendo o uso do contraste de iodo são diferentes como a angiografia TC e a TC abdominal e que a aplicação dos mesmos princípios poderiam ser realizadas em doses reduzidas