MRI Liver STIR imaging

Short inversion-time inversion recovery (STIR)
MR is a sensitive technique for detection of
hepatic lesions that is performed as part of
hepatic MR protocols. Studies have
demonstrated that STIR MR images have a
higher sensitivity than other non-enhanced
MR sequences and sensitivity similar to CT
during arterial portography (CTAP) for
detection of hepatic lesions. STIR sequences
provide fat-suppressed images with additive
T1 and T2 contrast. Since both primary and
secondary hepatic malignancies typically
demonstrate prolongation of both T1 and
T2, STIR sequences are especially useful for
detection of pathology. However, malignant
and benign lesions both tend to be very
bright on STIR images, so they are best used
to detect lesions but not to characterize them
once detected.
Clinically, STIR images may depict focal
hepatic lesions that are either not seen or
are more subtle on other pulse sequences.
STIR Images
• Used for both lesion detection only.
• Benign and malignant lesions are
hyperintense.
• Has a nonspecific form of fat
suppression.
• Sensitivity approaches CTAP for lesion
detection.
• Have additive T1 and T2 contrast.

Axial dual in-phase and out-of phase in Liver MRI imaging

The purpose of using dual-phase chemical-shift imaging is to detect lipid either in hepatic parenchyma or within hepatocellular neoplasms. This is a non-enhanced breath-hold T1-weighted spoiled gradient-echo (SPGR) sequence in which periodic chemically selective fat-saturation pulses have been incorporated. Short TRs and short TEs are used. When TE is in phase (4.2 ms at 1.5 T), fat and water signals combine (in-phase imaging). Out-of-phase imaging is performed with a TE of 2.1 ms at 1.5 T. Fat will lose signal intensity on out-of phase images, because the signals from fat and water protons cancel each other. This sequence is also helpful to look for iron deposition in liver parenchyma. In patients with iron accumulation, parenchymal signal is lower on the longer TE in-phase images.

--> Axial dual in-phase and out-of phase in Liver  MRI imaging

• Select 2 echoes, system automatically acquires in and out-of-phase images.
• User CV: Select turbo mode before entering the matrix values. Turbo mode reduces the RF pulse width and therefore shortens the TR. As the turbo mode gets faster, tissue contrast decreases but vessel-background contrast increases.
• Scan from top of liver to bottom of liver. Breath-holding is critical. Repeat as necessary for optimum image quality.

True FISP MRI sequence structure

True FISP MRI sequence structure with balanced gradients. Net effect of gradients allows spins that are stationary as well as those moving with constant velocity to reach a steady state. Gz = slice select gradient, Gy = phase encode gradient, and Gx = frequency encode gradient.

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Fast STIR MRI sequence structure

Fast STIR MRI sequence structure. This is analogous to FLAIR sequence, except that TI time is shorter to null fat signal, and low-amplitude phase-encode steps are acquired earlier. S = slice-select direction, R = “read” or frequency- encode direction, P = phase-encode direction

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EPI diffusion- MRI sequence structure

EPI diffusion- MRI sequence structure. The 90° and 180° RF pulses are followed by a bipolar, trapezoidal frequency encode gradient (Gx) for rapid collection of multiple echos. DWI is applied by symmetrical gradients along a frequency-encoded direction (black rectangles). Subsequent sequence acquisitions would apply diffusion weighting along phase (Gy) and slice-select (Gz) directions

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Gradient echo (GE) in spinal MR imaging

Gradient echo (GE) in spinal MR imaging does not use a 180° pulse to achieve the echo. This gradient-driven echo allows for rapid imaging with very short repetition time (TR). Intrinsic to good image quality in GE imaging is the choice of flip angle, which has optimal values for specific TRs and tissue types, the Ernst angle (the longer the T1 of the tissue, the smaller the best flip angle). There are two types of GE imaging; spoiled and steady-state. Spoiled sequences (fast low-angle shot [FLASH] and spoiled gradient-recalled acquisition in steady state [GRASS]) destroy the residual transverse magnetization after each alpha pulse. In steady-state sequences (fast-imaging steady precession [FISP], steady-state free precession [SSFP], and GRASS), this transverse magnetization is maintained and stabilizes after a few pulses. For tissue with a short T2 (e.g., fat, muscle), or sequences requiring long TR, the spoiled and steady-state sequences look the same. If the T2 of interest is long (e.g., CSF), then the steady-state sequence will give the familiar CSF myelogram effect. Flip angle is a powerful modifier of GE contrast. Spoiled GE sequences will be more T1-weighted with higher flip angles approaching 90°. For steady-state sequences where the TR is shorter than the T2, tissues with long T1 and T2 will show preferentially increased signal with increasing flip angle. Spin-density images can be obtained with a GE technique with short TR if a small flip angle is used. T2-like contrast (T2*) can be obtained with increasing echo time (TE), as with conventional SE imaging.

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Fast FLAIR sequence structure

--> Fast FLAIR sequence structure. Typical FSE sequence structure of multiple 180° pulses is modified by addition of a 180° inversion pulse, followed by a delay time until the alpha pulse (inversion time or TI). CSF is suppressed by appropriate selection of inversion time, which for FLAIR is approximately 2000 ms. Effective TE is determined by low-amplitude phase-encoding steps (central k-space). S = slice-select direction, R = “read” or frequency-encode direction, P = phase-encode direction

PORTAL MRI Protocol

• Axial 2D Time of Flight with Superior Sat band.  3D RECONS 
• Axial FIESTA (AKA: Balanced FFE, TrueFISP)  
• Coronal FIESTA (AKA: Balanced FFE, TrueFISP)  
• 3D T1 weighted Fat Sat Gradient echo

Portal venous image depicts solitary hypointense lesion (arrow) in segment IVa adjacent to middle hepatic vein.

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Coronal 3D Gd MRA sequence use in renal transplant patients MRI

This is the main sequence to evaluate the allograft vasculature for stenosis or occlusion and to roughly assess allograft perfusion by observing the degree of renal enhancement. It evaluates function by looking at gadolinium excretion into the urinary tract.
The 3D volume is centered on the allograft. It should encompass the lower abdominal aorta and extends sufficiently anteriorly to include the femoral heads, it is necessary to include the internal and external iliac in the imaging volume to ensure that the anastomosis is included. Use Smart-prep ensure synchronization of central k-space with arrival of the bolus to acquire the center of k-space data during the arterial enhancement before venous enhancement.

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PELVIS VENOGRAM MRI Protocol

• AXIAL2D Time of Flight (SUPERIOR SAT BAND)
• AXIAL Phase Contrast
• AXIAL  2D FIESTA  
• Contrast enhanced MRV

 

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MRI DACRYOCYSTOGRAPHY

Technique: 

• First normal T1 and T2 to rule out any tumor or lesions
• Then do the high resolution Dynamic T2 weighted thick slice (20-30mm) images while an admixture of saline-lidocaine hydrochloride solution was injected

Magnetic resonance imaging dacryocystography is a technique used to evaluate patients with epiphora. It is comparable with digital dacryocystography in detection and localization of nasolacrimal system obstruction. MRI dacryocystography has significant advantages over digital and CT dacryocystography in terms of superior soft tissue contrast resolution and lack of ionizing radiation. However, CT dacrocystography remains superior for evaluation of congenital bony stenosis, atresia of the bony segment of the nasolacrimal duct, and detection of intracanicular bony fragments in facial trauma. MRI dacryocystography is performed by topical administration of a diluted mixture of Gd-based contrast agents,which provides similar results to catheterization of the lacrimal canaliculi. It may be the best technique for evaluation of the lacrimal system in children.

MR dacryocystography uses stationary or slowly flowing water injected into the lacrimal draining system as a substitute for contrast media. The imaging strategy of MR dacryocystography involves the acquisition of a series of heavily T2-weighted images. Because fluidfilled nasolacrimal ducts have long longitudinal and transverse relaxation times, they have high signal intensity on T2-weighted images. In these hydrographic images, everything looks black and white. Observers can evaluate the nasolacrimal abnormalities indirectly using these “all or nothing” images. The fast spin-echo sequence used in the current study is relatively immune to local magnetic field inhomogeneity. Thus, the sequence is less affected by field inhomogeneity created by air in the maxillary sinus or artificial teeth in the oral cavity. 

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A saline-lidocaine solution is less viscous than iodinated contrast media and flows readily through a thin catheter with a narrow lumen; thus patients can easily self-inject an appropriate amount of the solution while lying on a cradle in the small bore of the MR imager. This solution's lower viscosity helps fill any narrowed lumen in the lacrimal pathways and enables the use of thinner and softer cannulas for intubation of the lacrimal canaliculi, which ensures maximum patient comfort. Concerning safety margins, a saline-lidocaine solution is safe and minimally irritating.

Entire Aorta for Aneurysm MRI protocol

• DB HasteAxGated.
• DB HasteObl SagGated.
• Axial true FISP
• 3D FLASH Obl Sag

Timing Run-Thru mid descending aorta 

• 3D FLASH Obl Sag(2 measures (7 sec gap; 2nd run may be done on inspiration)
• VIBE Ax( Chest and Abdomen)

Technical notes "Entire Aorta for Aneurysm MRI protocol"

• Right sided IV.
• 30cc Gadolinium contrast

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Foot-Toes Infection / Tumor MRI protocols

• Axial T1
• Axial T2
• Axial STIR
• Coronal T1
• Coronal STIR
• Sagittal STIR

Optional Post Gad 

• Axial T1 Fat Sat
• Coronal T1 Fat Sat

The routine examination is performed with the patient lying supine with the foot positioned in an extremity coil. Alternatively the forefoot may be imaged in the prone position with the toes in an extremity coil. The foot is normally placed in the neutral position but may be plantar flexed if there is concern regarding the tendons.

T1    Anatomically detailed with high resolution. Sensitive for bone marrow changes, however may miss bone marrow edema in the smaller phalanges.

T2    Less sensitive to bone marrow edema, especially when fast spin echo sequences are employed due the bright signal of edema blending with the bright signal of the fatty bone marrow. T2 with fat saturation avoids this problem, but the foot may difficult to obtain a uniform fat saturation. Inhomogeneous fat saturation may lead to diagnostic error.

STIR Very sensitive to bone marrow edema changes. Uniform fat saturation easily obtained.

Intavenous gadolinium is generally not needed on a routine basis.  It may improve sensitivity for small abscesses or sinus tracts.

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Nasopharynx MRI technique

• 3 Plane Loc
• Sag T1 Flair 
• Ax Flair T1 
• Cor Flair T1 
• Ax FrFSE T2 
• Cor FrFSE T2 
• Ax FrFSE T2 FS  (frontal sinus to hyoid*only*)
• OPT-Ax FSE T1 post gad T1 fat sat(frontal sinus to epliglottis)
• OPT-Cor FSE T1 post gad  T1 fat sat

Axials – Frontal Sinus to epiglottis, if Neck required – continue axials to sternal notch. 
Coronals – posterior clinoid to anterior nose (do not clip). *Cover tumour if seen

--> If neck required: GE - Ax T1 and T2 are continued as a second set of axials (smaller FOV) overlapping Ax locations from above and continuing to top of aorta (sternal notch).
Upper and Lower axial T1’s and T2’s are bound together and saved as separate series.

Abdominal Aorta for Mesenteric Ischemia MRI Protocol

• HASTE Cor and Axial
• VIBE Ax
• Axial Gradient in/out phase abdomen
• 3D FLASHSAG
• Timing Run 
• 3D FLASH SAG(2 measures with7 sec b/w)
• VIBE Ax
• LAVA 3D coronal

3D FLASH sag-Try to get effective thickness less than 1.5 mm.Want to include celiac and SMA and renal arteries

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Guidelines on Performing APPENDICITIS MRI

• Optional Axial/Coronal STIR

• Gadolinium is relatively contra-indicated in ALL pregnant patients. 

• Even though MRI has to date demonstrated no adverse effects to the fetus, it is relatively contra-indicated in the first trimester due to the amount of organogenesis in early pregnancy. 

• Because the long-term effects of MRI on the fetus are still unknown, MRI is a second-line test to evaluate right abdominal pain after an inconclusive ultrasound, when the only available other imaging options involve ionizing radiation. 

• Radiologist’s option: oral mixture of 300cc or GastroMark and 300cc ReadiCat ingested 90 minutes before imaging may improve visualization of the cecum and appendix by providing negative contrast. 

• The on-call radiologist must be actively involved during the exam, checking all sequences before the patient leaves the scanner.

Source://fwdr.pbworks.com/

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Pulmonary Angiogram MRI Protocol

• DB Haste Axial
• TrueFISPAxial
• 3D FLASH Coronal
• Timing Run -Thru main pulmonary artery.
• 3D FLASH Coronal 2 measures (7 sec gap; 2nd run may be done on inspiration) Inject 20cc of Gd at 2cc/sec followed by 20cc saline at 2cc/sec.
• VIBE Axial

VIBE provides a gray scale that enables readers to distinguish between the clot, or thrombus, and the lung, which both appear dark on MRPA. 

The true FISP test does not require contrast agent or a breath hold, an important consideration for embolism patients who often cannot hold their breath long enough for image acquisition on MRPA. 

Pulmonary Angiogram MRI Protocol

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