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Native MRA renal arteries

Native MRA (Magnetic Resonance Angiography) Technique

Native MRA refers to non-contrast MR angiography techniques that utilize intrinsic physiological processes for contrast generation, eliminating the need for gadolinium-based contrast agents. Siemens offers two native MRA techniques under the category of NATIVE: NATIVE TrueFISP and NATIVE SPACE.

NATIVE TrueFISP: NATIVE TrueFISP is based on the TrueFISP (True Fast Imaging with Steady-state Precession) sequence, which is a balanced steady-state gradient echo technique. In this technique, contrast is achieved by using a spatially selective inversion pulse to prepare the imaging volume. This pulse suppresses signal from stationary tissues within the imaging volume and venous blood, enhancing the visibility of arteries. Blood flowing into the imaging volume during the inversion time exhibits high-signal characteristics. This technique can be tailored for arteries or veins by positioning the inversion pulse accordingly. NATIVE TrueFISP can accommodate 3D, 2D, breath-hold, syngo PACE (Prospective Acquisition CorrEction) navigated, and respiratory triggered approaches based on the clinical context.

NATIVE SPACE: NATIVE SPACE is a modified 3D Turbo Spin Echo (TSE) sequence with variable flip angles. It relies on the difference in signal intensity between maximal and minimal blood flow during the cardiac cycle. By subtracting images acquired at different phases of the cardiac cycle, background and venous signals are suppressed, and arterial vasculature becomes more prominent. The sequence enables immediate Inline subtraction and Inline Maximum Intensity Projection (MIP) generation, producing non-invasive MR angiograms in real-time. NATIVE SPACE can also support multi-phase imaging for dynamic angiography in regions like the lower legs.

Clinical Importance and Applications: The development of native MRA techniques like NATIVE TrueFISP and NATIVE SPACE addresses concerns about the use of gadolinium-based contrast agents and offers alternatives for imaging blood vessels. These techniques can be particularly valuable in situations where contrast agent administration is contraindicated or undesirable, such as in patients with renal failure or allergies. By utilizing the inherent flow properties of blood, native MRA provides clinically relevant information about vascular structures without the need for contrast agents, thus enhancing patient safety and reducing healthcare costs.

Challenges and Considerations: While native MRA techniques have advantages, they also have limitations. They may be less effective in cases where physiological processes influencing blood flow are disrupted or altered, such as in patients with severe pathologies. Additionally, patient-specific factors, such as heart rate, respiratory patterns, and overall blood flow, can impact the quality of the images obtained using native MRA techniques. Therefore, careful patient selection and protocol optimization are crucial for achieving high-quality results.

NATIVE MRA Raw Data Images

NATIVE MRA Raw Data Images

Indications for magnetic resonance angiography (MRA) renals

Contraindications

Patient preparation

Positioning

Magnetic resonance angiography (MRA) renal artery positioning photo

Table sensors

Advanced MRI scanners are equipped with built-in table sensors that detect the respiratory waveform and trigger data acquisition during the expiration phase of the respiratory cycle. Proper patient positioning over the sensor is critical for accurate respiratory gating. This method eliminates the need for external respiratory gating equipment, such as sensors and belts.

If this feature is unavailable on your scanner, please utilize the respiratory bellows. Refer to the manufacturer’s instructions for guidance on using the bellows.

Advanced MRI scanners are equipped with built-in table sensors

Suggested protocols, parameters and planning

localiser

To localize and plan the sequences, it is essential to acquire a three-plane T2 HASTE localizer initially. These fast single-shot localizers have an acquisition time of under 25 seconds and are highly effective in accurately localizing abdominal structures.

MRA NATIVE non contrast renal artery scan localizer image

T1 VIBE DIXON 3mm axial BH pre GD(In-opposed phase and water sat)

Plan the axial slices on the coronal plane; angle the position block parallel to the right and left renal pelvis. Check the positioning block in the other two planes. An appropriate angle must be given in the sagittal plane (perpendicular to the long axis of kidney). Slices must be sufficient to cover both kidneys from two slices above the upper pole of kidneys down to two slices below the lower pole of kidney. Phase oversampling and, in the case of 3D blocks, slice oversample, must be used to avoid wrap around artefacts. Consider adding saturation bands at the top and bottom of the block to minimize artifacts caused by fat signal, arterial pulsation, and breathing. Instruct the patient to hold their breath during image acquisition.

MRA NATIVE non contrast renal artery scan axial 3d images

Parameters

TR

6-7

TE

2.39   4.77

FLIP

10

NXA

1

SLICE

3 MM

MATRIX

320×320

FOV

320-350

PHASE

A>P

OVERSAMPLE

20%

BH

YES

T2 tse\haste fat sat breath hold 4mm axial

Plan the coronal slices on the axial plane and angle the positioning block parallel to the right and left kidneys. Check the positioning block in the other two planes. Ensure an appropriate angle is given in the sagittal plane (parallel to the long axis of the kidney). The slices should adequately cover both kidneys from the anterior to posterior direction. Phase oversampling should be used to prevent wrap-around artifacts. Consider adding saturation bands at the top and bottom of the block to minimize artifacts caused by fat signal, arterial pulsation, and breathing. Instruct the patient to hold their breath during image acquisition.

MRA non contrast renal artery scan axial image planning

Parameters HASTE FAT SAT

TR

2000-2500

TE

90-110

FAT SAT

SPAIR

NEX

1

SLICE

4MM

MATRIX

320×256

FOV

300

PHASE

R>L

OVERSAMPLE

50%

TRIGGER

NO

Parameters T2 FAT SAT

TR 6000-7000

TE

150

FAT SAT

SPAIR

NEX

1

SLICE

4MM

MATRIX

256×208

FOV

280-300

PHASE

A>P

OVERSAMPLE

80%

IPAT

ON

NATIVE TrueFISP axial respiratory gated 1mm

This particular sequence is performed using a table sensor respiratory-gated sequence. Please choose the appropriate sequence from the protocol.

Plan the axial native block on the coronal plane by first carefully positioning the imaging Field of View (FOV). Ensure that the upper border of the FOV is placed very close to the origin of the targeted vessel. Avoid incorporating an excessive amount of the proximal aorta within the FOV. Now, adjust the positioning block’s angle to run parallel with both the right and left renal pelvis.

To ensure accurate positioning, verify the positioning block in the other two planes as well. It’s essential to maintain an appropriate angle in the sagittal plane, ensuring alignment horizontally across the kidney. For an enhanced inflow effect, make sure that the upper limit of the inversion band aligns precisely with the upper FOV limit. This alignment prevents any loss of signal originating from the inflowing arterial blood.

For improved accuracy and to avoid venous contamination, it’s highly recommended to employ two inversion bands. The upper band should have an inversion time (TI) of 1300-1400ms, while the lower band should possess a TI of 800ms.

The acquisition time for the scan typically falls within a range of 2 to 5 minutes. However, this duration may vary based on factors such as the patient’s breathing cycle. Throughout the scan, diligently monitor the respiratory sensor signal. This ongoing observation ensures the successful completion of the scan and helps uphold image quality standards.

MRA NATIVE non contrast renal artery scan planning and protocol

Parameters

TR

2000-3000

TE

1.5  2

FLIP

90

NXA

1

SLICE

1 MM

MATRIX

256×256

FOV

320-350

PHASE

A>P

OVERSAMPLE

10%

IPAT

YES

MIP (Maximum Intensity Projection) of NATIVE MRA raw data

MIP (Maximum Intensity Projection) reconstruction is a technique used in MRI (Magnetic Resonance Imaging) to create a two-dimensional image that displays the maximum intensity along a chosen projection path. It involves projecting the highest signal intensity voxel from each slice along a specific viewing direction onto a single image plane. MIP reconstructions are commonly used in vascular imaging to enhance the visualization of blood vessels and highlight areas of high signal intensity. This technique allows for a comprehensive overview of the vasculature and aids in identifying abnormalities or areas of interest in a three-dimensional volume dataset.

NATIVE MRA renal arteries