Incidental finding of F-18 FDG skin uptake in a patient with psoriasis during the evaluation of a recurrent papillary thyroid carcinoma.

We report the case of a patient, referred in our institution for a PET/CT for a suspected recurrence of papillary thyroid carcinoma. An intense cutaneous uptake of FDG was seen in the upper neck region. The clinical examination showed an indurate and thickened red descamative plaque evocative of psoriasis, and the patient reported a long history of psoriatic lesions of the skin, evolving for many years. This case illustrates an incidental finding which must be recognized, and not confounded with other causes of skin uptake. The FDG image is not surprising, as FDG uptake is expected in active inflammatory disease.

Single-photon emission computed tomography combined with computed tomography (SPECT/CT) in bone diseases.

Radionuclide bone scanning was proven effective many years ago. Its main advantages are good sensitivity, limited radiation exposure, and noninvasiveness. However, increased radionuclide uptake by a lesion is not specific, and differentiating malignant from nonmalignant disorders may therefore be difficult. An additional structural imaging study is often needed to establish the final diagnosis. Furthermore, the limited resolution of radionuclide bone scanning images does not allow accurate localization of the lesions. Single-photon emission computed tomography (SPECT) combined with computed tomography (CT) provides both structural and functional information. SPECT/CT has been proven useful for interpreting radionuclide bone scan results in patients with bone malignancies, showing far better specificity than planar imaging or SPECT alone, most notably in the evaluation of spinal abnormalities. SPECT/CT provides an accurate evaluation of the site of the lesions and also supplies other information that can be useful in nonmalignant conditions such as injuries, infections, and degenerative disease. Nevertheless, there are only a few published studies on the usefulness of SPECT/CT in nonmalignant conditions. However, SPECT/CT is only starting to become available and may become a routine investigation for a number of rheumatic disorders.

Positron Emission Tomography in oncology: present and future of PET and PET/CT.

PET is a crucial technique in molecular imaging, allowing in vivo assessment and localization of pathological processes, thanks to its ability to detect very small amounts of radioactive molecules. This is of particular interest in oncology where abnormal metabolism or synthesis in tumor cells but also various tumor characteristics can be studied using this nuclear medicine technique. FDG is currently the most widely used tracer, nowadays essential in the management of various malignancies, with large applications in diagnosis, initial assessment, therapy monitoring, and recurrence detection. The combination of anatomical information provided by PET/CT further increased its interest. Beyond its spread use in daily practice, future applications of PET will involve other tracers than FDG and develop research applications in humans as well as in small animals.

The growing development of multimodality imaging in oncology.

The first decade of the century has been the beginning of an era of new practice in daily medical imaging, that is the multimodality involving functional or metabolic imaging brought by nuclear medicine techniques directly associated with anatomical information brought by CT (Computed X-Ray Tomography) devices combined with nuclear medicine detectors. PET (Positron Emission Tomography)/CT and SPECT (Single Photon Emission Computed Tomography)/CT are now established to further increase the interest of PET and SPECT, thanks to improved localization of the pathologic processes, and in many instances thanks to a gain in specificity. An even better use of the combined information will necessitate redefining some protocols and indications, and the future will probably see the continued development of multimodality imaging in practice. Besides the combination with CT, another modality is expected in the future: PET/MRI (Magnetic Resonance Imaging).

SPECT/CT in localization of parathyroid adenoma or hyperplasia in patients with previous neck surgery.

PURPOSE: Single photon emission computed tomography/computed tomography (SPECT/CT) now makes it possible to use combined morphologic CT and functional scintigraphy information. It has proved useful for localization of abnormal parathyroid glands, especially in the case of an ectopic gland. We experienced that it was also beneficial for patients with a history of previous neck surgery, and we report 4 cases in this entity. MATERIALS AND METHODS: Four patients with prior neck surgery and hyperparathyroidism underwent parathyroid Tc-99m MIBI scintigraphy with SPECT/CT. Two patients had undergone surgery for hyperparathyroidism and 2 had undergone thyroidectomy, 1 for thyroid cancer and 1 for multinodular goiter. Parathyroid hormone levels were assessed during surgery, and patients were followed several months after treatment. RESULTS: SPECT/CT successfully localized the abnormal gland, including an uncommon anterior situation for which previous surgery guided by planar imagery failed to cure the hyperparathyroidism. It allowed efficient surgical treatment, as confirmed by parathyroid hormone level normalization, without complications and with a relatively short operation time in those challenging cases. CONCLUSIONS: SPECT/CT seems to be a useful tool for presurgical assessment in hyperparathyroidism, not only for ectopic glands but also for patients with previous neck surgery.

Respiratory motion artefact in the liver dome on FDG PET/CT: comparison of attenuation correction with CT and a caesium external source.

PURPOSE: Respiratory motion has been reported to be a potential cause of artefacts on PET/CT, and of errors in the quantification of lesion activity due to inaccurate attenuation correction. We examined FDG images corrected for attenuation with CT and a caesium external source in the same patients to study this artefact and to assess its impact on detection of lesions in the upper part of the liver. METHODS: A total of 122 patients underwent the examination using both attenuation correction techniques, with the Gemini PET/CT scanner. No breathing instructions were given. The images obtained were visually compared, and standardised uptake values (SUVs) in 35 lesions were measured (mean SUV/normal liver SUV) in 14 patients with lesions in the upper part of the liver (less than 5 cm from the upper border). RESULTS: CT-corrected images of the liver included an artefactual cold area in 84 patients (69%); this area was located in the posterior upper part of the liver (65 patients, 53%), included the top of the liver (ten patients, 8%) or affected both the top and the posterior part (nine patients, 8%). In lesions (and also in normal liver outside the artefactual area), SUVs obtained with CT correction were higher than those obtained with Cs correction (p<0.05), though this was usually without relevance for lesion detection. However, in patients with lesions situated inside the artefactual area, SUVs were lower with CT correction, and ability to detect two lesions (6%) was affected. CONCLUSION: Failure to detect a liver lesion (especially in the superior and posterior parts) is a rare but possible pitfall when using only CT-corrected FDG images.

Ultrasonography and gastric emptying in children: validation of a sonographic method and determination of physiological and pathological patterns.

BACKGROUND: The association between gastric emptying and gastro-esophageal reflux (GER) has been widely recognised from scintigraphic studies. OBJECTIVE: A prospective study to (a) validate US as a means of measuring gastric emptying, (b) determine physiological patterns of gastric emptying and (c) measure gastric emptying in symptomatic refluxers. MATERIALS AND METHODS: Three cohorts were studied: (a) Ten babies in whom gastric emptying was measured by US and scintigraphy; (b) gastric emptying in 330 asymptomatic children aged between 15 days and 10 years to determine physiological variations; and (c) gastric emptying in 552 children with GER, manifesting as vomiting or cardiorespiratory problems. RESULTS: US and scintigraphic techniques showed general concordance in 90% of cases. In the remaining 10%, discordant results were related to overlapping of duodenum and stomach during scintigraphy and shadowing of the gastric antrum by air during US. Tremendous variations were induced by change of feed volume or type of formula, underlining the need for a standardised procedure. Twenty-two percent of cases showed a peculiar 'plateau' which differed significantly from the physiological patterns. Most of these babies had esophagitis or acute life-threatening events. CONCLUSIONS: Investigation of gastric emptying seems to be a key element in the assessment of children with 'pathological' GER. US is a safe and cheap alternative to scintigraphy for the assessment of gastric emptying.

Computer-aided intrapatient comparison of brain SPECT images: the gray-level normalization issue applied to children with epilepsy.

UNLABELLED: A tool was developed for automated intrapatient comparison of brain SPECT images, with specific emphasis on gray-level normalization. METHODS: Ictal and interictal (99m)Tc-ethyl cysteinate dimer SPECT images were acquired for 6 children with partial epilepsy (age range, 2-10 y). For each patient, 3-dimensional rigid geometric ictal-to-interictal image registration optimizing different classic criteria (correlation coefficient, ratio uniformity) in a multiscale translation-rotation 6-parameter space was first performed. Gray-level normalization was then performed with different methods, using a 1- or 2-parameter linear model. In the 1-parameter case, the scaling factor was equal to the interictal-to-ictal ratio of the maximum, mean, or median values calculated within different reference volumes (whole brain or cerebellum) or obtained by linear regression between ictal and interictal counts in the brain or by maximizing a robust criterion, the number of deterministic sign changes in the subtraction images. In the 2-parameter case, the scaling factor and additive constant were estimated using these last 2 methods. For each patient, registration validity and normalization plausibility were assessed by considering the correlation scatterplot together with the different normalization lines and by comparing interictal and registered normalized ictal images using a twin display (with isocontours) in the 3 orthogonal planes. Three-dimensional volumes of interest could be selected on coupled interictal-subtraction images for further focused numeric comparison. RESULTS: After a satisfactory and stable geometric registration with both criteria, the different normalization methods led to similar subtraction images for 5 of 6 patients, except the maxima ratio, which gave noticeably different results in 2 patients. For the remaining patient, with highly dissimilar ictal-interictal images, the maxima ratio normalization was obviously wrong and the other 1-parameter methods probably better depicted the data than did the 2-parameter methods. CONCLUSION: When comparing intrapatient brain SPECT images, one should be aware of the potential impact of the gray-level normalization method on clinical interpretation. For ictal-interictal images, simple robust scaling should be recommended. In particular, image maximum should generally not be considered a valid reference, and no additive constant is needed in the linear gray-level normalization model.