Saturday, August 22, 2009

What Is An MRI (Magnetic Resonance Imaging)?

After the development of computed tomography (aka the CT scan), the next big jump in radiology was the development of the imaging modality known as magnetic resonance imaging, or MRI.

The History of Magnetic Resonance Imaging (MRI) Development

The basis of MRI lies in understanding how to apply the chemical principle of nuclear magnetic resonance to living tissue to produce an image (discussed more fully below). While there are many people involved in the research that brought MRI to fruition, the Nobel Prize Committee recognized two individuals in particular: Paul C. Lauterbur and Sir Peter Mansfield. In Lauterbur's own words, here is how he came upon the idea of using NMR for biomedical imaging:
After I returned to Stony Brook, by a long, leisurely automobile drive from California with my family, and settled in again to my department (where I found the same arguments continuing that had been going on when I left) another unexpected event occurred. It had its beginning several years earlier, when a field service engineer for Varian, the leading NMR company, saw an opportunity and asked for my opinion on his idea of starting his own company to make or distribute specialized NMR equipment and supplies. His business plan seemed reasonable, and I encouraged him to go ahead. For a time the company thrived, and I was a member of the Board of Directors.

In May of 1971, however, some other members of the board compared notes with the company's banker and found that the company had engaged in some very dubious business practices and was, in fact, bankrupt. At a hastily-called Board meeting, appropriate actions were weighed, and the banker, there as a guest, threatened to close the company that day unless someone he trusted could be persuaded to take over as President, Chairman of the Board, and Chief Executive Officer. I was the only academic on the Board, the semester had just ended, and the others believed that I was free for the summer, so that I was asked to take the job. I agreed, flew to the company headquarters in New Kensington, PA, near Pittsburgh, at the beginning of each week and back to Stony Brook and my family and students for the weekend.

The developments at the company could supply the plot for a novel, but the incident that is important for my purpose here is that a post-doc arrived with tumor-bearing rats to check the proton NMR relaxation times of their tumors and normal tissues and organs. I was there to observe the experiments, and noted that large and consistent differences were observed for specimens from all parts of the sacrificed animals and that the experiments seemed well-done. Some individuals were speculating that similar measurements might supplement or replace the observations of cell structure in tissues by pathologists, but the invasive nature of the animal procedure was distasteful to me, the data too complex, and the sources of differences too obscure, to be relied upon for medical decisions. As I pondered the problem that evening, I realized that there might be a way to locate the precise origins of NMR signals in complex objects, and hence to form an image of their distributions in two or even three dimensions. That story, and its consequences, is told more fully elsewhere.
As for the first MRI image itself, here is Mansfield's account:
I was still very much concerned with imaging speed and also the question of sliced definition. After a lot of thought and discussion with Peter Grannell we came up with a method of slice selection which looked as though it might work reasonably well. Alan Garroway also came up with a different method of slice selection using a string of short pulses to define the slice and between us we thought that the sensible approach would be to combine our efforts and publish a short note on the general technique of slice selection. This was sent to the Journal of Physics and was published in the form of a letter. The question of imaging times was still concerning me and during the course of 1974 I spent a great deal of time turning over my thoughts on how this may be achieved. One way forward was what I called line scan imaging. In this method a line of magnetization in a specimen was selectively excited and read out. This process was repeated until the object had been scanned. The technique was much faster than the sensitive point scan method of Hinshaw and also turned out to be faster than the projection reconstruction method of Paul Lauterbur, but I was still not satisfied. Nevertheless, line scanning was used to produce a number of images and in particular it was used to scan the finger of one of my early research students, Dr Andrew Maudsley. The scan times for these finger images were 15-23 minutes. These were the first images of a live human subject and were presented at a special meeting of the Medical Research Council which was convened in 1976 to review the work of the several imaging groups that had sprung up both at Nottingham and also in Aberdeen. All groups were vying for MRC support and this meeting was called specially to review the topic and to decide how best to support the work. The images demonstrating live human anatomy were annotated by Professor Rex Coupland, then head of the Department of Human Morphology. They produced a startling response at this meeting and convinced the MRC that our work should be supported. We produced a grant application requesting a substantial sum of money to produce a whole body MRI machine.
Since the 1970s, the rapid development of technology in broad terms has fostered the development of MRI as a practical, and in some cases now, essential tool for physicians, changing the standard of care forever.

The Principles Behind Magnetic Resonance Imaging (MRI)

A detailed explanation of the physics and chemistry that go into using magnets to produce images is beyond the scope of this blog. However, Wikipedia has a nice section that explains MRI in plain and easy-to-follow terms:
The body is largely composed of water molecules which each contain two hydrogen nuclei or protons. When a person goes inside the powerful magnetic field of the scanner, the magnetic moments of these protons align with the direction of the field.
A radio frequency electromagnetic field is then briefly turned on, causing the protons to alter their alignment relative to the field. When this field is turned off the protons return to the original magnetization alignment. These alignment changes create a signal which can be detected by the scanner. The frequency of the emitted signal depends on the strength of the magnetic field. The position of protons in the body can be determined by applying additional magnetic fields during the scan which allows an image of the body to be built up. These are created by turning gradients coils on and off which creates the knocking sounds heard during an MR scan.
Diseased tissue, such as tumors, can be detected because the protons in different tissues return to their equilibrium state at different rates. By changing the parameters on the scanner this effect is used to create contrast between different types of body tissue.

Contrast agents may be injected intravenously to enhance the appearance of blood vessels, tumors or inflammation. Contrast agents may also be directly injected into a joint in the case of arthrograms, MR images of joints. Unlike CT, MRI uses no ionizing radiation and is generally a very safe procedure. Patients with some metal implants, cochlear implants, and cardiac pacemakers are prevented from having an MRI scan due to effects of the strong magnetic field and powerful radio frequency pulses.

The Future of Magnetic Resonance Imaging (MRI)

MRI has found many applications in the medical field. Functional MRIs are used to assess how differential delivery of glucose reflects neurological function in conscious subjects. There are many potential applications of functional MRIs, ranging from studies in psychology and economics to more medically-related applications in psychiatry. In oncology, MRIs are being paired with PET scans to further improve the sensitivity of tumor detection. If the last few decades are any indication, the next ten years will likely see an explosion of MRI installations and application development, to the degree that one day an MRI might be as routine as a plain x-ray.

Friday, August 14, 2009

What is PACS?

Imagine you writing a blog about, say, vegetarian Indian food recipes. The blog would consist of a collection of recipes (text data) and images of the food prepared (visual data). To transfer this information to other people, you would need some kind of system that would store the data and then be able to transfer it at will to other interested parties. This structure is the blog software and the server hardware. In other words, this is a picture archival and communication system, or PACS.

The History of Picture Archival and Communication System (PACS)

The concept of a PACS was first discusssed in the early 1980s. While no one individual can be credited with the full development of PACS, this article in Imaging Economics describes some of the contributions of early leaders in PACS development:
"Any image, anytime, anywhere—that's the mantra," says Reuben Mezrich, MD, PhD, describing the capability of the modern PACS (picture archiving and communications system). "But none of this could have happened without DICOM (digital imaging and communication in medicine).

"If you could give a Nobel Prize for DICOM, that would be a good thing," adds Mezrich, professor of radiology and chairman of the radiology department at the University of Maryland School of Medicine, Baltimore.

DICOM is a meticulously developed set of standards that allow systems to interface. It specifies how devices built in conformance with the standards react to commands and data being exchanged. DICOM, for instance, lets a CT scanner made by one manufacturer, an MRI scanner made by a second company, and an ultrasound machine made by a third company all communicate with the same PACS. It is because of DICOM that images from all three modalities, and others as well, can be displayed and interpreted at the same PACS workstation. The images can all be sent to the same PACS archive. DICOM is the computer standard that lets a PACS do its work.

If, as Mezrich suggests, a prize were given for DICOM, the recipient would most likely be Steven C. Horii, MD, who is now a professor of radiology and clinical director of medical informatics at the Hospital of the University of Pennsylvania, Philadelphia. By informal acclaim from his peers, Horii is credited with being the DICOM point man. He is cited for putting in the long hours and the blood, sweat, and perseverance that were necessary to DICOM's creation.
As with the development of any new standard, many people from many different backgrounds were involved to help create PACS and DICOM and secure their interoperability with other systems, which was the key to the success of the standard.

Picture Archival and Communication System (PACS) And Radiology

Almost all modern radiology services now use some kind of PACS system to manage their data and communicate with other services. The four basic components of PACS are:
  • Imaging Modality - CT, MRI, X-ray
  • Secure Network - to transmit data, typically over a VPN or SSL connection
  • Workstations - to view and manipulate images
  • Archives - to store and retrieve images
The most common format used on PACS is DICOM (Digital Imaging and Communication in Medicine). Although the format is widely used, it is not a strictly defined format. Vendors have the ability to define their own metadata tags for new features unique to their own systems. While this gives DICOM flexibility, it limits interoperability, as legacy viewers are unable to interpret novel metadata tags. Another issue for PACS is the integration of full field digital mammography (FFDM) into existing PACS systems versus the non-integrated solution of buying separate mini PACS workstations for digital mammography.

Regardless, PACS is key to the functioning of a modern filmless radiology department. Beyond simply proving image archival and display, a PACS must be able communicate with other hospital information systems, such as the hospital information server (typically where the full patient's EMR and biodata is stored) as well as the radiology information server (RIS).

The future of radiology is dependent on the continual development of PACS as a standard and as a tool that lets radiologists communicate their findings to their own colleagues, to other specialties, and ultimately to patients themselves.

Friday, August 7, 2009

Mammographer Salary For 2009

Many of you have heard about mammography and the various trends in this field over the past 10 or 15 years. After hitting a low point a few years ago, the field seems to be making a comeback, primarily due to tort reform. The field has many opportunities for young practitioners.

What is a mammographer?

Before discussing salary issues, we should first define which field and specialists we are talking about. Mammographers are diagnostic radiologists who are fellowship-trained in imaging of the breast. Some centers are moving away from the name of 'mammography' towards the broader field of women's imaging, which would include imaging of the female genitourinary tract, as well as have a broader role in patient care, specifically women's health issues. Regardless, the main focus would still remain on diagnosing and intervening on disease of the breast using various imaging modalities. The main modality is, of course, a mammogram, which uses intense radiation beams in special machines at various planes to produce 2-D images of the breast. However, new imaging including MRI and musculoskeletal radiology are opening new avenues for imaging of the breast. Some programs now offer a combined mammography/musculoskeletal fellowship for radiology residents interested in pursuing the cutting edge in mammography.

In addition to diagnosing lesions of the breast, mammographers are involved in biopsying such lesions through stereotactic biopsies, in which the biopsy is performed via large bore needles in the radiology suites instead of in an operating room. Furthermore, a mammographer may be heavily involved in patient care, as the mammographer often may be the first physician to inform a patient of a suspicious breast lesion which may turn out to be cancerous. Such a diagnosis can have a huge impact on a patient's life, even if the lesion eventually turns out to be benign. Given the gravity of the situation, it is important for mammographers to be fully trained to deal with all the dimensions of their job.

Why is mammography making a comeback?

A few years ago, litigation posed a serious threat to mammography. A mammogram is a screening tool, but it offers no guarantee of preventing breast cancer. Sometimes, unfortunately, women would receive regular mammograms and still receive a diagnosis of advanced breast cancer. There is no way for the mammographer to prevent this unfortunate combination of circumstance and genetics. However, a subset of these patients would involve a lawyer. Once a lesion has been diagnosed, it is easy for a lawyer to look back at old mammograms and highlight the suspicious area and ask of the mammographer why more was not done at an earlier time. This approach utilizes a logical fallacy which can be easily summarized as "hindsight 20/20." In reality, there are many suspicious lesions on mammograms, but working up every questionable spot on a mammogram would lead to more harm than good, so the mammographer must be judicious in following questionable areas, with the risk that sometimes this conservative approach more produce more harm in a particular individual.

Some states have realized that this puts the mammographer in an untenable positions. By instituting tort reform, they do not free the mammographer of liability but rather acknowledge that such errors are not born out of malice but rather are a function of the system we inhabit. This reform has helped mammographers function more appropriately, thus increasing demand for the field. According to the Centers for Medicare Services, mammographers are one of the highest compensated medical specialities as of 2008:
Diagnostic Radiology - M.D.s Interventional - $463,219
Diagnostic Radiology - M.D.s Neuro-Interventional - $500,000
Diagnostic Radiology - M.D.s Non-Interventional - $420,858
Mammography - $540,028
Nuclear Medicine (M.D.s Only) - $331,866
Radiation Therapy (M.D.s Only) - $395,166

Given this data, if you were considering mammography before but were unsure of the future of the field, give it another look. You might be surprised by what you find.