June 2011
ARRS CT & MR Reporter’s Notebook
Radiology Today
Vol. 12 No. 6 P. 14
Editor’s Note: This article is based on research presented during scientific press conferences at the American Roentgen Ray Society annual scientific meeting in Chicago in May.
Updated Algorithm Reduces Motion Artifacts in Full-Body MRI
New research from Cleveland’s University Hospitals Case Medical Center has revealed an updated algorithm that can dramatically improve how radiologists capture and interpret full-body MRIs, particularly in the abdominal region
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“Almost every acquisition during an MR abdominal exam requires a breath hold to limit motion,” said Candice Bookwalter, MD, presenting author for the study. “For example, a routine liver exam includes at least nine breath holds. Even with fast imaging techniques, these breath holds are often long and difficult for patients, and failed breath holds are almost always identified only after image acquisition. This is particularly problematic in timed postcontrast imaging.”
To address the issue, Bookwalter and colleagues developed the Motion Artifact Removal by Retrospective Resolution Reduction (MARs) algorithm to identify the transition between a breath hold and free breathing to allow for better retrospective reviews of an image and reduce the need for additional imaging. In the study, the researchers showed that the MARs technique allows radiologists and technicians to create clinically useful images even in the presence of motion.
“MARs detected and removed motion-corrupted data automatically in our asymptomatic volunteers and patients, which improved the overall image quality,” Bookwalter said.
She believes the revised algorithm will be a useful tool for image interpretation. “The MARs algorithm requires very little alteration of the clinical MR protocol,” she said. “We envision the final application of this technique to be completely automatic and likely applied by the clinical technologist prior to presentation to the radiologist.”
Susceptibility-Weighted Imaging Aids Stroke Diagnosis
In the United States, stroke is the third leading cause of death and, overall, affects almost 1 million people each year, said Mark D. Mamlouk, MD, lead author of a study from the University of California, Irvine (UC-Irvine). But susceptibility-weighted imaging (SWI) helped physicians characterize stroke and speed treatment in a study at the university.
Traditionally, the SWI sequence has been used as a secondary tool to evaluate intracerebral hemorrhages and detect clots with middle cerebral artery (MCA) infarctions, according to Mamlouk. But the study at UC-Irvine suggested that the SWI sequence has value as part of a primary imaging protocol when stroke is suspected.
“There are different causes of stroke, of which the thromboembolic subtype is one of the most common,” Mamlouk said. “Any patient that has a suspicion of stroke, we can add the SWI sequence as part of their MRI brain protocols to better characterize the [origin of the] stroke.”
To reach that conclusion, the researchers assessed 35 patients with thromboembolic infarctions, and SWI detected thromboemboli in 30 patients. Additionally, 14 of these thromboemboli were located in arteries other than the anterior division of the MCA.
“At our institution, we are amazed at how often SWI detects thromboemboli in all major cerebral arteries, not just the MCA,” Mamlouk said. “Given SWI’s high sensitivity—86%—of thromboemboli detection, we found that there is an adjunctive role of SWI in classifying cerebral infarctions in patients.”
While MRI has been the gold standard for evaluating infarctions, study coauthor Anton Hasso, MD, noted that adding SWI to the routine MRI sequences for evaluating patients with a clinical suspicion of stroke will hasten their time to treatment and improve overall recovery.
“The utility of SWI extends beyond the evaluation of hemorrhage,” Mamlouk said. “Using SWI in patients with cerebral infarctions will decrease further imaging and its associated costs and radiation exposure, but more importantly, this imaging technique will guide direct management in a timelier manner.”
New Contrast Protocols Eliminate New NSF Cases
Implementing strict protocols for administering gadolinium-based contrast agents before imaging eliminated new cases of nephrogenic systemic fibrosis (NSF), according to research from Massachusetts General Hospital.
Implementing this protocol is particularly important for patients with diminished kidney function, said Ozden Narin, MD, who presented data from the study during the annual meeting of the American Roentgen Ray Society. “In the past, we had some patients who developed NSF after they were given a gadolinium-based agent before imaging. We implemented this new policy to see if we could make any change in preventing this condition,” she said.
In a retrospective review of 52,954 contrast-enhanced MRIs at Massachusetts General Hospital during a 2.5-year period after this protocol was enforced, no new cases of NSF were identified.
After analyzing the study results and recognizing that this protocol is indeed effective for preventing NSF, Narin was hopeful the procedure will continue to make a difference at her institution and other medical centers.
“Now, we only use [gadolinium-based contrast agents] in patients with decreased kidney function in emergent cases, and we have procedures in place to pay special attention to those patients and to take all the necessary precautions,” she said.
The Dog-tor Will See You Now — Study Suggests Animal-Assisted Therapy Decreases Patient Anxiety Before MRI
Playing with a dog before undergoing MRI may be an effective substitute for antianxiety medication, according to a preliminary study conducted at Monmouth Medical Center in Long Branch, N.J. A high school student who subsequently became a certified dog therapist conceived the idea and worked with researchers in the study.
Fifteen-year-old Allison Ruchman experienced anxiety and claustrophobia during her own MR exam. She relieved her tension by creating a mental picture of her dog, Wally, and believed that her experience could be applicable to other patients who often need antianxiety drugs in order to complete an MRI examination. She subsequently became a certified dog therapist and conducted the research on this project, assisting physicians who compiled and analyzed data and prepared an abstract of the study.
Twenty-eight patients who were scheduled to undergo outpatient MRI were selected for an intervention with a certified therapy dog. Patients interacted with the dog at various levels of intensity for 15 minutes, approximately 30 minutes prior to their scheduled MRI. Six patients did not spend any time with a therapy dog.
“The most significant aspect of our findings was the fact that time spent with a dog could substitute for pharmacologic anxiolysis [antianxiety medication] often needed to assist patients having an MRI,” said radiologist Richard Ruchman, MD, who is Allison Ruchman’s father and a study author.
“A great deal of research is currently being conducted on animal-assisted therapy in the medical environment. To my knowledge, this is the first study that has particularly addressed animal-assisted therapy in the radiology department, and I believe that many applications could flow from our findings. Current estimates are that 15% or more of patients cannot proceed with an MRI due to anxiety, and a nonpharmacologic solution is noteworthy,” Richard Ruchman said.
MRI Identifies Primary Endometrial and Cervical Cancer
MRI can determine whether a patient has endometrial vs. cervical cancer even when a biopsy can’t make that distinction, helping physicians determine the appropriate treatment, according to a new study from MD Anderson Cancer Center in Houston. Researchers looked at a series of 48 patients who had inconclusive biopsy results and found radiologists using MRI could correctly identify the primary site of cancer in 79% of cases (38 of 48 patients).
The study also examined various MR sequences to determine which was the most useful in making a diagnosis. Heather He, MD, PhD, of MD Anderson Cancer Center, noted that sagittal T2 fast spin echo weighted sequences and 2D and 3D T1-weighted dynamic enhanced sequences are the most helpful in determining the primary cancer site.
Endometrial and cervical cancers are common cancers in women, according to He, who presented the study results at the annual meeting. “In about 3% of the cases, there is difficulty determining the primary cancer site,” He said. “Knowing the primary cancer site means that we can give the patients the most appropriate therapy and save some patients from unnecessary surgery.”
Two radiologists—one with five years of experience and one with 18—read the images in the study. Their diagnoses matched most of the time, which meant the readers’ level of experience didn’t have much impact on the results, according to He. “MRI can be applied on a broader scope; you don’t have to have someone on staff with extensive experience to be able to offer this imaging service,” she said.
Dual-Energy CT May Help Evaluate Gout
The incidence of gout is on the rise, and dual-energy CT has the potential to allow for a noninvasive diagnosis of the disease, according to radiologists at the University of British Columbia in Vancouver.
Gout is caused by deposits of monosodium urate monohydrate crystals that stimulate acute episodes of inflammation. Chronic tophaceous gout often presents as juxtarticular soft-tissue masses, distinct erosions, overhanging bony margins, and thickening of the synovium. It affects more than 6 million people in the United States, and “a noninvasive means of diagnosing gout would be highly desirable,” said Khalid Khashoggi, MD, a study author.
“Dual-energy CT can detect monosodium urate in different tissues in the body, which will have a huge impact on the understanding of gout and will help in detecting subclinical cases and will allow monitoring response to treatment,” Khashoggi said. “The technology will also help in problem solving in atypical cases of gout.”
CT Finds More Shoulder Lesions After Surgery
Multidetector CT arthrography (MDCTA) is better than MR arthrography for diagnosing glenoid rim osseous lesions, which have been identified as potential causes of lesion recurrence after shoulder surgery, according to French researchers.
The study, done at Hôpital Sainte Marguerite in Marseille, France, included 40 patients scheduled for shoulder surgery. The patients underwent both MDCTA and MR arthrography (the current standard exam).
“Our study found that MDCTA was as accurate as MR arthrography for the study of labro-ligamentous injuries, glenoid cartilage lesions, and Hill-Sachs fractures related to anterior shoulder instability,” said Thomas Le Corroller, MD, a study author. Le Corroller added that CT outperformed MR in detecting glenoid rim fractures.
“MDCTA showed a sensitivity of 100% and a specificity of 96%, whereas MR arthrography demonstrated a sensitivity of 67% and a specificity of 100%,” Le Corroller said.
Selecting the proper surgical treatment for glenoid rim fractures is crucial, Le Corroller said. Patients demonstrating a glenoid rim osseous lesion may require more extensive treatment to stabilize the shoulder without long-term arthritic degeneration. He said Hôpital Sainte Marguerite uses CT whenever surgical treatment of anterior shoulder instability is considered.
Because the exam exposes the patient to ionizing radiation, implementing a dose-reduction strategy is important, especially in younger patients who face shoulder surgery.
Low-Dose CT Cuts Radiation for Heart Surgery Pre-Op Evaluation
Recent studies have shown that a 64-detector CT angiography utilizing prospective electrocardiographic gating produces a quality image and considerably reduced patient radiation dose when compared with retrospective electrocardiographic gating, according to research from University Hospitals Case Medical Center in Cleveland.
Researchers evaluated 29 patients who underwent prospectively gated 100-kV whole-chest CT for preoperative cardiothoracic surgery. The mean radiation dose was determined and compared with a group of regular-dose prospectively gated exams.
“The most significant aspect of our study was to demonstrate that preoperative evaluation of cardiothoracic surgery patients can be reliably and accurately performed with low-dose chest CT that results in a radiation dose reduction of 42% when compared with traditional dose chest CT exams,” said Sonali Mehandru, MD, a study author. “In an era of heightened awareness of radiation exposure to patients from medical imaging, this is a significant finding.
“In particular, our study showed that low-dose chest CT can provide accurate assessment of the coronary arteries in a sizable percentage of patients,” Mehandru added. “The coronary arteries are particularly important to evaluate prior to cardiothoracic surgery because the presence of coronary artery disease impacts a patient’s risk for perioperative morbidity and mortality.”
Mehandru noted that the preoperative evaluation was traditionally done using cardiac catheterization, but the study found that 23 of 38 patients had noninvasive assessment of the coronary arteries on low-dose chest CT that was accurate enough and did not require evaluation with cardiac catheterization before surgery.
“This is a preliminary study, and further research with larger cohorts of patients is needed,” Mehandru said. “However, it is a good starting point in demonstrating that radiation dose from chest CTs can be significantly reduced without compromising accuracy or reliability of anatomic evaluation. In preoperative patients who are especially prone to undergoing repeated imaging studies, this radiation dose reduction can be very significant.”
