“Multislice computed tomography is the wave of the future. In 5 years it will be the only type of CT scanner being sold.”

That bold prediction is shared by William Carter, MD, chief of radiology, and Michael Calvin, associate administrator imaging services, at the Medical Center Clinic, PA (MCC) in Pensacola, Fla, where one of the first multislice CT scanners in the United States is now installed.

“This new technology is so brutally fast,” Carter notes, “that image generation now has very little to do with how long it takes to do an examination. When you can do eight images a second, you cannot possibly read the studies as fast as they can be done.”

“It does CT fluoroscopy and CT angiography,” Calvin says. “It also allows users to do true isotropic imaging. Images acquired in an axial plane can be reconstructed in a sagittal or coronal plane in the same resolution. About the only thing you can’t do with it is cook breakfast.”

MCC is a 160-physician group practice that embraces every type of medical specialty from podiatry to neurosurgery. Established in 1939, it owns an 11-story office building, a 40,000-sq-ft cancer treatment center, and a 25,000-sq-ft surgical center, all of which are located adjacent to the 450-bed West Florida Regional Medical Center (WFRMC), a primary care facility.

MCC’s latest venture, a 36,000-sq-ft outpatient imaging center, is currently one of only a half-dozen US locations where a multislice helical CT is up and running. The new center was built at a cost of $4 million and incorporates an array of state-of-the-art imaging modalities, all from the same manufacturer. The hardware, which is on lease, has a capitalized value of $10-$11 million. This figure represents a discount from individual unit prices. The new center, which began accepting patients on March 7, 2000, is the largest freestanding, privately owned imaging facility in the United States, according to Calvin. It also is totally filmless except for its four mammography units. A PACS (picture archiving and communications system) makes images available almost instantly to physicians. “With the speed and flexibility of the multislice scanner, you need to manage the logistics of the examination — how you prep the patients and get them on and off the table,” Carter says. “Rather than use the CT room and table time to set up the contrast IV and get the patient’s consent before biopsies, we created areas outside the imaging suites where the nursing staff can do that. Now the only time the patient spends in the room is getting on the table, getting the scan, and getting off the table.” During the first 3 months of operation, the multislice was averaging between 30 and 35 cases in an 8-hour day. “But I think we have only scratched the surface on that number,” Calvin says. “I think we can comfortably get up to 45 to 50 in an 8- or 9-hour day.”

Calvin is projecting an overall volume of 120,000 procedures a year for the center, but that is expected to increase when MCC begins to actively seek referrals from physicians outside the group practice. In addition to this workload, Carter and his 10 staff radiologists also read computed radiography images and films generated at 14 wholly owned MCC satellite clinics in northwestern Florida and south Alabama. The MCC radiologists also are contracted to read the films and images produced by the hospital’s imaging systems, which include two CTs and an MRI. “There is a lot of pathology being imaged, and they have a very busy emergency department,” says Carter, who had been with MCC for 9 years before being named chief of radiology 2 years ago.

MCC decided in 1998 to build the imaging center to complement its other outpatient services. To make that happen, it recruited Calvin from a private radiology group in McAllen, Tex. He was chosen to spearhead the project because of his previous experience setting up imaging centers in California and Texas. Working closely with Carter, Calvin proposed MCC should use a single source to outfit the facility so it could become a national showcase site — but also command optimal lease terms.

In selecting a supplier for the new center, getting a multislice CT — one with cutting edge technology and maximum flexibility — was the most critical factor. “The way I looked at it,” Calvin explains, “a general radiography room is a general radiography room. Same thing with an R&F room. These are pretty straightforward pieces of equipment. There really are not any bells and whistles that make one vendor stand out over another.”

Evaluating multislice CTs proved relatively easy for MCC as there were only two suppliers of such systems at the time it was looking. Even so, peer recommendations were hard to come by as there were — and still are — only a handful of multislice units in operation. Calvin and Carter did visit one site overseas, but by then they were already on the verge of a decision based on specifications and the reputation of the vendor.

Speed Is The Thing

In comparing the new multislice CT to the 5-year-old single-slice helical CT at WFRMC that the MCC radiologists were familiar with, “the most dramatic difference is speed,” Carter says, “which has improved image quality and provides greater flexibility. We went from a 1.2-second single-slice scanner to one capable of four .5-mm-thick slices in .5 seconds. That is probably a factor of 10 times the raw speed from a per slice point of view.”

Next to speed, the ability to do CT fluoroscopy was another key MCC requirement. “Since we do a fair number of outpatient biopsies on CT, we felt CT fluoroscopy would be a big productivity enhancement,” Carter notes.

The other multislice CT that MCC looked at could produce only four 1.3-mm- thick slices in 1.2 seconds. And its inability to do CT fluoroscopy was a major drawback, as it would have required MCC to buy a second CT to get that capability. “We could not justify that expense,” Carter says.

Scan speed was not the only speed consideration. The multislice also has eliminated the delays arising from tube heating, “a big deal on the older system,” Carter says. Doing a chest-abdomen-pelvis study on the single-slice CT required stopping the examination to allow the patient to breathe during the 90-second procedure, and also pausing to allow the tube to cool down. “You can make those pauses correspond to those times when you are letting the patient catch his breath, but the pauses needed for tube cooling were longer than those needed to breathe the patient, which introduced additional delays.”

Dividends In Oncologic Imaging

As oncologic chest-abdomen-pelvis studies are MCC’s most frequently conducted imaging procedures, the speed of the multislice is paying immediate dividends. The study is now being done in about 20 seconds with no need for pauses to accommodate the patient or to allow tube cooling.

While MCC’s new CT is able to do very thin slices, that capability is not needed on every procedure. “Sometimes you don’t need a sledgehammer to drive a nail,” Carter says. MCC now routinely images the chest-abdomen-pelvis at 3 mm. Previously, with the single-slice helical, the same study was done routinely with 7-mm slices.

And with an older nonhelical single-slice CT at WFRMC, slice thickness routinely was 10 mm. “We are getting better, sharper images,” Carter says. “They are sharper because they do not have the fuzz that is introduced with thicker slices. But to make reading easier, we often display the images at a greater thickness than what we acquired them at. Acquiring an image at 1 mm but displaying it at 2 mm yields a significantly sharper image than if we had just acquired a thicker slice. While it makes the images easier to read, this technique is also more challenging, because we now can see certain things that we never saw before.

“For example, we are picking up an enormous number of adrenal nodules. These are usually benign, but everyone struggles with what to do about them. Probably 10% of the population has undiscovered adrenal nodules. We were missing the smaller ones previously, but now we are seeing 5- and 6-mm nodules with increased regularity. You do not want to subject someone to an invasive procedure for something that is almost certainly benign, but then again you are a bit nervous about totally ignoring things like that. So we will probably end up following a number of these nodules for a while, especially the ones that are somewhat larger.”

Screening Applications

The ability to do submillimeter, subsecond scanning also has opened the door to cardiac scoring for screening purposes, Calvin notes. Cardiac scoring is a noninvasive outpatient procedure in which the patient gets a venous injection. The 7-second procedure involves doing thin-slice scans of the coronary arteries looking for calcium formations that could be a forerunner of a stenosis.

“We think multislice scanners have a real future in diagnostic arteriography,” Carter says, “because they can cover larger areas with ever thinner slices in a very short amount of time, thus providing peak enhancement of the arterial vasculature. We have a 3-D software modeling program with which we can reconstruct images that look virtually identical to catheter angiography, and we have done a few very stunning studies. It is simply a case of getting technologists trained to use the unit, and coping with the volume, and working out all the logistics. Eventually we will be doing real arteriograms only when we are pretty certain there is a need to do an intervention.”

Although for most routine examinations radiation doses will be significantly lower for multislice CTs, other procedures need to be carefully monitored, Carter notes. “Because of the ability to do superthin slices, it is possible to generate a 900- to 1,000-image study for an aortogram with a runoff of the legs in just a few minutes. The radiation dosage for such a study is lower than having an arteriogram, but it is still substantial and cannot be ignored.

“Multislice CT users will need to pay attention to the dosimetry of what they are doing. Although dosages will decline on a per scan basis, because of the increased speed you will be doing far more scans. That is a critical factor that cannot be overlooked when you purchase a machine and when you do protocols.”

Richard B. Elsberry is a contributing writer for Decisions in Axis Imaging News.