What are you getting when you choose either digital or analog MRI?
Patients and physicians often have questions. After all, everyone wants to ensure that they have the best possible chance for an accurate and timely diagnosis.
The underlying message is that you can get virtually identical imaging from both when tested under the same conditions (as has been tested here). However, there are also pros and cons to each type of machine, so let’s take a closer look at those:
Digital MRI: Pros and Cons
The first digital broadband MRI scanner was cleared for use in the United States in 2011. While there have been some newer models since, it is still an emerging technology across the country. Most facilities are still using analog scanners and are happy to do so.
One of the key differences between digital and analog is that digital signal acquisition and processing happens directly at the patient. The signal is digitized directly in the radio-frequency (RF) receive coil nearest to the patient and is then transferred and processed throughout the imaging chain. Tests have found that it is able to generate up to a 40 percent improvement in signal-to-noise ratio.
Digital capabilities help physicians with accurate diagnosis across a range of clinical applications, including cardiac, neurological and musculoskeletal. Digital also helps clinics to overcome RF channel scalability limitations that can be problematic with analog. This means that hospitals can be flexible, without always needing to invest in hardware upgrades.
At the same time, improvements in software are allowing for multiple contrasts from a single acquisition, at a fraction of the time taken for conventional imaging. Technicians also may have the ability to manipulate MR images retrospectively, leading to significant time savings, fewer rescans and therefore cost savings. These features combined can assist the clinician in making a more decisive diagnosis.
Additional benefits include:
- Digital software improvements are allowing physicians to do more with MRI. For example, lung MRI was almost impossible to perform – lungs have a low density of hydrogen atoms required for imaging due to being full of air. New “ultrashort” technology allows clinicians to view the tissue during the brief relaxation periods.
- Digital easier to scale. For example, during a cardiac MRI, a full volume dataset of a chest in motion creates a large amount of data that would normally clog the average picture archiving and communication system (PACS) and post-processing 3-D image workstation. Cloud computing technology means that these volumes of data can now be processed safely and stored efficiently.
- Digital has led to some improvements in patient comfort. For example, the SEEit prostate MR imaging solution from Siemens dispenses with the need for an endorectal coil, often a source of patient discomfort. The full exam can be completed in ten minutes.
Cons of digital MRI
There are some cons to be aware of with digital MRI. The machines are significantly more costly than analog. For many hospitals, this puts them out of reach. Additionally, the digital machine can be more sensitive to ambient temperature than analog.
Analog MRI: Pros and Cons
Analog MRI machines are familiar to most technologists today. Why? Because they’re still heavily used and available.
On analog MRI machines, the RF receiver coil is analog. It picks up the signal from the patient and reconstructs analog data into an image. Typically, they have 16 or 32 channel receivers that work to produce a digital image.
One of the first questions that any patient or physician will ask is “will the image be of high enough quality to determine an accurate diagnosis?” The answer to that is yes. We mentioned a study previously where digital and analog were tested under the same conditions. The resulting image quality was shown to be similar, as shown in the image below:
Images a) and b) were acquired using the analog transceiver, with a) captured without a 30 dB gain-stepping scan, and b) with it. You can see an improvement in signal to noise ratio with the 30 dB gain-stepping scan.
Images c) and d) were acquired with a digital transceiver. Image c) was captured without the 30 dB gain-stepping scan while image d) was captured with it. As with the analog scans, the image with the gain-stepping scan demonstrates improved signal to noise ratio as well as spatial recognition.
So importantly, while digital does have some advantages over analog, an analog machine can do the job it is meant to do, very well. For many clinics, this means that they can be confident in using the lower-cost analog option. This is a clear advantage that analog has over digital, especially in areas where there might not be as high a demand for MRI, or where throughput isn’t as much of an issue.
Cons of analog
Here are a few cons of analog MRI:
- Systems are dependent. RF receive channels may need upgrading to keep up with new coil technology. However, since many of these systems have been around for years, a facility may be able to acquire a used coil at a relatively affordable price point.
- Signal to noise ratio tends to be lower than digital MRI. This has to be accommodated when producing images.
- There may be more artifacts showing in analog images than digital (although several studies have found these to be relatively minor).
Whether digital or analog MRI will be a better choice very much depends upon the situation in which it is being used. Analog is still more predominantly used around the country and is quite sufficient for the majority of scans.
Digital has the advantage where facilities need a faster throughput or for some very specific types of scan where technological advances make digital more comfortable.
Cost is often a huge part of the consideration and analog is a cheaper option. Clinics should weigh up their specific needs with the pros and cons of each type of MRI machine.