Daniela Schmidt

Impact of 131I SPECT/Spiral CT on Nodal Staging of Differentiated Thyroid Carcinoma at the First Radioablation

The purpose of this study was to determine the diagnostic value of 131I SPECT/spiral CT (SPECT/CT) on nodal staging of patients with thyroid carcinoma at the first ablative radioiodine therapy. Methods: Fifty-seven patients were studied using SPECT/CT 3–4 d after receiving 3.96 ± 0.5 GBq of 131I for radioablation of thyroid remnants after a thyroidectomy for differentiated thyroid carcinoma. In addition to planar whole-body scintigraphy, SPECT/CT of the neck was performed using a hybrid camera combining a double-head SPECT camera with either a 2-slice (n = 23) or a 6-slice (n = 34) spiral CT scanner. The planar scans and the SPECT/CT images were evaluated for cervical tracer uptake independently of each other and of the clinical findings. Results: SPECT/CT led to a revision of the original diagnosis in 28 of 143 cervical foci of radioiodine uptake seen on planar imaging. In particular, SPECT/CT reclassified as benign 6 of 11 lesions considered to be lymph node metastases and 11 of 15 lesions considered to be indeterminate. Furthermore, SPECT/CT allowed the identification of 11 lymph node metastases classified as thyroid remnant or as indeterminate on planar imaging. Based on this revision, SPECT/CT yielded a gain in information on nodal stage in 20 of the 57 patients studied (35%, P < 0.03). SPECT/CT altered nodal stage from N0 to N1 in 2 of 20 patients and from indeterminate (Nx) to N1 in 6 of 30 patients. The result was a change in risk stratification conforming to the classification proposed by the International Union Against Cancer in 14 patients (25%). Conclusion: SPECT/CT determines lymph node involvement at radioablation performed for thyroid cancer more accurately than does planar imaging. SPECT/CT may alter management in roughly one quarter of patients with thyroid carcinoma by upstaging or downstaging their disease.

Topographic segregation and convergence of verbal, object, shape and spatial working memory in humans

This functional magnetic resonance imaging study investigates commonalties and differences in working memory (WM) processes employing different types of stimuli. We specifically sought to characterize topographic convergence and segregation with respect to prefrontal cortex involvement using verbal, spatial, real object and shape memory items in a two-back WM task. Both the dorsolateral and ventrolateral prefrontal cortices are conjointly activated across all stimulus types. No stimulus-specific differences in the activation patterns of the prefrontal cortex could be demonstrated giving support to the view of an amodal prefrontal involvement during WM processes. However, extra-frontal regions specialized on feature processing and involved in the preprocessing of the stimuli were selectively activated by these different subtypes of WM. These selectively activated regions are assigned to parts of the ventral and dorsal stream.

Implication of 2-18fluor-2-deoxyglucose positron emission tomography in the follow-up of Hürthle cell thyroid cancer.

The aim of this retrospective study was to investigate the value of positron emission tomography (PET) with 2-18fluor-2-deoxy-glucose (FDG) in the follow-up of Hürthle cell thyroid cancer (HTC), a rare variant of thyroid malignancies. FDG-PET studies were performed in 17 patients with HTC. In subgroup A (n = 13) PET was initiated because of an elevated thyroglobulin (Tg) level whereas in subgroup B (n = 4) the study was performed to evaluate suspect findings of morphologic imaging while Tg remained undetectable. Pathologically increased FDG uptake was found in all patients of subgroup A. In 10 studies, PET results were proven as true-positive either by surgery or by morphologic imaging. One study was false-positive. Final evaluation was not possible in two cases. In subgroup B, PET was true-negative in three and false-positive in one patient. For the detection of recurrent HTC by means of FDG-PET a meta-analysis including data of a multicenter study revealed an overall sensitivity of 92%, a specificity of 80%, a positive predictive value of 92%, and a negative predictive value of 80% while the accuracy was 89%. This study supports the efficiency of FDG-PET in the follow-up of HTC.

Network analysis in episodic encoding and retrieval of word-pair associates: a PET study.

The involvement of distributed brain regions in declarative memory has been hypothesized based on studies with verbal memory tasks. To characterize episodic declarative memory function further, 14 right‐handed volunteers performed a visual verbal learning task using paired word associates. The volunteers underwent positron emission tomography. 15O‐butanol was used as a tracer of regional cerebral blood flow (rCBF). Inter‐regional functional interactions were assessed based on within‐task, across‐subject inter‐regional rCBF correlations. Anatomical connections between brain areas were based on known anatomy. Structural equation modelling was used to calculate the path coefficients representing the magnitudes of the functional influences of each area on the ones to which it is connected by anatomical pathways. The encoding and the retrieval network elicit similarities in a general manner but also differences. Strong functional linkages involving visual integration areas, parahippocampal regions, left precuneus and cingulate gyrus were found in both encoding and retrieval; the functional linkages between posterior regions and prefrontal regions were more closely linked during encoding, whereas functional linkages between the left parahippocampal region and posterior cingulate as well as extrastriate areas and posterior cingulate gyrus were stronger during retrieval. In conclusion, these findings support the idea of a global bihemispheric, asymmetric encoding/retrieval network subserving episodic declarative memory. Our results further underline the role of the precuneus in episodic memory, not only during retrieval but also during encoding.

The translating brain: cerebral activation patterns during simultaneous interpreting

Brain activation was measured in professional interpreters during simultaneous interpreting (SI) vs. repetition (shadowing) of auditorily presented text by positron emission tomography (PET). SI into the native language (Finnish) elicited left frontal activation increases. SI into the non-native language (English) elicited much more extensive left-sided fronto-temporal activation increases. Our results indicate that SI activates predominantly left-hemispheric structures (particularly the left dorsolateral frontal cortex) previously related to lexical search, semantic processing and verbal working memory. Brain activation patterns were clearly modulated by direction of translation, with more extensive activation during translation into the non-native language which is often considered to a be more demanding task.

Encoding and retrieval in declarative learning : a positron emission tomography study

We present neuroanatomical correlates of encoding and retrieval in an episodic memory task using visually presented highly imaginable word-pair associates. A total of 13 right-handed normal male volunteers took part in the study. Each subject underwent six (15)O-butanol PET scans. On each of the six trials the memory task began 30 s before the injection of a bolus of (15)O-butanol. The subjects had to learn and retrieve 12 word pairs (highly imaginable words, not semantically related, hard associations). The presentation of nonsense words served as a reference condition. Recall accuracy after 2-4 presentations was 66.1%+/-21.1 correct during the PET measurement so that scanning during the retrieval of word pair associates was appropriate to capture the brain activity associated with retrieval. The results obtained support the hypothesis of the presence of an asymmetric network consisting of distributed brain structures subserving associative memory. We show left dorsolateral prefrontal activation during the encoding of visually presented word pair associates, whereas retrieval led to bilateral frontal activation. Furthermore, the importance of the precuneus in the retrieval of highly imaginable word-pair associates using visual imagery as a mnemonic strategy is demonstrated.

Neuronal correlates of encoding and retrieval in episodic memory during a paired-word association learning task: a functional magnetic resonance imaging study.

Abstract The investigation of memory function using functional magnetic resonance imaging (fMRI) is an expanding field of research. The aim of this study was to demonstrate brain-activity patterns related to a word-pair association task employing a whole-brain EPI sequence. Six right-handed, healthy male volunteers (mean age: 27.5 years) took part in the study. fMRI was performed at a field strength of 1.5 Tesla with 26–32 slices parallel to the AC-PC line, depending on individual brain size. Distributed brain regions were activated in episodic encoding and retrieval with similarities, but also (distinct) differences in activation patterns. Bilateral prefrontal cortical areas were involved when comparing encoding as well as retrieval to the reference condition (nonsense words). Furthermore, activation was observed in cerebellar areas during encoding, and activation in bilateral parietal areas (precuneus and inferior parietal cortex) was differentially more pronounced during retrieval. The activation of left dorsomedial thalamus during retrieval of high imagery-content word-pair associates may point to the role of this structure in episodic retrieval. The direct cognitive subtraction of encoding minus retrieval yielded a differentially larger left prefrontal activation. There was a differentially higher right prefrontal activation during retrieval than during encoding, underlining the proposed right/left asymmetry for episodic memory processes.

Brain systems engaged in encoding and retrieval of word-pair associates independent of their imagery content or presentation modalities

In this study, we aimed to characterize commonalities and differences of activation patterns during verbal episodic memory processes across different presentation modalities (visual or auditory) and different imagery content (low or high) of the presented verbal memory items. Twelve right-handed normal male volunteers took part in the study. Each subject underwent six O-15-butanol positron emission tomography scans. In six of the subjects the verbal material was presented visually, and in six subjects auditorily. The subjects had to encode and retrieve two sets of 12 word-pair associates of high (set 1) or low (set 2) imagery content (not semantically related). The presentation of nonsense words served as reference condition. Images were analyzed with statistical parametric mapping. Conjunction analysis was used to identify commonalities, and cognitive subtraction analysis was used to identify differences. The use of conjunction analyses enabled us to identify commonly activated regions involved in episodic encoding and retrieval of verbal material irrespective of the presentation modality or the imagery content. Our results add further evidence to recent findings that bilateral prefrontal activations are important for episodic retrieval and thus the role of the left prefrontal cortex has been underestimated during episodic retrieval. Furthermore, our results support the idea of functionally segregated areas in the prefrontal cortex. Finally, our results provide strong evidence that mesial parietal cortex (precuneus) involvement is not restricted to processes involving imagery.

Lexical decision of nonwords and pseudowords in humans: a positron emission tomography study

In this functional positron emission tomography study brain activations during an auditory lexical decision task with two experimental conditions were investigated. First, the subjects had to discriminate between real words and nonwords; second, real words varied with pseudowords. Comparing each of these tasks to an auditory control condition we found bilateral activation of the superior temporal and inferior frontal gyrus, lateralized to the left in the pseudoword condition. The comparison of the lexical decision tasks revealed higher rCBF during the pseudo-/real word decisions within BA 47, adjacent to Brocas area, and the anterior cingulate. The data support the notion that the lexical decision during a nonword task is mainly based on a phonological discrimination process, whereas a pseudoword task more strongly requires lexical access resulting in activation of BA 47.

3-[123I]Iodo-α-methyl-L-tyrosine uptake in cerebral gliomas: relationship to histological grading and prognosis

Abstract. 3-[123I]Iodo-α-methyl-L-tyrosine (IMT) is employed clinically as a tracer of amino acid transport in brain tumours using single-photon emission tomography (SPET). This study investigates the role of IMT SPET in the non-invasive histological grading and prognostic evaluation of cerebral gliomas. The files of patients investigated by IMT SPET in our clinic between 1988 and 1996 were evaluated retrospectively. Complete follow-up was available for 58 patients with cerebral gliomas investigated by IMT SPET shortly after tumour diagnosis. Seventeen patients had low-grade gliomas (WHO grade II), 14 had anaplastic gliomas (WHO grade III) and 27 had glioblastomas (WHO grade IV). Thirty-six cases were primary tumours and 22 cases, recurrences. Maximal and mean tumour-to-brain (T/B) ratios of IMT uptake at the first IMT SPET investigation were related to histological grading and survival time. Patients with low-grade gliomas showed significantly longer survival than patients with high-grade (grade III or IV) tumours. Gliomas without contrast enhancement on computed tomography or magnetic resonance imaging scans were associated with longer patient survival than tumours with contrast enhancement. The T/B ratios of IMT SPET showed no differences in relation to histological grading [WHO grade II: 1.73±0.59; WHO grade III: 1.74±0.38; WHO grade IV: 1.59±0.35, (mean±SD, T/B ratios of mean tumour uptake)]. The median survival time of patients with a high T/B ratio on IMT SPET was not significantly different from that of patients with a low T/B ratio (T/B ratio <1.6, 14.8 months; T/B ratio ≥1.6, 13.0 months). Thus, no evidence could be found for a relationship between IMT uptake in cerebral gliomas and either histological grading or survival time. Nevertheless, IMT SPET constitutes a useful method for the detection of primary and recurrent gliomas, determination of tumour extent and individual follow-up.