Molecular imaging and stroke

Hyperpolarized 13C Magnetic Resonance Imaging Can Detect Metabolic Changes Characteristic of Penumbra in Ischemic Stroke

Magnetic resonance imaging (MRI) is increasingly the method of choice for rapid stroke assessment in patients and for guiding patient selection in clinical trials. The underlying metabolic status during stroke and following treatment is recognized as an important prognostic factor; thus, new methods are required to monitor local biochemistry following cerebral infarction, rapidly and in vivo. Hyperpolarized MRI with the tracer [1-¹³C]pyruvate enables rapid detection of localized [1-¹³C]lactate production, which has recently been shown in patients, supporting its translation to assess clinical stroke. Here we show the ability of hyperpolarized ¹³C MRI to detect the metabolic alterations characteristic of endothelin-1-induced ischemic stroke in rodents. In the region of penumbra, determined via T2-weighted ¹H MRI, both [1-¹³C]pyruvate delivery and [1-¹³C]pyruvate cellular uptake independently increased. Furthermore, we observed a 33% increase in absolute [1-¹³C]lactate signal in the penumbra, and we determined that half of this increase was due to increased intracellular [1-¹³C]pyruvate supply and half was mediated by enhanced lactate dehydrogenase-mediated [1-¹³C]lactate production. Future work to characterize the kinetics of delivery, uptake, and enzymatic conversions of hyperpolarized tracers following ischemic stroke could position hyperpolarized ¹³C MRI as an ideal technology for rapid assessment of the penumbra during the critical time window following ischemic stroke in patients.

Commonly asked questions: imaging stroke and other types of neurovascular disorders

The medical management of patients requiring imaging of the head is often complex. This is confounded by growth and development of neuroimaging technology. Summarizing established guidelines and provided answers to commonly asked questions about neurovascular imaging may aid in providing efficient medical care. Noncontrast head computed tomography (CT) is usually the first line in imaging because of its speed and wide-spread availability. More advanced techniques are reserved for more specific questions or when the CT head is non-diagnostic. MRI is the modality of choice for indications that include chronic headache, pulsatile tinnitus, and cerebrovascular diseases including stroke in the subacute or chronic setting. The imaging of stroke is evolving and many advanced techniques including CT and magnetic resonance perfusion are playing an increasing role in diagnosis. Digital subtraction angiography is widely accepted as the gold standard for evaluation of vascular pathology including aneurysm, vascular malformations, Moyamoya syndrome, carotid stenosis and dissection; and offers treatment options. Alternatives such as MR angiography, MR venography, and CT angiography offer similar sensitivity and specificity to conventional digital subtraction angiography. Safety considerations are an important concern. When using iodinated and gadolinium contrast agents, there are potential complications including allergic reactions, lactic acidosis, and nephrogenic systemic fibrosis. Impaired renal function requires modification in the use of contrast during neuroimaging. Neuroimaging during pregnancy is also discussed.