Stroke imaging. Why image stroke patients? Stroke. Treatment of infarct. Methods for infarct diagnosis. Treatment of infarct.

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1 Stroke imaging Stroke Infarct: -Arterial thrombosis/embolus -Hypoxic/ischemic -Venous thrombosis Non-traumatic hemorrhage: -Intracerebral -Subarachnoid Johan Wikström MD PhD Associate Professor of Radiology Uppsala University 2 Why image stroke patients? Identification of patients w infarct who may benefit from therapy (i.v. thrombolysis or endovascular) Identification of patients with bleeding or other diagnoses yes Salvageable tissue? yes no Ischemic lesion? yes no ICH/SAH? no Other diagnosis? Treatment of infarct Higher likelihood of good outcome after i v thrombolysis (tpa) if: -Symptom duration 4.5 h -No hemorrhage -Infarct 33% of media territory -No occlusion of carotid siphon branching -Tissue at risc of infarction (penumbra) 20% av perfusion deficit 4 yes no Treatment of infarct I a thrombolysis or thrombectomy can be considered if: -Proximal occlusion (and available interventionist) CT CTA CTP MR MRA MRP Methods for infarct diagnosis 5 6

2 Diagnosis of acute infarct with CT Diagnosis of acute infarct with CT Gray-white matter differentiation (e.g. insular ribbon) Gray-white matter differentiation (e.g. insular ribbon) 7 8 Diagnosis of acute infarct with CT Diagnosis of acute infarct with CT Gray-white matter differentiation (e.g. insular ribbon) Swelling Chronic Acute Gray-white matter differentiation (e.g. insular ribbon) Swelling Dense vessel 9 10 Diagnosis of acute infarct with CT Diagnosis of acute infarct with CT Gray-white matter differentiation (e.g. insular ribbon) 1h 1h 24h Swelling Dense vessel 11 Sensitivity 1:st 24h: 58%* (*Yousem, Grossman: Neuroradiology. The requisites) 12

3 Diagnosis of acute infarct with CT Gray-white matter differentiation (e.g. insular ribbon) Swelling Dense vessel CTA: arterial occlusion CTA MIP Why CTA? Find arterial occlusion: confirms diagnosis, identify lesions that can be endovascularly treated Dissection Carotid stenosis Sinus thrombosis Aneurysm/AVM CTA technique in suspected stroke I v injection rate 5-6 ml/s Synchronization of injection and scanning w test bolus or triggering techniques Volume and scan time dependent on scanner Thin collimation Low pitch Evaluation: source images and MIP (4/2mm) 3 planes MIP 1 mm MPR 1 mm MIP 5 mm MPR 5mm 17 18

4 Diagnosis of acute infarct with CT MIP 50 mm MPR 50 mm Gray-white matter differentiation (e.g. insular ribbon) Swelling Dense vessel CTA: arterial occlusion CTP: penumbra CTP Hemodynamic changes in ischemia Mean transit time (MTT) (s) Cerebral blood flow (CBF) (ml/s x 100g) Cerebral blood volume (CBV) (ml/100g) MTT CBV CBF Penumbra I n f a r c t Autoregulation range 21 Decreasing perfusion pressure CTP in acute ischemia Penumbra ( ): mismatch mellan MTT och CBV CTP in acute ischemia CBV< 2 ml/100g : infarct rmtt> 145% : threatening infarct AJR 2011;196:

5 1h CBF CBV Right-sided symptoms, 2 h MTT CBV CBF 24h Problems with CTP No standardised computation algorithms No standardiserad limits Complicated relation between perfusion deficit, time and evolution of infarct Value of penumbra identification for selection of thrombolysis candidates not shown in randomised studies CBV At admission 24 h post i.v. thrombolysis 29 30

6 Diagnosis of acute infarct with MRI 2/3 with FLAIR whithin 6h DWI in minutes DWI: 90-95% sensitivity DWI: <5% reversible restriction Penumbra: mismatch DWI/MTT Glucose and oxygen depletion causes dysfunction of ATP-dependent cell membrane Na-K-pump Cell swelling Changes in intra- and extracellular space in acute infarct causes diffusion restriction Increase in ICF, decrease in ECF Intracellular changes? 31 Appearance of DWI changes Within minutes in animal models Reported after 11 minutes in humans DWI signal evolution DWI Early Late DWI signal affected by not only diffusion, but also T2 t Speed of diffusion abnormality evolution? Day after % positive ictus DWI lesions <1 (n=93) >20 0 Accuracy of DW-MRI for acute infarct? n Sens. (%) Spec. (%) Study (133/151) 95 (41/43) Lövblad, AJNR (157/190) 96 (246/255) Chalela, Lancet 2007 Burdette, AJR:171, September1998

7 Predictors of false negative DWI exam Brainstem Time from ictus<3h NIHSS score<4 Chalela, Lancet 2007;369: Reversibility of DWI changes In animal models Anecdotal reports of spontaneous reversible DWI lesions Reversibility of DWI changes after iv thrombolysis ADC cut-off for reversibility? Mintorovitch Magn Reson Med 1991 Kidwell Stroke 1999, Marks Radiology 1996 Kidwell Ann Neurol No, large heterogenity in cellular metabolic injury in regions w ADC decrease Nicoli Stroke 2003, Guadagno Neurology 2006 Differential diagnoses (intraaxial) with diffusion restriction Images from scanner: Other causes of cytotoxic edema (seizures, migraine, tumor, trauma, toxic) Some blood products Abscess B 0 B 1000 ADC Evaluation of DWI T2 shine through 1. Look at mean DWI 2. Confirm finding at ADC B 0 B 1000 ADC DWI ADC

8 T2 shine through Log SI T2-shine through High diffusion Equal DWI signal Low diffusion DWI ADC Signal intensity in DWI depends on initial (at b=0) SI and diffusivity (ADC) High initial SI can give high DWI SI without diffusion restriction! b Brain stem infarct Brain stem infarct CT T2w DWI ADC Multiple lesions; what s new? DWI ADC

9 Non-traumatic hemorrhages Subarachnoid (SAH) Intracerebral (ICH) SAH Aneurysm AVM Dissection Venous (Traumatic) Diagnosis of SAH CT: sensitivity 95% 1st 24h, <50% after 1w MR: FLAIR high sens. but low spec. LP Flow artefacts FLAIR 51 FLAIR 52 SAH 80-90% of non-traumatic caused by ruptured aneurysms Age: peak at y M:F 1:2 risk rebleeding disturbance of CSF flow vasospasm, ischemia Intracranial aneurysms Predilection sites: 90% at circulus Willisi+ a cer mediabifurcation Look at source images+thin MIPs (e.g. 4/2 mm) 53 54

10 ICH due to aneurysm ICH due to aneurysm Most often also SAH ICH close to large arterial branch (fissura Sylvii!) ICH in younger Evaluation of CTA Source images MIP e.g. 4/2 mm, 3 planes VRT for demonstration 20% multiple! Which has bled? Assess blood distribution, irregularity, spasm in vicinity Look in all three planes! Transverse: MCA, AComA Coronal: BA, SCA, PICA Sagittal: A Pericallosa, PComA Diagnosis of ICH CT: high attenuation due to coagulation (60-80HU) Low attenuation and possible levels in acute phase and in coagulation disturbance MIP 4/

11 Spot sign Predicts hematoma expansion Stroke. 2007; 38: Etiology ICH Hypertonia Amyloid angiopathy Anticoagulative treatment Vasculitis AVM Aneurysm Cavernoma Tumour Hemorragic infarct 62 Etiology ICH Older: Hypertonia Arterial hemorrhagic infarct Amyloid angiopathy Tumour Younger: AVM Cavernoma Venous hemorrhagic infarct Vasculopathy Tumour Investigation of ICH? All? Normotensive? Depending on age? CTA? DSA? MR? Diagnosis of ICH: MRT As high sensitivitity as CT Dependent on sequence type Diagnosis of ICH: MRT As high sensitivitet as CT Dependent on sequence type 65 T1 TSE T2 TSE T2 GRE 66

12 ? MRI in ICH T1, T2, diffusion restriction, susceptibility effects Oxy-Hb (hyperacute): Deoxy-Hb (acute): Met-Hbintracellular (early subacute): Met-Hbextracellular (late subacute): Ferritin/Hemosiderin (chronic): NAC: no accurate calculation T1 T2 DWI ADC NAC NAC or NAC Hypertonic hemorrhage Thalamus Basala ganglia Pons Cerebellum...but can have any location!...and vascular anomalies in 25% of patients w HT and ICH Acta Radiol 1997; 38: from Diffusion-weighted MR imaging of the brain, Springer, 2nd ed Amyloid angiopathy Amyloid replaces normal tissue in vessel wall 27-33% of normal elderly Causes 15-20% of sich>60 y Frontal and parietal lobes Bleedings of different ages MRI (GRE T2, SWI): microbleeds Amyloid angiopathy Lobar hemorrhage Remnants of old hemorrhages Amyloid angiopathy AVM MRI with blood sensitive sequence (T2 GRE, SWI) Lobar microbleeds 71 72

13 Radiological findings in AVM Dilated arteries and veins Intervening nidus Shunting Flow related aneurysms (a and v) Steal phenomena MR: flow voids Radiological findings in AVM Dilated arteries and veins Intervening nidus Shunting Flow related aneurysms (a and v) Steal phenomena MR: flow voids CT: often Ca CTA 7 år girl Acute headache DSA Investigation of suspected AVM DSA golden standard MR with dynamic MRA? 77 78

14 MR in AVM Preferrably 3T 3D TOF MRA Dynamic Gd-MRA Investigation of suspected AVM DSA golden standard MR with dynamic MRA? CT with dynamic CTA/CTP? Tumoral hemorrhage Astrocytoma grade III-IV Metastases: lung, breast, melanoma, kidney... Repeated bleedings; gives inhomogeneous appearance More edema, mass effect Dual energy CT Separate enhancement from blood Plain Dual energy CTA Virtual iodine AJNR Am J Neuroradiol : Virtual non-contrast enhanced Fusion Take home points infarct Findings at plain CT: loss of gray-white matter differentiation, dense vessel, swelling CTA can confirm ischemic diagnosis and establish differential diagnoses (dissection, sinus thrombosis, AVM, aneurysm) CTP/MRP can establish diagnosis and possibly identify candidates for i v thrombolysis/i a thrombectomy DWI is highly sensitive for acute ischemia from early timepoint until around two weeks after ictus 83 Take home points non-traumatic hemorrhage SAH: CTA of good quality (>300 HU) MIP e.g. 4/2 MM. structured evaluation of predilection sites for aneurysms ICH: CTA on wide indications, especially younger spot sign bad prognostic sign dual energy technique can separate iodine and hematoma amyloid angiopathy common source in elderly, often characteristic microbleeds at MRT consider sinus thrombosis blood has varying appearance at MRI blood can cause diffusion restriction (diff infarct, abscess!) 84