When the non-contrast-enhanced phase is unnecessary in abdominal computed tomography scans? A retrospective analysis of 244 cases

Abstract

Objective: To evaluate the necessity of the non contrast-enhanced phase in abdominal computed tomography scans. Materials and Methods: A retrospective, cross-sectional, observational study was developed, evaluating 244 consecutive abdominal computed tomography scans both with and without contrast injection. Initially, the contrast-enhanced images were analyzed (first analysis). Subsequently, the observers had access to the non-contrast-enhanced images for a second analysis. The primary and secondary diagnoses were established as a function of the clinical indications for each study (such as tumor staging, acute abdomen, investigation for abdominal collection and hepatocellular carcinoma, among others). Finally, the changes in the diagnoses resulting from the addition of the non-contrast-enhanced phase were evaluated. Results: Only one (0.4%; p > 0.999; non-statistically significant) out of the 244 reviewed cases had the diagnosis changed after the reading of non-contrast-enhanced images. As the secondary diagnoses are considered, 35 (14%) cases presented changes after the second analysis, as follows: nephrolithiasis (10%), steatosis (3%), adrenal nodule (0.7%) and cholelithiasis (0.3%). Conclusion: For the clinical indications of tumor staging, acute abdomen, investigation of abdominal collections and hepatocellular carcinoma, the non-contrast-enhanced phase can be excluded from abdominal computed tomography studies with no significant impact on the diagnosis. Keywords: Computed tomography; Ionizing radiation; Abdomen; Contrast media.Objetivo: Avaliar a necessidade da fase sem contraste nos exames de tomografia computadorizada de abdome. Materiais e Métodos: Foi realizado estudo retrospectivo, transversal e observacional, no qual foram avaliados 244 exames consecutivos de tomografia computadorizada de abdome realizados sem e com a injeção do meio de contraste. Procurou-se estabelecer, mediante análise das fases com o uso do meio de contraste (primeira análise), e posteriormente com o acréscimo da avaliação da fase sem meio de contraste (segunda análise), o diagnóstico principal e os secundá-rios em função da indicação clínica do exame (estadiamento tumoral, abdome agudo, pesquisa de coleção abdominal e hepatocarcinoma, entre outros). Foram medidas as mudanças nos diagnósticos principais e secundários, decorrentes do acréscimo da fase sem meio de contraste. Resultados: Dos 244 casos avaliados, apenas um (0,4%; p > 0,999; não significante) teve o seu diagnóstico modificado após a leitura da fase sem meio de contraste. Com relação aos diagnósticos secundários, 35 exames (14%) foram modificados após a segunda análise, sendo: nefrolitíase (10%), esteatose (3%), nódulo de adrenal (0,7%) e colelitíase (0,3%). Conclusão: Para as indicações clínicas de estadiamento tumoral, abdome agudo, pesquisa de coleção abdominal e carcinoma hepatocelular, a supressão da fase sem meio de contraste não apresentou impacto diagnóstico expressivo. Unitermos: Tomografia computadorizada; Radiação ionizante; Abdome; Meio de contraste.

Reevaluation of technical protocols and other ways to reduce the radiation dose in computed tomography

“…In the present issue of Radiologia Brasileira, Costa et al (4) present an interesting research article whose results demonstrate that non-contrast-enhanced CT images acquired previously to the dynamic contrast injection, does not significantly contribute for the final diagnosis in most cases with indication for abdominal evaluation (4) and, therefore, could be suppressed. In a previous issue of Radiologia Brasileira, another equally interesting article written by the same group of researchers demonstrated that the equilibrium phase also adds little value to abdominal CT studies for certain indications such as tumor staging, acute abdomen and investigation of abdominal collections (5) and therefore it would be expendable.…”

Readjustment of abdominal computed tomography protocols in a university hospital: impact on radiation dose

“…Most of the major abdominal syndromes have a presentation that allows for the elimination of some acquisition phase, considering a complete four-phase protocol (non-contrast-enhanced, arterial, portal and equilibrium phases) ( 7 , 8 ) . Thus, a careful evaluation of the clinical suspicion allows for the reduction of the number of phases to a justifiable minimum ( 3 ) .…”

“…Once this stage was completed, a survey on the most common indications for abdominal CT scans at the authors' institution was carried out in order to determine which ones should have the scan protocols reviewed. Once the necessary acquisition phases for the selected clinical indications were determined with basis on the authors' previous experience ( 7 , 8 ) , a set of scan protocols was designed in order to cover the clinical indications in a simplified way, utilizing guidelines and recommendations widely published in the literature ( 4 ) .…”

“…"Contrast-enhanced single phase" protocol: such protocol was adopted for the restaging of hypovascular tumor ( 11 ) , acute pancreatitis ( 12 ) , complicated pyelonephritis ( 13 ) , and investigation of intracavitary collections ( 7 , 8 ) .…”

“…Recent studies demonstrated that it is possible to decrease the number of acquisition phases in accordance with the clinical indication, maintaining the diagnostic effectiveness unchanged ( 7 , 8 ) . Such a fact motivated a complete review of abdominal computed tomography protocols at the author's institution as well as the deployment of a training program for all professionals involved in the performance of scans, including radiologists, residents, technicians and nursing personnel.…”