Monday, June 18, 2012

Placenta previa..


 Axial

Placenta praevia (placenta previa AE) is an obstetric complication in which theplacenta is attached to the uterine wall close to or covering the cervix.[1] It can sometimes occur in the later part of the first trimester, but usually during the second or third. It is a leading cause of antepartum haemorrhage (vaginal bleeding). It affects approximately 0.5% of all labours.[2]

          

MRI OF PLACENTA SHOWING PLACENTA  PREVIA

Coronal



Sagittal        
Axial
                                                           





Non-contrast MRA of ArterIes and Veins










 NATIVE (Non-contrast MRA of ArTerIes and VEins)

syngo NATIVE is a contrast-free MR angiography technique for visualizing the vessels of the body. The package contains protocols tailored for use in different body regions (e.g. renal arteries, peripheral vessels). Inline Subtraction and Inline Maximum Intensity Projection (MIP) further simplify the workflow.

Clinical Applications

Alternative to contrast-enhanced MRA examinations when there is contraindication to use of Gadolinium.

Additional Information

For non-contrast MR Angiography Siemens currently offers two techniques under the category of syngo NATIVE —syngo NATIVE TrueFISP and syngo NATIVE SPACE. syngoNATIVE TrueFISP is based on the TrueFISP (True Fast Imaging with Steady state Precession) sequence, which is a balanced steady state gradient echo technique. The contrast mechanism for syngo NATIVE TrueFISP comes from the preparation of the imaging volume with a spatially selective inversion pulse, resulting in the suppression of stationary tissue within the imaging volume and suppression of signal from blood in the imaging volume (e.g. venous blood). Blood which flows into the imaging volume during the inversion time has the same high-signal characteristics exhibited in that TrueFISP. The contrast is further enhanced by the suppression of the background by the inversion pulse. The sequence can be made selective for arteries or veins by appropriate positioning of the inversion pulse, which can be positioned independently from the imaging volume. The sequence accommodates 3D, 2D, breath-hold, syngo PACE (Prospective Acquisition CorrEction) navigated and respiratory triggered approaches depending on clinical environment.
The syngo NATIVE SPACE technique is a modified variable flip angle 3D Turbo Spin Echo sequence in which the contrast mechanism for visualizing vessels is based on the difference in intravascular signal between maximal and minimal flow during the cardiac cycle. The subtracted image is calculated Inline and with Inline MIP generation, instantaneous clinical results are produced for completely non-invasive MR angiography, further improving workflow at the scanner. The syngoNATIVE SPACE technique can also accommodate multi-phase imaging that enables dynamic angiography — for example, in the lower legs.



curtsy to
https://www.medical.siemens.com.

Friday, June 15, 2012

Parallel imaging




Parallel imaging is the one of the advanced techniques recently developed in MRI. It is based on the spatial information inherent in phased array Radio frequency coils and reduces the scan time. In PAT the number of sampled K –space line is reduced, often by a factor of two or greater there by significantly shortening the acquisition time .It can be used in FSE (or TSE) and SS FSE (or HASTE) to improve spatial resolution by reducing ETL. It is used in 90 % of the sequences in higher Tesla machines. The limitations of PAT include reduced SNR and reconstruction artifacts.



History of PAT


The introduction of multiple overlapping small coils replace the large coils,as it cover the same volume as the large coil. when the signals from individual coils are combined, the noise is substantially reduced and SNR is significantly improved. the introduction of multiple overlapping  small coils leads to the introduction of phased-array Coils.
The phased array coils operate typically as receive only coils. In that case, in  the MRI device  implemented body coil act as thetransmitter and sends the radio frequency energy to generate the excitation pulses. State-of-the-art array coil systems include the use of 4 (up to 32) coils with separate receivers. This method is often referred to as a phased array system, although the signals are not added such that the signal phase information is included. The use of phased array coils allows the decreasing of the number of signal averages, which shortens the scan time by high SNR and resolution. 

Theory –(basic)

The basis of these techniques is the concept that acquisition time is proportional to the number of phase-encoding lines in a Cartesian acquisition. Increasing the distance between phase-encoding lines in k-space by a factor R while keeping the spatial resolution fixed reduces the acquisition time by the same factor. This also decreases the field of view (FOV), resulting in aliasing or wraparound artifact .In parallel imaging, the spatial dependence of the phased-array coil elements is used to remove or prevent the aliasing in Fourier transform. Different  vendors uses verity of techniques based on PAT .

The different vendors and their techniques are shown in a table 



fig-2

Figure 2. Example of the SENSE technique. Reference image of a phantom (a), obtained with the
body receiver coil. Sum-of-squares image (b) from two individual coil elements. Spins at spatial locations closer to the coil elements (arrowheads) exhibit higher signal levels than those that are farther away (arrow). A corresponding reference k-space containing 20 phase-encoding views is shown at left.    FT = Fourier transform. Low-resolution full-FOV calibration images (c and d) for each coil, which were obtained to calculate the complex sensitivity profiles of each coil element. Sensitivities (s1 and s2) of each coil element are illustrated at two arbitrary points. Reduced-FOV SENSE images (e and f) from each coil element contain extensive wraparound artifacts along the superior-to-inferior phase-encoding axis. a1 and a2 represent the signal intensities of the aliased images that correspond to the arbitrary points chosen in c and d. Diagram of the unaliased image (g) with desired pixel intensities p1 and p2. These intensities can be calculated because the sensitivities of the individual coil elements and the pixel intensities of the aliased images are known. Unaliased image without (h) and with (i) intensity correction, which represents the SENSE-reconstructed image.


Applications of PAT
  1. MR Angiography-  fig-3
  2. Dynamic Contrast-enhanced Imaging -  fig-4
  3. Fast SE Imaging - fig-5
  4. Cardiac Imaging - fig-6
  5. Breast Imaging - fig 7
  6. MR Enterography and Colonography - fig 8

Limitations of PAT

Limitations of parallel imaging include reduced SNR and reconstruction artifacts. It is important to consider these limitations when deciding when to employ these techniques.




fig-3
Figure 3-Partial volume maximum intensity projection images from renal MR angiography of a patient with fibromuscular dysplasia, obtained without (a) and with (b) SENSE (acceleration factor = 2, applied in the inplane right-left phase-encoding direction). In the standard image, early filling of the left renal vein limits visualization of the left renal artery. Venous contamination is eliminated in the SENSE image, which was obtained with the acquisition time reduced by half. Collecting system activity in the SENSE image is due to excretion of contrast material from the first non-SENSE acquisition








Figure 4 Axial arterial phase (a, b) and portal venous phase (c, d) fat-saturated 3D SPGR images of a patient
with a metastatic neuroendocrine tumor. The images were obtained with SENSE (acceleration factor 2, applied in
the anteroposterior phase-encoding direction), with and acquired slightly superior to and d. SENSE was used
to achieve both excellent temporal and excellent spatial resolution. In this case, achieving optimal timing and adequate
coverage in the arterial phase was crucial because many of the early enhancing hepatic and osseous metastases
could not be visualized on images from subsequent phases.



Figures 5) Coronal single-shot fast SE image obtained without (a) and with (b) SENSE (acceleration
factor 2). Although the SENSE image has slightly diminished SNR, it also has slightly less blurring. (13) Maximum
intensity projection image from 3D fast-recovery fast SE MR cholangiopancreatography. SENSE (acceleration
factor 2) was used to reduce the acquisition time sufficiently so that an adequate volume could be obtained within
a comfortable breath hold.




Figure 6. Short-axis cardiac steady-state free precession cine images (in end diastole) obtained
from apex to base by using SENSE (acceleration factor = 2). Three sections were acquired per
breath hold, allowing the total acquisition time to be considerably shortened.



Figure 7. Sagittal image of a patient with residual breast carcinoma after an excisional biopsy, obtained with a dynamic contrast-enhanced 3D fat-saturated SPGR sequence. Use of
SENSE (acceleration factor = 2) allowed coverage of both breasts with adequate spatial resolution and adequate temporal resolution.







Figure 8. Coronal contrast-enhanced fatsaturated 2D SPGR image of a patient with
Crohn disease shows mild thickening and enhancement of the terminal ileum. SENSE (acceleration factor  2) was used to reduce the acquisition time and thereby decrease motion artifact caused by peristalsis


Note-PAT-Parallel Acquisition Technique, FSE-Fast Spine Echo, TSE-Turbo Spine Echo,
SS FSE-Single Shot Fast Spine Echo, HASTE-Half Acquisition study Time Echo, SNR-signal to Noise Ratio, ETL-Echo Train Length, FT = Fourier transform, SPGR-Spoiled Gradient Recalled Acquisition, Crohn disease –it is an inflammatory disease of the intestines

Susceptibility artifacts when changing bandwidth.

Hi friends see the difference in Susceptibility artifacts when changing bandwidth......
   


SE and GRE

See the diffrence between SE and GRE images ,
The intensity profile shows more than 50% signal intensity lose ... 
so don't trust GRE post contrast study . do at least one SE series  in brain  post contrast study....

"Trigonocephaly"


"Trigonocephaly"

 MRI is better to demonstrate Trigonocephaly (Without radiation exposure)


See Trigonocephaly  shown in MR-SSD..............








Impression :- Trigonocephaly -Premature closure of metopic suture
Read more about Trigonocephaly

Intresting Neurofibroma


"Neurofibroma"
---Patients History
  --->young age patient comes for MRI KNEE(Left)
----->C/o Pain and small & hard swelling on popliteal fossae

See from where it starts .............


 


Neurofibroma is a benign nerve sheath tumor in the peripheral nervous system
Read more about Neurofibroma