Comparison of 12-Bit and 8-Bit Gray Scale Resolution in Mr Imaging of the CNS

A reduction in gray scale resolution of digital images from 12 to 8 bits per pixel usually means halving the storage space needed for the images. Theoretically, important diagnostic information may be lost in the process. We compared the sensitivity and specificity achieved by 4 radiologists in reading laser-printed films of original 12-bit MR images and cathode ray tube displays of the same images which had been compressed to 8 bits per pixel using a specially developed computer program. Receiver operating characteristic (ROC) curves showed no significant differences between film reading and screen reading. A paired 2-tailed t-test, applied on the data for actually positive cases, showed that the combined, average performance of the reviewers was significantly better at screen reading than at film reading. No such differences were found for actually negative cases. Some individual differences were found, but it is concluded that gray scale resolution of MR images may be reduced from 12 to 8 bits per pixel without any significant reduction in diagnostic information.

MR analysis of the transverse ligament in the late stage of whiplash injury

Purpose: To analyse and classify structural changes in the transverse ligament in the late stage of whiplash injury by use of high-resolution MRI, and to evaluate the reliability of our classification.

Material and Methods: Ninety-two whiplash-injured (2–9 years previously, mean 6 years) and 30 non-injured individuals underwent proton-weighted MR imaging of the craniovertebral junction in three orthogonal planes. Structural changes in the transverse ligaments were graded twice (grades 1–3) based on increased signal, independently by 3 radiologists with a 4-month interval. Inter- and intraobserver statistics were calculated by ordinary and weighted kappa (K).

Results: Image quality was excellent in 109 cases and slightly reduced in 13. Twenty-two out of 30 ligaments in the control group were classified as normal (73%) compared with only 32 out of 92 in the injured group (36%). Two or all 3 observers agreed in their grading in 101 out of 122 ligaments (83%). Intraobserver agreement (weighted K) was fair to good (0.33–0.73). Pair-wise interobserver agreement was fair (0.24–0.39). Reasons for divergent grading were insufficient knowledge of normal variations, low signal intensity in the peridental soft tissue obscuring the ligament and interpretation flaw.

Conclusion:Whiplash trauma can damage the transverse ligament. By use of high-resolution proton-weighted MR images such lesions can be detected and classified. The reliability of this classification still needs improvement.

Clinical implications of increased use of MRI in TIA

BACKGROUND

Transient ischemic attack has been redefined as a tissue-based diagnosis and MRI recommended as the preferred imaging modality. We aimed to investigate whether an increased use of MRI leads to a decrease in the proportion of TIA as compared to cerebral infarction. We also sought to see whether DWI-positive patients with transient ischemic symptoms <24 h differ from DWI-negative TIA patients in terms of performed diagnostic investigations and clinical characteristics.

METHODS

Patients admitted with cerebral infarction or TIA in the period 2006-2011 were prospectively registered. The use of MRI in patients with transient ischemic symptoms <24 h and proportion of TIA were annually recorded. DWI-positive and DWI-negative patients with transient ischemic symptoms <24 h were compared in univariate analyses regarding baseline data, diagnostic investigations, and etiology. Multivariate analyses were performed to identify predictors of DWI lesions.

RESULTS

The use of MRI increased from 65.0% in 2006-2008 to 89.0% in 2009-2011 (P < 0.001). The proportion of TIA as compared to cerebral infarction decreased from 12.2% in 2006-2008 to 8.3% in 2009-2011 (P = 0.002). DWI-positive patients were more often examined with 24-h Holter monitoring (P < 0.001) and echocardiography (P < 0.001). Lower age (P < 0.001) and prior myocardial infarction (P < 0.029) were independently associated with DWI lesions in patients with transient ischemic symptoms <24 h.

CONCLUSIONS

An increased use of MRI and a tissue-based TIA definition resulted in a decrease in the proportion of TIA at discharge as compared to cerebral infarction. DWI-positive patients had a more extensive cardiac work-up and were associated with lower age and prior myocardial infarction.

A vascular approach to mild amnestic cognitive impairment: a pilot study

OBJECTIVE

Mild cognitive impairment (MCI) is a subtle memory disorder not matching criteria for dementia. There is evidence for vascular comorbidity in several types of dementia. We hypothesized that neurovascular workup would detect a high degree of vascular disease in patients with MCI.

MATERIALS AND METHODS

In cooperation with our memory clinic, patients with amnestic MCI were referred to our department for neurovascular investigation. The workup encompassed ultrasound examination with carotid duplex including Intima-Media-Thickness (IMT) measurement, and transcranial Doppler (TCD) including one-hour microemboli monitoring, cerebrovascular reactivity measurement and Bubble test. Cerebral MRI for the evaluation of vascular and white-matter lesions, brain atrophy, hippocampal volumes, and amyloid angiopathy was performed.

RESULTS

Ten patients were included. Vascular risk factors were present in six patients. Four patients had atherosclerotic lesions, three classified as mild, and one as moderate carotid stenosis. IMT > 1 mm was found in two patients, with a maximum IMT of 1.11 mm. None of the patients with acceptable bone window had intracranial stenosis in TCD. Vasoreactivity was pathologically low in one patient. Permanent right-left shunt was found in three patients, of which one showed spontaneous cerebral microembolism. Hippocampal volume reduction and cortical atrophy were found in four patients. Chronic ischemic changes in MRI were present in one patient, and three patients had subcortical infarctions. Cortical infarctions, microbleeds, or amyloid angiopathy were not found.

CONCLUSIONS

Pure amnestic MCI is probably less associated with cerebrovascular disease and may be more consistent with evolving Alzheimer's disease. However, vascular risk factors are common in these patients.

Pseudoprogression in high-grade glioma

Pseudoprogression is a treatment-related effect seen on imaging in high-grade glioma. Enhancement of gadolinium contrast on control MRI can be misinterpreted as tumor recurrence and is also difficult to distinguish from radiation necrosis. Pseudoprogression is seen in up to 30% after standard treatment for glioblastoma multiforme (GBM), which is radiotherapy concurrent with chemotherapy with temozolomide (TMZ) and adjuvant cycles of TMZ. In this article, the current literature on pseudoprogression in high-grade glioma is reviewed by searches in PubMed. We also present two clinical cases, one of which had medullary pseudoprogression. No articles on this subentity of pseudoprogression were found in PubMed. Standard MRI with gadolinium contrast cannot differentiate between pseudoprogression, tumor recurrence and radiation necrosis. More advanced imaging techniques are often not available. Pseudoprogression seems to be related to methylated promoter of the O(6)--methyl-guanine methyl transferase (MGMT) gene, which is associated with improved treatment effect. Discontinuation or change of therapy on the basis of misinterpretation of MRI as disease progression is thus unfortunate. MRI should be interpreted with caution the first 6 months after standard treatment of high-grade glioma. In a GBM patient with contrast enhancement on MRI but few or no new symptoms and/or stable steroid doses, treatment should be continued and control imaging performed after 2-3 months.

Autosomal recessive mitochondrial ataxic syndrome due to mitochondrial polymerase gamma mutations

OBJECTIVE

To investigate three families and one sporadic case with a recessively inherited ataxic syndrome.

METHODS

Clinical and genetic studies were performed in six individuals. Southern blotting and real time PCR were used to detect deletions of mtDNA and mutations in the POLG gene were identified using a combination of DHPLC and direct DNA sequencing.

RESULTS

The patients have a distinctive, progressive disorder that starts with episodic symptoms such as migraine-like headache or epilepsy. Ataxia, which is a combination of central and peripheral disease, develops later as does ophthalmoplegia. The commonest form of epilepsy was focal and involved the occipital lobes. Myoclonus was common and patients have a high risk of status epilepticus. MRI typically shows signal changes in the central cerebellum, olivary nuclei, occipital cortex, and thalami. COX negative muscle fibers were found in four of six; in one patient these were rare and in another absent. Multiple mtDNA deletions were identified in all patients, although in two these were not apparent on Southern blotting and real time PCR was required to demonstrate the defect. Two families were homozygous for a previously described POLG mutation, G1399A (A467T). One family and the sporadic case had the same two new mutations, a G to C at position 1491 (Q497H) and a G to C at 2243 (W748S).

CONCLUSIONS

Mutations in POLG cause a recessively inherited syndrome with episodic features and progressive ataxia. Characteristic changes on MRI are seen and although skeletal muscle may appear morphologically normal, multiple mtDNA deletions can be detected using real-time PCR.

Electroencephalography and magnetic resonance imaging in neurological decompression sickness

The purpose of this study was to evaluate the use of electroencephalography (EEG) and magnetic resonance imaging (MRI) in the clinical evaluation of acute decompression sickness (DCS) in the central nervous system (CNS). Twenty-one patients treated because of acute DCS in the CNS during 1999-2001 were included, 15 patients with clinical cerebral DCS and five with clinical spinal cord DCS. Seven patients had abnormalities in their EEG, five with cerebral DCS and two with spinal cord DCS. MRI showed high intensity lesions in the spinal cord in four patients with clinical spinal cord DCS and in one with clinical cerebral DCS. Cerebral lesions were not identified by MRI in any patient. In conclusion, EEG showed unspecific abnormalities in only one third of the cases. Conventional MRI with a 1.5 T scanner may be of help in the diagnosis of DCS in the spinal cord, but not in the brain. EEG and MRI have low sensitivity in the diagnosis of acute DCS in the CNS. Recompression treatment of DCS should still be guided by clinical neurological examination and assessment of symptoms.

MR analysis of the transverse ligament in the late stage of whiplash injury

PURPOSE

To analyse and classify structural changes in the transverse ligament in the late stage of whiplash injury by use of high-resolution MRI, and to evaluate the reliability of our classification.

MATERIAL AND METHODS

Ninety-two whiplash-injured (2-9 years previously, mean 6 years) and 30 non-injured individuals underwent proton-weighted MR imaging of the craniovertebral junction in three orthogonal planes. Structural changes in the transverse ligaments were graded twice (grades 1-3) based on increased signal, independently by 3 radiologists with a 4-month interval. Inter- and intraobserver statistics were calculated by ordinary and weighted kappa (K).

RESULTS

Image quality was excellent in 109 cases and slightly reduced in 13. Twenty-two out of 30 ligaments in the control group were classified as normal (73%) compared with only 32 out of 92 in the injured group (36%). Two or all 3 observers agreed in their grading in 101 out of 122 ligaments (83%). Intraobserver agreement (weighted K) was fair to good (0.33-0.73). Pair-wise interobserver agreement was fair (0.24-0.39). Reasons for divergent grading were insufficient knowledge of normal variations, low signal intensity in the peridental soft tissue obscuring the ligament and interpretation flaw.

CONCLUSION

Whiplash trauma can damage the transverse ligament. By use of high-resolution proton-weighted MR images such lesions can be detected and classified. The reliability of this classification still needs improvement.

MRI of the tectorial and posterior atlanto-occipital membranes in the late stage of whiplash injury

Our aim was to characterise and classify permanent structural changes in the tectorial and posterior atlanto-occipital membranes several years after a whiplash injury, and to evaluate the reliability of our classification. We obtained sagittal proton density-weighted images of the craniovertebral junction of 92 whiplash-injured and 30 uninjured individuals. Structural abnormalities in the two membranes were classified as grades 1-3 independently by three radiologists blinded for clinical information. Grading criteria were based on reduced tectorial membrane thickness, and elongation or rupture of the posterior atlanto-occipital membrane/dura mater complex. The same images were reassessed 4 months later. Image quality was graded good in 104 cases, slightly reduced in 13 and unsatisfactory in five. Of 117 tectorial membranes 31 (26.5%) showed grade 2 or 3 lesions, in the uninjured group none were grade 3 and only three were grade 2. Pair-wise interobserver agreement (weighted kappa) was moderate (0.47-0.50), while the intraobserver agreement was moderate to good (0.51-0.70). Of 117 posterior atlanto-occipital membranes 20 (17.1%) had grade 2 or 3 lesions; there was no grade 3 and only one grade 2 lesion in the uninjured group. Inter- and intraobserver agreement was good (0.61-0.74 and 0.65-0.86, respectively). Reduced image quality was the main reason for disagreement, but partial thinning and lateral tapering, as normal tectorial membrane variations, created difficulties in some cases. This study strongly indicates that whiplash trauma can damage the tectorial and posterior atlanto-occipital membranes; this can be shown on high-resolution MRI. Better knowledge of normal anatomical variations and improved image quality should increase the reliability of lesion classification.

MRI assessment of the alar ligaments in the late stage of whiplash injury--a study of structural abnormalities and observer agreement

Our aim was to characterise and classify structural changes in the alar ligaments in the late stage of whiplash injuries by use of a new MRI protocol, and to evaluate the reliability and the validity of this classification. We studied 92 whiplash-injured and 30 uninjured individuals who underwent proton density-weighted MRI of the craniovertebral junction in three orthogonal planes. Changes in the alar ligaments (grades 0-3) based on the ratio between the high signal area and the total cross-sectional area were rated twice at a 4-month interval, independently by three radiologists. Inter- and intraobserver statistics were calculated by ordinary and weighted kappa. Cases classified differently were reviewed to identify potential causes for disagreement. The alar ligaments were satisfactorily demonstrated in all cases (244 ligaments in 122 individuals). The lesions, 2-9 years after the injury, varied from small high-signal spots to high signal throughout the cross-sectional area. Signal was highest near the condylar insertion in 82 of 94 ligaments, indicating a lesion near that insertion, and near the dental insertion in eight, indicating a medial lesion. No grade 2 or 3 lesion was found in the control group. At least two observers assigned the same grade to 214 ligaments (87.7%) on the second occasion. In 30 ligaments (12.3%) this agreement was not obtained. Pair-wise interobserver agreement (weighted kappa) was fair to moderate (0.31-0.54) in the first grading, improving to moderate (0.49-0.57) in the second. Intraobserver agreement (weighted kappa) was moderate to good (0.43-0.70). Whiplash trauma can cause permanent damage to the alar ligaments, which can be shown by high-resolution proton density-weighted MRI. Reliability of classification of alar ligament lesions needs to be improved.

[Hemiballismus in cerebral infarction]

BACKGROUND

Hemiballismus has traditionally been linked to lesions in the subthalamic nucleus.

MATERIAL AND METHODS

We studied six patients with hemiballismus presumably caused by ischaemic stroke. They were followed for up to two years.

RESULTS

Cerebral MRI with special projections showed that four out of six patients had ischaemic lesions in other parts of the brain than the subthalamic nucleus. Knowledge of the basalganglio-thalamocortical circuits is used to try to explain the cause of hemiballismus. Neuroleptics and benzodiazepines are the usual medical treatment for hemiballism and were helpful also in our patients. The prognosis in hemiballismus is good; four of our six patients had spontaneous recovery within nine months.

INTERPRETATION

The prognosis was not related to the site of the lesion.

[Intravenous thrombolytic treatment of acute basilar artery occlusion]

BACKGROUND

Acute stroke with basilar artery occlusion is a serious condition with high mortality and severe disability.

MATERIAL AND METHODS

We describe three patients with acute artery basilar occlusion treated with thrombolytic agent given intravenously.

RESULTS

One patient demonstrated early and considerable clinical improvement parallel to thrombolytic therapy started two and a half hour after ictus, but suffered a new occlusion and died in a "locked-in syndrome". One patient demonstrated moderate clinical improvement after less than six hours and survived with disability. One patient demonstrated no clinical improvement with thrombolytic therapy started six hours after ictus and later died of an injured brainstem. No patients had serious bleeding.

INTERPRETATION

Intravenous, systemic thrombolytic treatment may have a beneficial effect in acute basilar occlusion.

Acoustic neuroma--treatment modalities. Surgery, gamma-knife or observation?

We present our results of 211 patients with acoustic neuroma over a period of 10 years, 1988-97. We operated on 100 and 111 had Gamma-knife (GK) treatment (69 were available to follow-up). The results are excellent for surgery on small and intracanalicular tumours. In tumours of the same size, surgery and GK treatment give comparable, but somewhat different, results. In the GK group of 54 primary treated patients, 3 patients had to be operated on and another 4 developed hydrocephalus. A group of 35 acoustic tumours was observed for more than 3 years. Nineteen did grow (54%). Hearing was unchanged in 23%. We performed surgery in 11 patients and gave 2 patients GK treatment because of tumour growth of > 2 mm in diameter a year. We conclude that either treatment is effective for small and medium-sized acoustic neuromas. Hearing preservation was best in the GK-treated group (80%), compared to only 12.5% in the group operated via the suboccipital route. Larger tumours and most medium-sized tumours should be operated, as should smaller tumours with persistent symptoms of vertigo and pain. Medical contraindications to surgery or reluctance to undergo surgery make GK treatment a good alternative. Treatment of residual tumours with the GK could also be a solution to a difficult problem.

[Cerebral amyloid angiopathy]

Cerebral amyloid angiopathy affects the cerebral vasculature selectively, and there is no systemic amyloidosis. Amyloid is deposited in small and medium-sized vessels of the cortex and leptomeninges. Cerebral amyloid angiopathy is a common cause of spontaneous lobar haemorrhage in elderly patients. However, cerebral amyloid angiopathy may have atypical clinical and radiological presentations. We report on five patients (three males and two females, aged 43-77 years) with histologically verified cerebral amyloid angiopathy. One patient experienced an acute headache attack and classical lobar haemorrhage. The other patients had various neurological symptoms and signs, such as seizure, disturbed vision, pareses, aphasia, and dementia that were initially diagnosed as cerebral infarction or tumour. Two patients with cerebral amyloid angiopathy and granulomatous angiitis responded to immunosuppressive treatment.

Basilar artery fenestration aneurysms treated with guglielmi detachable coils

SUMMARY

Four patients with basilar artery fenestration aneurysms at the vertebra basilar junction were admitted after subarachnoid haemorrhage. In two of them attempted surgery failed. Subsequently, all four were embolised with Guglielmi Detachable Coils (GDC), three of them in the acute phase. In one case the initial embolisation was incomplete, but follow-up angiography demonstrated spontaneous total occlusion. In another, partial reopening was treated with further embolisation. Three patients recovered completely after treatment. One patient still has deficits related to surgery of an accompanying aneurysm at the middle cerebral artery. He is clinically improving but still not back at work. In two cases the fenestration was combined with a hypoplastic upper vertebral artery on one side. A hypoplastic veretebral artery on one side may frequently be part of the developmental anomaly of basilar fenestration aneurysms. The anatomical configuration and location of these aneurysms is such that their true nature is sometimes difficult to disclose at cerebral angiography and is only realised during embolisation. Treatment with GDC coils seems superior to surgery in basilar artery fenestration aneurysms.

[Interstitial laser coagulation in the treatment of benign prostatic hyperplasia. Preliminary results]

51 patients aged 68 (range 52-81) years with lower urinary tract symptoms compatible with obstruction from benign prostatic hyperplasia were treated with interstitial laser coagulation (ILC). Postoperative urinary retention lasting less than one week was seen in the majority of cases. All patients were followed up for three months and ten cases had further follow-up after one year. Three months after treatment the international prostate symptom score decreased from 23.3 +/- 0.7 to 8.9 +/- 0.8 and was 10.2 +/- 2.1 after one year. Peak urinary flow increased concomitantly from 8.3 +/- 0.4 to 12.2 +/- 0.7 at three months and was 11.5 +/- 1.4 ml/sec after one year. Three patients received other, additional treatment because the ILC-treatment failed. In conclusion, interstitial laser coagulation had marked effects on symptoms, whereas the effects on objective parameters were less pronounced in this selected group of patients. However, more extensive follow-up, is essential for further evaluation of this new treatment procedure.

[Intracranial venous thrombosis]

Cerebral venous thrombosis has traditionally been considered to be a severe and rare condition. Our knowledge of this condition has increased, however, along with the development of better radiological methods for visualization of the brain and its vasculature. Cerebral angiography, computed tomography (CT) and, in particular, magnetic resonance imaging (MRI) have made it easier to diagnose this condition earlier. It has thus been discovered that cerebral venous thrombosis occurs more frequently than previously supposed and shows a wide variation of the clinical spectrum. We describe a series of eight patients with cerebral venous thrombosis who were admitted to the Neurosurgical Department, Haukeland Hospital, over a period of three years. The presentation shows the great variation in the clinical and radiological picture of this disease and the consequent diagnostic and therapeutic challenges. We conclude that this diagnosis should be considered in patients with cerebral symptoms of uncertain cause, and that MRI is an important tool in diagnosis.

Expanding cava septi pellucidi and cava vergae in children: report of three cases

Three children with hydrocephalus and expanding cysts of the cavum septi pellucidi and cavum vergae are reported. In all the patients, the hydrocephalus was present before the persistent cava started to expand. The cava increased gradually, until they became cystic, but their growth did not affect the size of the ventricles. Two of the patients were treated with internal cystoventricular shunts, causing a prompt collapse of the cysts but no change in the concomitant hydrocephalus. In the third patient, the persistent cava started to expand only when a previously implanted ventriculoperitoneal shunt failed temporarily. The cyst disappeared when the shunt resumed its function. The possible mechanisms underlying the expansive growth of persistent cava are discussed. We propose the theory that the growth of the cava in our patients may be the result, rather than the cause, of the hydrocephalus.

Comparison of 12-bit and 8-bit gray scale resolution in MR imaging of the CNS. An ROC analysis

A reduction in gray scale resolution of digital images from 12 to 8 bits per pixel usually means halving the storage space needed for the images. Theoretically, important diagnostic information may be lost in the process. We compared the sensitivity and specificity achieved by 4 radiologists in reading laser-printed films of original 12-bit MR images and cathode ray tube displays of the same images which had been compressed to 8 bits per pixel using a specially developed computer program. Receiver operating characteristic (ROC) curves showed no significant differences between film reading and screen reading. A paired 2-tailed t-test, applied on the data for actually positive cases, showed that the combined, average performance of the reviewers was significantly better at screen reading than at film reading. No such differences were found for actually negative cases. Some individual differences were found, but it is concluded that gray scale resolution of MR images may be reduced from 12 to 8 bits per pixel without any significant reduction in diagnostic information.