Low dose radiation 18F-fluoride PET/CT in the assessment of Unilateral Condylar Hyperplasia of the mandible: preliminary results of a single centre experience.

BACKGROUND: Unilateral condylar hyperplasia (UCH) of the mandible, or Hypercondylia, is a pathological condition that determines an abnormal growth of the affected condyle.Bone SPECT with Tc99m-diphosphonates is a successful tool in the diagnosis of UCH. EANM guidelines also suggest the use of 18F-NaF PET/CT, though it leads to a higher radiation exposure. AIM: As UCH patients are young, we aimed to develop a low dose 18F-Fluoride PET/CT protocol and compare it to a standard injected activity scan, to assess if the image quality remains unchanged. MATERIALS AND METHODS: We prospectively enrolled 20 patients (7 males, 13 females, mean age 23.2) with UCH, who underwent 18F-NaF PET/CT to assess the hypercondylia. We administered a low activity of 18F-NaF (2.9 MBq/kg) in 15 patients and a standard activity (5.3 MBq/kg) in 5 patients. Activity range was chosen according to 2015 EANM guidelines.To determine if the scans with low radiotracer activity were "diagnostic" such as those with standard activity, two expert nuclear medicine physicians, unaware of the administered activity, independently reviewed the scans and expressed a final qualitative judgment in terms of "diagnostic"/"non-diagnostic" scan. Furthermore, we compared the effective dose of a low injected activity PET/CT to the standard one and to a Bone SPECT performed with standard injected activity of Tc99m-diphosphonates. RESULTS: Reviewers classified 19 of 20 scans as "diagnostic". Only one of them was classified as "non diagnostic" due to condylar arthrosis that disturbed the correct evaluation of condylar radiotracer uptake. The effective dose of a 18F-Fluoride PET/CT, in patient of 70 kg, is about 3.5 mSv in scans performed with 2.9 MBq/kg [0.017 mSv/MBq × 2.9 MBq/kg × 70 kg] and about 6.3 mSv in ones performed with 5.3 MBq/kg [0.017 mSv/MBq × 5.3 MBq/kg × 70 kg]. The effective dose of 99mTc-MDP bone SPECT is about 3.2 mSv [0.0043 mSv/MBq × 740 MBq of 99mTc-MDP]. DISCUSSION: 18F-NaF PET/CT performed with a low radiotracer activity allows a good assessment of UCH similar to that performed with an ordinary activity. The effective radiation dose of a low-injected activity PET/CT is significantly lower than an ordinary-injected activity and is not significantly higher than the most used Bone SPECT. Moreover PET/CT is performed in 1.5 h while Bone SPECT requires at least 3.5 h. CONCLUSIONS: The 18F-Fluoride PET/CT procedure could be performed with 2.9 MBq/Kg (minimum 185 MBq, recommended at least 200 MBq) of 18F-NaF to minimize the effective radiation dose received, maintaining the quality of the scan. Further studies including a larger number of patients and clinical follow-up are needed to confirm our preliminary findings.

Evaluation of mosaic pattern areas in HRCT with Min-IP reconstructions in patients with pulmonary hypertension: could this evaluation replace lung perfusion scintigraphy?

PURPOSE: The aim of this study is to evaluate a possible correlation between areas of lung attenuation, found in minimum intensity projection (Min-IP) reconstruction images performed with high resolution computed tomography without contrast medium (HRCT), and areas of lung perfusion alteration, found in lung perfusion scintigraphy (LPS). MATERIALS AND METHODS: Two independent radiologists, unaware of LPS results, evaluated retrospectively a group of 113 patients affected by pulmonary hypertension (HP) of different aetiology. These have been examined in a period of two years in our centre both by spiral computed tomography (CT) with and without contrast-medium and by LPS. The final diagnosis was determined on clinical data, right heart catheterisation and contrast enhanced CT in angiographic phase (CTPA). We reconstructed the Min-IP images of lung parenchyma in all the cases both in HRCT without contrast-medium, and in contrast enhanced CT in angiographic phase (CTPA) in axial, sagittal and coronal planes. The obtained images were qualitatively graded into three categories of pulmonary attenuation: homogeneous, inhomogeneous with non-segmental patchy defects, inhomogeneous with segmental defects. The same criteria of classification were used also for LPS images. In the group of patients with chronic thromboembolic pulmonary hypertension (CTEPH) we also compared the number of areas of lung attenuation found in Min-IP images in HRCT without contrast-medium, and their exact localization, with not perfused areas in LPS. Gold standard for the diagnosis of pulmonary embolism was spiral contrast enhanced CT in angiographic phase (CTPA). RESULTS: In all cases we found exact correspondence between the Min-IP images in HRCT with and without contras agent. The attenuation pattern seen on Min-IP images was concordant with those of LPS in 96 out of 113 patients (85%). In the remaining 17 cases (15%) it was discordant: in 12 cases inhomogeneous in Min-IP images (7 with non-segmental patchy defects, 5 with segmental defects) and homogeneous in LPS, in 5 cases inhomogeneous (1 with non-segmental patchy defects, 4 with segmental defects) in LPS images and homogeneous in Min-IP. In a general view, Min-IP reconstruction without contrast-medium showed a sensitivity of 100% and specificity of 96.1%, positive predictive value (PPV) of 92.3% and negative predictive value (NPV) of 100%, to recognize a pattern of lung attenuation inhomogeneous with segmental defects correspondent to a chronic thromboembolic condition, no false negative cases and three false positive cases; on the other hand LPS, on its own, showed a sensitivity of 91.67% and specificity of 93.51%, positive predictive value (PPV) of 86.84% and negative predictive value (NPV) of 96%, 3 false negative cases and 5 false positive cases. CONCLUSION: Min-IP obtained in HRCT without contrast-medium and in CTPA were equivalent. Min-IP images generally showed a higher sensitivity and specificity than LPS in the evaluation of lung perfusion regarding patients with pulmonary hypertension caused by different etiology, particularly in CTEPH patients. These results can be completed with the evaluation of HRCT and CTPA basal scans, providing more informations than ventilation/perfusion lung scintigraphy. HRCT images integrated by Min-IP reconstruction can represent the first step in the diagnostic algorithm of patients affected by dyspnoea and pulmonary hypertension of unknown causes, reserving the use of contrast-medium only in selected patients and reducing the patients' X-ray-exposition.

Dose and test for dipyridamole infusion and cardiac imaging early after uncomplicated acute myocardial infarction.

To evaluate the relation of the dose of intravenous dipyridamole on results of thallium and echocardiographic testing, the results of standard- (0.56 mg/kg/4 minutes) versus high- (0.84 mg/kg/10 minutes) dose dipyridamole were obtained 9 +/- 3 days after uncomplicated acute myocardial infarction in 57 patients. New wall motion abnormalities were compared with redistribution of thallium imaging and results of discharge coronary angiography. The sensitivity of thallium in predicting the presence of multivessel coronary artery disease was significantly (p < 0.01) higher (85%) than echocardiography (53%) and was unaffected by the dose. However the sensitivity of echocardiography was better with the higher dose (53 vs 14%). Minor adverse effects occurred in 34 patients (59%) after receiving the high dose and only in 4 patients (7%) after the standard dose (p < 0.001). Thus, thallium-201 scintigraphy during standard-dose dipyridamole infusion is more effective than high-dose dipyridamole echocardiographic testing in safely identifying patients who could benefit from early invasive evaluation and therapy.

Brain circulation during sleep and its relation to extracerebral hemodynamics.

Regional cerebral blood flow (rCBF) was measured in rabbits during the sleep-waking cycle, using radioactive microspheres. rCBF does not change significantly in the transition from wakefulness (W) to synchronized sleep (SS), while it significantly increases during desynchronized sleep (DS). No correlation was found between CBF changes and changes in cardiac output or regional blood flows in the transition from SS to DS. This suggests that the CBF increase in DS is not relevantly affected by changes in extracerebral hemodynamic factors.

Regional spinal cord blood flow during sleep-waking cycle in rabbit.

Spinal cord blood flow (SCBF) was measured in rabbits during the sleep-waking cycle with the use of radioactive microspheres. The values obtained during wakefulness (W), synchronized sleep (SS), and desynchronized sleep (DS) were 18.1 +/- 2.1, 18.9 +/- 2.6, and 34.4 +/- 2.5 (SE) ml X min-1 X 100 g-1, respectively. Differences relative to SS were not significant in W and were significant at the 0.05 level in DS (modified t test and Bonferroni's method). The increase in blood flow during DS was due to a decrease in vascular resistance. The mechanism of the vasodilation during DS has yet to be identified.

Neural control of vasomotion in rabbit ear is impaired during desynchronized sleep.

In a warm environment the skin vessels of the rabbit ear, dilated during synchronized sleep (SS), reduce their caliber during desynchronized sleep (DS). In a cold environment the ear skin vessels, constricted during SS, increase their caliber during DS. These vascular changes contrast with thermoregulatory homeostasis. They can be accounted for by the decrease in both local transmural pressure and sympathetic vasoconstrictor discharge accompanying the DS phase. A decrease in local transmural pressure prevails in a warm environment and a decrease in sympathetic discharge in a cold environment. Accordingly, the vessel caliber decreases in the heat and increases in the cold. The results of the sympathetic denervation of the ear and of the alpha-receptor blockade confirm the passive nature of vascular changes in the rabbit ear during DS.

Cutaneous vasomotion during REM sleep in the rabbit's ear, after alpha-receptor blockade.

Cutaneous vasoconstriction in the rabbit's ear during REM sleep in a warm environment is not abolished by alpha-receptor blockade (phenoxybenzamine 6 mg/kg i.v.), thus confirming that the vasomotor response during REM sleep is independent of the activity of circulating catecholamines. The decrease in cardiac output during REM sleep may be responsible for the slight fall in transmural pressure which underlies cutaneous ear vasoconstriction during REM sleep.

Vasomotor adjustments in the rabbit's ear during REM sleep.

In the rabbit auricolar vessels constrict during REM sleep at high ambient temperatures (26-30 degrees C) and dilate a low ambient temperatures (0-5 degrees C). These opposite vasomotor adjustments during REM sleep are inconsistent with the logic of a thermoregulatory mechanism; they can only be understood as new equilibria of the vessels calibre to the drop in sympathetic vasoconstrictor tone and fall in transmural pressure during REM sleep. By cutting the sympathetic nerve supply to the ear we can rule out the neurogenic origin of ear vasoconstriction during REM sleep.