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2nd ISNVD

SE

Spin Echo

T1 weighted images are achieve using a short TE and short TR
T2 weighted images are achieve using a long TE and long TR
Proton density images are achieve using a short TE and long TR

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The abbreviation of sequence name

SE (spin echo) for all routine examinations, T1 & T2 & proton density contrast

IR (inversion recovery) especially for heavily T1 weighted sequences in pediatrics

STIR an IR sequence to suppress the signal originating from fat, for orthopedics

FLAIR an IR sequence to suppress the signal originating from water, also called Dark-Fluid-IR; for multiple sklerosis

FLASH a gradient echo sequence with T1 contrast; also called SPGR, T1-FFE

FISP a gradient echo sequence with T1/T2 contrast; also called GRASS or FFE

PSIF a time inversed Fisp gradient echo sequence with T2 contrast, also called CE-FAST

TurboFLASH a fast gradient echo sequence with T1 contrast; also called TFE

DESS a 3D multiecho gradient echo sequence with T2 contrast for orthopedic imaging; Siemens proprietary sequence

CISS a 3D multiecho gradient echo sequence with high resolution T2 contrast for inner ear imaging with reduced flow artifacts; Siemens proprietary sequence

MEDIC a multi echo gradient echo sequence with T2 contrast for neck, c-spine and orthopedic imaging; improved spinal cord contrast, no visible artifacts; Siemens proprietary sequence

TurboSE a multiecho spin echo sequence with T1 & T2 & Proton density contrast; also called FSE or TSE; improves acquisition time typ. by factor 3 to 4 compared to a standard SE

TurboIR, TurboSTIR, TurboFLAIR are IR sequences with TurboSE benefits (see IR, STIR, FLAIR)

single shot TurboSE a very fast TurboSE sequence with heavy T2 contrast which collects all image information in one single run with up to 240 echos; MRCP, urography and myelography

HASTE a single shot multiecho spin echo sequence with T2 contrast in half fourier technique; for uncooperative patients, myelography, urography and MRCP; one image in less than 1 sec.

EPI a single shot ultrafast sequence with T2 contrast; acquires 128 echos in about 100ms to freeze motion; diffusion, perfusion, fMRI

TOF time-of-flight or inflow angiography based on blood exchange in the vessels; uses 2D and 3D gradient echo sequences; mainly for arteries in the brain

PC phase contrast angiography based on the phase information; slow acquisition times; slowly replaced by contrast enhanced angiography

CE MRA or TurboMRA utilize the fast relaxation of intravenously injected contrast; 3D acquisition in 10 to 20 seconds only; no flow artifacts; abdominal and peripheral angiography

The invention of MRI

Sir Peter Mansfield

super moon

Publish Post

ISMRM 2011

Easy way to fill the hole on the image

Is there are a better way to fill the hole in the image? The function just like the imfill in the matlab. Yes, there is the answer.

The just we need is to find a marker image, which labeled the background and the holes in different value, then find the holes position set the value with object; To label the image, 1. get the implement of the image; 2. apply the region grow find the connected object, define the object which connect with edge of the image as background, label a value to express the background, others labeled a value express the hole; 3. find the hole position and take place the value with the object value.

It’s obvious easy to understand than the morphology method to fill hole.

A Yoga dog

MRI take home point (11) Done

• Most artifacts in PE direction (such as motion) but chemical shift artifact which in FE direction.
• Ringing artifacts by insufficient sample points, Wraparound artifacts by insufficient FOV.
• Gd-chelates’ primary effect is marked shortening of T1; thus heavily T1-weighted sequences are essential for high sensitivity to cancer.
• Gd-chelate contrast agents have the potential to cause a new, potentially serious disease (nephrogenic systemic fibrosis or NSF) in patients who have moderate to end-stage kidney disease at the time of administration of contrast agent

MRI take home point (10)

• Image SNR increases linearly with pixel size.
• When two similarly acquired images are added or subtracted, the resulting image has a noise level that is square root of 2 higher than that in either image.
• The larger the lesion area or contrast, and the lower the noise, the easier the lesion is to detect.
• The rose model describes the relationship between lesion area, contrast, and noise for lesion detection; the larger the lesion area or contrast, and the lower the noise, the easier the lesion is to detect.
• Artifacts can be caused by imperfection of hardware including B0, B1, gradients, shielding, RF coils.
• Cross-talking in multi-slice MRI. Partial-volume artifacts.

MRI take home point (9)

• “Fast STIR” imaging collects multiple phase-encoding views (or lines in k-space) for each
• 180-TI-90-TE/2-180-TE/2-ADC pulse train, making it a practical alternative
• to FSE for obtaining fat-suppressed T2-weighted images.
• Noise is best measured as the standard deviation in the background of an MRI.
• Image SNR increases approximately linearly with static magnetic field strength above 0.5 tesla.

MRI take home point (8)

• Fast spin-echo (FSE) sequences provide similar contrast weighting to SE sequences, but with reduced scan times.
• The echo train length (ETL) in FSE describes the number of echoes acquired after each excitation; each echo corresponds to a different phase-encoding view (or line in k-space).
• Echo planar imaging (EPI) acquires extremely fast images but at limited spatial resolution and contrast weighting; more sensitive to chemical shift artifacts.
• Short TI inversion recovery (STIR) sequences provide fat suppression by selection of a TI value that nulls the signal from fat; STIR is a useful substitute for fat-suppressed T2W SE or FSE sequences.

MRI take home point (7)

• The data in the center of k-space determine SNR.
• The spin-echo pulse sequence consists of a 90-TE/2-180-TE/2-ADC.
• Total scan time for 2D spin-echo imaging is determined by the product of TR, the number of phase-encoding steps, and the number of excitations per phase-encoding step.
• In multislice SE, many slices are collected in the same scan time as a single slice. The maximum number of slices is determined by TR and TE, the longer TR and the shorter TE, the more slices that can be acquired.
• Gradient-echo pulse sequences speed image acquisitions by using partial flip angles (less than 90 degree) and gradient-reversal to form a signal echo.

MRI take home point (6)

• The data in the center of k-space determine SNR.
• The spin-echo pulse sequence consists of a 90-TE/2-180-TE/2-ADC.
• Total scan time for 2D spin-echo imaging is determined by the product of TR, the number of phase-encoding steps, and the number of excitations per phase-encoding step.
• In multislice SE, many slices are collected in the same scan time as a single slice. The maximum number of slices is determined by TR and TE, the longer TR and the shorter TE, the more slices that can be acquired.
• Gradient-echo pulse sequences speed image acquisitions by using partial flip angles (less than 90 degree) and gradient-reversal to form a signal echo.

MRI take home point (5)

• T1-weithted SE images are achieved with TR set near the T1 values of tissues of interest, with very short TE values to minimize T2-weithting.
• T2-weighted SE images are achieved by setting TR very long to minimize T1-weighting and setting TE near the T2 values of tissues of interest.
• Spin-density-weighted SE images are achieved by setting TR long and TE very short.
• Dual-echo pulse sequence can be used to produce Spin-density and T2-weighted images from the first and second echoes during the same TR, respectively.
• K-space is the best way to descript how MRI data are sampled.

MRI take home point (4)

 The uptake of Gd-chelates in tissues causes T1, and to a lesser extent T2, to shorten dramatically; this makes lesions with Gd-chelate uptake bright on T1-weighted sequences because with shorter T1 values have higher signal.
Unlike T2, the stronger B0, the longer T1.
 The spin-echo pulse sequence consists of a 90 Pulse followed by a 180 Pulse followed an equal time later by signal collection.
The two user selectable delay times in spin-echo imaging are the sequence repetition time, TR, and the echo time, TE.
TR controls the T1-weihting, while TE controls the T2-weighting of the spin-echo pulse sequence.

MRI take home point (3)

• Longitudinal and transverse relaxation times are determined largely by the macromolecular environment of hydrogen nuclei. T1 > T2
• The more macromolecules of the correct size, the shorter T1.
• The more slowly water molecules move and the longer they spend in the vicinity of larger molecules, the shorter T2 > T2*
• Diseased tissues tend to have longer T1 and T2 values, and higher spin-densities, than normal tissues.

MRI take home point (2)

•  The smaller the receive coil, the higher the sensitivity
•  High-field MRI systems use superconducting magnets to produce highly uniform magnetic fields over the body.
•  Radiofrequency transmitter and receiver coils are required to excite tissue and to measure the signal emitted from tissue.
•  Magnetic gradients applied in three orthogonal directions are used to localize the sources of signal in MR images.
•  The MRI pulse sequence describes the RF pulses sent into the patient, the gradient manipulations, and the signal measurements taken by the MRI system to produce an MR image – the scale of T1, T2.

DCE-MRI for Pulmonary pharechyma

The chemotherapy is most common therapy method for lung cancer, whatever in prior or posterior, surgery or radiotherapy, there always combines chemotherapy. So trail the therapy of lung cancer become more important, PET/CT is the standard method which use radioactive isotopes Tc99 labeled macro-aggregated albumin, but ionization exposure and low spatial resolution are the disadvantage. Although magnetic resonance imaging of pulmonary parenchyma has been blocked by several factor, but as improvement in MRI techniques, there are wide investigation of pulmonary parenchyma, such as ventilation imaging and perfusion imaging. Dynamic contrast enhancement magnetic resonance (DCE-MRI) offers assessment pulmonary perfusion. There are advantages of non-invasive and high spatial contrast of parenchyma compare with CT and PET/CT. Some preliminary studies have been done in quantitative of DCE-MRI.

MRI take home point (1)

• Atomic nuclei with either an odd number of protons or an odd number of neutrons have nuclear magnetic dipole moments.
• The signal in MRI results from the magnetic dipole moments of hydrogen nuclei.
• A strong magnetic field is needed to align hydrogen nuclear magnetic dipole moments preferentially along the magnetic field, the longitudinal direction.
• The larmor frequency is determined by the magnetic field strength and the nucleus of interest.
• Radio-frequency electromagnetic waves applied at the larmor frequency are used to flip the collective magnetization of tissue into the transverse plane where it can be measured.
• The precession of magnetic dipole moments around the direction of the magnetic field at the larmor frequency causes tissue magnetization to induce an alternating electric current in a nearby receiver coil, enabling signal measurement.

how to find the DTI information from DICOM image file

DTI information is not the standard information in MRI dicom file, so different company store them maybe in different place(under different tag value).Here is the DTI information from GE and siemens scanner.
DTI information include B-value, 3 gradient value of each direction. But these information is not the standard information for DICOM file, so different company store these information in differendt parts.
For GE data
(0x0043,0x1039) b value
(0x0019,0x10bb) x direction gradient value
(0x0019,0x10bc) y direction gradient value
(0x0019,0x10bd) z direction gradient value
For Siemens data
(0x0019,0x100c) b value
(0x0019,0x100e) gradient value