Quantitative MR renography using a calibrated internal signal (ERETIC) F. Franconi a, *, C. Chapon b , L. Lemaire b , V. Lehmann c , L. Barantin d , S. Akoka e a SCAS, Universite ´ d’Angers, Angers, France b INSERM ERIT-M0104, Universite ´ d’Angers, Angers, France c BRUKER ANALYTIK NMR microscopy application, Rheinstetten, Germany d INSERM U316, Universite ´ de Tours, Tours, France e UMR-CNRS 6006, Universite ´ de Nantes, Nantes, France Received 18 July 2002; accepted 10 September 2002 Abstract To measure MR renograms, cortical and medullary kidney signal intensity evolution is followed after contrast agent injection. To obtain an accurate quantitative signal measurement, the use of a reference signal is necessary to correct the potential MRI system variations in time. The ERETIC method (Electronic Reference To access In vivo Concentrations) provides an electronic reference signal. It is synthesized as an amplitude modulated RF pulse applied during the acquisition. The ERETIC method was as precise as the external tube reference method but presents major advantages like its free adjustability (shape, location and magnitude) to the characteristics of the organ studied as well as its not taking room inside the magnet. Even though ERETIC showed a very good intrinsic stability, systems’ variations still affect its signal in the same way as real NMR signals are affected. This method can be easily implemented on any imaging system with two RF channels. © 2002 Elsevier Science Inc. All rights reserved. Keywords: MR renography; Quantitative; Reference; ERETIC 1. Introduction Dynamic magnetic resonance imaging is a powerful tool to retrieve functional information from organs in human body. In the case of kidney perfusion after administration of a contrast agent, dynamic MRI allows separation of func- tional behavior of the cortex and medulla. Contrast agents, such as Gd_DOTA, enter the arterial space and the intersti- tium as well as the nephrons and increase the image inten- sity in both the cortex and medulla. The transit of the contrast agent through the kidney can be followed by MRI to assess renal function. The time course signal intensity follow up, called MR renogram, have shown differences in the curves pattern between normal and pathologic kidneys (such as ischemic kidney [1], renal failure [2] or renal transplantation [3]). In these studies, it is crucial to be able to measure quantitatively and accurately these subtle signal intensity changes over time and therefore to be able to correct these values from potential MRI system variation in time. Typically, this can be performed by acquiring a ref- erence signal from a phantom simultaneously to the imaging process [4 –5]. This phantom is classically a small test tube filled with doped water attached to the patient’s or the animal’s side. Still, the reference phantom has to satisfy several constraints: 1. The water must be doped to produce a signal whose intensity remains in the range of the tissues observed. In practice, a set of test tubes with different relaxation times is needed and the most adequate one is experimentally chosen for each study. 2. The phantom has to be located within the field of view. In some cases, it could be difficult to position correctly the reference tube close to the organ observed, in the direction fitting the slice orientation. Furthermore, B 0 and B 1 charac- teristics depend on location and so are often different for the observed tissue and the test tube. In this study, we propose to use an NMR-like electron- ically produced signal as a reference signal for dynamic * Corresponding author. Tel.: +33-0241-735006; fax: +33-0241- 735007. E-mail address: florence.franconi@univ-angers.fr (F. Franconi). Magnetic Resonance Imaging 20 (2002) 587–592 0730-725X/02/$ – see front matter © 2002 Elsevier Science Inc. All rights reserved. PII: S0730-725X(02)00593-3