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Introduction | 5

               Figure  1.3:  Standard  inversion-recovery  sequence  used  for  conventional  (bright-blood)  late
               gadolinium  enhancement  (LGE).  A  non-selective  180  degrees  inversion  radiofrequency  pulse
               inverts all magnetization levels. A time delay follows, called the inversion time or TI, in which
               all longitudinal magnetization (Mz) levels recover with a rate determined by the tissue-dependent
               T1 relaxation time. Following the TI, acquisition of the signal takes place. Tissues with shorter T1
               relaxation times recover faster and therefore yield more signal in the resulting MR image. Note
               that for conventional LGE the TI is set to null the magnetization level of the normal myocardium
               magnetization level (green line at 0), leading to a black appearance of the normal myocardium
               on a magnitude image. The magnitude grayscale bar is shown on the right, indicating only minor
               differences between the scar (cyan) and blood pool (orange) magnetization levels.

               types.  A  time  delay  follows,  called  the  ‘inversion  time’  (TI).  During  this  delay,  all
               magnetization levels will recover back to their equilibrium with a rate determined by
               the  tissue-specific  T 1  relaxation  time.  Finally,  after  the  TI,  a  spoiled  gradient-echo
               readout of approximately 100-150 ms is performed to acquire the MR signal.

               A ‘Look-Locker’ scan, also known as TI scout, that provides a series of low-resolution
               images with increasing TI is usually performed beforehand to determine the desired TI
               (Figure 1.4).  Traditionally, the TI is set so that the longitudinal magnetization level of
               normal  myocardium  is  exactly  zero  when  the  MR  signal  is  acquired.   Nulling  the
               normal myocardium will then lead to a black appearance on magnitude images, while
               the blood pool and areas of MI appear bright due to their shortened T 1 relaxation time.
               As  the  blood  pool  is  appearing  bright  using  the  conventional  LGE  sequence  (with
               myocardium nulling), it is referred to as ‘bright-blood’ LGE.
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