The target audience is basic scientists and clinical scientists who are interested in ultrafast T2 mapping.MR parameters mapping provides useful quantitative information for characterization of tissue properties [1]. However, the long acquisition time usually hinder its real-time applications. Problems will occur due to the motion; especially the unrepeatable physiological activities will make the real-time MR parameter mapping impossible [2]. Many kinds of imaging methods have been proposed to overcome this problem [3]. However, several seconds are still needed. In this work, a novel single-shot T2 mapping method was proposed based on conventional SE-EPI acquisition scheme, and termed overlapping-echo detachment planar imaging (OLED) method. Two overlapping echo signals with the different T2 weighting were obtained simultaneously through two small flip angle excitation pulses and corresponding echo-shifting gradients. The detachment algorithm based on joint sparsity constraint was proposed to separate the two echo signals. The robustness and efficiency of the OLED sequence were demonstrated through phantom experiments. The reliable T2 mapping can be obtained in the order of milliseconds. Two echo signals with different evolution time for OLED sequence will be acquired synchronously, expressed respectively as: $$\begin{cases} s_{1}(TE_{1})=\int_{}^{} \rho(r)|sina\times cosa|e^{-TE_{1}/T_{2}(r)}dr , first echo \\ s_{2}(TE_{2})=\int_{}^{} \rho(r)\frac{1}{2}|sina\times (1+cosa)|e^{-TE_{2}/T_{2}(r)}dr , second echo\end{cases} $$ , where α=45^o is the flip angle of the excitation pulses, the echo times TE₁ and TE₂ are determined by the echo-shifting gradients G₁ and G₂. The T2 value is calculated in a pixel-wise fashion from Eq. (1). To separate the two echo signals, the following minimization problem is resolved: , $$ \left\{x_{1},x_{2}\right\}=argmin\left[||x_{1}-x_{10}||_2^2+\lambda_{1}||\triangledown x_{1} ||_1+\lambda_{2}||\triangledown x_{2} ||_1+\lambda_{3}||\triangledown \left(x_{1}-\beta x_{2}\right) ||_1\right] $$ (2) where x₁₀, x₂₀, x₁ and x₂ are the preliminary and separated images from the first and second echo signals respectively, λ₁, λ₂, and λ₃ are Lagrange multipliers adjusting constraint weights, and we have: $$ x_{1}e^{i\phi_{1}\left(r\right)}+x_{2}e^{i\phi_{2}\left(r\right)}=x_{0} $$ , where φ₁(r) and φ₂(r) are the linear phase ramps of the first and second images . The experiments were performed on a whole-body 3T scanner ( MAGNETOM Trio TIM, Siemens Healthcare, Erlangen, Germany) with a phantom consisting of multiple vials filled with water doped with MnCl2 of different concentrations. For single-shot EPI and OLED sequences, scan time was 153.5 ms and 141.6ms respectively with acquisition matrix 64×128 and FVO 20x20cm2. Conventional SE sequence was also used for comparison, with 8 different TEs and acquisition matrix = 128×128, and the total scan time was about 1 hour. The results are shown in Fig. 2. In Fig.2, we can see that the T2 values from single-shot OLED sequence are coincident with those from conventional SE sequence (Pearson’s correlation coefficient = 0.9995 for the average T2 value in the different compartments). The maximum deviation is about 4.7% (△T2=-1.5ms) for compartment 1 which has the shortest T1 and T2 values. However, the deviation is mainly from the relative low SNR for compartment 1. The distortions are obvious for EPI and OLED sequences because of the inhomogeneous background field. All the amplitude images (b~e), denoted by the red arrows in Fig. 2, have the inhomogeneous signal intensities in the same compartment. The inhomogeneous signal intensities in SE image mainly come from the inhomogeneous coil sensitivity maps, while the peripheral hyperintense in EPI and OLED sequences may also come from the B0 inhomogeneity. From Fig. 2 (g), we can see that the reconstructed T2 map from OLED is still quite homogeneous comparing to the corresponding signal intensity.Robustness of the OLED method was demonstrated by phantom experiments. Our preliminary results indicate that the OLED can provide single-shot T2 mapping in the order of milliseconds, which is promising for dynamic imaging, and will propel single-shot EPI from a qualitative method to a quantitative method.