K. Sartor

CT and diffusion-weighted MR imaging in randomized order: diffusion-weighted imaging results in higher accuracy and lower interrater variability in the diagnosis of hyperacute ischemic stroke.

Background and Purpose— Diffusion-weighted MRI (DWI) has become a commonly used imaging modality in stroke centers. The value of this method as a routine procedure is still being discussed. In previous studies, CT was always performed before DWI. Therefore, infarct progression could be a reason for the better result in DWI. Methods— All hyperacute (<6 hours) stroke patients admitted to our emergency department with a National Institutes of Health Stroke Scale (NIHSS) score >3 were prospectively randomized for the order in which CT and MRI were performed. Five stroke experts and 4 residents blinded to clinical data judged stroke signs and lesion size on the images. To determine the interrater variability, we calculated &kgr; values for both rating groups. Results— A total of 50 patients with ischemic stroke and 4 patients with transient symptoms of acute stroke (median NIHSS score, 11; range, 3 to 27) were analyzed. Of the 50 patients, 55% were examined with DWI first. The mean delay from symptom onset until CT was 180 minutes; that from symptom onset until DWI was 189 minutes. The mean delay between DWI and CT was 30 minutes. The sensitivity of infarct detection by the experts was significantly better when based on DWI (CT/DWI, 61/91%). Accuracy was 91% when based on DWI (CT, 61%). Interrater variability of lesion detection was also significantly better for DWI (CT/DWI, &kgr;=0.51/0.84). The assessment of lesion extent was less homogeneous on CT (CT/DWI, &kgr;=0.38/0.62). The differences between the 2 modalities were stronger in the residents’ ratings (CT/DWI: sensitivity, 46/81%; &kgr;=0.38/0.76). Conclusions— CT and DWI performed with the same delay after onset of ischemic stroke resulted in significant differences in diagnostic accuracy. DWI gives good interrater homogeneity and has a substantially better sensitivity and accuracy than CT even if the raters have limited experience.

Effect of Intravenous Thrombolysis on MRI Parameters and Functional Outcome in Acute Stroke <6 Hours

Background and Purpose— The goals of this study were to examine MRI baseline characteristics of patients with acute ischemic stroke (AIS) and to study the influence of intravenous tissue plasminogen activator (tPA) on MR parameters and functional outcome using a multicenter approach. Methods— In this open-label, nonrandomized study of AIS patients with suspected anterior circulation stroke, subjects received a multiparametric stroke MRI protocol (diffusion- and perfusion-weighted imaging and MR angiography) within 6 hours after symptom onset and on follow-up. Patients were treated either with tPA (thrombolysis group) or conservatively (no thrombolysis group). Functional outcome was assessed on day 90 (modified Rankin Score; mRS). Results— We enrolled 139 AIS patients (no thrombolysis group, n=63; thrombolysis group, n=76). Patients treated with tPA were more severely affected (National Institutes of Health Stroke Scale score, 10 versus 13;P =0.002). Recanalization rates were higher in the thrombolysis group (Thrombolysis in Myocardial Infarction criteria 1 through 3 on day 1; 66.2% versus 32.7%;P <0.001). Proximal vessel occlusions resulted in larger infarct volumes and worse outcome (P =0.02). Thrombolysis was associated with a better outcome regardless of the time point of tPA treatment (≤3 hours or 3 to 6 hours) (univariate analysis: mRS ≤2, P =0.017; mRS ≤1, P =0.023). Age (P =0.003), thrombolytic therapy at 0 to 6 hours (P =0.01), recanalization (P =0.016), lesion volume on day 7 (P =0.001), and initial National Institutes of Health Stroke Scale score (P =0.001) affected functional outcome (mRS on day 90) positively (multivariate analysis). The time point of tPA therapy affected the recanalization rate (P =0.024) but not final infarct volume. Conclusions— In this pilot study, tPA therapy had a beneficial effect on vessel recanalization and functional outcome. Multiparametric MRI delineates tissue at risk of infarction in AIS patients, which may be helpful for the selection of patients for tPA therapy. tPA therapy appeared safe and effective beyond a 3-hour time window. This study delivers the rationale for a randomized, MR-based tPA trial.

Stroke Magnetic Resonance Imaging Is Accurate in Hyperacute Intracerebral Hemorrhage: A Multicenter Study on the Validity of Stroke Imaging

Background and Purpose— Although modern multisequence stroke MRI protocols are an emerging imaging routine for the diagnostic assessment of acute ischemic stroke, their sensitivity for intracerebral hemorrhage (ICH), the most important differential diagnosis, is still a matter of debate. We hypothesized that stroke MRI is accurate in the detection of ICH. To evaluate our hypotheses, we conducted a prospective multicenter trial. Methods— Stroke MRI protocols of 6 university hospitals were standardized. Images from 62 ICH patients and 62 nonhemorrhagic stroke patients, all imaged within the first 6 hours after symptom onset (mean, 3 hours 18 minutes), were analyzed. For diagnosis of hemorrhage, CT served as the “gold standard.” Three readers experienced in stroke imaging and 3 final-year medical students, unaware of clinical details, separately evaluated sets of diffusion-, T2-, and T2*-weighted images. The extent and phenomenology of the hemorrhage on MRI were assessed separately. Results— Mean patient age was 65.5 years; median National Institutes of Health Stroke Scale score was 10. The experienced readers identified ICH with 100% sensitivity (confidence interval, 97.1 to 100) and 100% overall accuracy. Mean ICH size was 17.3 mL (range, 1 to 101.5 mL). The students reached a mean sensitivity of 95.16% (confidence interval, 90.32 to 98.39). Conclusions— Hyperacute ICH causes a characteristic imaging pattern on stroke MRI and is detectable with excellent accuracy. Even raters with limited film-reading experience reached good accuracy. Stroke MRI alone can rule out ICH and demonstrate the underlying pathology in hyperacute stroke.

Comparison of CT and CT Angiography Source Images With Diffusion-Weighted Imaging in Patients With Acute Stroke Within 6 Hours After Onset

Background and Purpose— Although stroke MRI has advantages over other diagnostic imaging modalities in acute stroke patients, most of these individuals are admitted to emergency units without MRI facilities. There is a need for an accurate diagnostic tool that rapidly and reliably detects hemorrhage, extent of ischemia, and vessel status and potentially estimates tissue at risk. We sought to determine the diagnostic accuracy of the combination of non–contrast-enhanced CT, CT angiography (CTA), and CTA source images (CTA-SI, showing early parenchymal contrast enhancement) in comparison with a multiparametric stroke MRI protocol in patients with acute stroke within 6 hours after onset. Methods— Non–contrast-enhanced CT, CTA, stroke MRI including diffusion-weighted imaging (DWI), and MR angiography (MRA) were performed in patients with symptoms of acute stroke within 6 hours after onset. We analyzed infarct volumes on days 1 and 5 as shown on CTA-SI, DWI, and T2-weighted images (Wilcoxon, Mann-Whitney, Spearman tests), estimated the collateral status, and assessed clinical outcome (modified Rankin Scale, Barthel Index, National Institutes of Health Stroke Scale, Scandinavian Stroke Scale). Results— We analyzed the data of 20 stroke patients who underwent CT and MRI scanning within 6 hours (mean, 2.83 and 3.38 hours, respectively). Vessel occlusion was present in 16 of 20 patients. CTA-SI volumes did not differ from DWI volumes (P =0.601). Furthermore, the CTA-SI lesion volumes significantly correlated with the initial DWI lesion volumes (P <0.0001, r =0.922) and with outcome lesion volumes (P =0.013 r =0.736). Patients with poor collaterals experienced infarct growth (P =0.0058) and had a significantly worse clinical outcome (all P <0.012); patients with good collaterals did not (P =0.176). Conclusions— The combination of non–contrast-enhanced CT (exclusion of intracranial hemorrhage), CTA (vessel status), and early contrast-enhanced CTA-SI (demarcation of irreversible infarct) allows diagnostic assessment of acute stroke with a quality comparable to that of stroke MRI. Furthermore, it is possible to distinguish patients at risk of infarct growth from those who are not according to the collateral status, in analogy with the stroke MRI mismatch concept.

Somatotopic mapping of the human primary sensorimotor cortex during motor imagery and motor execution by functional magnetic resonance imaging.

The human primary sensorimotor cortex was investigated for somatotopic organization during motor imagery (IM) which was compared to motor execution (EM). Block designed BOLD (blood oxygen level dependent)-functional magnetic resonance imaging at 1.5 Tesla was applied in 14 right handed volunteers during imagined and executed tongue, finger and toe movements. BOLD-clusters were assessed for anatomically correct sensorimotor localization. Euklidian coordinates, relative signal change and correlation to the applied reference function were determined. Statistical means were calculated. IM recruited somatotopically organized primary sensorimotor representations of the precentral gyrus that reflected the homunculus and overlapped in part with EM representations. Mean BOLD-signals ranged from 1.93 to 3.18% for EM, and from 0.73 to 1.47% for IM. The results support the hypothesis that the primary sensorimotor cortex is active during IM and that IM and EM share common functional circuits.

Magnetic resonance imaging after transsphenoidal surgery of clinically non-functional pituitary macroadenomas and its impact on detecting residual adenoma.

Summary.Summary.u2003Background and Purpose: In clinically non-functional pituitary macroadenomas, prospective follow-up magnetic resonance imaging (MRI) was conducted after transsphenoidal surgery both to study the changes of the sellar contents at the post-operative site over time and to assess the amount of residual adenoma tissue.u2003Methods: A total of 50 patients with clinically non-functional pituitary macroadenomas were treated by transsphenoidal tumour resection and were examined by MRI before and directly after surgery (early MR) and 3 months (intermediate MR) and 1 year after surgery (late MR). Changes in the sellar contents over time and the degree of tumour excision were studied on T1-weighted enhanced and unenhanced scans. All patients underwent complete neuro-ophthalmological and endocrinological assessments before and 3 months after surgery. For the interpretation of the post-operative images the results of the endocrinological examinations after surgery were also taken into account.u2003Results: The maximum size of tumour extension on coronal T1-weighted images ranged from 1.2 cm to 5.0 cm (mean 2.3 cm). Despite tumour resection, early post-operative images still showed a persistent mass in the sella in 83% that was usually caused by post-operative haemorrhage, fluid collection and implanted fat material. However, rapid improvement in visual symptoms was noted in 89%. Changes in the sellar region at the early post-operative site markedly hindered the interpretation of MR images for detecting residual tumour tissue, which was suspected in half of the patients (1 intrasellar, 13 suprasellar, and 11 parasellar). Regression of the post-operative mass in the sella was present 3 months after surgery, resulting in a 50% change in the volume of the coronal sellar extension, which also improved the reliability in interpreting the post-operative MR images. On the intermediate MR images residual tumour tissue was detected in 30% of the patients (4 intrasellar, 2 suprasellar and 9 parasellar). Because the suprasellar mass descended over time, an increasing rate of tumour remnant within the sella was seen 3 months following surgery. Before surgery the pituitary gland was visible superiorly or posterosuperiorly to the macroadenomas in 35 patients. However, at the early post-operative site the remaining gland was only visible in 12 patients. Under the condition that endocrinological function tests confirmed adequate hormonal function, the remaining gland was detectable by MRI in 36 patients 3 months after surgery.u2003Conclusion: Delayed regression of the sellar contents after transsphenoidal surgery of pituitary macroadenomas was demonstrated by this prospective MR study. Owing to the changes at the post-operative site, it was difficult to interpret early post-operative images and detect residual adenoma tissue. With respect to the delayed regression of the sellar contents, the interpretation of post-operative images for detection of residual adenoma was improved 3 months after surgery. At this time, residual adenoma tissue was found in 30% of clinically non-functional macroadenomas, mostly at the parasellar and, after descent from the suprasellar space, at the intrasellar site.

The value of magnetic resonance imaging in the diagnosis of orbital floor fractures

Abstract. The value of MRI in the diagnosis of acute orbital floor fractures has not been clearly defined. We therefore compared MR findings with CT findings in patients with orbital trauma. In 30 patients with isolated orbital trauma both coronal CT and coronal MRI were used to examine the orbits and the adjacent paranasal sinuses. Visualization of anatomical landmarks, the kind and extent of traumatic lesions, as well as artifacts were scored. The scores were compared using the Wilcoxon matched-pairs signed-rank test. Interexamination agreement between the two methods was calculated using a kappa analysis. All examinations had diagnostic quality: 30 fractures of the orbital floor (9 right and 21 left orbital floor fractures) were identified. In addition, CT showed fractures of the medial orbital wall in 19 patients (63.3%), of the lateral wall in 10 patients (33.3%), of the zygomatic arch in 2 patients (6.7%), and of the maxillary sinus in 4 patients (13.3%). Soft tissue herniation was shown in 13 patients (inferior rectus muscle twice, orbital fat in 11 cases). Magnetic resonance imaging demonstrated soft tissue herniation in 21 patients: muscle in 4, orbital fat in 17 cases. Magnetic resonance imaging is able to demonstrate orbital floor fractures as sensitively as CT, but CT is superior to MRI in showing small and associated fractures; therefore, CT remains in orbital fractures the imaging modality of choice. Magnetic resonance imaging is superior to CT in showing soft tissue herniations; therefore, MRI may have a role as an adjunct to CT if soft tissue entrapment remains unclear.

In vivo monitoring of age-related changes in rat brain using quantitative diffusion magnetic resonance imaging and magnetic resonance relaxometry

Diffusion-weighted magnetic resonance imaging (MRI) has been proven to be a sensitive diagnostic tool to examine age associated acute and chronic changes in brain tissue. The aim of our study was to examine whether there are differences in brain diffusion and transverse relaxation time between young and adult rats. In an experimental MR scanner, 24 young (age: 3 months) and 26 adult rats (age: 12 months) were examined using diffusion-weighted and transverse relaxation time (T2)-weighted MRI sequences. There were no differences in the T2 relaxation time between the two animal groups, either local or global. However, the mean apparent diffusion coefficient (ADC) within the whole brain was significantly lower (P<0.0005) in the adult animals (765+/-35 x 10(-6) mm(2)/s) than in the young animals (829+/-45 x 10(-6) mm(2)/s). ADC decrease was mainly found in the cerebral cortex. These results can be attributed to an activity-related or central nervous system damage-related internal water shift from the extracellular to the intracellular space without a net increase in water content in brain tissue. Our study also shows that age-related changes in diffusion should be considered when performing longitudinal studies in rats.

Magnetic resonance imaging of metastatic disease to the brain with gadobenate dimeglumine.

Abstract. Seventy-four patients with one to eight proven intraaxial brain metastases received a total cumulative dose of 0.2xa0mmol/kg bodyweight gadobenate dimeglumine, administered as sequential injections of 0.05, 0.05 and 0.1xa0mmol/kg over a 20-min period. MR imaging was performed before the first administration (T2- and T1-weighted sequences) and after each injection of contrast agent (T1-weighted sequences only). Quantitative assessment of images revealed significant (P<0.01) dose-related increases in lesion-to-brain (L/B) ratio and percent enhancement of lesion signal intensity. Qualitative assessment by two independent, blinded assessors revealed additional lesions in 22%, 25% and 38% (assessor 1) and 29%, 32% and 34% (assessor 2) of patients after each cumulative dose when compared with combined T1- and T2-weighted pre-contrast images. Significantly more lesions (P≤0.01) were noted by both assessors after the first injection and by one assessor after each subsequent injection. For patients with just one lesion observed on unenhanced T1- and T2-weighted images, additional lesions were noted in 12%, 16% and 28% of patients by assessor 1 following each dose and in 24%, 27% and 30% of patients by assessor 2. Contemporaneously, diagnostic confidence was increased and lesion conspicuity improved over unenhanced MRI. For patients with one lesion observed after an initial dose of 0.05xa0mmol/kg, additional lesions were noted by assessors 1 and 2 in 9.1% and 11.8% of patients, respectively, after a cumulative dose of 0.1xa0mmol/kg and in a further 9.1% and 5.9% of patients, respectively, after a cumulative dose of 0.2xa0mmol/kg. No safety concerns were apparent.

New Method of Embolus Preparation for Standardized Embolic Stroke in Rabbits

Background and Purpose— Although thromboembolic stroke is caused by red, white, or mixed clots, the emboli previously used in animal studies on thrombolysis were more often red than white. Because this might be one of the reasons why thrombolysis is less effective in patients than in experimental stroke, we developed a new method of preparing highly standardized red and fibrin-rich white emboli. Methods— The middle cerebral artery of 20 rabbits was embolized with either red or fibrin-rich white autologous emboli. Cerebral perfusion was monitored by MRI. Results— Red emboli consisted of closely packed erythrocytes within a sparse fibrin net and white emboli of a dense mass of fibrin with only few other blood cells. Infarct volumes were 26±4% (mean±SD) of the ischemic hemisphere with red and 27±6% with white emboli. The relative regional cerebral blood volume dropped below 50% 90 minutes after vascular occlusion with either type of embolus. Late spontaneous lysis and hemorrhagic complications occurred in 37.5% of red but not in white embolus cases. Conclusions— Emboli prepared by our technique result in standardized cerebral infarctions. Size and composition of the emboli continuously can be adjusted according to the experimental requirements.