Evaluation of Myocardial Perfusion by Computed Tomography - Principles, Technical Background and Recommendations / Avaliação da Perfusão Miocárdica por Tomografia Computadorizada - Princípios, Fundamentação Técnica e Recomendações

Abstract Coronary computed tomography angiography (CCTA) has gained a prominent role in the evaluation of coronary artery disease. However, its anatomical nature does not allow the evaluation of the functional repercussion of coronary obstructions. It has been made possible to evaluate Myocardial computed tomography perfusion (Myocardial CTP) recently, based on myocardial contrast changes related to coronary stenoses. Several studies have validated this technique against the anatomical reference method (cardiac catheterization) and other functional methods, including myocardial perfusion scintigraphy and fractional flow reserve. The Myocardial CTP is performed in conjunction with the CCTA, a combined analysis of anatomy and function. The stress phase (with assessment of myocardial perfusion) can be performed before or after the resting phase (assessment of resting perfusion and coronary arteries), and different acquisition parameters are proposed according to the protocol and type of equipment used. Stressors used are based on coronary vasodilation (e.g. dipyridamole, adenosine). Image interpretation, similar to other perfusion assessment methods, is based on the identification and quantification of myocardial perfusion defects. The integration of both perfusion and anatomical findings is fundamental for the examination interpretation algorithm, allowing to define if the stenoses identified are hemodynamically significant and may be related to myocardial ischemia.

Resumo A angiografia coronariana por tomografia computadorizada (ACTC) assumiu um papel de destaque na avaliação da doença arterial coronariana. Entretanto, sua natureza anatômica não permitia a avaliação da repercussão funcional das obstruções coronarianas. Recentemente, tornou-se possível a avaliação da perfusão miocárdica por tomografia computadorizada (PMTC), baseando-se nas alterações de contrastação miocárdicas relacionadas às estenoses coronarianas. Diversos estudos permitiram validar esta técnica perante o método anatômico de referência (cateterismo cardíaco) e outros métodos funcionais, incluindo cintilografia de perfusão miocárdica e a reserva de fluxo fracionada. A PMTC é realizada conjuntamente com a ACTC, em uma análise combinada de anatomia e função. A fase de estresse (com avaliação da perfusão miocárdica) pode ser realizada antes ou depois da fase de repouso (avaliação da perfusão de repouso e artérias coronárias), e diferentes parâmetros de aquisição são propostos conforme o protocolo e o tipo de equipamento utilizados. Os agentes estressores utilizados baseiam-se na vasodilatação coronariana (ex: dipiridamol, adenosina). A interpretação das imagens, semelhante a outros métodos de avaliação perfusional, baseia-se na identificação e quantificação de defeitos de perfusão miocárdicos. A integração dos achados perfusionais e anatômicos é parte fundamental do algoritmo de interpretação do exame, permitindo definir se as estenoses identificadas são hemodinamicamente significativas, podendo se relacionar com isquemia miocárdica.

An augmented patient-specific approach to administration of contrast agent for CT renal angiography

ABSTRACT Purpose This hybrid retrospective and prospective study performed on 200 consecutive patients undergoing renal CTA, investigates the opacification of renal vasculature, radiation dose, and reader confidence. Materials and Methods 100 patients were assigned retrospectively to protocol A and the other 100 were allocated prospectively to protocol B. Both protocols implemented a contrast material and saline flow rate of 4.5 mL/sec. Protocol A utilized a 100 mL of low-osmolar nonionic IV contrast material (Ioversol 350 mg I/mL) while protocol B employed a patient-tailored contrast media formula using iso-osmolar non-ionic (Iodixanol 320 mg I/mL). Results Arterial opacification in the abdominal aorta and in the bilateral main proximal renal arteries demonstrated no statistical significance (p>0.05). Only the main distal renal artery of the left kidney in protocol B was statistically significant (p<0.046). In the venous circulation, the IVC demonstrated a significant reduction in opacification in protocol B (59.39 HU ± 19.39) compared to A (87.74 HU ± 34.06) (p<0.001). Mean CNR for protocol A (22.68 HU ± 13.72) was significantly higher than that of protocol B (14.75 HU ± 5.76 p< 0.0001). Effective dose was significantly reduced in protocol B (2.46 ± 0.74 mSv) compared to A (3.07 ± 0.68 mSv) (p<0.001). Mean contrast media volume was reduced in protocol B (44.56 ± 14.32 mL) with lower iodine concentration. ROC analysis demonstrated significantly higher area under the ROC curve for protocol B (p< 0.0001), with inter-reader agreement increasing from moderate to excellent in renal arterial visualization. Conclusion Employing a patient-tailored contrast media injection protocol shows a significant refinement in the visualization of renal vasculature and reader confidence during renal CTA.