Persistent neuronal firing in the medial temporal lobe supports performance and workload of visual working memory in humans

The involvement of the medial temporal lobe (MTL) in working memory is controversially discussed. Recent findings suggest that persistent neural firing in the hippocampus during maintenance in verbal working memory is associated with workload. Here, we recorded single neuron firing in 13 epilepsy patients (7 male) while they performed a visual working memory task. The number of coloured squares in the stimulus set determined the workload of the trial. Performance was almost perfect for low workload (1 and 2 squares) and dropped at high workload (4 and 6 squares), suggesting that high workload exceeded working memory capacity. We identified maintenance neurons in MTL neurons that showed persistent firing during the maintenance period. More maintenance neurons were found in the hippocampus for trials with correct compared to incorrect performance. Maintenance neurons increased and decreased firing in the hippocampus and increased firing in the entorhinal cortex for high compared to low workload. Population firing predicted workload particularly during the maintenance period. Prediction accuracy of workload based on single-trial activity during maintenance was strongest for neurons in the entorhinal cortex and hippocampus. The data suggest that persistent neural firing in the MTL reflects a domain-general process of maintenance supporting performance and workload of multiple items in working memory below and beyond working memory capacity. Persistent neural firing during maintenance in the entorhinal cortex may be associated with its preference to process visual-spatial arrays.

Dynamic human and avatar facial expressions elicit differential brain responses

Computer-generated characters, so-called avatars, are widely used in advertising, entertainment, human–computer interaction or as research tools to investigate human emotion perception. However, brain responses to avatar and human faces have scarcely been studied to date. As such, it remains unclear whether dynamic facial expressions of avatars evoke different brain responses than dynamic facial expressions of humans. In this study, we designed anthropomorphic avatars animated with motion tracking and tested whether the human brain processes fearful and neutral expressions in human and avatar faces differently. Our fMRI results showed that fearful human expressions evoked stronger responses than fearful avatar expressions in the ventral anterior and posterior cingulate gyrus, the anterior insula, the anterior and posterior superior temporal sulcus, and the inferior frontal gyrus. Fearful expressions in human and avatar faces evoked similar responses in the amygdala. We did not find different responses to neutral human and avatar expressions. Our results highlight differences, but also similarities in the processing of fearful human expressions and fearful avatar expressions even if they are designed to be highly anthropomorphic and animated with motion tracking. This has important consequences for research using dynamic avatars, especially when processes are investigated that involve cortical and subcortical regions.

The Effects of Dynamic and Static Emotional Facial Expressions of Humans and Their Avatars on the EEG: An ERP and ERD/ERS Study

This study aimed to examine whether the cortical processing of emotional faces is modulated by the computerization of face stimuli ("avatars") in a group of 25 healthy participants. Subjects were passively viewing 128 static and dynamic facial expressions of female and male actors and their respective avatars in neutral or fearful conditions. Event-related potentials (ERPs), as well as alpha and theta event-related synchronization and desynchronization (ERD/ERS), were derived from the EEG that was recorded during the task. All ERP features, except for the very early N100, differed in their response to avatar and actor faces. Whereas the N170 showed differences only for the neutral avatar condition, later potentials (N300 and LPP) differed in both emotional conditions (neutral and fear) and the presented agents (actor and avatar). In addition, we found that the avatar faces elicited significantly stronger reactions than the actor face for theta and alpha oscillations. Especially theta EEG frequencies responded specifically to visual emotional stimulation and were revealed to be sensitive to the emotional content of the face, whereas alpha frequency was modulated by all the stimulus types. We can conclude that the computerized avatar faces affect both, ERP components and ERD/ERS and evoke neural effects that are different from the ones elicited by real faces. This was true, although the avatars were replicas of the human faces and contained similar characteristics in their expression.

Machine Learning Techniques for Personalized Detection of Epileptic Events in Clinical Video Recordings

Continuous patient monitoring is essential to achieve an effective and optimal patient treatment in the intensive care unit. In the specific case of epilepsy it is the only way to achieve a correct diagnosis and a subsequent optimal medication plan if possible. In addition to automatic vital sign monitoring, epilepsy patients need manual monitoring by trained personnel, a task that is very difficult to be performed continuously for each patient. Moreover, epileptic manifestations are highly personalized even within the same type of epilepsy. In this work we assess two machine learning methods, dictionary learning and an autoencoder based on long short-term memory (LSTM) cells, on the task of personalized epileptic event detection in videos, with a set of features that were specifically developed with an emphasis on high motion sensitivity. According to the strengths of each method we have selected different types of epilepsy, one with convulsive behaviour and one with very subtle motion. The results on five clinical patients show a highly promising ability of both methods to detect the epileptic events as anomalies deviating from the stable/normal patient status.

The relation between neuronal firing, local field potentials and hemodynamic activity in the human amygdala in response to aversive dynamic visual stimuli

The amygdala is a central part of networks of brain regions underlying perception and cognition, in particular related to processing of emotionally salient stimuli. Invasive electrophysiological and hemodynamic measurements are commonly used to evaluate functions of the human amygdala, but a comprehensive understanding of their relation is still lacking. Here, we aimed at investigating the link between fast and slow frequency amygdalar oscillations, neuronal firing and hemodynamic responses. To this aim, we recorded intracranial electroencephalography (iEEG), hemodynamic responses and single neuron activity from the amygdala of patients with epilepsy. Patients were presented with dynamic visual sequences of fearful faces (aversive condition), interleaved with sequences of neutral landscapes (neutral condition). Comparing responses to aversive versus neutral stimuli across participants, we observed enhanced high gamma power (HGP, >60 ​Hz) during the first 2 ​s of aversive sequence viewing, and reduced delta power (1-4 ​Hz) lasting up to 18 ​s. In 5 participants with implanted microwires, neuronal firing rates were enhanced following aversive stimuli, and exhibited positive correlation with HGP and hemodynamic responses. Our results show that high gamma power, neuronal firing and BOLD responses from the human amygdala are co-modulated. Our findings provide, for the first time, a comprehensive investigation of amygdalar responses to aversive stimuli, ranging from single-neuron spikes to local field potentials and hemodynamic responses.

Dataset of human medial temporal lobe neurons, scalp and intracranial EEG during a verbal working memory task

We present an electrophysiological dataset recorded from nine subjects during a verbal working memory task. Subjects were epilepsy patients undergoing intracranial monitoring for the localization of epileptic seizures. Subjects performed a modified Sternberg task in which the encoding of memory items, maintenance, and recall were temporally separated. The dataset includes simultaneously recorded scalp EEG with the 10-20 system, intracranial EEG (iEEG) recorded with depth electrodes, waveforms and spike times of neurons recorded in the medial temporal lobe, and localization information on the depth electrodes. Subject characteristics and information on each trial (set size, match/mismatch, correct/incorrect, response, and response time) are given. For technical validation of data, we provide spike sorting quality metrics and the spectra of iEEG and scalp EEG signals. This dataset enables the investigation of working memory by providing simultaneous scalp EEG and iEEG recordings, which can be used for connectivity analysis, along with hard-to-obtain neuronal recordings from humans.

Persistent hippocampal neural firing and hippocampal-cortical coupling predict verbal working memory load

The maintenance of items in working memory relies on persistent neural activity in a widespread network of brain areas. To investigate the influence of load on working memory, we asked human subjects to maintain sets of letters in memory while we recorded single neurons and intracranial encephalography (EEG) in the medial temporal lobe and scalp EEG. Along the periods of a trial, hippocampal neural firing differentiated between success and error trials during stimulus encoding, predicted workload during memory maintenance, and predicted the subjects' behavior during retrieval. During maintenance, neuronal firing was synchronized with intracranial hippocampal EEG. On the network level, synchronization between hippocampal and scalp EEG in the theta-alpha frequency range showed workload dependent oscillatory coupling between hippocampus and cortex. Thus, we found that persistent neural activity in the hippocampus participated in working memory processing that is specific to memory maintenance, load sensitive and synchronized to the cortex.

Resection of high frequency oscillations predicts seizure outcome in the individual patient

High frequency oscillations (HFOs) are recognized as biomarkers for epileptogenic brain tissue. A remaining challenge for epilepsy surgery is the prospective classification of tissue sampled by individual electrode contacts. We analysed long-term invasive recordings of 20 consecutive patients who subsequently underwent epilepsy surgery. HFOs were defined prospectively by a previously validated, automated algorithm in the ripple (80–250 Hz) and the fast ripple (FR, 250–500 Hz) frequency band. Contacts with the highest rate of ripples co-occurring with FR over several five-minute time intervals designated the HFO area. The HFO area was fully included in the resected area in all 13 patients who achieved seizure freedom (specificity 100%) and in 3 patients where seizures reoccurred (negative predictive value 81%). The HFO area was only partially resected in 4 patients suffering from recurrent seizures (positive predictive value 100%, sensitivity 57%). Thus, the resection of the prospectively defined HFO area proved to be highly specific and reproducible in 13/13 patients with seizure freedom, while it may have improved the outcome in 4/7 patients with recurrent seizures. We thus validated the clinical relevance of the HFO area in the individual patient with an automated procedure. This is a prerequisite before HFOs can guide surgical treatment in multicentre studies.

Prediction of seizure outcome improved by fast ripples detected in low-noise intraoperative corticogram

OBJECTIVE

Fast ripples (FR, 250-500Hz) in the intraoperative corticogram have recently been proposed as specific predictors of surgical outcome in epilepsy patients. However, online FR detection is restricted by their low signal-to-noise ratio. Here we propose the integration of low-noise EEG with unsupervised FR detection.

METHODS

Pre- and post-resection ECoG (N=9 patients) was simultaneously recorded by a commercial device (CD) and by a custom-made low-noise amplifier (LNA). FR were analyzed by an automated detector previously validated on visual markings in a different dataset.

RESULTS

Across all recordings, in the FR band the background noise was lower in LNA than in CD (p<0.001). FR rates were higher in LNA than CD recordings (0.9±1.4 vs 0.4±0.9, p<0.001). Comparison between FR rates in post-resection ECoG and surgery outcome resulted in positive predictive value PPV=100% in CD and LNA, and negative predictive value NPV=38% in CD and NPV=50% for LNA. Prediction accuracy was 44% for CD and 67% for LNA.

CONCLUSIONS

Prediction of seizure outcome was improved by the optimal integration of low-noise EEG and unsupervised FR detection.

SIGNIFICANCE

Accurate, automated and fast FR rating is essential for consideration of FR in the intraoperative setting.

Human intracranial high frequency oscillations (HFOs) detected by automatic time-frequency analysis

OBJECTIVES

High frequency oscillations (HFOs) have been proposed as a new biomarker for epileptogenic tissue. The exact characteristics of clinically relevant HFOs and their detection are still to be defined.

METHODS

We propose a new method for HFO detection, which we have applied to six patient iEEGs. In a first stage, events of interest (EoIs) in the iEEG were defined by thresholds of energy and duration. To recognize HFOs among the EoIs, in a second stage the iEEG was Stockwell-transformed into the time-frequency domain, and the instantaneous power spectrum was parameterized. The parameters were optimized for HFO detection in patient 1 and tested in patients 2-5. Channels were ranked by HFO rate and those with rate above half maximum constituted the HFO area. The seizure onset zone (SOZ) served as gold standard.

RESULTS

The detector distinguished HFOs from artifacts and other EEG activity such as interictal epileptiform spikes. Computation took few minutes. We found HFOs with relevant power at frequencies also below the 80-500 Hz band, which is conventionally associated with HFOs. The HFO area overlapped with the SOZ with good specificity > 90% for five patients and one patient was re-operated. The performance of the detector was compared to two well-known detectors.

CONCLUSIONS

Compared to methods detecting energy changes in filtered signals, our second stage - analysis in the time-frequency domain - discards spurious detections caused by artifacts or sharp epileptic activity and improves the detection of HFOs. The fast computation and reasonable accuracy hold promise for the diagnostic value of the detector.

Brain electrical responses to high- and low-ranking buildings

Since the ancient world, architecture generally distinguishes two categories of buildings with either high- or low-ranking design. High-ranking buildings are supposed to be more prominent and, therefore, more memorable. Here, we recorded event-related potentials (ERPs) to drawings of buildings with either high- or low-ranking architectural ornaments and found that ERP responses between 300 and 600 ms after stimulus presentation recorded over both frontal lobes were significantly more positive in amplitude to high-ranking buildings. Thus, ERPs differentiated reliably between both classes of architectural stimuli although subjects were not aware of the two categories. We take our data to suggest that neurophysiological correlates of building perception reflect aspects of an architectural rule system that adjust the appropriateness of style and content ("decorum"). Since this rule system is ubiquitous in Western architecture, it may define architectural prototypes that can elicit familiarity memory processes.

[Incidental finding: left sided solid adrenal mass]

In a 49 year old male patient diagnostic evaluation of pneumonia performed by computed tomography revealed a left sided adrenal mass. The results of laboratory examination and MR-imaging of the adrenal glands suggested a hormonal inactive adrenal adenoma. Two years later, due to an increase in size, a surgical procedure was performed which revealed a gastrointestinal stromal tumor of the posterior gastric wall, rather than the suspected adrenal mass. Radiologic evaluation of adrenal masses and the clinical and pathologic characteristics of stromal tumors are discussed.

[Incidental finding: left sided cystic adrenal mass]

Because of the widespread use of imaging techniques the incidental diagnosis of an adrenal mass without clinical symptoms and pathologic laboratory values becomes more and more common. To avoid unnecessary therapeutic interventions an intensive evaluation should take place including blood and urine testing as well as radiologic examination. An accurate assessment is often helpful in making the diagnosis of a benign process to avoid an invasive procedure and to determine the frequency and intensity of further controls. Nevertheless, in some cases the invasive approach is necessary because of an unclear situation or because of influences caused by the patient. An advantage is the possibility of laparoscopic intervention because of the minimal morbidity and until now no reported mortality.

[Long-term monitoring]

The electroencephalography (EEG) keeps its essential role in the differential diagnosis of epileptic and non-epileptic seizure disorders and in the classification of the different types of epilepsies and epileptic seizures, mainly due to its unique capability to directly show epileptic malfunction. The routine EEG usually records the EEG between seizures (interictal EEG) and remains a cost effective, highly specific, but not very sensitive method in epileptology. However, a diagnosis based on clinical data and routine EEG alone if often difficult and 20-30% of patients referred to an epilepsy centre due to medical refractory seizures do not have epilepsy. The different methods of long-term monitoring (cable and radio telemetry, ambulatory EEG monitoring) can continuously record EEG and other biosignals for many hours up to several days and allow a direct assessment of seizures (ictal EEG). In combination with the video-recorded symptomatology, these methods establish a precise diagnosis and follow-up of uncertain seizure disorders in the majority of cases. Although technical and personnel investment is relatively high the method used in expert hands is efficient, accepted and cost effective.

Twenty years of ictal EEG-EMG

This study aimed to evaluate the use of ictal EEG recordings combined with simultaneous surface EMG in the diagnosis and analysis of motor events, both epileptic and nonepileptic. All ictal registrations were performed utilizing radio/cable telemetry. Routine recordings consisted of 18-channel EEG plus 8-channels bipolar surface EMG in freely moving patients. Combined ictal EEG-EMG recordings in freely moving patients enabled us to identify and define the following pathomechanisms of epileptic drop seizures, epileptic axial spasms, atonic, myoclonic-atonic, and akinetic seizures. Precise differentiation could be made between tonic and nontonic postural seizures and between startle-induced reflex seizures and hyperekplexia. The findings from telemetered ictal recordings in freely moving patients with combined EEG and surface EMG offer the only means of identifying, defining, and differentiating motor events, both epileptic and nonepileptic, of a short duration that cannot be properly differentiated by clinical examination alone.

From clinical observation to long-term monitoring: diagnostic developments in conservative epileptology

The diagnostic goals in nonsurgical (conservative) epileptology differ from presurgical diagnostic aims. The resulting development of diagnostic methods in a tertiary-level epilepsy center is shown and the major technical and organizational consequences of this difference for diagnostic long-term monitoring (LTM) as opposed to presurgical LTM are investigated. A total of 133 consecutive daytime LTM investigations using radio telemetry were reviewed and seizure parameters such as type, duration, method of seizure detection, and need of mobility were evaluated and compared to presurgical LTM. Compared to presurgical LTM, partial seizures were relatively rare (17.8%) and short epileptic or nonepileptic motor events lasting <1 s, such as myoclonic, atonic, short tonic seizures, spasms, tics, or startle reactions, are frequent (34.9%). Of all seizures, 23% had no or minor ictal EEG changes, subtle symptomatology without signaling by a patient or accompanying person, and could be detected only by continuous online surveillance by an experienced EEG technician. Due to the nature of the patient population in diagnostic LTM, there is an increased need for ictal and interictal mobility (radio telemetry). LTM in conservative epileptology requires more intense human surveillance for seizure detection and increased patient mobility compared to presurgical LTM.

Temperature mapping of magnetic resonance-guided laser interstitial thermal therapy (LITT) in lymphangiomas of the head and neck

BACKGROUND AND OBJECTIVE

Lymphangiomas of the tongue and neck are uncommon benign congenital lymphatic tumors. These vascular lesions are difficult to treat, frequently recur, and can cause patients significant morbidity. Treatment may also be complicated by adjacent vital anatomic structures. Magnetic resonance (MR)-controlled laser-induced interstitial thermotherapy (LITT) has been proven to be a noninvasive safe treatment. Real-time monitoring of tissue temperature with thermosensitive sequences allows controlled coagulation necrosis.

STUDY DESIGN/MATERIALS AND METHODS

LITT was performed in a lymphangioma specimen ex vivo. In four patients (eight procedures) with lymphangiomas of the tongue and neck, MR-guided LITT was performed with a percutaneous approach in a multiapplicator technique. The laser system consisted of a titanium catheter and a protective catheter. The dome of the fiber end had a diameter of 1.4 mm with an active length of 20 mm. Temperature sensitive sequences were used in a 0.5 T open-configured MR scanner with the proton frequency shift technique to map the spatial and temporal distribution of Nd:YAG laser effects (7 Watts, 30 pulses per second, 10 minutes/location). Postoperative MR follow-up was performed at 1 week and at 3 months. In three patients, partial resection of the tumor was performed 6 months after LITT.

RESULTS

In three patients, MR clearly showed a diminished tumor volume. All four patients reported subjective amelioration and in three patients former functional problems, such as speech and swallowing were improved. MR thermometry allowed accurate demarcation of changes by heat and distinction of affected tumor volume (3.0 cm +/- 0.3 cm). The histology of the patients 6 months after LITT showed laser-induced fibrosis of former lymphatic tissue.

CONCLUSION

The results suggest that LITT can be performed safely with tissue preserving of vital structures and can be effective in the treatment of deep tumors, such as lymphangiomas. However, given the nature of the lesion, the potential for recurrence exists no matter what modality is chosen.

Abdominal pulsatile tumor after endovascular abdominal aortic aneurysm repair

A 70 years old patient was successfully treated for infrarenal aortic aneurysm by an endovascular bifurcated prosthesis. Three months later, because of dysuria, he underwent urological examination revealing an abdominal pulsatile tumor. Thereafter, the patient was sent to our emergency ward with suspected symptomatical endoleak. Radiological screening by computer tomography and magnetic resonance angiography showed good post-operative results without endoleak. Patient was treated with antispasmodic medication and is doing well today. Because endovascular repair of aortic aneurysm, in contrast to an open approach, does not eliminate the aneurysm itself, post-operative abdominal palpation can be ambiguous. Magnetic resonance angiography--without the need of nephrotoxic contrast medium--compares favourably to CT and provides excellent pictures with less artefacts for post-operative screening of endoleak. If reperfusion can be excluded, pulsation is due to the transmission of the blood-pressure wave to the thrombosed aneurysm.

Magnetic resonance angiography versus duplex sonography for diagnosing renovascular disease

Noninvasive testing for renovascular disease is required to identify patients who may benefit from revascularization procedures without exposing an unnecessary amount of patients to the risks of catheter angiography. All available methods of diagnosing renal artery stenosis have significant limitations. We compared a new technique, contrast-enhanced magnetic resonance angiography, with an established technique, duplex ultrasonography, for the detection of renal artery stenosis using catheter angiography as the standard of reference. Eighty-nine patients with clinically suspected renovascular disease underwent duplex renal scanning and contrast-enhanced magnetic resonance angiography. Sixty of these also underwent catheter angiography. All studies were interpreted for the presence of renal artery stenosis blinded to the results of the other imaging modalities. For detection of hemodynamically significant (>/=60% diameter reduction) main renal artery stenosis, sensitivity and specificity were 90% and 86%, respectively, for magnetic resonance angiography and 81% and 87% for duplex sonography. Most false readings involved differential grading of stenoses detected with all 3 techniques. When patients with fibromuscular dysplasia were excluded from the analysis, the sensitivity of magnetic resonance angiography increased to 97%, with a negative predictive value of 98%. Magnetic resonance angiography detected 96% and duplex 5% of accessory renal arteries seen at catheter angiography. Contrast-enhanced magnetic resonance angiography is a useful technique for diagnosing atherosclerotic renovascular disease. It overcomes the major limitations of duplex renal scanning. However, duplex has the advantage of providing hemodynamic information and appears better suited for the assessment of patients with suspected fibromuscular dysplasia.

[Endovascular treatment of the abdominal aortic aneurysm: assessment, implantation technique, after-care and results]

BACKGROUND

Endovascular treatment of abdominal aortic aneurysm (AAA) is a new minimally invasive alternative to surgical repair. Patient selection, perioperative management, the procedure itself and postoperative follow-up are new aspects.

PATIENTS

From June 1997 to June 1998, 37/70 patients (53%) with AAA were treated by the endovascular method. There were 35 males and two females, mean age 74 +/- 7 years, with a mean ASA class of 3.5 +/- 0.5. Graft repair was performed in 33 patients, due to inappropriate aortic anatomy for the endovascular technique in 24 and leaking aneurysm in 9.

METHODS

Feasibility is based upon computed tomography and angiography. The procedure was performed in the operating room, under general, regional and local anaesthesia in 14, 3 and 20 patients, respectively. 36 bifurcated and one tube endoprosthesis were implanted. An open access on one femoral or iliac artery and, in case of bifurcated prosthesis, usually a percutaneous access (10 Fr) on the other side were performed. Positioning and delivery were monitored under fluoroscopy.

RESULTS

All the AAA could be sealed by the endovascular technique. In one patient, an iliac limb was removed surgically because of proximal misplacement, but the procedure was completed by the endovascular technique. Mean operation time was 140 +/- 67 minutes. ICU stay was 1.4 +/- 1.6 days and patients were discharged after 6.5 +/- 3.5 days. Postoperative radiological follow-up showed totally sealed aneurysms in 34/37 patients (91%). In 3 patients a residual perfusion originating from a lumbar artery was observed. In 7/14 patients with AAA diameter > 6 cm and without residual leakage on the control CT scan, aneurysm pulsation remained after endovascular treatment. There was no early or late death after endovascular repair. During the follow-up period of 4 +/- 3 months patients are doing well. One patient needed balloon dilatation of an iliac limb.

CONCLUSIONS

Endovascular treatment of AAA is a minimally invasive technique with short recovery time. This technique seems to be particularly advantageous in elderly or severely ill patients. Long-term controls are mandatory to identify potential complications, particularly when residual perfusion or aneurysm pulsation persists.

Role of duplex color Doppler ultrasound, computed tomography, and MR angiography in the diagnosis of septic puerperal ovarian vein thrombosis

BACKGROUND

Septic puerperal ovarian vein thrombosis (SPOVT) is one of the underlying etiologies of puerperal fever. A correct diagnosis of this condition is important because adequate treatment requires additional administration of anticoagulants. The purpose of this study was to evaluate the role of duplex color Doppler ultrasound (CDUS), computed tomography (CT), and magnetic resonance angiography (MRA) in the detection of SPOVT.

METHODS

Twenty-six patients with puerperal fever suspected to be due to SPOVT and unresponsive to broad antibiotic treatment for at least 48 h were included in a prospective study using CDUS, CT, and MR imaging including MRA. Examinations were analyzed and then correlated to a standard of reference gathered from surgical and clinical follow-up data and from results of imaging.

RESULTS

SPOVT was present in nine patients (right side n = 8, bilateral n = 1). CDUS was inconclusive due to gaseous distention of the bowel or obesity in 13 of 26 cases. After counting inconclusive findings as wrong results for statistical purposes, sensitivity, specificity, and accuracy for CDUS were 55.6%, 41.2%, and 46.2%, respectively. CT had a sensitivity of 77.8% with a specificity of 62.5%; accuracy was 68.0%. MRA rendered conclusive results in all evaluated patients, resulting in a sensitivity and specificity of 100%.

CONCLUSION

MRA is recommended in all patients with inconclusive CDUS findings and persistent suspicion for SPOVT. CT has the advantage of more rapid access and lower cost and thus will probably remain a sufficiently accurate alternative. Septic puerperal ovarian vein thrombosis (SPOVT)-Computed tomography-Magnetic resonance angiography-Ultrasound.

Fast spin-echo inversion-recovery imaging versus fast T2-weighted spin-echo imaging in bone marrow abnormalities

RATIONALE AND OBJECTIVES

The purpose of this investigation is to compare a fat-suppressed T2-weighted fast spin-echo (FSE) sequence in bone marrow abnormalities with an FSE STIR sequence that recently has become commercially available.

METHODS

Fast spin-echo images (repetition time [TR], 3500-5000 mseconds; echo time [TE], 96-114 mseconds) and FSE STIR images (TR, 3000-5000 mseconds; TE, 32-40 mseconds; inversion time [TI], 140-150 mseconds) were compared quantitatively and qualitatively calculating signal-to-noise ratios (SNRs), contrast-to-noise ratios (CNRs), and lesion conspicuity and using a qualitative scoring system.

RESULTS

Signal-to-noise ratio (mean +/- standard deviation) was 36.4 +/- 19.3 for the FSE and 29.0 +/- 15.9 for the FSE STIR images (P = .002). Contrast-to-noise ratio (mean +/- standard deviation) was 18.7 +/- 14.3 for the FSE and 20.3 +/- 16.0 for the FSE STIR images (P = .45). Lesion conspicuity (mean +/- standard deviation) was 1.7 +/- 1.5 for the FSE and 3.5 +/- 4.0 for the FSE STIR images (P = .025). The most important difference in the qualitative evaluation related to the better signal homogeneity on the FSE STIR images.

CONCLUSIONS

Fast spin-echo STIR images may be preferable to FSE images with fat suppression due to better image homogeneity and lesion conspicuity.

Detection and evolution of rhytmic components in ictal EEG using short segment spectra and discriminant analysis

An automated method for analysis of ictal EEG is described which aims to reliably detect one or several rhythmic components in short EEG segments (2 sec) and to display their presence, frequency, amplitude, location, and temporal evolution. Spectra were estimated and compared using fast Fourier transform (FFT) and autoregressive modelling (AR). A subsequent linear discriminant analysis decided whether a spectral peak is likely to be caused by rhythmic activity or by the inherent statistical variability. FFT was found to perform better than AR in the detection of rhythmic components, yielding a false-positive rate of 0.825%, a false-negative rate of 2% (signal to noise ratio -4.6 dB), a frequency resolution of 2 Hz, and a temporal resolution of 0.5 sec. Seizure analysis revealed that the ictal scalp EEG of even short seizures can show a complex evolution of rhythmic patterns which are impossible or difficult to recognize by visual inspection or conventional spectral analysis. The following phenomena are demonstrated: superposition of two rhythmic components suggesting two cerebral regions discharging simultaneously and independently with their own pacemakers, sudden and gradual change of frequencies, and gradual development of harmonic frequencies. It is suggested that a more precise correlation between rhythmic generators and seizure symptomatology might allow more predictable pharmacological responses in antiepileptic therapy.

Normal and myopathic propagation of surface motor unit action potentials

With the aid of a computer-assisted multichannel EMG system, the propagation of motor unit action potentials is analysed during isometric voluntary muscular contraction under normal and myopathic conditions. A linear array of 30 surface electrodes is fixed above the biceps brachii muscle, parallel to the longitudinal muscle axis and centered over the end-plate zone. The EMG is simultaneously recorded on all channels and displays the propagation of surface potentials on both sides of the innervation band. The mean muscle fibre conduction velocity is computed by a cross-correlation technique. Five adult patients in a late stage of progressive muscular dystrophy show a highly altered propagation behaviour of motor unit action potentials without a time shift between potentials of adjacent electrodes. A mathematical model is described which predicts such a behaviour and suggests that it must be due to a pathological longitudinal spread of end-plates in this patient group. In 5 boys with Duchenne muscular dystrophy and only moderate impairment of the biceps muscle the mean muscle fibre velocity was reduced (2.81 +/- 0.34 m/sec) compared to 17 healthy subjects (4.42 +/- 0.37 m/sec). Each myopathic patient examined could be separated clearly from the group of healthy subjects on the basis of the surface EMG analysis.