Cobalt-55 positron emission tomography in vascular dementia: significance of white matter changes

Non-invasive radionuclide imaging of trace metal trafficking in health and disease: "PET metallomics"

Several specific metallic elements must be present in the human body to maintain health and function. Maintaining the correct quantity (from trace to bulk) and location at the cell and tissue level is essential. The study of the biological role of metals has become known as metallomics. While quantities of metals in cells and tissues can be readily measured in biopsy and autopsy samples by destructive analytical techniques, their trafficking and its role in health and disease are poorly understood. Molecular imaging with radionuclides - positron emission tomography (PET) and single photon emission computed tomography (SPECT) - is emerging as a means to non-invasively study the acute trafficking of essential metals between organs, non-invasively and in real time, in health and disease. PET scanners are increasingly widely available in hospitals, and methods for producing radionuclides of some of the key essential metals are developing fast. This review summarises recent developments in radionuclide imaging technology that permit such investigations, describes the radiological and physicochemical properties of key radioisotopes of essential trace metals and useful analogues, and introduces current and potential future applications in preclinical and clinical investigations to study the biology of essential trace metals in health and disease.

Radiometals for imaging and theranostics, current production, and future perspectives

The aim of this review is to make the reader familiar with currently available radiometals, their production modes, capacities, and quality concerns related to their medical use, as well as new emerging radiometals and irradiation technologies from the perspective of their diagnostic and theranostic applications. Production methods of ¹⁷⁷ Lu serve as an example of various issues related to the production yield, specific activity, radionuclidic and chemical purity, and production economy. Other radiometals that are currently used or explored for potential medical applications, with particular focus on their theranostic value, are discussed. Using radiometals for diagnostic imaging and therapy is on the rise. The high demand for radiometals for medical use prompts investigations towards using alternative irradiation reactions, while using existing nuclear reactors and accelerator facilities. This review discusses these production capacities and what is necessary to cover the growing demand for theranostic nuclides.

Cyclotron Production of High-Specific Activity 55Co and In Vivo Evaluation of the Stability of 55Co Metal-Chelate-Peptide Complexes

This work describes the production of high-specific activity 55Co and the evaluation of the stability of 55Co-metal-chelate-peptide complexes in vivo. 55Co was produced via the 58Ni(p,α)55Co reaction and purified using anion exchange chromatography with an average recovery of 92% and an average specific activity of 1.96 GBq/μmol. 55Co-DO3A and 55Co-NO2A peptide complexes were radiolabeled at 3.7 MBq/μg and injected into HCT-116 tumor xenografted mice. Positron emission tomography (PET) and biodistribution studies were performed at 24 and 48 hours postinjection and compared to those of 55CoCl2. Both 55Co-metal-chelate complexes demonstrated good in vivo stability by reducing the radiotracers' uptake in the liver by sixfold at 24 hours with ~ 1% ID/g and at 48 hours with ~ 0.5% ID/g and reducing uptake in the heart by fourfold at 24 hours with ~ 0.7% ID/g and sevenfold at 48 hours with ~ 0.35% ID/g. These results support the use of 55Co as a promising new radiotracer for PET imaging of cancer and other diseases.

Topographic distribution of white matter changes and lacunar infarcts in neurodegenerative and vascular dementia syndromes: A post-mortem 7.0-tesla magnetic resonance imaging study

BACKGROUND

White matter changes and lacunar infarcts are regarded as linked to the same underlying small-vessel pathology. On magnetic resonance imaging, white matter changes are frequently observed, while the number of lacunar infarcts is probably underestimated. The present study post-mortem 7.0-tesla magnetic resonance imaging study compares the severity and the distribution of white matter changes and lacunar infarcts in different neurodegenerative and vascular dementia syndromes in order to determine their impact on the disease evolution.

PATIENTS AND METHODS

Eighty-four post-mortem brains consisting of 15 patients with pure Alzheimer's disease and 12 with associated cerebral amyloid angiopathy, 14 patients with frontotemporal lobar degeneration, 7 with Lewy body dementia, 10 with progressive supranuclear palsy, 14 with vascular dementia and 12 control brains were examined. Six hemispheric coronal sections of each brain underwent 7.0-tesla magnetic resonance imaging. Location and severity of white matter changes and lacunar infarcts were evaluated semi-quantitatively in each section separately.

RESULTS

White matter changes predominated in the prefrontal and frontal sections of frontotemporal lobar degeneration and in the post-central section of associated cerebral amyloid angiopathy brains, while overall increased in vascular dementia cases. Lacunar infarcts were more frequent in the vascular dementia brains and mainly increased in the centrum semiovale.

CONCLUSIONS

White matter changes have a different topographic distribution in neurodegenerative diseases and are most severe and extended in vascular dementia. Lacunar infarcts predominate in the deep white matter of vascular dementia compared to the neurodegenerative diseases. Vascular cognitive impairment is mainly linked to white matter changes due to chronic ischaemia as well as to lacunar infarcts due to small-vessel occlusion.

The incidence of post-mortem neurodegenerative and cerebrovascular pathology in mixed dementia

BACKGROUND

The clinical picture of dementia in most aged patients is due to a combination of different neurodegenerative processes and frequently associated to cerebrovascular lesions. They are called mixed dementia (MixD) cases, to be differentiated from those with pure vascular dementia (VaD) and those with Alzheimer's dementia (AD). The present study compares the frequency of different associated lesions in these disease groups.

MATERIALS AND METHODS

Out of a series of 252 autopsied patients 36 with MixD, 20 with VaD and 64 with AD disease were compared concerning the frequency of the associated lesions. Small cerebrovascular lesions were evaluated on a large coronal section of a cerebral hemisphere. Mean values of frequency and severity were compared between the 3 groups.

RESULTS

Of the 120 examined brains 30% were classified as MixD, 17% as VaD and 53% as AD. In 20% of the AD patients Lewy body pathology (LBP) was observed with a low incidence of cerebrovascular lesions, except for cerebral amyloid angiopathy (CAA). The MixD patients had more severe CAA and were significantly older than those with VaD and AD. Lacunar infarcts, on the other hand, were significantly more frequent in the VaD patients.

DISCUSSION

The most responsible vascular lesions in MixD and VaD are different. There is an inverse correlation between the presence of LBP and vascular pathology. MixD has to be considered as the end stage of AD.

Evaluation of nuclear reaction cross sections for optimization of production of the emerging diagnostic radionuclide ⁵⁵Co

The excitation functions of the (54)Fe(d,n)(55)Co, (56)Fe(p,2n)(55)Co and (58)Ni(p,α)(55)Co reactions were analyzed with relevance to the production of the β(+)-emitter (55)Co (T½=17.53 h), a promising cobalt radionuclide for PET imaging. The nuclear model codes ALICE-IPPE, EMPIRE and TALYS were used to check the consistency of the experimental data. The statistically fitted excitation function was employed to calculate the integral yield of the product. The amounts of the radioactive impurities (56)Co and (57)Co were assessed. A comparison of the three investigated production routes is given.

Traumatic brain injury induces elevation of Co in the human brain

Following acute brain injury (<3 hours post-event), cobalt levels in the brain are significantly elevated. This elevation may have important implications for positron emission tomography neuroimaging for assessing brain injury severity.

Calculation of excitation functions for the production of Cu and Co medical isotopes

Copper and cobalt radioisotopes have been used for both diagnostic and therapeutic purposes in the field of nuclear medicine. There is considerable interest in 60 ,61,64,67Cu and 55,57Co radioisotopes for some applications like PET, SPECT imaging and targeted radiotherapy of tumors. In present study, the production of 60,61,64,67Cu and 55,57Co via 64Zn(p,α)61Cu, 67Zn(p,α)64Cu, 70Zn(p,α)67Cu, 58Ni(p,α)55Co, 60Ni(p,α)57Co, 64Zn(p,nα)6°Cu and 68Zn(p,nα)64Cu reactions have been investigated in the range of 5–40 MeV proton incident energy. The new version of the code ALICE-2011 is used to determine the excitation functions of these nuclear reactions. The calculated excitation functions were compared with experimental results and semi-empirical cross section values of a previously developed model.

Dithiocarbamate complexes as radiopharmaceuticals for medical imaging

Over the past 30 years dithiocarbamate ligands have found application in radiopharmaceutical metal-ligand complexes to image a range of disease states. The vast majority of research and applications, and the widest range of complex structures, have involved radionuclides of technetium and rhenium. Considering the extent of coordination chemistry of dithiocarbamate ligands described elsewhere in this issue, the extent of radiopharmaceutical application with metallic radionuclides is surprisingly narrow. Here we summarise the types of radiopharmaceutical complexes studied and the uses, and potential uses, to which they have been put in nuclear medicine.

Brain Glucose Metabolism in Vascular White Matter Disease With Dementia

Background and Purpose— The boundary between vascular dementia and Alzheimer disease (AD) continues to be unclear. Some posit that gradually progressive vascular dementia, as with small vessel disease, is simply vascular disease plus AD. Because AD presents a characteristic pattern on fluorodeoxyglucose positron emission tomography, we sought to determine whether the fluorodeoxyglucose pattern of vascular dementia resembled more AD or the pattern in nondemented patients with severe microvascular brain disease.

Methods— Vascular disease patients were selected on the basis of confluent white matter lesions on both hemispheres. Among them, with a similar degree of vascular disease on MRI, neuropsychological testing separated groups with dementia and without dementia. Patients with AD and healthy controls were also studied. The 4 groups, with 12 subjects each, were matched by age, gender, and educational level. Fluorodeoxyglucose distribution was analyzed using both voxel-based and volume of interest methods.

Results— The AD group had the characteristic pattern of bilaterally decreased metabolism in parieto-temporal association cortex and precuneus. By contrast, patients with vascular disease and dementia had a similar anatomic pattern to that of the vascular patients without dementia, but with greater metabolic abnormalities, particularly in the frontal lobes and deep nuclei.

Conclusions— The anatomy of metabolic abnormalities in vascular disease with dementia suggests that, at least in some cases, dementia with vascular disease may be independent of AD. The metabolic abnormality involves the thalamus, caudate, and frontal lobe, a pattern concordant with the neuropsychological findings of impaired executive function characteristic of vascular dementia.

ARRONAX, a high-energy and high-intensity cyclotron for nuclear medicine

PURPOSE

This study was aimed at establishing a list of radionuclides of interest for nuclear medicine that can be produced in a high-intensity and high-energy cyclotron.

METHODS

We have considered both therapeutic and positron emission tomography radionuclides that can be produced using a high-energy and a high-intensity cyclotron such as ARRONAX, which will be operating in Nantes (France) by the end of 2008. Novel radionuclides or radionuclides of current limited availability have been selected according to the following criteria: emission of positrons, low-energy beta or alpha particles, stable or short half-life daughters, half-life between 3 h and 10 days or generator-produced, favourable dosimetry, production from stable isotopes with reasonable cross sections.

RESULTS

Three radionuclides appear well suited to targeted radionuclide therapy using beta ((67)Cu, (47)Sc) or alpha ((211)At) particles. Positron emitters allowing dosimetry studies prior to radionuclide therapy ((64)Cu, (124)I, (44)Sc), or that can be generator-produced ((82)Rb, (68)Ga) or providing the opportunity of a new imaging modality ((44)Sc) are considered to have a great interest at short term whereas (86)Y, (52)Fe, (55)Co, (76)Br or (89)Zr are considered to have a potential interest at middle term.

CONCLUSIONS

Several radionuclides not currently used in routine nuclear medicine or not available in sufficient amount for clinical research have been selected for future production. High-energy, high-intensity cyclotrons are necessary to produce some of the selected radionuclides and make possible future clinical developments in nuclear medicine. Associated with appropriate carriers, these radionuclides will respond to a maximum of unmet clinical needs.

55Cobalt complexes with pendant carbohydrates as potential PET imaging agents

Bis-ligand cobalt(II) complexes of four 3-hydroxy-4-pyridinone ligands with pendant carbohydrates were synthesized and examined for their potential as radiopharmaceuticals. Non-radioactive complexes were prepared on the macroscopic scale and characterized by elemental analysis, mass spectrometry, IR and UV/visible spectroscopy. Facile radiolabeling produced the 55Co complexes in high radiochemical yields (>95%). Identification of the radiolabeled compounds was accomplished by HPLC comparison with the corresponding non-radioactive complexes.

Computed tomographic changes in lacunar syndromes

BACKGROUND

Lacunes are small deep infarcts due to occlusion of long-perforating arterial branches. The clinical presentation and outcome are variable. The present study investigates the prognostic value of comparing repeated computed tomographic (CT) scans in patients with a lacunar syndrome (LACS).

PATIENTS AND METHODS

From a series of 220 patients, subsequently admitted with a first-ever stroke, 32 were diagnosed as LACS. CT scans without contrast enhancement were performed on day 3 and 10 after onset of the symptoms. A lacune was considered as responsible for the LACS when its location corresponded to the expected cerebral hemisphere and when it changed in size and/or in X-ray attenuation on the CT scans from day 3 to 10. The size of the lacune was also measured and compared on both time points. The patients were divided into two groups according to the modified Rankin (R) scale at 3 months, in those who were independent (R 0-1-2) and in those who remained handicapped (R 3-4-5).

RESULTS

The patients who remained disabled at 3 months were older and more severely impaired on admission, and had more frequent cardiac problems and cognitive decline than the independent ones. On CT scans of the brain a higher incidence of leukoaraiosis was observed in this group. Only in three patients of each group no relevant lacune could be observed both on day 3 and 10. The average size of the symptomatic lacune on day 3 and 10 was not statistically different between both groups, when comparing all patients with a LACS. When comparing only those patients with a visible symptomatic lacunar infarct on one of the CT scans, however, the average size of the symptomatic deep infarct was smaller in the independent than the handicapped patients on day 3 as well as on day 10. The lacune decreased in average size from day 3 to 10 in the former group but remained unchanged in the group of disabled patients.

CONCLUSION

The outcome of patients with a LACS depends on several factors including age, cognitive and cardiac status, the presence of leukoaraiosis and also the size of the symptomatic lacune.

Vascular cognitive impairment in patients with late-onset seizures after an ischemic stroke

BACKGROUND

Cognitive impairment and seizures are both common conditions in patients with cerebrovascular disease.

PURPOSE

The present study investigates whether the occurrence of late-onset seizures, following an ischemic stroke, contributes to vascular cognitive impairment.

PATIENTS AND METHODS

The mean Mini-Mental State Examination (MMSE) and the median modified Rankin (mR) scores were compared between 125 patients who developed late-onset seizures (66 with a single seizure and 59 with repeated seizures or epilepsy) following an ischemic stroke and 125 patients who did not during, at least, a 2-year follow-up.

RESULTS

There were no differences in age, gender, etiology and degree of neurological impairment on admission for their stroke between the groups with and without seizures. Although the mean MMSE score was similar between both groups the median mR score was significantly higher in the seizure patients. Comparing the patients with a single seizure to the non-seizure ones showed the same results. On the other hand, comparison of the patients with epilepsy to the non-seizure group revealed, in addition to the higher median mR score, a significantly lower mean MMSE score in the former group.

CONCLUSION

Repeated seizures following an ischemic stroke promote vascular cognitive impairment.

Arterial oxygen saturation, COPD, and cerebral small vessel disease

OBJECTIVE

To study whether lower arterial oxygen saturation (SaO(2)) and chronic obstructive pulmonary disease (COPD) are associated with cerebral white matter lesions and lacunar infarcts.

METHODS

We measured SaO(2) twice with a pulse oximeter, assessed the presence of COPD, and performed MRI in 1077 non-demented people from a general population (aged 60-90 years). We rated periventricular white matter lesions (on a scale of 0-9) and approximated a total subcortical white matter lesion volume (range 0-29.5 ml). All analyses were adjusted for age and sex and additionally for hypertension, diabetes, body mass index, pack years smoked, cholesterol, haemoglobin, myocardial infarction, and left ventricular hypertrophy.

RESULTS

Lower SaO(2) was independent of potential confounders associated with more severe periventricular white matter lesions (score increased by 0.12 per 1% decrease in SaO(2) (95% confidence interval 0.01 to 0.23)). Participants with COPD had more severe periventricular white matter lesions than those without (adjusted mean difference in score 0.70 (95% confidence interval 0.23 to 1.16)). Lower SaO(2) and COPD were not associated with subcortical white matter lesions or lacunar infarcts.

CONCLUSION

Lower SaO(2) and COPD are associated with more severe periventricular white matter lesions.

Cobalt-55 positron emission tomography in symptomatic atherosclerotic carotid artery disease: borderzone versus territorial infarcts

BACKGROUND

Borderzone as well as territorial infarcts can occur in severe atherosclerotic carotid artery disease. It remains controversial whether the borderzone distribution of infarcts is due to hypoperfusion or due to artery-to-artery embolism.

PURPOSE

The present study investigates whether cobalt-55 (55Co) positron emission tomography (PET) shows a different pattern of ischaemia according to the topography of the infarct in severe atherosclerotic carotid artery disease.

PATIENTS AND METHODS

Five patients with a cortical borderzone and seven with a territorial infarct, due to symptomatic carotid artery disease, were investigated with 55Co PET 3-6 months after stroke. Average 55Co counts in the infarct area, the adjacent cortical zone, the deep white matter and, contralateral cerebral cortex and white matter, were compared to the values in the cerebellum used as reference.

RESULTS

No differences in 55Co ratio were observed in the different regions of interest (ROIs) between patients with cortical borderzone and those with territorial infarcts. The 55Co uptake was similar or lower than the reference value for all ROIs in all individual patients.

CONCLUSION

In patients with borderzone as well as with territorial infarcts no evidence was found for subclinical ischaemic injury in or around the infarcts. These data do support the conclusion that cortical borderzone infarcts may not be due to ongoing chronic haemodynamic impairment, but by no means is this conclusive evidence.

Positron emission tomography and single-photon emission computed tomography brain imaging in the evaluation of dementia

The role of PET and SPECT brain imaging in the initial assessment and differential diagnosis of dementia is beginning to evolve rapidly. Numerous studies confirm the value of functional brain imaging, particularly with FDG-PET imaging, as a potentially cost-effective means of establishing an earlier diagnosis of Alzheimer's disease. Such an approach should allow for a more objective means of establishing which patients will benefit from treatment with cholinesterase inhibitors. In the future, neuroreceptor and plaque burden imaging studies should further enhance the sensitivity and specificity of dementia detection and patient management.