[German guidelines for brain tumour imaging by PET and SPECT using labelled amino acids]. / PET- und SPECT-Untersuchungen von Hirntumoren mit radioaktiv markierten Aminosäuren.

For the primary diagnosis of brain tumours, morphological imaging by means of magnetic resonance imaging (MRI) is the current method of choice. The complementary use of functional imaging by positron emitting tomography (PET) and single photon emitting computerized tomography (SPECT) with labelled amino acids can provide significant information on some clinically relevant questions, which are beyond the capacity of MRI. These diagnostic issues affect in particular the improvement of biopsy targeting and tumour delineation for surgery and radiotherapy planning. In addition, amino acid labelled PET and SPECT tracers are helpful for the differentiation between tumour recurrence and non-specific post-therapeutic tissue changes, in predicting prognosis of low grade gliomas, and for metabolic monitoring of treatment response. The application of dynamic PET examination protocols for the assessment of amino acid kinetics has been shown to enable an improved non-invasive tumour grading. The purpose of this guideline is to provide practical assistance for indication, examination procedure and image analysis of brain PET/SPECT with labelled amino acids in order to allow for a high quality standard of the method. After a short introduction on pathobiochemistry and radiopharmacy of amino acid labelled tracers, concrete and detailed information is given on the several indications, patient preparation and examination protocols as well as on data reconstruction, visual and quantitative image analysis and interpretation. In addition, possible pitfalls are described, and the relevant original publications are listed for further information.

Postural imbalance and falls in PSP correlate with functional pathology of the thalamus.

OBJECTIVE: To determine how postural imbalance and falls are related to regional cerebral glucose metabolism (PET) and functional activation of the cerebral postural network (fMRI) in patients with progressive supranuclear palsy (PSP). METHODS: Sixteen patients with PSP, who had self-monitored their frequency of falls, underwent a standardized clinical assessment, posturographic measurement of balance during modified sensory input, and a resting [¹8F]FDG-PET. In addition, patients performed an fMRI paradigm using mental imagery of standing. Results were compared to healthy controls (n = 16). RESULTS: The frequency of falls/month in patients (range 1-40) correlated with total PSP rating score (r = 0.90). Total sway path in PSP significantly correlated with frequency of falls, especially during modulated sensory input (eyes open: r = 0.62, eyes closed: r = 0.67, eyes open/head extended: r = 0.84, eyes open/foam-padded platform: r = 0.87). Higher sway path values and frequency of falls were associated with decreased regional glucose metabolism (rCGM) in the thalamus (sway path: r = -0.80, falls: r = -0.64) and increased rCGM in the precentral gyrus (sway path: r = 0.79, falls: r = 0.64). Mental imagery of standing during fMRI revealed a reduced activation of the mesencephalic brainstem tegmentum and the thalamus in patients with postural imbalance and falls. CONCLUSIONS: The new and clinically relevant finding of this study is that imbalance and falls in PSP are closely associated with thalamic dysfunction. Deficits in thalamic postural control get most evident when balance is assessed during modified sensory input. The results are consistent with the hypothesis that reduced thalamic activation via the ascending brainstem projections may cause postural imbalance in PSP.

Thalamic infarctions cause side-specific suppression of vestibular cortex activations.

H2O15-PET was performed during caloric vestibular stimulation of the right and left external ears in eight right-handed patients with acute unilateral infarctions or haemorrhages of the posterolateral thalamus (four right, four left). The posterolateral thalamus is the relay station for ipsi- and contralateral ascending vestibular input to the multiple multisensory vestibular cortex areas. The aim of this study was to evaluate the differential effects of unilateral vestibular thalamic lesions on thalamo-cortical projections, right hemispheric dominance and reciprocal inhibitory visual-vestibular interaction, as well as perceptual and ocular motor consequences during caloric irrigation. The major findings of the group analyses of the patients with right-sided and those with left-sided lesions were as follows: (i) activation of the multisensory vestibular temporo-parietal cortex was significantly reduced in the hemisphere ipsilateral to the thalamic lesion when the ipsilesional or contralesional ear was stimulated; (ii) activation of multisensory vestibular cortex areas of the hemisphere contralateral to the irrigated ipsilesional ear was also diminished; and (iii) the right hemispheric dominance in right-handers described above was preserved in those with right and left thalamic lesions. Simultaneous deactivations were often restricted to only one hemisphere--the one contralateral to the stimulation and contralateral to the vestibular cortex areas activated. There was, however, one area in the inferior insula which was also activated by either right or left ear stimulation in the hemisphere ipsilateral to the lesion. This supports the assumption that there is a bilateral direct ascending vestibular projection from the vestibular nuclei to the inferior part of the insula, which bypasses the posterolateral thalamus and is stronger in the right hemisphere. The cortical asymmetry of the pattern of activation during horizontal semicircular canal stimulation by calorics was not associated with a significant direction-specific asymmetry of caloric nystagmus or perceived body motion. Thus, the data demonstrate the functional importance of the posterolateral thalamus as a unique relay station for vestibular input to the cortex, of the dominance of the right hemisphere in right-handedness, and of ipsilateral ascending pathways. Furthermore, the normal interaction between the two sensory systems--the vestibular and the visual--appears to be impaired.

A H(2)(15)O positron emission tomography study on mental imagery of movement sequences--the effect of modulating sequence length and direction.

Motor imagery is a state of mental rehearsal of single movements or movement patterns and has been shown to recruit motor networks overlapping with those activated during movement execution. We wished to examine whether the brain areas subserving control of sequential processes could be delineated by pure mental imagery, their activation levels reflecting the processing demands of a sequential task. We studied six right-handed volunteers (39.0 +/- 14 years) with H(2)(15)O positron emission tomography (PET) while they continuously mentally pursued with their right hand one of five sequences differing in complexity (i.e., increases in sequence length, single-finger repetitions, and reversals). Conditions were repeated twice, alternating with two rest scans. Each imagined single motor element was paced at a frequency of 1 Hz. Significant activation increases (P < 0.05, corrected) associated with imagination of right finger movement sequences (conditions I to V combined)--compared to the rest condition--were observed in left sensorimotor cortex (M1/S1) and the adjacent inferior parietal cortex. Further activation increases (P < 0.001, uncorrected) occurred in bilateral dorsal premotor (PMd) cortex, left caudal supplementary motor area, bilateral ventral premotor cortex, right M1, left superior parietal cortex, left putamen, and right cerebellum. Activation decreases occurred in bilateral prefrontal and right temporo-occipital cortex. Activation increases that correlated with sequence complexity were observed only in specific areas of the activated network, notably in left PMd, right superior parietal cortex, and right cerebellar vermis (P < 0.05, corrected). In conclusion, our study, by varying the sequence structure of imagined finger movements, identified task-related activity changes in parietopremotor-cerebellar structures, reflecting their role in mediating sequence control.

Thalamic stimulation for essential tremor activates motor and deactivates vestibular cortex.

BACKGROUND: The functional effects of deep brain stimulation in the nucleus ventralis intermedius (VIM) of the thalamus on brain circuitry are not well understood. The connectivity of the VIM has so far not been studied functionally. It was hypothesized that VIM stimulation would exert an effect primarily on VIM projection areas, namely motor and parietoinsular vestibular cortex. METHODS: Six patients with essential tremor who had electrodes implanted in the VIM were studied with PET. Regional cerebral blood flow was measured during three experimental conditions: with 130 Hz (effective) and 50 Hz (ineffective) stimulation, and without stimulation. RESULTS: Effective stimulation was associated with regional cerebral blood flow increases in motor cortex ipsilateral to the side of stimulation. Right retroinsular (parietoinsular vestibular) cortex showed regional cerebral blood flow decreases with stimulation. CONCLUSIONS: Beneficial effects of VIM stimulation in essential tremor are associated with increased synaptic activity in motor cortex, possibly due to nonphysiologic activation of thalamofrontal projections or frequency-dependent neuroinhibition. Retroinsular regional cerebral blood flow decreases suggest an interaction of VIM stimulation on vestibular-thalamic-cortical projections that may explain dysequilibrium, a common and reversible stimulation-associated side effect.

Neurophysiological processes underlying the phantom limb pain experience and the use of hypnosis in its clinical management: an intensive examination of two patients.

In a pilot study with 2 patients suffering from phantom limb pain (PLP), hypnotic suggestions were used to modify and control the experience of the phantom limb, and positron emission tomography (PET) was used to index underlying pathways and areas involved in the processing of phantom limb experience (PLE) and PLP. The patients' subjective experiences of pain were recorded in a semistructured protocol. PET results demonstrated activation in areas known to be responsible for sensory and motor processing. The reported subjective experiences of PLP and movement corresponded with predicted brain activity patterns. This work helps to clarify the central nervous system correlates of phantom limb sensations, including pain. It further suggests that hypnosis can be incorporated into treatment protocols for PLP.

Reduction of regional cerebral blood flow and cognitive impairment in patients with Alzheimer's disease: evaluation of an observer-independent analytic approach.

The aim of the study was to evaluate an observer-independent semiquantitative analysis of brain imaging by single-photon emission computed tomography (SPECT) in patients with Alzheimer's disease (AD). Patients (n = 45, mean age 70 +/- 11 years) with a clinical diagnosis of AD according to NINCDS/ADRDA criteria were examined by 99mTc-ethylcysteine dimer SPECT. Following anatomic normalization and data extraction using three-dimensional stereotactic surface projection, a pixelwise comparison of ECD uptake was performed with the reference values of 10 cognitive intact controls of comparable age. The global relative decrease of cerebral blood flow in cortical association areas showed a significant inverse association with the overall level of cognitive functioning as assessed with the Mini Mental State Examination and with the cognitive section (CAMCOG) of the Cambridge Mental Disorders of the Elderly Examination. There were significant region-specific associations between left temporoparietal perfusion deficit and language performance and between right temporoparietal regional cerebral blood flow reduction and praxis. The results suggest that this observer-independent analysis of SPECT data provides a valid assessment of the pattern and severity of cortical perfusion abnormalities in patients with AD.

Focal metabolic activation in the predominant left auditory cortex in patients suffering from tinnitus: a PET study with [18F]deoxyglucose.

Eleven patients suffering from chronic disabling tinnitus underwent an FDG-PET study (positron emission tomography with [18F]deoxyglucose). Nine tinnitus patients revealed a significantly increased metabolic activity in the left, 1 in the right primary auditory cortex (PAC, Brodmann area 41). These results were statistically significant when compared to 14 healthy control individuals without tinnitus. A negative result was obtained from a chronic tinnitus patient but who had no subjective complaints during the period of PET investigation. One patient was first investigated during a disabling tinnitus period, later during a period with tinnitus relief and again when suffering from severe tinnitus. The metabolic activity of his left PAC was in good accordance with the subjective degree of tinnitus complaints present during each PET investigation. Although for the first time these results give objective evidence of tinnitus sensation and localization, they are difficult to interpret because of the limited research data available that combine functional brain imaging and acoustic stimuli.

[Comparison of D2 receptor scintigraphy (123I-IBZM) with cerebral perfusion (99m-Tc-HMPAO) in extrapyramidal disorders]. / D2-Rezeptorszintigraphie (123J-IBZM) im Vergleich zur zerebralen Perfusion (99mTc-HMPAO) bei extrapyramidalen Erkrankungen.

The aim of this SPECT study was to determine whether there is a correlation between rCBF (99mTc-HMPAO) and D2 receptor binding (123I-IBZM) in disorders of the extrapyramidal system and in which situation the 99mTc-HMPAO scan could predict the outcome of the 123I-IBZM study. 13 patients with Parkinson's syndrome and 13 patients with hyperkinetic extrapyramidal disorders were studied. In all patients the two SPECT studies were performed within 2-7 days. ROIs were placed over the basal ganglia (BG), the frontal cortex (FC) and the cerebellum (CE). The ratios BG/FC and BG/CE were calculated. In both groups the scatter was lower when the frontal cortex was used as reference region. Among the patients with hyperkinetic extrapyramidal disorders the two patients with Huntington's chorea had lower rCBF and D2 receptor binding compared to other hyperkinetic extrapyramidal disorders. There was no correlation between D2 receptor binding and rCBF in the basal ganglia. The 99mTc-HMPAO studies did not provide clinically useful information, except in Huntington's chorea.