Those simple and practical MRI scan positions!

Although many parts can now use 3D isotropic sequence scanning - post-reconstruction to obtain better display results without taking special positions, it takes longer than 2D sequences, and the disadvantages of many models such as 3D obtaining extremely limited contrast images have not been popularized enough in clinical scanning. In clinical diagnosis and treatment, many times it is necessary to better avoid the corresponding artifacts under different or special positions, and to better display and observe certain anatomical tissue structures to evaluate their pathological changes. This issue focuses on sharing the positions of MRI scans that are more practical in clinical scans.

Reasonable, user-friendly asana is the basis for obtaining excellent MRI images, and it is also the key to alleviating related artifacts, so what is a reasonable asana:

Ensure adequate comfort for the subject.

Avoid associated artifacts due to postural factors.

Excellent image quality is achieved.

The resulting images are sufficient to meet the needs of the clinic.

Physiological motion artifacts are mainly improved by compensating techniques in MRI scans, and non-physiological motion artifacts are mainly improved by the application of external measures.

Physiological motion artifacts are mainly improved by applying compensation techniques, such as respiratory compensation, flow compensation, correction techniques, and so on. Above △, MRI scan of the supine position + respiratory compensation sternum area.

Non-physiological motion artifacts are mainly improved by applying external measures, of which reasonable positioning is the key to alleviating non-physiological motion artifacts, above△

Try to avoid placing the limbs in areas where there is movement.

Try to keep the subject in a relaxed and comfortable state.

Use sandbags, sponge pads, etc. to moderately compress the area under examination, abdomen, neck, limb joints, etc.

Standardized and reasonable positioning in clinical scans is the basis for obtaining excellent image quality, and it is also an important guarantee for obtaining standardized clinical images.

When it is necessary to display the local subtle anatomy of the scan site, in the case of ensuring the comfort of the subject, try to scan according to its standardized position, as shown in the above figure △, in the shoulder joint scan position.

In the scan of the hip joint, the scan with the tiptoes together (pay attention to avoid direct contact between the limbs) can effectively ensure that the femoral neck and the femoral head are displayed at the same level. Especially in the scanning of unilateral hip joints, the use of tiptoe-together scanning is more conducive to oblique coronal and oblique sagittal positioning, and can effectively avoid the image reversal after the positioning angle is greater than 45° (can effectively reduce the angle between the femoral neck and the femoral head and the horizontal line).

In the actual scan, if the angle of the scan line positioning is greater than 45 °, the image will be flipped, and attention should be paid to the influence of the subject's position on the scanning positioning angle, and this should be paid attention to in the pendulum position.

For example, knee flexion is usually used in clinical scans with 15-30 °, (there are also requirements for external rotation of 10-15 °, which personally feels unnecessary) to make the anterior cruciate ligament better away from the upper edge of the intercondylar fossa, so that the slender anterior cruciate ligament can be displayed in a complete and continuous 1-2 layer image, which is more conducive to the evaluation of the anterior cruciate ligament, and it is recommended to routinely use the positional scan in the clinic.

For posterior cruciate ligaments, a larger angle needs to be flexed, such as a rigid cylindrical coil that cannot be covered, in which case a flexible coil-wrapped scan is required.

While the position of the scan is important, the positioning angle in the scan is equally important. It should be noted that different scanning and positioning angles are required for the same tissue structure in different positions to better display its anatomy. For example, in ankle injuries, injuries to the anterior and posterior ligaments of the fibula and the heelofibular ligament are more common, and the scanning angle needs to be adjusted according to the position of the subject when positioning.

In neutral position:

The anterior and posterior ligaments of the fibula are angled at 80-90° to the fibula long axis.

The heelofla ligament, at an angle of 40-50° to the fibula long axis.

At plantar flexion:

Distance from the anterior ligament of the fibula, tilted 5-10° to the side of the foot.

Heel-fibular ligament, tilted 15° to the side of the head at an angle.

Some inconclusive lesions in clinical scans also need to be differentially diagnosed by scanning by changing the person's position.

For example, patients with suspected Hirayama disease should be examined with a 35° flexion of the cervical spine ≥ during MRI.

Hirayama disease will encounter some patients after the head is raised after the upper coil can not fit, at this time can use a sponge pad at the bottom of the coil to properly raise the coil to solve this problem.

In daily work, it is often encountered due to the patient's own reasons, such as taking a routine scan position and not being able to normalize the position at all. When encountering a hunchback subject, if you follow the conventional positioning position, the scanning part will not be completely placed in the corresponding scanning coil, and we need to make corresponding position adjustments when facing such subjects.

For example, for the scan of the skull, for the hunchback subject, the sponge pad (part of which is equipped with a special pad) can be reasonably used to raise the back of the subject, and the coil is also properly raised at the same time, so that the problem can be solved perfectly.

In actual clinical work, although most of them are scanned using the standardized position of the supine position with a high degree of comfort, many times they will encounter subjects who cannot lie on their backs, or in order to improve the image quality, they can adjust their scanning position according to their actual situation, such as prone position, lateral position, etc.

Lesions in the sternum area can be scanned in the supine position + respiratory compensation, and also in the case of the subject's tolerance, it can be scanned in the prone position, above △ , MRI scan of the sternum.

Although the scan of the foot and ankle is usually scanned in the supine position, some hospitals take the prone method to scan the foot and ankle in order to obtain better image quality or meet some special clinical needs. Although the use of this position can obtain a better image quality, the scanning method is less comfortable for the subject.

For the scanning of the wrist and elbow joints, the arm is usually lifted up or placed next to the side, and a special coil or other alternative coil with good fit is used for scanning.

However, in actual clinical scans, it is often encountered that the subject cannot cooperate and cannot be scanned using a special coil. At this time, we must be good at using all the resources around us, not a special coil can only do a specific part.

For example, for patients with elbow scans with a large angle of flexion, it is difficult for special coils and flexible coils to meet their scanning requirements, and coil scans with similar coil shapes and morphological structures to the scan site should be selected as much as possible. For example, an ankle coil or shoulder coil after the baseplate has been removed can be used for scanning. As shown in the figure above, the elbow joint can be placed in the shoulder coil after the bottom plate is removed to keep the subject in the most comfortable state, and then fixed with a sandbag. This type of coil is just "L" shaped, which can be better fitted to the scanning part, and the multi-channel hard coil has better image uniformity than the flexible coil.

Image of the elbow joint obtained using a rigid shoulder coil coil, above △ .

Similarly, in the actual scan, if no special coil is configured, a coil with similar structure and morphology and good fit should be selected as much as possible for scanning. If the multi-channel shoulder coil changes the placement direction just in an "L" shape, which is similar to the morphological structure of the ankle joint and has a good fit, this will be a very good choice for scanning the ankle neutral position.

If in the scan of the foot, if the position taken and the selected coil are improper, it is difficult to obtain the ideal image quality.

The foot scan can be carried out in a supine position, the knee is flexed with a soft cushion, and the foot is "stepped" on the coil for scanning, above △ . (In this way, if the aperture is too small to enter the subject, the coil can be properly raised to solve.) However, so far, I have not encountered such a situation). However, it should be noted that the gap between the scanning site and the coil should be filled and fixed with sandbags, which can effectively alleviate the relevant artifacts.

The same method is suitable for ankle scans.

In the figure above, scanning with a foot "stepping" on the coil can not only ensure sufficient signal-to-noise ratio, but also obtain a very ideal fat pressing effect.

Although standardized positioning is the key to obtaining excellent MRI image quality, in actual clinical work, scanning technicians must take into account various factors and cannot perform standardized positional scans of each subject. In the clinical scanning work, scanning technicians should adapt and flexibly grasp the clinical needs and actual situations, adjust the scanning strategy, and achieve personalized scanning on the basis of standardization, so as to obtain excellent MRI image quality while ensuring scanning efficiency.

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