Orbital “blow-in” fracture: MRI

A case of traumatic orbital encephalocele following a blow-in fracture is presented. Computed tomography (CT) and magnetic resonance imaging (MRI) findings are shown. Although CT was useful for identifying the orbital roof fracture, bone fragments and soft tissue abnormalities, MRI was more sensitive to brain herniation and an intraorbital haematoma.     

In vitro and in vivo characterisation of nor-β-CIT: a potential radioligand for visualisation of the serotonin transporter in the brain

Radiolabelled 2-Cabomethoxy-3-(4-iodophenyl)tropane (-CIT) has been used in clinical studies for the imaging of dopamine and serotonin transporters with single-photon emission tomography (SPET). 2-Carbomethoxy-3-(4-iodophenyl)nortropane (nor--CIT) is a des-methyl analogue of -CIT, which in vitro has tenfold higher affinity (IC₅₀=0.36 nM) to the serotonin transporter than -CIT (IC₅₀=4.2 nM). Nor--CIT may thus be a useful radioligand for imaging of the serotonin transporter. In the present study iodine-125 and carbon-11 labelled nor--CIT were prepared for in vitro autoradiographic studies on post-mortem human brain cryosections and for in vivo positron emission tomography (PET) studies in Cynomolgus monkeys. Whole hemisphere autoradiography with [¹²⁵I]nor--CIT demonstrated high binding in the striatum, the thalamus and cortical regions of the human brain. Addition of a high concentration (1 M) of citalopram inhibited binding in the thalamus and the neocortex, but not in the striatum. In PET studies with [¹¹C]nor--CIT there was rapid uptake of radioactivity in the monkey brain (6% of injected dose at 15 min) and high accumulation of radioactivity in the striatum, thalamus and neocortex. Thalamus to cerebellum and cortex to cerebellum ratios were 2.5 and 1.8 at 60 min, respectively. The ratios obtained with [¹¹C]nor--CIT were 20%–40% higher than those previously obtained with [¹¹C]-CIT. Radioactivity in the thalamus and the neocortex but not in the striatum was displaceable with citalopram (5 mg/kg). In conclusion, nor--CIT binds to the serotonin transporter in the primate brain in vitro and in vivo and has potential for PET and SPET imaging of the serotonin transporter in human brain.     

γ-Glutamyltransferase test as a new tool for identification of seminal stains

Summary A simple qualitative method for identification of seminal stains based on a high activity of -glutamyltransferase (-GTP) in human semen is described. It employs the release of -naphthylamine from N--glutamyl--naphthylamide by the -GTP action; -naphthylamine couples with Fast Garnet GBC salt to produce a strong brownish-red color. The data on its simplicity, specificity, and stability show that the present method is suitable for medicolegal examination of seminal stains as a preliminary test.     

Characterization of IMPY as a potential imaging agent for β-amyloid plaques in double transgenic PSAPP mice

Deposition of -amyloid (A) plaques in the brain is likely linked to the pathogenesis of Alzheimers disease (AD). Developing specific A aggregate-binding ligands as in vivo imaging agents may be useful for diagnosis and monitoring the progression of AD. We have prepared a thioflavin derivative, 6-iodo-2-(4-dimethylamino-)phenyl-imidazo[1,2-a]pyridine, IMPY, which is readily radiolabeled with ¹²⁵I/¹²³I for binding or single-photon emission computerized tomography (SPECT) imaging studies. Characterization of [¹²⁵I]IMPY binding to plaque-like structures was evaluated in double transgenic PSAPP mice. [¹²⁵I]IMPY labeled A plaques in transgenic mouse brain sections, and the labeling was consistent with fluorescent staining and A-specific antibody labeling. Significant amounts of A plaques present in the cortical, hippocampal, and entorhinal regions of the transgenic mouse brain were clearly detected with [¹²⁵I]IMPY via ex vivo autoradiography. In contrast, [¹²⁵I]IMPY showed little labeling in the age-matched control mouse brain. Tissue homogenate binding further corroborated the A plaque-specific distribution in various brain regions of transgenic mouse, and correlated well with the known density of A deposition. Using a tissue dissection technique, [¹²⁵I]IMPY showed a moderate increase in the cortical region of transgenic mice as compared to the age-matched controls. In vitro blocking of [¹²⁵I]IMPY by carrier observed via autoradiography in mouse brain sections was not replicated by an in vivo blocking experiment in living TT mouse brain. The failure was most likely due to a significant carrier effect, which slows down the tracer in vivo metabolism, leading to an increased brain uptake. Taken together, these data indicate that [¹²³I]IMPY is a potentially useful SPECT imaging agent for in vivo labeling of A plaques in the living brain.     

Comparison of iodine-123 labelled 2β-carbomethoxy-3β-(4-iodophenyl)tropane and 2β-carbomethoxy-3β-(4-iodophenyl)-N-(3-fluoropropyl)nortropane for imaging of the dopamine transporter in the living human brain

Several cocaine congeners are of potential for imaging the dopamine transporter (DAT). Previous studies have shown that iodine-123 labelled 2-carbomethoxy-3-(4-iodophenyl)tropane ([¹²³I]-CIT) is a promising radiotracer for imaging the serotonin (5-HT) and dopamine (DA) transporters in the living human brain with single-photon emission tomography (SPET). [¹²³I]-CIT was found to be not very practical for 1-day DAT imaging protocols since peak DAT uptake occurs later than 8 h. Here we report a pilot comparison of [¹²³I]-CIT and 2-carbomethoxy-3-(4-iodophenyl)-N-(3-fluoropropyl)nortropane ([¹²³I]-CIT FP), using SPET imaging in four healthy male subjects. Peak uptake of [¹²³I]-CIT-FP into the basal ganglia occurred earlier (3–4 h after injection of tracer) than that of [¹²³I]-CIT (>8 h). However, the specific DAT binding of [¹²³I]-CIT-FP in the basal ganglia was somewhat less (0.813±0.047) than that of [¹²³I]-CIT (0.922±0.004). Imaging quality is excellent with both tracers and they are potentially of value for brain imaging in various neuropsychiatric disorders.     

“Menigeal sign”: a characteristic finding of meningiomas on contrast-enhanced MR images

Summary In meningiomas, a flat, contrast-enhancing, probably dural structure adjacent to the tumor can occasionally be observed on Gadolinium-DTPA enhanced MR images. This so called meningeal sign was evaluated with respect to the differential diagnosis of meningiomas in MR imaging. The study included 29 patients with intracranial meningiomas and 24 patients with non-meningeal brain tumors. In all meningiomas, MR studies included T2-weighted as well as unenhanced and Gadolinium-DTPA-enhanced T1-weighted images. In all nonmeningeal tumors, Gd-DTPA-enhanced MR images were available. All images were evaluated with respect to the presence of the meningeal sign. In meningiomas, a meningeal sign was seen in 15/29 cases on Gadolinium-DTPA-enhanced images. No abnormalities corresponding to the areas of contrast enhancement were found on unenhanced T2- and T1-weighted MR images. In nonmeningeal tumors only 2/24 cases showed a meningeal sign. In conclusion, with a sensitivity of 52% and a specificity of 92%, the demonstration of the meningeal sign improved the differential diagnosis of intracranial meningiomas in contrast-enhanced MR imaging.     

Die besonderen konstruktionsmerkmale des japanischen „Tan-to“-(Messers) als Kriterien für dessen Gefährlichkeit

Zusammenfassung Es wird auf die besondere Klingenform japanischer Blankwaffen und auf die Neuentwicklung eines Verwandlungs-Tan-to verwiesen. Bei letzterem läßt sich die Klinge in der Handgriffmitte um 90° drehen und arretieren, eine ideale Fixierung dieses Messers durch Faustschluß am Quergriff. Durch diese Bedingungen ist eine hohe Verletzungsgefährdung mit tödlichem Ausgang gegeben. Diese seit kurzer Zeit im Handel erhältlichen Messer sollten nach § 37 Waff G umgehend als verbotene Gegenstände definiert werden.     

Population data of the HLA DQα locus in Dutch caucasians

Summary The HLA DQa amplification and typing kit has been designed to be used by the forensic community for purposes of identity testing. The introduction of any new DNA marker in forensic identity testing requires the establishment of a population database for the relevant population(s) [1]. To this end allele and genotype frequencies for the HLADQ locus were determined in a Dutch Caucasian population sample and compared with 7 other population genetic studies. In our population sample the HLA DQ genotype frequencies did not deviate from Hardy-Weinberg expectations and for this locus the power of discrimination is 0.94. A test for homogeneity of the HLA DQ population data based on the allele frequency counts for 8 Caucasian population samples was performed and significant differences were found (P = 0.007) . The differences in the frequency of the HLADQ 2 and 3 alleles are the major cause of this deviation. No deviation from population homogeneity was observed when we compared thegenotype frequency distributions among the 8 Caucasian population samples. Combined with the extensive validation studies from Comey and Budowle [7] and Helmuth et al. [8] this population genetic study will allow HLADQ typing to be used in forensic identity testing in the Netherlands.     

Interleukin-1α (IL-1α) and N-formyl-methionyl-leucyl-phenylalanine (FMLP) as potential inducers of supravital chemotaxis

The phenomenon of artificially induced local leucocyte reactions during the supravital period could be of practical importance, but has not yet been comprehensively investigated. For a more detailed evaluation, experiments with the chemotactic agents interleukin-1 (IL-1) and N-formyl-methionyl-leucyl-phenylalanine (FMLP) were performed by subcutaneous injection into various anatomical regions (back, abdomen, limbs) of NMRI-mice (National Medical Research Institute) and pigs 0–5 min after circulatory arrest. Phosphate buffered saline (PBS) without effective components was administered to equivalent areas of the animals as a control. Tissue specimens were collected at 6 h postmortem (mice) and 12–14 h postmortem (pigs), cut into serial sections, stained with H & E and examined under the microscope. A leucocyte reaction did not develop in pigs (n = 10, 30 tissue samples) following injection of FMLP, however, dermal, subcutaneous and perivascular infiltration of leucocytes (in particular mononuclear cells and a few granulocytes) was found in 3 out of 30 tissue specimens in murine experiments. In addition intravascular cell accumulations were detected in 2 out of 30 samples. The injection of IL-l to mice gave similar results, i.e. aggregations of leucocytes and intravascular cell accumulations in 4 out of 30 and 3 out of 30 tissue samples, respectively. In negative controls no leucocyte reaction was detectable. This shows that potent chemotactic factors such as IL-1 and FMLP administered in the early supravital period can induce moderate local leucocyte reactions in animal models in at least some cases. A clear morphological differentiation between vital and supravital chemotaxis does not seem to be possible. The supravitally stimulated accumulations of leucocytes are interpreted as an aggregation of resident macrophages in combination with a slight migration of blood leucocytes. Presumably, these alterations are restricted to the very early supravital period as long as sufficient energy reserves are available. It must be stated that the observed changes are reactions, not spontaneous actions, so that the general validity of the phenomenon of leucocyte infiltration as a vital parameter is not affected.     

Detection of ileocecal Crohn’s disease using ultrasound as the primary imaging modality

At our hospital ultrasound (US) is used as an initial screening procedure in all patients with abdominal symptoms. The purpose of this study was to assess the effect of this policy on the detection of ileocecal Crohns disease. We retrospectively studied all patients with a new diagnosis of ileocecal Crohns disease from our institute over the period 1990–2001. The final diagnosis was based on clinical follow-up and pathological, surgical, US, and other radiological findings. We noted who referred the patient to the radiology department, what the initial clinical presumption was, and what the first imaging study was. US diagnoses were determined from the initial US report and US findings were registered from the images. There were a total of 47 patients (20 men, 27 women) with a mean age of 30 years and a median age of 27 years (range 14–75 years). In all patients the initial imaging study was an abdominal US. Using US, a confident diagnosis of ileocecal Crohns disease was made in 35 of the 47 patients, Crohns disease was suggested among the differential diagnosis in 10, and an incorrect diagnosis was made in 2 patients. In 28 of 47 patients, the referring physician did not consider Crohns disease when requesting the initial US examination. In eight patients with appendicitis-like symptoms, the US findings strongly influenced the decision to refrain from operation at that point in time. US, when used as a low-threshold diagnostic procedure, is a reliable and noninvasive means for making an early diagnosis of ileocecal Crohns disease in patients who present with atypical symptoms. It may prevent both unnecessary therapeutic delay as well as unnecessary surgery.     

Dopamine transporter SPECT using fast kinetic ligands: <Superscript>123</Superscript>I-FP-β-CIT versus <Superscript>99m</Superscript>Tc-TRODAT-1

A comparative study was carried out on two promising presynaptic dopamine transporter single-photon emission tomography (SPECT) radioligands with a fast pharmacokinetic profile, ¹²³I-FP--CIT (FP) and ^99mTc-TRODAT-1 (TR), in order to assess their differential diagnostic power in early parkinsonism and their sensitivity for detection of disease progression. This cross-sectional study was conducted on 96 patients with early-stage parkinsonism referred in a tertiary clinical setting. Mean disease duration was 2.0±1.3 years, and patients had a modified Hoehn and Yahr (H&Y) stage of 1–2 (average 1.2). Forty-seven patients received TR, and 49 received FP. In both groups, ten patients with normal presynaptic function were included as a control population; all other patients were clinically diagnosed as having idiopathic Parkinsons disease. Groups were matched for gender, age, disease duration and modified H&Y stage. Triple-head gamma camera SPECT was analysed using a semiquantitative index of transporter binding (BI). Discriminant analysis with cross-validation resulted in a maximal classification accuracy for FP of 93% (sensitivity 95% and specificity 86%) for the contralateral putamen BI. For TR, the corresponding values were 87% accuracy, 92% sensitivity and 70% specificity. For FP, disease duration was correlated with both the putamen BI (–8.8%/year, =–0.41, P=0.025) and the putamen/caudate ratio (–7.4%/year, =–0.51, P=0.004), but for TR no significant correlation was found (all P values >0.5). In conclusion, both FP and TR show high sensitivity in a clinically relevant setting, but FP has superior accuracy for early differential diagnosis of idiopathic parkinsonism and non-degenerative extrapyramidal disorders, as well as better sensitivity for disease follow-up.     

Observation of null alleles apparently due to deletions

After examining 2 paternity cases in 17 classical, 4 RFLP and 5 PCR-VNTR systems, isolated pseudoexclusions were observed in the polymorphism D2S44 (YNH24). In both cases the exclusions were due to apparent opposite homozygosity. The application of different restriction enzymes, PCR amplification and varying electrophoretic conditions each led to an equivalent result of a 1-band-pattern with a mismatch between both father/child pairs. From these results the authors conclude that a complete or almost complete loss of the alleles is the most probable explanation.     

Comparison of FP-CIT SPECT with F-DOPA PET in patients with de novo and advanced Parkinson’s disease

Purpose Diagnosis of Parkinsons disease (PD) can be difficult. F-DOPA PET is able to quantify striatal dopa decarboxylase activity and storage capacity of F-dopamine, but is expensive and not generally available. FP-CIT binds to the dopamine transporter, and FP-CIT SPECT is cheaper and more widely available, but has a lower resolution. The aim of this study was to compare these two methods in the same patients with different stages of PD to assess their power in demonstrating deficits of the striatal dopaminergic system.Methods Thirteen patients with de novo PD and 17 patients with advanced PD underwent FP-CIT SPECT and static F-DOPA PET. After data transfer to standard stereotactic space, a template with regions of interest was used to sample values of the caudate, putamen and an occipital reference region. The outcome value was striato-occipital ratios. Patients were clinically examined in the off state (UPDRS-III and H&Y stage).Results Good correlations were found between striatal F-DOPA uptake and striatal FP-CIT uptake (r=0.78) and between putaminal F-DOPA uptake and putaminal FP-CIT uptake (r=0.84, both p<0.0001). Both striatal uptake of FP-CIT and that of F-DOPA correlated moderately with H&Y stage (=–0.52 for both techniques), UPDRS-III (=–0.38 for F-DOPA; =–0.45 for FP-CIT) and disease duration (=–0.59 for F-DOPA; =–0.49 for FP-CIT, all p<0.05).Conclusion FP-CIT values correlate well with F-DOPA values. Both methods correlate moderately with motor scores and are equally able to distinguish patients with advanced PD from patients with de novo PD.     

Virtopsy

Zusammenfassung Computed-tomography-Verfahren sind während der letzen 10 Jahre weiterentwickelt worden und haben verschiedene Anwendungen im rechtsmedizinischen Fachgebiet gefunden. Die neueste Entwicklung besteht in der multislice computed tomography, kombiniert mit photogrammetry-based surface optical scanning und Image-rendering-Techniken. Diese Kombination kann für die 3-dimensionale Darstellung von Verletzungsmustern zum Vergleich mit infrage kommenden Tatwaffen sowie zum Screening nach pathologischen Befunden in lebenden oder verstorbenen Personen eingesetzt werden. Es handelt sich um ein minimal-invasives Verfahren, mit dem forensisch relevante Bilder erfasst werden können, die auch im Gerichtssaal vorgeführt werden können. Die rasche Weiterentwicklung der Imaging-Technnik könnte in der Zukunft eine Alternative zur konventionellen Obduktionen darstellen.     

Intramuscular dissection of Baker′s cysts: report on three cases

Bakers cysts are fluid distensions of the gastrocnemius-semimembranosus bursa and are the most common cystic lesion around the knee. Typically cysts enlarge along intermuscular planes around the knee. We report three cases in which the expanding cyst did not respect these planes and dissected along an intramuscular route as confirmed by MR imaging. Such behaviour by Bakers cysts is hitherto unreported in the literature. Possible mechanisms to account for this phenomenon are discussed.     

β-Methyl-15-p-iodophenylpentadecanoic acid metabolism and kinetics in the isolated rat heart

The use of 15-p-iodophenyl--methyl-pentadecanoic acid (Me-IPPA) as an indicator of long chain fatty acid (LCFA) utilization in nuclear medicine studies was evaluated in the isolated, perfused, working rat heart. Time courses of radioctivity (residue curves) were obtained following bolus injections of both Me-IPPA and its straight chain counterpart 15-p-iodophenyl-pentadecanoic acid (IPPA). IPPA kinetics clearly indicated flow independent impairment of fatty acid oxidation caused by the carnitine palmitoyltransferase I inhibitor 2[5(4-chlorophenyl)pentyl]oxirane-2-carboxylate (POCA). In contrast, Me-IPPA kinetics were insenstive to changes in fatty acid oxidation rate and net utilization of long chain fatty acid. Analysis of radiolabeled species in coronary effluent and heart homogenates showed the methylated fatty acid to be readily incorporated into complex lipids but a poor substrate for oxidation. POCA did not significatly alter metabolism of the tracer, suggesting that the tracer is poorly metabolized beyond Me-IPPA-CoA in the oxidative pathway.     

Hyperextension strain or “whiplash” injuries to the cervical spine

Purpose To define whiplash radiologically. Material and methods. A full cervical spine radiographic series (including flexion and extension views) was reviewed in 40 patients with clinically proven whiplash injuries and compared to the radiographs in 105 normal controls. The level and degree of kinking or kyphosis, subluxation, and the difference in the amount of fanning between spinous processes on flexion and extension films were measured in each patient.Results Localized kinking greater than 10° and over 12 mm of fanning, often occurring at the level below the kinking or kyphosis, occurred mainly in the group of whiplash patients (sensitivity 81%, specificity 76%, accuracy 80%).Conclusions Localized kinking greater than 10° and fanning greater than 12 mm are useful measurements by which to separate patients with true whiplash injuries from those with minor ligamentous tears. Flexion and extension views are essential to help define whiplash and other ligamentous injuries of the cervical spine.     

Ossification and pseudoepiphysis formation in the “nonepiphyseal” end of bones of the hands and feet

Metacarpals, metatarsals, and phalanges were studied to assess the developmental morphology of secondary ossification in the nonepiphyseal ends of these bones as well as the formation of the pseudoepiphysis as an epiphyseal ossification variant. Both direct ossification extension from the metaphysis into the epiphysis and pseudoepiphysis formation preceded, and continued to be more mature than, formation and expansion of the classic epiphyseal (secondary) ossification center at the opposite end of each specific bone. Direct metaphyseal to epiphyseal ossification usually started centrally and expanded hemispherically, replacing both physeal and epiphyseal cartilage simultaneously. In contrast, when remnants of physis were retained, while juxtaposed epiphyseal cartilage was replaced, a pseudoepiphysis formed. There were three basic patterns of pseudoepiphysis formation. First, a central osseous bridge extended from the metaphysis across the physis into the epiphysis and subsequently expanded to create a mushroom-like osseous structure. In the second pattern a peripheral osseous bridge formed, creating either an osseous ring or an eccentric bridge between the metaphysis and the epiphysis. In the third pattern, multiple bridging occurred. In each situation the associated remnant physis lacked typical cell columns and was incapable of significantly contributing to the postnatal longitudinal growth of the involved bone. Pseudoepiphyses were well formed by 4–5 years and coalesced with the rest of the bone months of years before skeletal maturation was attained at the opposite epiphyseal end, which ossified in the typical pattern (i.e., formation of a secondary center de novo completely within the cartilaginous epiphysis). This process may also affect the development and appearance of ossification within the longitudinal epiphyseal bracket (delta phalanx).     

Usefulness of brain <Superscript>99m</Superscript>Tc-TRODAT-1 SPET for the evaluation of Parkinson’s disease

Nigral dopaminergic projections to the striatum are targeted in Parkinsons disease (PD). The extent of the degeneration of the dopaminergic system in PD can be visualised by dopamine transporter imaging using single-photon emission tomography (SPET). In this study in 188 patients with PD, we analysed the image patterns and compared them with the clinical features in order to verify the usefulness of technetium-99m TRODAT-1 brain SPET in the evaluation of patients with PD. Two independent readers visually assessed SPET slices from three brain axes according to a fine visual scale; results were also grouped according to a rough visual scale. Results of both visual and semi-quantitative analyses were compared among patients with different stages of PD and healthy controls. There was good agreement between the readers in the interpretation of the image patterns [kappa statistic ()=0.85 for the presence of PD; =0.88 for the rough scale and 0.81 for the fine scale]. Good concordance was obtained when visual interpretation was used to evaluate the presence of PD (sensitivity =98%, specificity =86%, =0.85). Semi-quantitative analyses revealed significant negative correlations between both striatal and putaminal uptake and disease severity as assessed using the Hoehn and Yahr scale (=–0.89 and –0.93 respectively). An apparent decrease in striatal uptake in early PD, hardly discernible from the uptake level in advanced PD, was commonly found in visual analyses. The results suggest that both visual and semi-quantitative analyses of ^99mTc-TRODAT-1 SPET images reflect neurodegeneration in PD, and that ^99mTc-TRODAT-1 SPET represents an adequate means for evaluation of the status of patients with PD.     

PET imaging of brain with the β-amyloid probe, [11C]6-OH-BTA-1, in a transgenic mouse model of Alzheimer’s disease

Purpose The purpose of this study was to evaluate the capacity of [¹¹C]6-OH-BTA-1 and positron emission tomography (PET) to quantify -amyloid (A) plaques in the Tg2576 mouse model of Alzheimers disease (AD).Methods PET imaging was performed with the NIH ATLAS small animal scanner in six elderly transgenic mice (Tg2576; age 22.0±1.8 months; 23.6±2.6 g) overexpressing a mutated form of human -amyloid precursor protein (APP) known to result in the production of A plaques, and in six elderly wild-type litter mates (age 21.8±1.6 months; 29.5±4.7 g). Dynamic PET scans were performed for 30 min in each mouse under 1% isoflurane inhalation anesthesia after a bolus injection of 13–46 MBq of [¹¹C]6-OH-BTA-1. PET data were reconstructed with 3D OSEM. On the coronal PET image, irregular regions of interest (ROIs) were placed on frontal cortex (FR), parietal cortex (PA), striatum (ST), thalamus (TH), pons (PO), and cerebellum (CE), guided by a mouse stereotaxic atlas. Time–activity curves (TACs) (expressed as percent injected dose per gram normalized to body weight: % ID-kg/g) were obtained for FR, PA, ST, TH, PO, and CE. ROI-to-CE radioactivity ratios were also calculated. Following PET scans, sections of mouse brain prepared from anesthetized and fixative-perfused mice were stained with thioflavin-S.Results TACs for [¹¹C]6-OH-BTA-1 in all ROIs peaked early (at 30–55 s), with radioactivity washing out quickly thereafter in both transgenic and wild-type mice. Peak uptake in all regions was significantly lower in transgenic mice than in wild-type mice. During the later part of the washout phase (12–30 min), the mean FR/CE and PA/CE ratios were higher in transgenic than in wild-type mice (1.06±0.04 vs 0.98±0.07, p=0.04; 1.06±0.09 vs 0.93±0.08 p=0.02) while ST/CE, TH/CE, and PO/CE ratios were not. Ex vivo staining revealed widespread A plaques in cortex, but not in cerebellum of transgenic mice or in any brain regions of wild-type mice.Conclusion Marked reductions in brain uptake of this radioligand in transgenic mice may be due to reduced cerebral blood flow relative to that in wild-type mice. Specific [¹¹C]6-OH-BTA-1 binding to A plaques, if any, is probably very low, as reflected in the small FR/CE and PA/CE ratio differences. FR/CE and PA/CE ratios are considerably higher in AD patients while A plaque densities in 22-month-old transgenic mice may be expected to show essentially the same density as is observed in the AD brain. This implies that the absence of tracer retention in 22-month-old transgenic mice may be due to the smaller number of A plaque binding sites and/or to lower affinity of the binding sites for [¹¹C]6-OH-BTA-1 as compared with AD patients. [¹¹C]6-OH-BTA-1 shows excellent brain uptake in mice.This work was presented at the 51st Annual Meeting of the Society of Nuclear Medicine in Philadelphia, PA, June 19–23, 2004.