CT vs. MRI for Acute Strokes: Which to Use?

Should you use computed tomography or magnetic resonance imaging in the acute stroke setting? There are no easy answers to this question, according to Dr. Todd S. Miller.

Although CT has been the mainstay of acute stroke diagnosis for more than 2 decades, new practice guidelines state that diffusion weighted imaging (DWI) "should be considered more useful than noncontrast CT for the diagnosis of acute ischemic stroke within 12 hours of symptom onset" (Neurology 2010;75:177-85).

Historically, cost, time, and availability have favored CT in the acute stroke setting. MRI offers superior infarct visualization, but it is slower. In the emergency setting, there is pressure to quickly treat patients with cerebral ischemia, while triaging those whose symptoms are explained by alternative diagnoses.

The controversy overlies a background in which only a minority of stroke patients receive any intervention, said Dr. Miller, assistant professor of neuroradiology at Albert Einstein College of Medicine and Montefiore Medical Center, Bronx, N.Y.

"In the acute stroke setting, there’s a significant opportunity to improve outcomes. But as reported as recently as 2009, only 1% of patients (Emerg. Med. Clin. North Am. 2009;27:115-9) who are having a stroke receive thrombolytic therapy," he said in an interview.

"In the United States, stroke is still a major cause of long-term disability, with huge economic and social costs. We want to identify individuals who are having an infarct and try to determine who we can help to improve functional outcomes," he added at the Veith symposium on vascular medicine sponsored by the Cleveland Clinic.

For patients who reach the hospital within 3 hours and for whom hemorrhage and stroke mimics are ruled out via noncontrast CT, the choice of imaging to assess the infarct core to guide treatment usually is based on experience and availability. "Although MRI is clearly more sensitive and specific, quite a few studies have suggested that both CT angiography [CTA] and CT perfusion are adequate. Use whatever is available," he said.

In a comparison of CT perfusion imaging (CTP) and MR DWI in 23 consecutive patients presenting within 12 hours of stroke onset, DWI was more sensitive than was CTP for parenchymal stroke detection, but both modalities were highly accurate predictors of final infarct volume. While DWI tended to underestimate final infarct size, CTP more closely approximated final infarct size (Stroke 2001;32:317).

Other data also suggest that the presence of hyperattenuation on CTP may predict hemorrhage (AJNR Am. J. Neuroradiol. 2007;28:1292-8). Identification of those at risk for hemorrhage allows clinicians to avoid doing harm and causing a worsening of symptoms.

Some clinicians are reluctant to use iodinated contrast for CTA/CTP because of concerns about contrast nephropathy. But in a retrospective study of 224 patients who had received CTA of the brain or neck to evaluate acute stroke syndrome, just 7 (3%) met the criteria for radiocontrast nephropathy, including 2 of 93 (2%) who had emergent CTA without knowledge of their creatinine value. None needed dialysis (Stroke 2007;38:2364-6).

Taken together, the data support CT for evaluating the core infarct and penumbra in stroke patients, as well as for predicting outcome from antithrombotic therapy. MRI allows far better visualization, but it’s hard to get patients into the magnet, it can’t be used in certain patients with metal in their bodies, and it isn’t available in many institutions.

Dr. Miller acknowledged his pro-CT bias, but he said a recent article has caused him to think twice. The study, involving 174 patients with presumed stroke, showed that without significantly increasing door-to-needle time, MRI was feasible in 88% of 161 who required acute imaging and that it supported treat/not treat decisions (Acta. Neurol. Scand. 2009;120:143-9).

"It has not been my experience that MRI and CT take an equal amount of time for the evaluation of acute cerebral ischemia, but if that is the case for you in your center, the evidence clearly favors MRI. Otherwise, CT is king," he said.

Should you use computed tomography or magnetic resonance imaging in the acute stroke setting? There are no easy answers to this question, according to Dr. Todd S. Miller.

Although CT has been the mainstay of acute stroke diagnosis for more than 2 decades, new practice guidelines state that diffusion weighted imaging (DWI) "should be considered more useful than noncontrast CT for the diagnosis of acute ischemic stroke within 12 hours of symptom onset" (Neurology 2010;75:177-85).

Historically, cost, time, and availability have favored CT in the acute stroke setting. MRI offers superior infarct visualization, but it is slower. In the emergency setting, there is pressure to quickly treat patients with cerebral ischemia, while triaging those whose symptoms are explained by alternative diagnoses.

The controversy overlies a background in which only a minority of stroke patients receive any intervention, said Dr. Miller, assistant professor of neuroradiology at Albert Einstein College of Medicine and Montefiore Medical Center, Bronx, N.Y.

"In the acute stroke setting, there’s a significant opportunity to improve outcomes. But as reported as recently as 2009, only 1% of patients (Emerg. Med. Clin. North Am. 2009;27:115-9) who are having a stroke receive thrombolytic therapy," he said in an interview.

"In the United States, stroke is still a major cause of long-term disability, with huge economic and social costs. We want to identify individuals who are having an infarct and try to determine who we can help to improve functional outcomes," he added at the Veith symposium on vascular medicine sponsored by the Cleveland Clinic.

For patients who reach the hospital within 3 hours and for whom hemorrhage and stroke mimics are ruled out via noncontrast CT, the choice of imaging to assess the infarct core to guide treatment usually is based on experience and availability. "Although MRI is clearly more sensitive and specific, quite a few studies have suggested that both CT angiography [CTA] and CT perfusion are adequate. Use whatever is available," he said.

In a comparison of CT perfusion imaging (CTP) and MR DWI in 23 consecutive patients presenting within 12 hours of stroke onset, DWI was more sensitive than was CTP for parenchymal stroke detection, but both modalities were highly accurate predictors of final infarct volume. While DWI tended to underestimate final infarct size, CTP more closely approximated final infarct size (Stroke 2001;32:317).

Other data also suggest that the presence of hyperattenuation on CTP may predict hemorrhage (AJNR Am. J. Neuroradiol. 2007;28:1292-8). Identification of those at risk for hemorrhage allows clinicians to avoid doing harm and causing a worsening of symptoms.

Some clinicians are reluctant to use iodinated contrast for CTA/CTP because of concerns about contrast nephropathy. But in a retrospective study of 224 patients who had received CTA of the brain or neck to evaluate acute stroke syndrome, just 7 (3%) met the criteria for radiocontrast nephropathy, including 2 of 93 (2%) who had emergent CTA without knowledge of their creatinine value. None needed dialysis (Stroke 2007;38:2364-6).

Taken together, the data support CT for evaluating the core infarct and penumbra in stroke patients, as well as for predicting outcome from antithrombotic therapy. MRI allows far better visualization, but it’s hard to get patients into the magnet, it can’t be used in certain patients with metal in their bodies, and it isn’t available in many institutions.

Dr. Miller acknowledged his pro-CT bias, but he said a recent article has caused him to think twice. The study, involving 174 patients with presumed stroke, showed that without significantly increasing door-to-needle time, MRI was feasible in 88% of 161 who required acute imaging and that it supported treat/not treat decisions (Acta. Neurol. Scand. 2009;120:143-9).

"It has not been my experience that MRI and CT take an equal amount of time for the evaluation of acute cerebral ischemia, but if that is the case for you in your center, the evidence clearly favors MRI. Otherwise, CT is king," he said.

Should you use computed tomography or magnetic resonance imaging in the acute stroke setting? There are no easy answers to this question, according to Dr. Todd S. Miller.

Although CT has been the mainstay of acute stroke diagnosis for more than 2 decades, new practice guidelines state that diffusion weighted imaging (DWI) "should be considered more useful than noncontrast CT for the diagnosis of acute ischemic stroke within 12 hours of symptom onset" (Neurology 2010;75:177-85).

Historically, cost, time, and availability have favored CT in the acute stroke setting. MRI offers superior infarct visualization, but it is slower. In the emergency setting, there is pressure to quickly treat patients with cerebral ischemia, while triaging those whose symptoms are explained by alternative diagnoses.

The controversy overlies a background in which only a minority of stroke patients receive any intervention, said Dr. Miller, assistant professor of neuroradiology at Albert Einstein College of Medicine and Montefiore Medical Center, Bronx, N.Y.

"In the acute stroke setting, there’s a significant opportunity to improve outcomes. But as reported as recently as 2009, only 1% of patients (Emerg. Med. Clin. North Am. 2009;27:115-9) who are having a stroke receive thrombolytic therapy," he said in an interview.

"In the United States, stroke is still a major cause of long-term disability, with huge economic and social costs. We want to identify individuals who are having an infarct and try to determine who we can help to improve functional outcomes," he added at the Veith symposium on vascular medicine sponsored by the Cleveland Clinic.

For patients who reach the hospital within 3 hours and for whom hemorrhage and stroke mimics are ruled out via noncontrast CT, the choice of imaging to assess the infarct core to guide treatment usually is based on experience and availability. "Although MRI is clearly more sensitive and specific, quite a few studies have suggested that both CT angiography [CTA] and CT perfusion are adequate. Use whatever is available," he said.

In a comparison of CT perfusion imaging (CTP) and MR DWI in 23 consecutive patients presenting within 12 hours of stroke onset, DWI was more sensitive than was CTP for parenchymal stroke detection, but both modalities were highly accurate predictors of final infarct volume. While DWI tended to underestimate final infarct size, CTP more closely approximated final infarct size (Stroke 2001;32:317).

Other data also suggest that the presence of hyperattenuation on CTP may predict hemorrhage (AJNR Am. J. Neuroradiol. 2007;28:1292-8). Identification of those at risk for hemorrhage allows clinicians to avoid doing harm and causing a worsening of symptoms.

Some clinicians are reluctant to use iodinated contrast for CTA/CTP because of concerns about contrast nephropathy. But in a retrospective study of 224 patients who had received CTA of the brain or neck to evaluate acute stroke syndrome, just 7 (3%) met the criteria for radiocontrast nephropathy, including 2 of 93 (2%) who had emergent CTA without knowledge of their creatinine value. None needed dialysis (Stroke 2007;38:2364-6).

Taken together, the data support CT for evaluating the core infarct and penumbra in stroke patients, as well as for predicting outcome from antithrombotic therapy. MRI allows far better visualization, but it’s hard to get patients into the magnet, it can’t be used in certain patients with metal in their bodies, and it isn’t available in many institutions.

Dr. Miller acknowledged his pro-CT bias, but he said a recent article has caused him to think twice. The study, involving 174 patients with presumed stroke, showed that without significantly increasing door-to-needle time, MRI was feasible in 88% of 161 who required acute imaging and that it supported treat/not treat decisions (Acta. Neurol. Scand. 2009;120:143-9).

"It has not been my experience that MRI and CT take an equal amount of time for the evaluation of acute cerebral ischemia, but if that is the case for you in your center, the evidence clearly favors MRI. Otherwise, CT is king," he said.