The comparison of MRI imaging In 3.0 T & 1.5T By a.r.shoaie

The doubling of the overall signal-to-noise ratio is major difference (SNR) at The 3.0 T (ie, S/N is directly proportional to B0).

 3.0 T (MR) imaging offers higher (SNR) and contrast-to-noise ratio (CNR)than 1.5-T MR imaging does, which can be used to improve image resolution.  and shorten imaging time.

 An increase in SNR can be achieve good spatial resolution, good temporal resolution so imaging times decreased

At high magnetic field strengths is a function of increased SNR, which allows smaller pixels and thinner sections for a given field of view (FOV).

 T1 relaxation times for most tissues are about20%–40% longer at 3.0 T than they are at 1.5 T.  For comparable imaging times, this may result in lower soft- tissue contrast at 3.0 T than at 1.5 T.

Signal intensity–time curves show longer T1 relaxation times at MR imaging in liver (solid curves) and tumor tissue (dashed curves) at 3.0 T than at 1.5 T. To generate a level of T1 contrast between the two tissue types at 3.0 T commensurate with that at 1.5 T, longer repetition times (TR, represented by dotted vertical lines) are required.

 The problem with T1 prolongation is that it reduces the available signal in a reduction in available imaging sections in a given time.therefore, T1 contrast can be considerably decreased, especially with a multisection 2D GRE sequence.

 Increased CNR improves lesion conspicuity, requires less intravenous contrast agents material in Angiography&cholangiograp hy by increasing spatial and temporal resolution.

 The higher CNR seen at 3.0T imaging could lead to cost savings by halving the dose of gadolinium typically used at 1.5 T

 Cardiac cases are not suitable with 3.oT  Strength of magnet causes big changing in R-waves,so triggering is not good.  Therefore 1.5T machine is much better than 3.o T machine.

The ability of contrast-enhanced evaluation of organs, gadolinium-enhanced.  MR angiography, MR cholangiopancreatography, diffusion-weighted imaging.  Mr spectroscopy

 For the evaluation of liver lesions, higher SNR and greater resolution achieved with the 3.0-T system could translate into better detection of malignant lesions on T2-weighted images obtained with adjusted imaging parameters.

 MR spectroscopy are specific examinations that shows  improved spatial and temporal resolution at 3.oT.

 Diffusion-weighted sequences have various potential applications in  abdominal MR imaging  Diffusion-weighted images show  particular promise for monitoring how tumors respond to therapy.

 Diffusion-weighted imaging has important role in the  prostate, uterus, and rectum and for lymph node mapping

 Because the Larmor frequency increases with field strength, higher- frequency RF pulses are required, resulting in an increase in energy transmission and absorption in tissue. e (SAR) increases by a factor of four in a 3.0-T system compared with that in a 1.5-T system.

 Limitations on energy deposition in pulse sequence timing and flip angles. Magnetic susceptibility and chemical shift artifacts.

Chemical shift artifacts. Single-shot fast spin-echo images in a 41-year-old woman with normal kidneys at 1.5 T (a) and at 3.0 T (b) show chemical shift artifacts, which are caused by increased spectral separation. Note the increased water-fat misregistration at the renal cortex at 3.0 T (arrow).

 Clinical 3.0-T MR units are more expensive than 1.5 T units are;  they tend to cost as much as double what1.5 T units do.

 Three-tesla magnets tend to require at least triple the amount of cryogen needed for for 1.5-T magnets;  for example, they consume liquid helium  at a rate of approximately 0.09–0.15 L/hr, versus 0.03 L/hr for 1.5-T magnets.

 Because the wave velocity of the RF pulse is constant, the wavelength becomes shortened as frequency increases. With this shortening of RF wavelength and induction of eddy currents (small electrical currents caused by rapid on-and-off switching of the gradient), inhomogeneity of the RF field occurs.

 The dedicated receiver coils and increased gradient performance, 3.0-T magnetic resonance (MR) systems are gaining wider acceptance in clinical practice.  The expected twofold increase in signal-to- noise ratio (SNR) compared with that of 1.5-T MR systems may help improve spatial resolution or increase temporal resolution when used with parallel acquisition techniques.

 Because the Larmor frequency increases with field strength, higher-frequency RF pulses are required, resulting in an increase in energy transmission and absorption in tissue.  e (SAR) increases by a factor of four in a 3.0-T system compared with that in a 1.5- T system, causing patients to feel an unpleasant heating sensation.

 Potential advantages of 3.0-T imaging in children include acquisition of good- quality images even with a small field of view(FOV).  The shorter overall acquisition time of 3.0-T imaging is useful in childern who may not be able to cooperate for long time.

 T here are both advantages and disadvantages to imaging the abdomen at 3.0 T rather than at 1.5  The increase in SNR and CNR may be used to improve image resolution, shorten imaging time, or both.

Thank you for your attention