{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {
    "kernel": "SoS"
   },
   "source": [
    "## Other Saturation-Recovery T<sub>1</sub> Mapping techniques"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "kernel": "SoS"
   },
   "source": [
    "<p style=\"text-align:justify;\">\n",
    "Several variations of the inversion recovery pulse sequence were developed to overcome challenges like those specified above. Amongst them, the Look-Locker technique (Look and Locker 1970) stands out as one of the most widely used in practice. Instead of a single 90° acquisition per TR, a periodic train of small excitation pulses θ are applied after the inversion pulse, {θ<sub>180</sub> – 𝛕 – θ – 𝛕 – θ – ...}, where  𝛕 = TR/n and n is the number of sampling acquisitions. This pulse sequence samples the inversion time relaxation curve much more efficiently than conventional inversion recovery, but at a cost of lower SNR. However, because the magnetization state of each TI measurement depends on the previous series of θ excitation, it has higher sensitivity to B<sub>1</sub>-inhomogeneities and imperfect spoiling compared to inversion recovery (Gai et al. 2013; Stikov et al. 2015) . Nonetheless, Look-Locker is widely used for rapid T<sub>1</sub> mapping applications, and variants like MOLLI (Modified Look-Locker Inversion recovery) and ShMOLLI (Shortened MOLLI) are widely used for cardiac T<sub>1</sub> mapping (Messroghli et al. 2004; Piechnik et al. 2010)\n",
    "</p>\n",
    "\n",
    "<p style=\"text-align:justify;\">\n",
    "Another inversion recovery variant that’s worth mentioning is saturation recovery, in which the inversion pulse is replaced with a saturation pulse: {θ<sub>90</sub> – TI – θ<sub>90</sub>}. This technique was used to acquire the very first T<sub>1</sub> map (Pykett and Mansfield 1978). Unlike inversion recovery, this pulse sequence does not need a long TR to recover to its initial condition; every θ<sub>90</sub> pulse resets the longitudinal magnetization to the same initial state. However, to properly sample the recovery curve, TIs still need to reach the order of ~T<sub>1</sub>, the dynamic range of signal potential is cut in half ([0, M<sub>0</sub>]), and the short TIs (which have the fastest acquisition times) have the lowest SNRs.\n",
    "</p>"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "kernel": "SoS"
   },
   "outputs": [],
   "source": []
  }
 ],
 "metadata": {
  "kernelspec": {
   "display_name": "SoS",
   "language": "sos",
   "name": "sos"
  },
  "language_info": {
   "codemirror_mode": "sos",
   "file_extension": ".sos",
   "mimetype": "text/x-sos",
   "name": "sos",
   "nbconvert_exporter": "sos_notebook.converter.SoS_Exporter",
   "pygments_lexer": "sos"
  },
  "sos": {
   "kernels": [
    [
     "SoS",
     "sos",
     "",
     ""
    ]
   ],
   "version": "0.17.2"
  }
 },
 "nbformat": 4,
 "nbformat_minor": 2
}