CT: Supermodality

Faster than a breath hold, more effective than a single slice, and able to look inside the human body without invading it—look, everywhere in the hospital, it’s multislice CT! As the primary diagnostic exam for many conditions, CT is expanding into new realms and helping to save more lives than the fictitious Superman. As the technology has advanced—from single-slice to 16-slice to 64-slice to the 256-slice technology expected to debut commercially next year—its applications have expanded, and the modality today is in various states of adoption for a wide spectrum of procedures.

Cardiac imaging is driving overall innovation and enhancements in CT systems.

For instance, spectral CT—the use of different energies in the x-ray beam to better distinguish the different human elements, according to Scott Pohlman, director of CT clinical science for Philips Medical Systems, Cleveland—is in the innovator phase. The new technology is still in development, and its applications are under exploration, but any use of the modality is research and development related rather than clinical. CT colonography, or CTC, falls into the early adopter phase, in which the technique is in clinical use but data is still being collected and analyzed to establish performance and efficacy. Positive results can push an application into consensus adoption and eventually mainstream care. Routine CT includes exams for the diagnosis of trauma patients, for example. “Physicians refer to CT as the primary diagnostic exam for many conditions,” Pohlman said.

Shawn DeWayne Teague, MD, assistant professor of radiology and chief of cardiothoracic imaging at the Indiana University School of Medicine in Indianapolis, concurs. “If you go into any facility, CT really is the first stop in imaging for a lot of patients. It’s very good at providing a global idea of what is going on in that part of the body,” Teague said, noting new data continues to show the modality’s benefits.

CT’s advantages include faster exams times, a noninvasive nature, and clear images that can delineate small objects, such as plaque in coronaries, polyps in the colon, and tumors in the lung. Not surprisingly then, the modality has seen its use expand in the detection of disease. Areas in which much improvement has been made include cardiovascular diagnosis and care, stroke, colon cancer, and lung disease.

Heart

“In general, cardiac imaging is probably the one application driving most of the innovations and technical enhancements in CT systems,” Pohlman said. Many companies have aimed for scan times faster than the beating heart—and they are just about there. Systems with 64-slice technology can often complete a scan within a breath hold with which most patients can comply. “With a half-millimeter slice, we can cover the area in one breath hold,” said Robb Young, senior manager of the CT business unit at Toshiba America Medical Systems, Tustin, Calif.

“The faster temporal resolution of dual-source CT means physicians do not always have to slow down the heart [with medication],” Teague said. This reduces patient risk as well as shortens the exam since the patient does not have to remain on-site while the medication wears off. Faster acquisition also reduces artifact and improves the captured image.

High-resolution, 3D pictures of the heart and large vessels permit physicians to see obstructions, including calcium and fatty deposits. Newer CT angiography technologies (ie, 64-slice) enable physicians to see inside vessels as small as 1.5 mm in diameter, according to researchers at Johns Hopkins University in Baltimore.

A team at Johns Hopkins recently completed the CORE-64 trials [Coronary Artery Evaluation using 64-row Multidetector Computed Tomography], which compared the CT technology with invasive catheterization. According to a release, the study concluded that 64-slice CT is unlikely to replace catheterization in the inspection of arteries but can more quickly rule out those patients who do not need to undergo the invasive procedure.

The researchers found that 64-slice CT detected an average 91% of patients with blockages and was able to diagnose 83% of patients without blockages. Additional analysis of the data indicated that 64-slice CT is more accurate than older CT technologies (such as 16-slice) and matches invasive catheterization results 90% of the time (in 1 year of monitoring). The team concluded that the modality is useful in predicting coronary artery disease and can provide an alternative to cardiac stress testing.

Because of the emerging evidence supporting its use, adoption of CT to diagnose patients presenting to the emergency department with acute chest pain is also increasing. Teague notes that he is seeing this in practice. Further studies will encourage more widespread use.

As use increases, however, so do concerns about radiation. At Cedars-Sinai Medical Center in Los Angeles, researchers have developed two new coronary CTA techniques, “Mini-dose CCTA” and “low-dose CCTA” to improve the technology’s ability to see plaques while reducing radiation dose. Mini-dose CCTA uses x-rays produced during only one tenth of the cardiac cycle and results in one tenth of the radiation of a full coronary CT angiogram. Low-dose CCTA results in a three quarters reduction in radiation rather than nine tenths.

The team has successfully used the tests to diagnose blockages in symptomatic patients with abnormal but inconclusive results, producing better outcomes. The low-dose CCTA for one such patient, who had a normal myocardial perfusion scan, found a 90% blockage in the left main coronary artery. The patient successfully underwent a stent procedure, a more positive outcome than a bypass surgery or a myocardial infarction that may have resulted from a missed diagnosis.

Head

Another area where CT may be able to help avoid devastating outcomes is that of stroke. Its use in evaluating patients presenting to the ER with associated symptoms has increased. “Stroke imaging CT has become the first point of admission in the ER, especially for patients with brain injuries,” Young said.

CT perfusion offers advantages over MRI, primarily in accessibility. A study published in Neurology and led by Max Wintermark, MD, department of radiology, University of California, San Francisco, found little difference between the two modalities diagnostically. The team looked at 42 stroke patients who underwent both perfusion CT/CT angiography and MRI examinations and found the treatment decisions differed between the CT and MRI in only one patient.

In a letter to the editor of European Neurology, which will be published in a future issue of the journal, a group of researchers from the Sahlgrenska University Hospital in Goteburg, Sweden, summarize the role of CT in stroke:

“CTP [CT perfusion] using new generation multi-slice scanners is a relatively recent technique with the potential of becoming a widely used tool of standard stroke assessment ? In patients with suspected acute stroke, the site of vascular occlusion, infarct core, salvageable brain tissue, and collateral circulation is best assessed by a combination of CTP and CT angiography. CTP may help decision-making for thrombolysis when there is no clear time of symptom debut ? CTP may assist decision-making for endovascular neuroradiologic treatment in patients with stroke in progression.”

Philips’ Pohlman agrees that CT can potentially improve the diagnosis of stroke patients, as well as include patient populations previously excluded, but suggests these will complement new treatments in development. “For instance, whether it’s a mechanical clot retrieval device or new pharmaceuticals, advanced CT imaging could play an important role,” Pohlman said.

Stomach/Gastrointestinal

Where CT’s role is becoming more certain is the area of colon disease. The modality offers advantages that include minimal invasiveness, visualization of the entire colorectum from an endoluminal perspective, multidimensional inspection of the colon wall and extracolonic tissues without superimposed anatomic structure, and improved patient acceptance, according to the American College of Radiology Imaging Network (ACRIN).

CT colonography offers unique advantages including visualization of the entire colorectum from an endoluminal perspective.

However, data on CT’s use as a colon cancer screening tool has been mixed in the past, particularly those studies using older technologies and/or inexperienced readers. Recent multicenter trials addressed these deficiencies and provided stronger scientific evidence to potentially add the modality as a screening tool. Subsequently, the medical community has been waiting for larger, multicenter trials to address the deficiencies and provide more scientific evidence before recommending the modality as a screening tool. Many in the community have had their eye on the National CT Colonography Trial under way by ACRIN, which released preliminary results on more than 2,500 patients this fall. The data showed a 90% per-patient sensitivity for adenomatous colorectal lesions 1 cm or larger in diameter, on a par with optical colonoscopy.

Another study conducted at the University of Wisconsin Medical School in Madison, also found similar detection rates for CTC and optical colonoscopy for advanced neoplasia. The data included results from more than 3,000 patients.

“Both of these studies have really proven virtual colonoscopy as an accurate technique and go a long way toward eliminating the controversy surrounding its use,” Pohlman said. He expects that organizations that issue guidelines regarding colorectal screening will reconsider their recommendations when they are reviewed next year.

Recent research showed low-dose CT detected earlystage lung cancer in 85% of patients.

Lungs

While CTC moves into a consensus adoption phase, its use in the detection of lung cancer remains controversial. “I think that most in the medical community would accept the idea that CT can detect malignant lung cancers at an earlier stage than conventional methods. The controversy exists in the question of its clinical value. How does detecting the cancer earlier affect the diagnosis, prognosis, and outcome, especially considering cost-effectiveness and overall patient care?” Pohlman asks.

Studies in the past have raised questions about whether a longer survival rate is actually a result of early detection and treatment or a function of a slower-growing cancer. Early studies using radiographs found better survival rates but no concurring change in mortality and factored into the decision to not recommend the modality as a lung cancer screening tool.

Supporters believe, however, that the clinical value of early detection of lung cancer will be proven. The International Early Lung Cancer Action Project is dedicated to studying the benefits associated with early detection of lung cancer. The organization released research late last year that showed low-dose CT detected early-stage lung cancer in 85% of patients. Those who underwent prompt surgical removal showed a 10-year survival rate of 92%; all those who opted to forego treatment died within 5 years. Overall, the 10-year survival rate was 80%.

More studies will be needed to support the modality’s routine use in the early detection of lung cancer. Pohlman suggests it has already become a routine tool for detection of pulmonary embolism. “Evidence has mounted to where CT is a routine clinical procedure for every hospital that sees these types of patients,” Pohlman said.

Pohlman notes that the emerging applications, particularly those in cardiac, stroke, colon, and lung care, can each benefit millions of patients per year. As these technologies improve, so will those for routine exams, producing opportunities to continue to improve dose, workflow, and image quality.

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Renee Diiulio is a contributing writer for Medical Imaging. For more information, contact .