Modulating the experience of agency: a positron emission tomography study

This study investigated agency, the feeling of being causally involved in an action. This is the feeling that leads us to attribute an action to ourselves rather than to another person. We were interested in the effects of experimentally modulating this experience on brain areas known to be involved in action recognition and self-recognition. We used a device that allowed us to modify the subject's degree of control of the movements of a virtual hand presented on a screen. Four main conditions were used: (1) a condition where the subject had a full control of the movements of the virtual hand, (2) a condition where the movements of the virtual hand appeared rotated by 25 degrees with respect to the movements made by the subject, (3) a condition where the movements of the virtual hand appeared rotated by 50 degrees, and (4) a condition where the movements of the virtual hand were produced by another person and did not correspond to the subject's movements. The activity of two main brain areas appeared to be modulated by the degree of discrepancy between the movement executed and the movement seen on the screen. In the inferior part of the parietal lobe, specifically on the right side, the less the subject felt in control of the movements of the virtual hand, the higher the level of activation. A reverse covariation was observed in the insula. These results demonstrate that the level of activity of specific brain areas maps onto the experience of causing or controlling an action. The implication of these results for understanding pathological conditions is discussed.     

Combined positron emission tomography-computed tomography: the historical perspective

The 1990s witnessed the development of the first dual-modality imaging devices for clinical applications. A combined PET-CT prototype underwent clinical evaluation from mid-1998 onward. The results from the three-year evaluation program stimulated the demand for commercial designs and in 2001 the first commercial PET-CT scanner was installed in the clinic. The availability of designs from all the major vendors of medical imaging equipment was followed by a rapid adoption of the technology and today, over 2500 PET-CT scanners are in clinical operation world-wide. This article briefly summarizes the short history of PET-CT, and reviews the current status of the technology.     

From 3-D positron emission tomography to 3-D positron emission tomography/computed tomography: what did we learn?

The recent introduction of combined positron emission tomography (PET)/computed tomography (CT) scanners is having a far-reaching effect on the field of medical imaging by bringing functional imaging to the forefront in radiology, oncology and other specialties. The PET/CT scanner is an evolution in technology combining two well-developed imaging modalities: anatomical imaging with CT and functional imaging with PET. The first prototype PET/CT scanner was a consequence of a succession of steps that, in chronological order, included the development of the High Density Avalanche Chamber (HIDAC) PET camera, 3-D PET methodology and the rotating partial-ring tomograph (PRT). The successful completion of each step was a prerequisite to progress to the next phase, and the lessons learned could then be applied to subsequent initiatives. This review will map the milestones from 3-D PET to 3-D PET/CT and assess the role each step played in the development of PET instrumentation over the past two decades.     

The role of the basal forebrain in episodic memory retrieval: a positron emission tomography study

Human lesion data indicate that the basal forebrain or orbitofrontal cortex, or both, as well as medial temporal and diencephalic structures, is important for normal memory and that its disruption causes the pure amnesic syndrome, in which episodic memory is grossly impaired while other kinds of memory remain preserved. Among these critical areas, functional imaging studies have so far failed to detect activation of the basal forebrain, although activation in the nearby orbitofrontal cortex has been reported during episodic memory retrieval. We employed positron emission tomography to elucidate the neural basis of episodic memory recall utilizing two types of time cues and successfully detected activity in the basal forebrain for the first time. Specifically, recall of previously memorized words from temporal cues was associated with activity in the basal forebrain, right middle frontal gyrus, right superior temporal gyrus, and posterior cingulate gyrus, whereas their recall from person cues was associated with activity in the left insula, right middle frontal gyrus, and posterior cingulate gyrus. Furthermore, percentage increases of regional blood flow in the basal forebrain were correlated with behavioral data of successful recall. Our results provide clear evidence that the human basal forebrain has a specific role in episodic memory recall, especially that from time-contextual information.     

Clinical applications of positron emission tomography.

Positron emission tomography (PET) has been used extensively as a research tool in the investigation of human physiology and pathology for over a decade. By labelling suitable compounds (for example, glucose, amino acids, ammonia, DOPA or drugs) with positron emitting isotopes which are then administered in tracer amounts, the blood flow, metabolism and even the cell receptor or neurotransmitter distributions may be assessed in vivo. Advances in PET technology and experience now make PET a powerful clinical diagnostic tool, enabling investigation of disease at a molecular level, even in the absence of anatomical abnormalities apparent on computerised tomography (CT) or magnetic resonance imaging (MRI). Clinical PET is already utilised in the management of patients with epilepsy, cerebrovascular and cardiovascular disease, dementia and a wide variety of oncological applications. PET will become more widely available shortly in the UK, with the opening of centres such as the Guy's and St Thomas's Clinical PET Centre in 1992. It will therefore become increasingly important that clinicians are aware of those specific areas in which PET may be the investigation of choice to optimise patient diagnosis, treatment and/or follow-up. This review will endeavour to explain briefly the principles of the PET technique, and then outline those areas where PET has already had an impact on patient management in comparison with the more widely available diagnostic tests, finally outlining promising areas where PET may become more clinically useful in the future.     

The role of the dorsolateral prefrontal cortex in random number generation: a study with positron emission tomography

Random number generation (RNG) engages a number of executive processes. We used positron emission tomography (PET) to measure regional cerebral blood flow (rCBF) in six volunteers who performed RNG and a control counting (COUNT) task at six rates paced by a tone. This provided a systematic variation of difficulty of RNG. Relative to COUNT, RNG was associated with significant activation of the left dorsolateral prefrontal cortex (DLPFC), the anterior cingulate, the superior parietal cortex bilaterally, the right inferior frontal cortex, and the left and right cerebellar hemispheres. Faster rates of RNG were associated with a significant decrease in regional cerebral blood flow (rCBF) in the left and right DLPFC and the right superior parietal cortex. rCBF in the left DLPFC was significantly and negatively associated with count score 1, a measure of habitual counting during RNG. These results are discussed in relation to the network modulation model of RNG developed on the basis of our previous studies using transcranial magnetic stimulation and dual task paradigms. This suggests that during RNG, suppression of habitual counting is achieved through the modulatory (inhibitory) influence of the left DLPFC over a number associative network distributed in the superior temporal cortex. At faster rates of RNG the synchronization demands of paced RNG result in the breakdown of this modulatory influence, which is evident from decreased rCBF in the left DLPFC and increased habitual counting at faster rates.     

Hybrid method for the detection of pulmonary nodules using positron emission tomography/computed tomography: a preliminary study

Purpose

In this study, an automated scheme for detecting pulmonary nodules using a novel hybrid PET/CT approach is proposed, which is designed to detect pulmonary nodules by combining data from both sets of images.

Methods

Solitary nodules were detected on CT by a cylindrical filter that we developed previously, and in the PET imaging, high-uptake regions were detected automatically using thresholding based on standardized uptake values along with false-positive reduction by means of the anatomical information obtained from the CT images. Initial candidate nodules were identified by combining the results. False positives among the initial candidates were eliminated by a rule-based classifier and three support vector machines on the basis of the characteristic features obtained from CT and PET images.

Results

We validated the proposed method using 100 cases of PET/CT images that were obtained during a cancer-screening program. The detection performance was assessed by free-response receiver operating characteristic (FROC) analysis. The sensitivity was 83.0 % with the number of false positives/case at 5.0, and it was 8 % higher than the sensitivity of independent detection systems using CT or PET images alone.

Conclusion

   Detection performance indicates that our method may be of practical use for the identification of pulmonary nodules in PET/CT images.     

Is positron emission tomography a useful tool for studying migraine?

Despite the high prevalence of migraine in the population, the pathophysiology of this condition remains poorly understood. Vascular changes have been postulated. With positron emission tomography and various radiotracers, it is possible to have a non-invasive access to a number of parameters of interest in migraine research. These are presented and discussed in this article. PET has great potential for answering some basic questions concerning the physiological or biochemical changes that can occur during and between migraine attacks. Few studies have been published, however, probably because of (i) limitations inherent to the technique and (ii) problems in study design.     

Diagnostic accuracy of myocardial perfusion imaging with single photon emission computed tomography and positron emission tomography: a comparison with coronary angiography

Objective The aim of this study was to compare the diagnostic accuracy of myocardial perfusion imaging (MPI) by positron emission tomography (PET) with the diagnostic accuracy of MPI by single photon emission computed tomography (SPECT) in two comparable patient cohorts, using coronary angiography (CA) as the standard of reference. Methods A “SPECT-group” of 80 patients (15 female, 65 male; mean age 60 ± 9 years) and a “PET-group” of 70 patients (14 female, 56 male; mean age 57 ± 10 years) underwent a one day stress/rest examination either with attenuation-corrected ¹³N-ammonia PET or attenuation-corrected ²⁰¹TlCl SPECT or ^99mTc-hexakis-methoxy-isobutyl-isonitril (MIBI) SPECT. PET and SPECT results were semiquantitatively graded using a 6-segment heart model. All patients underwent CA, and stenoses were graded as a diameter reduction ≥50%. Results Coronary findings between both groups did not significantly differ at CA. For the SPECT-group overall sensitivity and specificity for localisation of stenoses was 77% and 84%. Respective values for the PET-group were 97% and 84%. The specificity of MPI by SPECT in the detection of ischemia was 74% and 91% for MPI by PET. The diagnostic accuracy of MPI improves when the individual coronary dominance and previous coronary revascularisations are taken into account. Conclusion MPI by ¹³N-ammonia PET is more sensitive in the detection and localisation of coronary stenoses, and more specific in the detection of ischemia than MPI by ²⁰¹TlCl/^99mMIBI SPECT.     

The effects of prior pain experience on neural correlates of empathy for pain: An fMRI study

Neuroimaging studies have revealed partially shared neural substrates for both the actual experience of pain and empathy elicited by the pain of others. We examined whether prior pain exposure increased neural activity in the anterior midcingulate cortex (aMCC) and bilateral anterior insula (AI) as a correlate of empathy for pain. Participants (N = 64: 32 women, 32 men) viewed pictures displaying exposure to pressure pain (pain pictures) and pictures without any cue of pain (neutral pictures). Prior to the experiment, half of the participants were exposed to the same pain stimulus as the one seen in the pain pictures (pain exposure condition); the other half had no such experience (touch exposure condition). A balanced sex ratio was kept, to investigate possible sex differences. In the region-of-interest analyses, participants of the pain exposure condition showed decreased activity in the right AI and the aMCC relative to participants of the touch exposure condition. While in men, no differences were found in relation to their exposure condition, women with pain exposure showed decreased activity in the aMCC and additionally, in bilateral AI. Based on the entire sample, whole brain analyses revealed stronger activation in the retrosplenial cortex, dorsomedial prefrontal cortex, and medial prefrontal cortex in the pain exposure condition. In conclusion, prior pain exposure did not increase, but decreased activity in regions regularly associated with empathy for pain. However, pain experience increased activity in regions associated with memory retrieval, perspective taking, and top-down emotion regulation, which might facilitate empathizing with others.     

正电子发射型断层成像在胃恶性肿瘤诊断中的作用

目的:评价正电子发射型断层扫描(PET)技术在胃恶性肿瘤中的诊断价值并与CT对照。方法:32例可疑胃恶性肿瘤患者术前行PET全身显像,22例行CT检查,将以上结果和病理分期对照。结果:32例中,25例为恶性肿瘤,7例为良性病变。18F-FDG-PET半定量分析对原发病灶的诊断敏感性、特异性分别为84%、5/7。CT对胃恶性肿瘤原发病灶诊断敏感性、特异性分别为88.9%和4/5。PET、CT对恶性肿瘤转移淋巴结检测准确率分别为80%和76.5%。PET、CT对远处转移病灶的诊断准确率分别为7/8和2/7。结论:PET对胃恶性肿瘤局部病灶和远处转移病灶检测较为敏感,在临床诊断有较高的应用价值。     

Fluorine-18 fluorodeoxyglucose positron emission tomography in the management of solitary pulmonary nodule: a review

Solitary pulmonary nodules are common radiologic findings and their detection has increased due to the introduction and improvement of diagnostics. Since a nodule can be an expression of early lung cancers, a proper classification and management are required because its treatment might lead to decreased morbidity and mortality. In this regard, prominent guidelines are available although they are characterized sometimes by discordant and misleading evidences. Furthermore, the same results of studies in the literature appear conflicting. Aim of this work is to evaluate the role of imaging through an extensive literature review but focusing on 18-fluorine fluorodeoxyglucose positron emission tomography combined with computed tomography (¹⁸F-FDG-PET/CT) in order to assess the limits and future perspectives of solitary pulmonary nodule characterization in early detection of lung cancer.

• Key messages

• Detection of solitary pulmonary nodules has increased.

• Management of solitary pulmonary nodules is still debated.

• Future perspectives of early solitary pulmonary nodule characterization.

     

Distribution of intranasal C-zolmitriptan assessed by positron emission tomography

Nine healthy volunteers aged 18-28 years were recruited into this open, single-centre, two-phase trial. In phase 1, two volunteers received a single dose of 11C-zolmitriptan 2.5 mg administered as a nasal spray and then underwent positron emission tomography (PET) scanning to determine the most appropriate times for scanning in phase 2. In phase 2, six volunteers received two doses and an additional volunteer one dose of 11C-zolmitriptan 2.5 mg intranasally. Volunteers underwent PET scanning over sectors covering one of the nasopharynx, lungs or abdomen, for up to 1.5 h postdose. The brain was also scanned and plasma zolmitriptan levels were measured. Almost 100% of the administered dose was detected in the nasopharynx immediately after dosing. This declined thereafter to about 50% at 20 min and to 35% at 80 min after dosing. Radioactivity appeared slowly in the upper abdomen, with 25% of given radioactivity detected at 20 min and persisting until 80 min after dosing. Minimal radioactivity was detected in the lungs. Radioactivity was detectable within brain tissue suggesting central penetration of zolmitriptan. Zolmitriptan in plasma had approached its maximum concentration by 15 min postdose. The data indicate initial absorption across the nasal mucosa contributing to an early systemic availability. 11C-Zolmitriptan administered intranasally was well tolerated.     

Positron emission tomography versus positron emission tomography/computed tomography: from "unclear" to "new-clear" medicine.

PET/CT is a new diagnostic imaging modality, which proves that adding PET and CT is not merely additive, but highly synergistic. While PET provides high sensitivity for lesion detection, CT provides the anatomic backdrop, which frequently is important in order to make a specific diagnosis. CT can, however, also add sensitivity to PET, as certain lesions such as small clearly pathological lung nodules may not at all be visualized on PET alone; and PET clearly adds specificity to CT because, e.g., indeterminate lymph nodes seen on CT can often be diagnosed unequivocally as benign or malignant, using PET information. Furthermore, attenuation correction of PET data, which is needed for best PET image quality, can also be obtained using the same CT data. Hence, PET/CT also provides a very fast solution for obtaining attenuation images. The major clinical applications of PET/CT are in tumor imaging of the body and the search for inflammatory foci, while for brain imaging, PET/CT is less relevant. In the brain, post acquisition fusion of PET and MRI data is relatively easy, while post acquisition fusion of PET and CT or MR data in the body is unreliable and cumbersome. We strongly feel that PET/CT is the oncological staging "one-stop-shop" examination of the future for many tumors. The key question in the next few years will be how much CT is needed in PET/CT for which clinical question? The advent of ever faster CT scanners suggests that PET/CT eventually may also provide a tool for a cardiac "one-stop-shop." So the future of PET/CT indeed looks bright.     

正电子发射断层扫描仪相互作用深度效应的校正方法

相互作用深度效应是影响PET成像质量的重要因素。本文主要针对这一效应的各种校正方法进行综述,包括硬件设计和软件校正,比较各种方法的优缺点,并对其发展方向进行展望。