Atherosclerotic Carotid Plaque Composition: A 3T and 7T MRI-Histology Correlation Study.

BACKGROUND AND PURPOSE: Carotid artery atherosclerotic plaque composition may influence plaque stability and risk of thromboembolic events, and noninvasive plaque imaging may therefore permit risk stratification for clinical management. Plaque composition was compared using noninvasive in vivo (3T) and ex vivo (7T) MRI and histopathological examination. METHODS: Thirty-three endarterectomy cross-sections, from 13 patients, were studied. The data sets consisted of in vivo 3T MRI, ex vivo 7T MRI, and histopathology. Semiautomated segmentation methods were used to measure areas of different plaque components. Bland-Altman plots and mean difference with 95% confidence interval were carried out. RESULTS: There was general quantitative agreement between areas derived from semiautomated segmentation of MRI data and histology measurements. The mean differences and 95% confidence bounds in the relative to total plaque area between 3T versus Histology were: fibrous tissue 4.99%(-4.56 to 14.56), lipid-rich/necrotic core (LR/NC) with hemorrhage -1.81%(-14.11 to 10.48), LR/NC without hemorrhage -2.43%(-13.04 to 8.17), and calcification -3.18%(-11.55 to 5.18). The mean differences and 95% confidence bounds in the relative to total plaque area between 7T and histology were: fibrous tissue 3.17%(-3.17 to 9.52), LR/NC with hemorrhage -0.55%(-9.06 to 7.95), LR/NC without hemorrhage -12.62%(-19.8 to -5.45), and calcification -2.43%(-9.97 to 4.73). CONCLUSIONS: This study provides evidence that semiautomated segmentation of 3T/7T MRI techniques can help to determine atherosclerotic plaque composition. In particular, the high resolution of ex vivo 7T data was able to highlight greater detail in the atherosclerotic plaque composition. High-field MRI may therefore have advantages for in vivo carotid plaque MRI.

Diffusion-weighted imaging in uterine artery embolisation: do findings correlate with contrast enhancement and volume reduction?

OBJECTIVES: The objective of this study was to determine the role of diffusion-weighted imaging (DWI) in uterine artery embolisation (UAE), and to assess the apparent diffusion coefficient (ADC) of the dominant fibroid and its relationship to contrast enhancement and fibroid volume reduction. METHODS: We carried out a retrospective study of 15 patients who underwent UAE. Calculations were performed at baseline and 6 months post-embolisation. Fibroid ADC (expressed in 10(-3) mm(2) s(-1)) was calculated using b=0 and b=1000 DWI values. Fibroid enhancement was compared with background myometrium by measuring signal-difference-to-noise ratio (SDNR). Fibroid volume was calculated using a prolate ellipse formula. RESULTS: There was a significant reduction (p<0.001) in fibroid ADC at 6 months (0.48; standard deviation, SD=0.26) as compared with baseline (1.01; SD=0.39). No significant change (p=0.07) was identified in 6-month myometrial ADC (1.09; SD=0.28) as compared with baseline (1.24; SD=0.20). Moderately strong and significant positive correlation was identified between baseline ADC and 6-month percentage volume reduction of the fibroid (correlation=0.66, p=0.007). No correlation was identified between SDNR and ADC at baseline or 6 months (r=0.01, p=0.97 and r=-0.13, p=0.64, respectively) or SDNR and percentage volume reduction at 6 months (correlation r=0.18, p=0.51). CONCLUSION: Baseline ADC of dominant fibroids shows a moderately strong correlation with subsequent volume reduction at 6 months following UAE. No correlation was identified between ADC values and contrast enhancement on the baseline or 6-month scans. Further prospective evaluation is needed before DWI can be utilised in clinical practice. Advances in knowledge DWI imaging may provide additional information about UAE and possibly help to predict uterine volume reduction.

High-resolution double inversion recovery black-blood imaging of cervical artery dissection using 3T MR imaging.

SUMMARY: We performed high-resolution DIR-BBI of the cervical arteries at 3T in 19 subjects with cervical dissection. It offered excellent visualization of both the lumen and arterial wall, allowing detection of the primary and secondary features of dissection. We suggest that this is a highly useful technique for diagnosis of cervical dissection, either routinely or in equivocal cases of suspected dissection. It also offers further insight into the pathogenesis of this disorder.

Diffusion-weighted imaging provides support for secondary neuronal damage from intraparenchymal hematoma.

It is controversial whether an intracerebral hematoma (ICH) causes ischemia of surrounding brain. By virtue of its high sensitivity to acute cerebral infarction, diffusion-weighted imaging (DWI) helps answer this question. We used this technique to assess the parenchyma surrounding ICH for restricted diffusion. Echoplanar DWI (b 1000 s/mm(2)) and conventional MRI sequences were performed in 30 subjects (symptom duration 7-75 h) with primary ICH, mean volume: 13+/-15 cm(3). We calculated mean apparent diffusion coefficients (ADC) within high signal regions around the hematoma on DWI or T2-weighted images and within the ICH itself, comparing them to the contralateral brain. We used the Student's t -test to examine for differences between these regions and linear regression to relate changes to the age of the ICH. A thin rim of high signal on DWI and a wider rim on T2-weighted images surrounded all hematomas. The ADC within the rim on DWI showed a maximum reduction of 40%, in two patients imaged within 10 h of symptom onset. They rose during the first day (r(2)=0.84; P <0.03) and then showed a mild decrease, becoming the same as ADC in other areas of the brain (r(2)=0.5; P <0.03). The rim on T2-weighting showed a mean increase of 50% and ADC within the ICH were reduced by a mean of 38%; these variations showed no relationship with ICH age and no group showed any relationship with ICH size. The ADC within the three regions was significantly different from each other. The presence of restricted diffusion in the parenchyma surrounding ICH provides support for secondary neuronal damage.

PROPELLER MRI: clinical testing of a novel technique for quantification and compensation of head motion.

While head motion is considered a significant problem in magnetic resonance imaging (MRI), there is no data to quantify its extent, severity, or effect on image quality. PROPELLER (Periodically Rotated Overlapping ParallEL Lines with Enhanced Reconstruction) MRI offers a novel means of quantifying and compensating for head motion. We performed axial T2-weighted PROPELLER (motion corrected: P-CR; uncorrected: P-UNCR) and conventional MRI (CONV), with equal scan times, in five normal volunteers and 35 clinical subjects. Volunteers were examined lying still and performing two separate head movements (shake "no" and nod "yes") to assess detection and compensation of in-plane motion by PROPELLER MRI. Images were examined by three radiologists for motion artifact and for overall image quality. Head rotation and translation was detected in all subjects during each slice acquisition, with expected changes occurring with volunteer head motion. Motion artifact was less commonly seen on PROPELLER than CONV MR (chi(2) test P < 0.001). PROPELLER was preferred over CONV in all subjects (P < 0.05) and P-CR was judged superior to P-UNCR (P = 0.02). Intracranial pathology was equally or better demonstrated with PROPELLER. PROPELLER MRI offers a means of quantifying head motion, reducing motion artifact, and improving image quality.

Do preliminary chest X-ray findings define the optimum role of pulmonary scintigraphy in suspected pulmonary embolism?

AIM: To investigate if preliminary chest radiograph (CXR) findings can define the optimum role of lung scintigraphy in subjects investigated for pulmonary embolism (PE). MATERIALS AND METHODS: The CXR and scintigraphy findings from 613 consecutive subjects investigated for suspected PE were retrieved from a radiological database. Of 393 patients with abnormal CXRs, a subgroup of 238 was examined and individual radiographic abnormalities were characterized. CXR findings were related to the scintigraphy result. RESULTS: Scintigraphy was normal in 286 subjects (47%), non-diagnostic in 207 (34%) and high probability for PE in 120 (20%). In 393 subjects (64%) the preliminary CXR was abnormal and 188 (48%) of scintigrams in this group were non-diagnostic. Individual radiographic abnormalities were not associated with significantly different scintigraphic outcomes. If the preliminary CXR was normal (36%), the proportion of non-diagnostic scintigrams decreased to 9% (19 of 220 subjects) (P < 0.05). CONCLUSION: In subjects investigated for PE, an abnormal CXR increases the prevalence of non-diagnostic scintigrams. A normal pre-test CXR is more often associated with a definitive (normal or high probability) scintigram result. The chest radiograph may be useful in deciding the optimum sequence of investigations.Forbes, K. P. N., Reid, J. H., Murchison, J. T.(2001). Clinical Radiology56, 397-400.

Assessment of silent embolism from carotid endarterectomy by use of diffusion-weighted imaging: work in progress.

BACKGROUND AND PURPOSE: Transcranial Doppler studies have suggested that microemboli are released into the arterial circulation during the majority of carotid endarterectomy (CEA) procedures. This, together with the observation that neuropsychological performance may decline postoperatively, has led to concern that cerebral infarction may occur unrecognized during CEA. Our objective was to examine this risk with diffusion-weighted imaging, a technique that is highly sensitive to acute cerebral infarction. METHODS: Eighteen participants (median age, 68 years; age range, 56-87 years) were assessed with diffusion-weighted imaging and the National Institutes of Health Stroke Scale before and after CEA. Imaging was performed using single-shot echo-planar imaging with a maximum diffusion sensitivity of b = 1000 s/mm(2) applied to three orthogonal planes. Preoperative imaging was performed a median of 2.5 hours before surgery (range, 0.5-12.5 hours) and 15 hours after surgery (range, 1.5-58.5 hours). Two neuroradiologists independently interpreted the diffusion-weighted images, blinded to operative status and clinical findings. RESULTS: There was no diffusion-weighted imaging evidence of silent embolism in this series of 18 participants (95% confidence interval limits, 0 to 10%). Clinical complications were confined to one case of confusion occurring after CEA; the diffusion-weighted imaging results were normal in this case. CONCLUSION: There is no evidence from our series that silent cerebral infarction is a common occurrence during CEA. These data provide further support for the safety of CEA.

Evidence for cytotoxic edema in the pathogenesis of cerebral venous infarction.

BACKGROUND AND PURPOSE: The pathogenesis of cerebral venous infarction (CVI) remains controversial, with uncertainty over whether cytotoxic edema plays a role. Recent animal studies have shown that cytotoxic edema reliably occurs in acute CVI and precedes the onset of vasogenic edema. Our hypothesis was that cytotoxic edema would also occur in acute human CVI and would be detectable as an area of restricted diffusion on diffusion-weighted images. METHODS: Twelve subjects with acute cerebral venous thrombosis confirmed by MR venography underwent both conventional MR and echo-planar diffusion-weighted imaging (maximum diffusion sensitivity [b=1000 s/mm(2)]). Images were examined for areas of CVI that were identified as T2 hyperintensity, diffusion hyperintensity, or hemorrhage. The percent change in apparent diffusion coefficient (ADC) and T2 signal as well as the T2/diffusion volume were calculated within areas of edematous CVI. Regression techniques were used to examine the relationship of these variables to symptom duration. RESULTS: Ten regions of CVI were detected in seven subjects, all showing T2 hyperintensity. Two of these regions were predominantly hemorrhagic and did not display diffusion hyperintensity. The remaining eight regions displayed diffusion hyperintensity that was associated with a decreased ADC. ADC values increased with symptom duration (r(2) = 0.96; P <.006). Both T2 hyperintensity and T2/diffusion volume peaked approximately 2 days after symptom onset. CONCLUSION: Restricted water diffusion suggesting cytotoxic edema is commonly found in subjects with acute CVI and decreases over time. This supports an important etiologic role for cytotoxic edema in the pathogenesis of CVI.

Neonatal hypoxic-ischemic encephalopathy: detection with diffusion-weighted MR imaging.

BACKGROUND AND PURPOSE: Although diffusion-weighted imaging has been shown to be highly sensitive in detecting acute cerebral infarction in adults, its use in detecting neonatal hypoxic-ischemic encephalopathy (HIE) has not been fully assessed. We examined the ability of this technique to detect cerebral changes of acute neonatal HIE in different brain locations. METHODS: Fifteen MR examinations were performed in 14 neonates with HIE (median age, 6.5 days; range, 2-11 days). Imaging comprised conventional T1-weighted, proton density-weighted, and T2-weighted sequences and echo-planar diffusion-weighted sequences. The location, extent, and image timing of ischemic damage on conventional and diffusion-weighted sequences and apparent diffusion coefficient (ADC) maps were compared. RESULTS: Although conventional sequences showed cerebral changes consistent with ischemia on all examinations, diffusion-weighted imaging showed signal hyperintensity associated with decreased ADC values in only seven subjects (47%). All subjects with isolated cortical infarction on conventional sequences had corresponding hyperintensity on diffusion-weighted images and decreased ADC values, as compared with 14% of subjects with deep gray matter/perirolandic cortical damage. The timing of imaging did not significantly alter diffusion-weighted imaging findings. CONCLUSION: Diffusion-weighted imaging, performed with the technical parameters in this study, may have a lower correlation with clinical evidence of HIE than does conventional MR imaging. The sensitivity of diffusion-weighted imaging in detecting neonatal HIE appears to be affected by the pattern of ischemic damage, with a lower sensitivity if the deep gray matter is affected as compared with isolated cerebral cortex involvement.

CNS involvement of virus-associated hemophagocytic syndrome: MR imaging appearance.

The MR imaging appearance of a case of virus-associated hemophagocytic syndrome complicated by diffuse CNS infiltration is presented. Virus-associated hemophagocytic syndrome is a rare condition, precipitated by viral infection and characterized by proliferation of benign histiocytes with phagocytosis. In severe cases, the CNS may be involved.

Nuclear and chloroplast poly(A) polymerases from plants share a novel biochemical property.

Poly(A) polymerases are centrally involved in the process of mRNA 3' end formation in eukaryotes. In animals and yeast, this enzyme works as part of a large multimeric complex to add polyadenylate tracts to the 3' ends of precursor RNAs in the nucleus. Plant nuclear enzymes remain largely uncharacterized. In this report, we describe an initial analysis of plant nuclear poly(A) polymerases (nPAPs). An enzyme purified from pea nuclear extracts possesses many features that are seen with the enzymes from yeast and mammals. However, the pea enzyme possesses the ability to polyadenylate RNAs that are associated with polynucleotide phosphorylase (PNP), a chloroplast-localized enzyme involved in RNA turnover. Similar behavior is not seen with the yeast poly(A) polymerase (PAP). A fusion protein consisting of glutathione-S-transferase and the active domain of an Arabidopsis-encoded nuclear poly(A) polymerase was also able to utilize PNP, indicating that the activity of the pea enzyme was due to an interaction between the pea nPAP and PNP, and not to other factors that might copurify with the pea enzyme. These results suggest the existence, in plant nuclei, of factors related to PNP, and an interaction between such factors and poly(A) polymerases.