I. 3.0T devices tend to be popular and practical
3.0T devices, which were proposed as one of the hot spots of MR development at the RSNA equipment exhibition in 2000, were available in 2001. So far, in addition to the application in the head, three 3.0T devices have been approved by the FDA for clinical applications in the abdomen and other areas. By the end of November, 46 units (all from GE) had been ordered or installed worldwide.
The magnets for 3.0T are available for whole-body general purpose (all three manufacturers) and head-specific (Siemens), while the magnets for whole-body general purpose are generally longer (e.g., 2.0m for Siemens), Philips has developed a short 1.57m-long magnet that weighs only 5.5 tons.
So far, the signal acquisition application of 3.0T equipment is body coil, and there is no dedicated surface coil yet. However, taking the equipment exhibited by GE as an example, the images acquired by 3.0T equipment applying body coils already have excellent signal-to-noise ratio and resolving power, which are significantly better than the image quality of 1.5T equipment.
Second, 7.0T devices have begun to be developed as one of the concepts for the development of next-generation MR devices.
GE has announced that it is developing a 7.0T device. 7.0T magnets are already available for industrial production, and the existing prototype gradient field strength can achieve 50mT / m, SR200 63cm ID effective shielding and 100mT / m, SR500 38cm ID effective shielding of removable gradients. With two-channel RF system, can be upgraded to 70-300MHZ 8-channel system. 8-channel 500MHZ receiving system, can be upgraded to 32 channels. At present, the advantages and disadvantages of the 7.0T device and the development prospects and market trends can not yet be specifically evaluated.
Third, the development trend of open magnet
Since the introduction of mid-field superconducting MR equipment at RSNA in 2000, several companies with such equipment have marketed their own equipment (GE0.7T; Philips0.6T; HitaChi0.7T; Siemens1.0T), but the market trend does not seem to be as strong as expected. The market situation for low-field open devices has been better, including 0.35T with superconductor type devices (Toshiba, GE). As the technology of high- and mid-field devices continues to be transferred to low-field open type devices, the functions and image quality of low-field devices have been improving, and they are the mainstream models with better performance/price ratio for MR devices. In addition, there is still a market for open 0.5T dual-magnet devices such as those designed by GE, and another smaller company has a similar model on display.
Some companies have updated the concept of “open”, i.e. short magnet type (compact) devices, such as Philips’ 1.5T (former Marconi product) magnets are only 140cm long, and some other specialized magnets of different field strengths are also very short. If these magnets can be further shortened, they are similar to the width of the CT scanning frame, and in a practical sense, they belong to the “open type” equipment.
Fourth, the development trend of midfield equipment
In the MR equipment market, the conventional (non-open) 0.5T models have been withdrawn from the market. In the context of 3.0T devices tend to be popular, 1.0T MR devices are expected to replace 1.5T devices with 3.0T or higher field strength devices in the future because they have almost most of the functions and better performance/price ratio of 1.5T devices.
V. Special MR devices
In addition to the 3.OT head-specific machine developed by Siemens, specialized MR devices for joints, heart, blood vessels (especially limb vessels) and other parts of the body have been marketed by various companies, many of which are small, specialized MR devices developed independently by other, smaller companies. The patient can be imaged standing up or in the prone position, which is particularly useful for functional display of some parts of the body.
Sixth, noise reduction measures
Noise reduction has been a common concern of all manufacturers in the magnet design. Through the built-in vacuum layer in the magnet, reducing eddy currents and the application of buffer materials, the noise level of most devices can be reduced to about 40% of the previous level.
Gradient magnetic field and switching rate
The improvement of gradient magnetic field and switching rate is one of the directions of continuous improvement for each company and each type of MR equipment within the allowed conditions. This year, GE has introduced a practical dual-gradient technology, that is, the gradient field and switching rate are determined by two gradient coils, the gradient field/switching rate of the small coil is 40mT/m, 150mT/m/ms; the gradient field/switching rate of the large coil is 23mT/m, 80mT/m/ms, the two gradients can be automatically switched according to the different fields of view (FOV), and when the FOV exceeds 40cm automatically switch to a large coil. According to GE, by the end of 2001, the world can be installed 75 units. Siemens 3.OT equipment head special machine gradient field / switching rate of up to 68mT / m, 180mT / m / ms.
VIII. Coil
This year, for the first time, the array of RF coils with 8 channels (GE), with an eye on optimizing the RF signal. In addition, companies have updated designs for surface coils, such as free combination coils with integration (philips), etc.. Smaller companies specializing in coil development also have a variety of specialized coils that can be matched to various MR devices, such as full-body flexible array coils and special small joint coils. In the past, phasearray was translated as “phased array”, but in the field of MRI (and ultrasound) there is no connotation of phase or phase control, but rather the proper arrangement of multiple acquisition coils to optimize the acquired signal, so it should be translated as “array”. “coil” is more meaningful.
Nine, SENSE (sensitivity encodingtechnique) technology popularization
SENSE technology, also known as ASSET (array Spatial sensitivilty encoding technique), is the use of higher local gradient magnetic field, in K-space to increase the distance of the sampling location, thereby reducing the sampling density in K-space, in a small field of view (FOV) through a special reconstruction algorithm, in order to maintain the spatial resolution does not decay, so that the acquisition of the spatial resolution of the signal. It is a fast imaging technique that reduces the acquisition time while maintaining the spatial resolution without degradation. Since its introduction as a new technology at last year’s RSNA, almost all of the manufacturers’ products now use this technology (the name varies, e.g., GE calls it ASSET). Philips, the first to apply SENSE technology, has equipped this technology with all devices from 0.23T-3.0T, with acquisition speeds of up to 50 layers / 12- 15 seconds.
The application of SENSE technology initially halved the imaging time, the latest technology has been able to improve the acquisition time by a factor of 4, and is expected to improve by a factor of 9. In addition, SENSE technology can also reduce the noise in the examination.
X. Extension of functions
(i) Prospective acquisition and processing methods
To varying degrees, companies have begun to adopt forward-looking acquisition and processing methods instead of the traditional manual setting of acquisition programs and retrospective post-processing, especially for compatibility with networked technologies. In Siemens’ design, for example, once a patient arrives in the MR room, an examination protocol is first set based on online clinical data, and then the device automatically sets acquisition parameters, reconstructs and reconstructs the acquisition, and automatically generates a report based on the clinician’s diagnosis or intelligent diagnosis. This greatly shortens the entire workflow and optimizes and simplifies the operation.
(ii) Computer-aided scanning parameters and sequence setting
In order to simplify the operation and get the best imaging effect, some devices are equipped with scanning assistance system, which can automatically set the scanning parameters and sequences, and can propose objections and modifications to the inappropriate scanning parameters set by the operator. In addition, some devices can also be operated interactively with the operator in the form of a menu, the operator clicked on the selected imaging purpose, the device set the scanning program. This is certainly a useful way to ensure the quality of the examination for less skilled operators.
(iii) Magnetic resonance spectroscopy (MRS)
The main developments of MRS are: 3D MRS, which is still used for 1.5T and 3.0T devices (GE); automatic MRS, which is a system that switches randomly according to the operator’s proficiency, can be set automatically for unskilled operators, and can suggest changes in parameters for skilled operators (Siemens); in addition to hydrogen proton MRS, a variety of nuclear spectrum functions have been developed in 3. In addition to the hydrogen proton MRS, a variety of nuclear spectra have been developed in the 3. Multi-voxel MRS, which has been implemented in previous years, has been popularized in high-field devices.
(iv) Diffusion tensor imaging
Diffusion tensor imaging is an imaging method that increases the acquisition direction (6-55 directions) to overcome the anisotropic diffusion characteristics of water within the imaging structure, and is currently used mainly for brain white matter bundle imaging. Due to the increased acquisition direction and improved resolution, three-dimensional white matter bundle images can now be obtained, and software is commercially available.
(v) Functional MRI (fMRI)
fMRI has become popular in high-field devices, and the latest advances include: functional brain imaging with multi-layer display; fMRI with real-time display; and fMRI with 3D reconstruction. Several companies have expanded fMRI to 1.0T devices. The facilities and software to match functional imaging are becoming more sophisticated. Other features under development include real-time motion detection/correction (trajectory-guided motion correction), coils in combination with impedance facilities (improved resolution and coverage); image fusion (with diffusion tensor images and MRA) and K-space spiral acquisition techniques (improved temporal resolution and reduced magnetic susceptibility artifacts), etc.
(vi) Expansion of other functions
MR myocardial perfusion imaging (including stress perfusion imaging) has become popular and has been extended to 1.0T devices by some manufacturers; MRA with K-space spiral acquisition can obtain excellent coronary artery display, and 3D reconstruction is feasible; MRA can be developed from the previous 10-20 seconds to sub-second completion, so it can be displayed in fluoroscopy, as much as 2D-3D display can be randomly switched. -The “partial image freeze” technique is a technique to display certain moving organs in a static manner under diaphragm navigation gating conditions. The “partial image freeze” technique is a technique for static display of certain moving organs under diaphragmatic navigation gating, particularly for cardiac and coronary artery viewing.
Hitachi has developed a laser therapy control system that uses the phase difference in temperature to monitor local temperature in laser therapy (mostly mediated human therapy techniques) to control the laser treatment process. Cardiac function analysis used to be handled offline, but now online rapid evaluation and dynamic display of function and morphology are feasible.
(vii) Propulsion (prope11er) technology
This is actually an abbreviation for Periodically Rotated Overlapping Parallel Lines with Enhanced Reconstruction (PERIODICALLY Rotated Overlapping Parallel Lines with Enhanced Reconstruction) technology. The technology includes consistent K-space sampling with multi-directional (lateral, rotational) motion correction to obtain better image quality for patients who cannot cooperate.
(viii) Online integrated design
Following the previously realized integrated design of CT+C-arm X-ray machine and MR+PET, the integrated design of MR+large C-arm vascular machine is introduced this year, which can place the vascular machine and MR equipment in the same room, and the same patient can complete two examinations and/or dispositions continuously.
XI. Dynamics of the next stage of MRI development
(A) Spiral MRI
It is a new acquisition method that is envisioned. In the examination, it is feasible to automatically feed the bed similar to CT scan, and the acquired information can be rapidly imaged, and 5 whole body coronal levels can be displayed in 2.5 minutes on the 1.5T prototype.
(ii) Array coil
In the past, due to technical and cost constraints, each coil was usually set up with 2-4-8 channels. Newly developed array coils, especially for large whole-body acquisitions, can be set up with 8-128 channels.
(iii) Delayed infiltration imaging of the myocardium.