Positron emission tomography scan in the diagnosis and follow-up of aortitis of the thoracic aorta

Diagnostic Approaches for Large Vessel Vasculitides

The large vessel vasculitides comprise giant cell arteritis (GCA), Takayasu arteritis (TAK), and chronic periaortitis. The diagnostic approach to these conditions involves the correct use and interpretation of clinical criteria, imaging techniques, and, in case of GCA, temporal artery biopsy. Ultrasound, magnetic resonance imaging (MRI), and computed tomography (CT) reveal a homogeneous, concentric, thickening of the arterial wall. MRI and CT may also reveal aneurysms and stenoses. 18F-Fluorodeoxyglucose (FDG)-PET shows increased FDG uptake of inflamed artery walls delineating increased metabolic activity. Ultrasound, FDG-PET, and MRI are the recommended imaging techniques in GCA and TAK. In patients with a high suspicion of GCA who present with visual disturbances, initiation of high-dose intravenous corticosteroids should not be delayed by imaging. Extracranial large vessel vasculitis may be confirmed by all three modalities, particularly by FDG-PET in case of atypical clinical pictures. In this article, we review the role of the GCA and TAK ACR classification criteria, temporal artery biopsy, conventional angiography, ultrasound, MRI, magnetic resonance angiography (MRA), CT angiography (CTA), and FDG-PET in the diagnostic approach of large vessel vasculitis.

Investigations in systemic vasculitis - The role of imaging

Imaging plays an increasing role for confirming a suspected diagnosis of giant cell arteritis (GCA) or Takayasu arteritis (TAK). Ultrasound, magnetic resonance imaging (MRI), and computed tomography demonstrate a homogeneous, most commonly concentric, arterial wall thickening. 18F-Fluorodeoxyglucose (FDG) positron emission tomography (PET) displays increased FDG uptake of inflamed artery walls delineating increased metabolism. Ultrasound and MRI are recommended to be the initial imaging modalities in cranial GCA and TAK, respectively. Extracranial disease can be confirmed by all four modalities, particularly by PET in case of inflammation of unknown origin. If the diagnosis remains uncertain, additional investigations including biopsy and/or additional imaging are recommended. Imaging should be performed by a trained specialist using appropriate operational procedures and settings with appropriate equipment. Further research is necessary on the role of imaging for disease monitoring. This review will discuss advantages and disadvantages of imaging modalities in the diagnosis of vasculitis.

Assessment of Therapy Response by FDG PET in Infection and Inflammation

Positron emission tomography (PET) is a well-known imaging modality in assessing the treatment response to chemotherapy or radiotherapy in various malignancies. A systematic review of the literature reveals a few publications reporting evaluation of the treatment response in benign conditions using PET/computed tomography. PET holds a promising future role in the follow-up of inflammatory or infectious diseases. In this article, [(18)F]Fluorodeoxyglucose PET as a tool in the evaluation, treatment, and follow-up of infectious and inflammatory diseases is discussed.

PET in vasculitis

[(18) F]Fluorodeoxyglucose positron emission tomography (FDG PET) can be used to visualize large-vessel inflammation in giant-cell arteritis, Takayasu arteritis, and other types of aortitis. In patients with symptoms compatible with polymyalgia rheumatica, findings of increased FDG-uptake in the shoulders, hips, as well as the spinous processes of the cervical and lumbar spine, may suggest this diagnosis. In patients with giant-cell arteritis, there is increased metabolic activity within the aortic wall on FDG PET scintigraphy, indicating inflammation of the aorta, which may be a predictor of a higher potential for aortic dilatation.

[Vasculitis assessment with [18F]FDG positron emission tomography]

[18F]fluorodeoxyglucose positron emission tomography (PET) is a noninvasive metabolic imaging modality that is well-suited to the assessment of activity and extent of large vessel vasculitis. PET imaging has demonstrated its usefulness in diagnosing giant cell arteritis (notably in its silent form), Takayasu's arteritis, and unclassified aortitis. PET imaging could be more effective than magnetic resonance imaging in detecting the earliest stages of vascular wall inflammation. The visual grading of vascular [18F]FDG uptake makes it possible to discriminate arteritis from active atherosclerosis, providing therefore high specificity. High sensitivity can also be achieved provided scanning is performed during active inflammatory phase, preferably before starting corticosteroid treatment. Prospective studies are needed to determine the exact value of PET imaging in assessing other vasculitis subsets, infectious aortitis, and large vessel vasculitis outcome and response to immunosuppressive treatment.

Feasibility of FDG imaging of the coronary arteries: comparison between acute coronary syndrome and stable angina

OBJECTIVES

This study tested the hypothesis that fluorodeoxyglucose (FDG) uptake within the ascending aorta and left main coronary artery (LM), measured using positron emission tomography (PET), is greater in patients with recent acute coronary syndrome (ACS) than in patients with stable angina.

BACKGROUND

Inflammation is known to play an important role in atherosclerosis. Positron emission tomography imaging with (18)F-FDG provides a measure of plaque inflammation.

METHODS

Twenty-five patients (mean age 57.9 +/- 9.8 years, 72% male, 10 ACS, and 15 stable angina) underwent cardiac computed tomographic angiography and PET imaging with (18)F-FDG after invasive angiography. Images were coregistered, and FDG uptake was measured at locations of interest for calculation of target-to-background ratios (TBR). Additionally, FDG uptake was measured at the site of the lesion deemed clinically responsible for the presenting syndrome (culprit) by virtue of locating the stent deployed to treat the syndrome.

RESULTS

The FDG uptake was higher in the ACS versus the stable angina groups in the ascending aorta (median [interquartile ranges] TBR 3.30 [2.69 to 4.12] vs. 2.43 [2.00 to 2.86], p = 0.02), as well as the LM (2.48 [2.30 to 2.93] vs. 2.00 [1.71 to 2.44], p = 0.03, respectively). The TBR was greater for culprit lesions associated with ACS than for lesions stented for stable coronary syndromes (2.61 vs. 1.74, p = 0.02). Furthermore, the TBR in the stented lesions (in ACS and stable angina groups) correlated with C-reactive protein (r = 0.58, p = 0.04).

CONCLUSIONS

This study shows that in patients with recent ACS, FDG accumulation is increased both within the culprit lesion as well as in the ascending aorta and LM. This observation suggests inflammatory activity within atherosclerotic plaques in acute coronary syndromes and supports intensification of efforts to refine PET methods for molecular imaging of coronary plaques.

[18F]fluorodeoxyglucose positron emission tomography is a useful tool to diagnose the early stage of Takayasu's arteritis and to evaluate the activity of the disease

Takayasu's arteritis (TA) is a rare disease that can be difficult to diagnose in its early stage. A young woman with a fever and neck pain was thought to have TA, although computed tomographic angiography did not show any specific changes of the arteries. [(18)F]fluorodeoxyglucose positron emission tomography ([(18)F]FDG-PET) was performed to detect the source of the inflammation. Specific accumulation of [(18)F]FDG-6-phosphate in the thoracic aorta and its direct branches was observed, leading to a diagnosis of TA. [(18)F]FDG-PET is therefore considered to be useful for the diagnosis of early-stage TA.

In vivo 18F-fluorodeoxyglucose positron emission tomography imaging provides a noninvasive measure of carotid plaque inflammation in patients

OBJECTIVES

Given the importance of inflammation in atherosclerosis, we sought to determine if atherosclerotic plaque inflammation could be measured noninvasively in humans using positron emission tomography (PET).

BACKGROUND

Earlier PET studies using fluorodeoxyglucose (FDG) demonstrated increased FDG uptake in atherosclerotic plaques. Here we tested the ability of FDG-PET to measure carotid plaque inflammation in patients who subsequently underwent carotid endarterectomy (CEA).

METHODS

Seventeen patients with severe carotid stenoses underwent FDG-PET imaging 3 h after FDG administration (13 to 25 mCi), after which carotid plaque FDG uptake was determined as the ratio of plaque to blood activity (target to background ratio, TBR). Less than 1 month after imaging, subjects underwent CEA, after which carotid specimens were processed to identify macrophages (staining with anti-CD68 antibodies).

RESULTS

There was a significant correlation between the PET signal from the carotid plaques and the macrophage staining from the corresponding histologic sections (r = 0.70; p < 0.0001). When mean FDG uptake (mean TBR) was compared with mean inflammation (mean percentage CD68 staining) for each of the 17 patients, the correlation was even stronger (r = 0.85; p < 0.0001). Fluorodeoxyglucose uptake did not correlate with plaque area, plaque thickness, or area of smooth muscle cell staining.

CONCLUSIONS

We established that FDG-PET imaging can be used to assess the severity of inflammation in carotid plaques in patients. If subsequent natural history studies link increased FDG-PET activity in carotid arteries with clinical events, this noninvasive measure could be used to identify a subset of patients with carotid atherosclerosis in need of intensified medical therapy or carotid artery intervention to prevent stroke.

Positron emission tomography/computed tomography improves diagnostics of inflammatory arteritis

Based on the unique property of fluorine-18 fluorodeoxyglucose, localization and follow-up of hypermetabolic processes is possible with positron emission tomography (PET). The dual-modality PET/computed tomography (CT) systems provide intrinsically fused morphologic and functional data in a single examination. We report on two patients with inflammatory aortitis and positive PET/CT findings. A 57-year-old woman with an inflammatory process involving the thoracolumbal aorta with an aneurysm and a 48-year-old woman with an aneurysm of the thoracic aorta and pronounced fluorodeoxyglucose-uptake. The advantages in differentiation of vessel wall structures compared with PET or CT alone are pointed out.

Noninvasive in vivo measurement of vascular inflammation with F-18 fluorodeoxyglucose positron emission tomography

BACKGROUND

Fluorine 18 fluorodeoxyglucose (FDG) has been shown to accumulate in inflamed tissues. However, it is not known whether vascular inflammation can be measured noninvasively. The aim of this study was to test the hypothesis that vascular inflammation can be measured noninvasively by use of positron emission tomography (PET) with FDG.

METHODS AND RESULTS

Inflamed atherosclerotic lesions were induced in 9 male New Zealand white rabbits via balloon injury of the aortoiliac arterial segment and exposure to a high cholesterol diet. Ten rabbits fed standard chow served as controls. Three to six months after balloon injury, the rabbits were injected with FDG (1 mCi/kg), after which aortic uptake of FDG was assessed (3 hours after injection). Biodistribution of FDG activity within aortic segments was obtained by use of standard well gamma counting. FDG uptake was also determined noninvasively in a subset of 6 live atherosclerotic rabbits and 5 normal rabbits, via PET imaging and measurement of standardized uptake values over the abdominal aorta. Plaque macrophage density and smooth muscle cell density were determined by planimetric analysis of RAM-11 and smooth muscle actin staining, respectively. Biodistribution of FDG within nontarget organs was similar between atherosclerotic and control rabbits. However, well counter measurements of FDG uptake were significantly higher within atherosclerotic aortas compared with control aortas (P < .001). Within the upper abdominal aorta of the atherosclerotic group (area of greatest plaque formation), there was an approximately 19-fold increase in FDG uptake compared with controls (108.9 +/- 55.6 percent injected dose [%ID]/g x 10(3) vs 5.7 +/- 1.2 %ID/g x 10(3) [mean +/- SEM], P < .001). In parallel with these findings, FDG uptake, as determined by PET, was higher in atherosclerotic aortas (standardized uptake value for atherosclerotic aortas vs control aortas, 0.68 +/- 0.06 vs 0.13 +/- 0.01; P < .001). Moreover, macrophage density, assessed histologically, correlated with noninvasive (PET) measurements of FDG uptake (r = 0.93, P < .0001). In contrast to this finding, FDG uptake did not correlate with either aortic wall thickness or smooth muscle cell staining of the specimens.

CONCLUSION

These data show that FDG accumulates in macrophage-rich atherosclerotic plaques and demonstrate that vascular macrophage activity can be quantified noninvasively with FDG-PET. As such, measurement of vascular FDG uptake with PET holds promise for the noninvasive characterization of vascular inflammation.

Use of ultrasonography and positron emission tomography in the diagnosis and assessment of large-vessel vasculitis

PURPOSE OF REVIEW

Ultrasonography and positron emission tomography have been increasingly studied and, in part, introduced in clinical practice to diagnose large-vessel vasculitides, such as temporal arteritis, Takayasu arteritis, large-vessel giant cell arteritis, and isolated aortitis.

RECENT FINDINGS

Ultrasonography reveals characteristic homogenous, concentric wall thickening in vasculitis, often combined with stenoses and, less frequently, with acute occlusions. Thirteen studies describe sensitivities of 40 to 100% (median, 86%) for temporal artery vessel wall edema compared with histology, and of 35 to 86% (median, 70%) compared with clinical diagnosis. If wall edema, stenoses, and occlusions are included, sensitivities increase to 91 to 100% (median, 95%) compared with histology, and to 83 to 100% (median, 88%) compared with clinical diagnosis. Specificities for wall edema are 68 to 100% (median, 93%) compared with histology, and 78 to 100% (median, 97%) compared with clinical diagnosis. One should be aware of large-vessel giant cell arteritis in all patients with temporal arteritis and polymyalgia rheumatica. Ultrasonography reveals characteristic wall thickening, particularly of the distal subclavian, axillary, and proximal brachial arteries. Findings in Takayasu arteritis are similar, but the vessel wall swelling is usually brighter. Positron emission tomography reveals vasculitis in arteries with a diameter of more than 4 mm. Ultrasonography and positron emission tomography agreed completely in the anatomic distribution of changes in patients with large-vessel giant cell arteritis. It reveals asymptomatic large-vessel vasculitis in giant cell arteritis and Takayasu arteritis. Positron emission tomography is not suitable for the assessment of temporal arteries.

SUMMARY

Ultrasonography and positron emission tomography are new, promising techniques to assess large-vessel vasculitides.

Evolving role of positron emission tomography in the management of patients with inflammatory and other benign disorders

Fluoro-2-deoxyglucose (FDG) positron emission tomography (PET) has evolved from a research imaging modality assessing brain function in physiologic and pathologic states to a pure clinical necessity. It has been successfully used for diagnosing, staging, and monitoring a variety of malignancies. FDG-PET imaging also is evolving into a powerful imaging modality that can be effectively used for the diagnosis and monitoring of a certain nononcological diseases. PET has been shown to be very useful in the diagnosis of osteomyelitis, painful prostheses, sarcoidosis, fever of unknown etiology, and acquired immunodeficiency syndrome. Based on recent observations, several other disorders, such as environment-induced lung diseases, atherosclerosis, vasculitis, back pain, transplantation, and blood clot, can be successfully assessed with this technique. With the development and the introduction of several new PET radiotracers, it is expected that PET will secure a major role in the management of patients with inflammatory and other benign disorders.

Vaskulitiden der gro�en Gef��e als Ursache eines Fiebers unklarer Genese (FUO) oder unklarer Entz�ndungskonstellationen

BACKGROUND

Diagnosis and treatment of FUO or systemic inflammation with unknown reason are still a great challenge for the treating physician. We used (18)F-FDG-PET for further diagnostic work in patients in whom a diagnosis could not be established despite intensive diagnostic efforts.

METHODS/RESULTS

We studied nine patients with (18)F-FDG-PET. Two female patients with known Takayasu's arteritis but undefined disease activity, and seven patients with the clinical suspicion of an underlying large vessel vasculitis. The diagnosis of active vasculitis could be confirmed by the PET-results in eight patients. Active vasculitis could be nearly ruled out in one. The diagnoses could be confirmed by follow-up visits.

CONCLUSION

(18)F-FDG-PET is a useful diagnostic tool in patients with unclear systemic inflammation and FUO. Especially when large vessel vasculitis is suspected, further diagnostic work by PET seems to be of benefit. Furthermore, it offers the opportunity to evaluate disease activity and to check which vessels are involved.

PET: a revolution in medical imaging

FDG-PET has had remarkable influence on the assessment of physiologic and pathologic states. The authors predict that FDG-PET imaging could soon become the most common procedure used by nuclear medicine laboratories and could remain so for an extended period of time. The power of molecular imaging lies in the vast potential for using biochemical and pharmacologic probes to extend applications arising from an understanding of cell biology to a large number of well-characterized pathologic states. Molecular imaging based upon tracer kinetics with positron-emitting radiopharmaceuticals could become the main source of information for the management of cancer patients. In that case, nuclear medicine procedures might become the most common imaging studies performed in the practice of medicine. This speculation is not farfetched when one realizes the enormous change that a single biologically important compound, FDG, has brought to the medical arena. The major challenge today is to attract the highly qualified individuals and to secure the resources needed to harness the opportunities in the specialty of molecular imaging.

Diagnostic imaging in Takayasu arteritis

PURPOSE OF REVIEW

New imaging modalities may help accurately diagnose and monitor Takayasu arteritis (TAK). Examination of the published literature on arterial imaging studies other than conventional angiography will help guide appropriate use of these studies in TAK. MRI, magnetic resonance angiography (MRA), Doppler ultrasound, CT, and positron emission tomography (PET) are all potentially useful for evaluation of TAK.

RECENT FINDINGS

MRI/A avoids the risks of arterial puncture, iodinated contrast load, and radiation exposure, while providing information on arterial wall anatomy and obtaining a generalized arterial survey in TAK. Ultrasound can be helpful in detecting sub-millimeter changes in wall thickness of the carotid arteries and in differentiating TAK from atherosclerotic disease based on minimal plaque content, concentric and long segmental involvement, and location of lesion. Like MRI, CT angiography can be used to detect areas of aortic wall thickening and obtain a generalized survey of the aorta and its proximal branches for areas of stenosis and without the risks associated with arterial puncture. However, CT provides less detailed resolution than ultrasound and incurs the risks of contrast administration. Finally, PET scanning may provide valuable information about cellular activity within an inflamed arterial wall before morphologic changes on other imaging studies.

SUMMARY

Although it is still unclear how often early arterial wall changes lead to stenotic lesions, use of these modalities in combination, for both routine monitoring and evaluation of new symptoms, may facilitate the detection of TAK disease activity at a more treatable stage.

Implications of PET based molecular imaging on the current and future practice of medicine

The last quarter century has witnessed the introduction of a variety of powerful techniques that have allowed visualization of organ structure and function with exquisite detail. This in turn has brought about a true revolution in the day-to-day practice of medicine. Structural imaging with x-ray computerized tomography and magnetic resonance imaging has added tremendously to many areas of medicine, including preoperative evaluation of patients. Many surgical procedures have been replaced by minimally invasive techniques, which have become a reality only because of the availability of modern imaging modalities. However, despite such accomplishments, structural imaging is quite insensitive for detecting early disease in which there often are no gross structural alterations in organ anatomy. Therefore, these modalities should be complemented by methodologies that can detect abnormalities at the molecular and cellular levels. The introduction of [(18)F]-fluorodeoxyglucose positron emission tomography (FDG-PET) in 1976 as a molecular imaging technique clearly has shown the power of this approach for treating a multitude of serious disorders. The impact of FDG-PET has been particularly impressive in patients with cancer diagnosis, for whom it has become important in staging, monitoring response to treatment, and detecting recurrence. In this review, we emphasize the role of FDG-PET in the assessment of central nervous system maladies, malignant neoplastic processes, infectious and inflammatory diseases, and cardiovascular disorders. New radiotracers are being developed and promise to expand further the list of indications for PET. These include novel tracers for cancer diagnosis and treatment capable of detecting hypoxia and angiogenesis. Prospects for developing new tracers for imaging other organ diseases also appear very promising.

The role of 18F-FDG PET in characterising disease activity in Takayasu arteritis

Takayasu arteritis (TA) is a rare, sporadic and chronic inflammatory arteritis, which predominantly affects the aorta and its branches. Diagnosis can be difficult and there are limitations to the current diagnostic work-up. By detecting areas of active glucose metabolism present in active vasculitis, imaging with fluorine-18 fluorodeoxyglucose positron emission tomography ((18)F-FDG PET) could potentially have a role in the management of TA. Our aim was to assess this role by reviewing 28 (18)F-FDG PET scans performed on 18 patients suspected of having TA. All patients had full clinical and laboratory assessment, cross-sectional imaging and angiography, and 16/18 satisfied the American College of Rheumatologists' criteria for TA. (18)F-FDG PET achieved a sensitivity of 92%, a specificity of 100%, and negative and positive predictive values of 85% and 100% respectively in the initial assessment of active vasculitis in TA. We conclude that (18)F-FDG PET can be used to diagnose early disease, to detect active disease (even within chronic changes) and to monitor the effectiveness of treatment.

Periaortitis: Gadolinium-enhanced Magnetic Resonance Imaging and Response to Therapy in Four Patients

The objective of this study was to define clinical and imaging characteristics of periaortitis prior to and after therapy with immunosuppressive drugs. Four consecutive patients with periaortitis (two secondary to atherosclerosis and two with rheumatic diseases) were studied with contrast-enhanced CT and magnetic resonance angiography (MRA), rheumatologic serologies, and acute-phase reactants. All were treated with corticosteroids and two patients received immunosuppressive agents. Patients were followed with serial MRA scans, CT scans, and clinical exams. Prior to treatment, all patients demonstrated a rind of periaortic tissue, which was enhanced with both contrast-enhanced CT as well as gadolinium-enhanced MRA. Clinical symptoms resolved and rind contracture occurred in all cases following therapy. Enhancement of the rind persisted despite the clinical improvement in all patients. No patient developed an aortic aneurysm or retroperitoneal fibrosis during the follow-up period. Corticosteroid/immunosuppressive treatment was continued for an average of 41 months. At 62 months of total follow-up, there has been no recurrence of periaortitis by clinical and/or radiologic exam. Treatment of periaortitis with corticosteroids and immunosuppression therapy leads to resolution of clinical symptoms and radiologic contracture of the periaortic rind. Patients responded to therapy without developing progressive fibrosis or aneurysm. MRA allows safe and repetitive imaging of periaortitis and provides excellent definition of lumenal abnormalities including plaque rupture.

Incidence and predictors of large-artery complication (aortic aneurysm, aortic dissection, and/or large-artery stenosis) in patients with giant cell arteritis: A population-based study over 50 years

OBJECTIVE

To determine the incidence and predictors of large-artery complication (aortic aneurysm, aortic dissection, and/or large-artery stenosis) in patients with giant cell arteritis (GCA).

METHODS

The cohort of all residents of Olmsted County, Minnesota, in whom GCA was diagnosed between January 1, 1950, and December 31, 1999, was followed up. The incidence of aortic aneurysm, aortic dissection, and large-artery stenosis was determined. Possible predictors and correlates of large-artery complication were assessed.

RESULTS

Forty-six incident cases of large-artery complication (representing 27% of the 168 patients in the cohort) were identified. These included 30 incident cases (18%) of aortic aneurysm and/or aortic dissection. Of these cases, 18 (11%) involved the thoracic aorta, with aortic dissection developing in 9 (5%). There were 21 incident cases (13%) of large-artery stenosis. Fifteen patients (9%) had incident cervical artery stenosis, and 6 (4%) had incident subclavian/axillary/brachial artery stenosis. One patient (0.6%) had incident iliac/femoral artery stenosis attributable to GCA. Hyperlipidemia and coronary artery disease were associated with aortic aneurysm and/or dissection (P < 0.05 for both). Cranial symptoms (headache, scalp tenderness, abnormal temporal arteries) were negatively associated with large-artery stenosis (hazard ratio [HR] 0.10 [95% confidence interval (95% CI) 0.03-0.35, P < 0.0005]), as was a higher erythrocyte sedimentation rate (HR 0.80 [95% CI 0.67-0.95, P < 0.05] per 10 mm/hour).

CONCLUSION

Large-artery complication is common in GCA. Increased awareness of large-artery complication in GCA, particularly early-occurring aortic dissection, may decrease associated mortality.

Early diagnosis and follow-up of aortitis with [(18)F]FDG PET and MRI

The aim of this prospective study was to compare fluorine-18 fluorodeoxyglucose ([(18)F]FDG) positron emission tomography (PET) with magnetic resonance imaging (MRI) in patients with early aortitis, at the time of initial diagnosis and during immunosuppressive therapy. The study population consisted of 15 patients (nine females and six males; median age 62 years, range 26-76 years) who presented with fever of unknown origin or an elevated erythrocyte sedimentation rate or elevated C-reactive protein and who showed pathological aortic [(18)F]FDG uptake. Fourteen of these patients had features of early giant cell arteritis (GCA), while one had features of early Takayasu arteritis. During follow-up, seven PET scans were performed in six patients with GCA 4-30 months (median 19 months) after starting immunosuppressive medication. The results of [(18)F]FDG imaging were compared with the results of MRI at initial evaluation and during follow-up and with the clinical findings. At baseline, abnormal [(18)F]FDG uptake was present in 59/104 (56%) of the vascular regions studied in 15 patients. Seven follow-up PET studies were performed in six patients. Of 30 regions with initial pathological uptake in these patients, 24 (80%) showed normalisation of uptake during follow-up. Normalisation of [(18)F]FDG uptake correlated with clinical improvement and with normalisation of the laboratory findings. All except one of the patients with positive aortic [(18)F]FDG uptake were investigated with MRI and MRA. Thirteen of these 14 patients showed inflammation in at least one vascular region. Of 76 vascular regions studied, 41 (53%) showed vasculitis on MRI. Of 76 vascular regions studied with both PET and MRI, 47 were concordantly positive or negative on both modalities, 11 were positive on MRI only and 18 were positive on PET only. MRI was performed during follow-up in six patients: of 17 regions with inflammatory changes, 15 regions remained unchanged and two showed improvement. Whole-body [(18)F]FDG PET is valuable in the primary diagnosis of early aortitis. The results of [(18)F]FDG PET and MRI in the diagnosis of aortitis in this study were comparable, but FDG imaging identified more vascular regions involved in the inflammatory process than did MRI. In a limited number of patients [(18)F]FDG PET was more reliable than MRI in monitoring disease activity during immunosuppressive therapy.

Positron emission tomography imaging in nonmalignant thoracic disorders

The role of the fluorodeoxyglucose (FDG) technique positron emission tomography (PET) is well established in the management of patients with lung cancer. Increasingly, it is becoming evident that FDG-PET can be effectively employed to diagnose a variety of benign pulmonary disorders. Knowledge of such applications further expands the domain of this powerful modality and further improves the ability to differentiate benign from malignant diseases of the chest. We describe pertinent technical factors that substantially contribute to optimal imaging of the thoracic structures. Particularly, the complementary role of attenuation correction (AC) to that of non-AC images is emphasized. We further outline the need for and the state of the art for co-registration of PET and anatomic images for diagnostic and therapeutic purposes. We then review patterns of physiologic uptake of FDG in thoracic structures, including the lung, the heart, the aorta and large arteries, esophagus, thymus, trachea, thoracic muscles, bone marrow, and joints and alterations following radiation therapy to the thorax. A great deal of information is provided with regard to differentiating benign from malignant nodules and in particular, we emphasize the role of dual time point imaging and partial volume correction for accurate assessment of such lesions. Following a brief review of the diagnostic issues related to the assessment of mediastinal adenopathies, the role of FDG-PET imaging in environment-induced lung diseases, including pneumoconiosis, smoking, and asthma are described. A large body of information is provided about the role of this technology in the management of patients with suspected infection and inflammation of the lungs such as acquired immunodeficiency syndrome, fever of unknown origin, sarcoidosis, chronic granulomatous disease and monitoring the disease process and response to therapy. Finally, the value of FDG-PET in differentiating benign from malignant diseases of the pleura including asbestosis-related disorders is described at the conclusion of this comprehensive review.

[Horton's disease and extra-temporal vessel locations: role of 18FDG PET scan. Report of 3 cases and review of the literature]

PURPOSE

We report three cases of Horton's disease, in which F18-Fluorine-2-Deoxy-D-Glucose (18FDG) positron emission tomography (PET) demonstrated a clinically unsuspected extra-cranial vessels hypermetabolism.

METHODS

Fully corrected whole-body PET was performed in three patients (two women, one man) for exploring a marked inflammatory syndrome. Scanning was acquired 60 min after i.v. injection of 222 MBq of 18FDG in average.

RESULTS

In two patients with histologically proven Horton's disease, PET alone showed increased glucose metabolism involving the carotid and sub-clavian arteries as well as the ascending aorta, aortic arch, thoracic and abdominal aorta, and the iliac and femoral arteries. In the third patient, by detecting cervical, thoracic and abdominal vessel hypermetabolism, PET non-invasively contributed to the diagnosis of giant cell arteritis. All patients had complete clinical and biological response to corticoids. PET controls performed 3- to 6-months post-treatment, confirmed the disappearance of the metabolic stigma.

CONCLUSION

18FDG PET may show an increased glucose metabolism in asymptomatic extracranial vessels locations of Horton's arterities. If these observations are confirmed on controlled trials, PET could be particularly useful for non-invasive diagnosing, staging and monitoring atypical clinical forms of Horton's disease. The metabolic imaging could also contribute to a better understanding of the pathogenesis of GCA.

Aortitis

Aortitis is defined as an inflammatory process that involves one or more layers of the aortic wall (internal elastic lamina, tunica media, and adventitia) and can be caused by multiple mechanisms. Clinical features are usually nonspecific and a high index of suspicion is required for making the diagnosis. Although noninvasive imaging studies are being increasingly used in evaluating patients for diagnosis, angiography remains the gold standard for confirming aortic involvement. When tissue is available, pathologic examination can aid in clarifying the diagnosis. Aortitis, irrespective of the underlying cause, frequently displays similar clinical, pathologic, and arteriographic features and therefore understandably presents a therapeutic and diagnostic dilemma. Whatever the cause, early identification and aggressive treatment is required in order to avert the potentially life-threatening sequelae. The treatment of aortitis is determined by the underlying cause. If diagnosed early, infectious aortitis responds to appropriate antimicrobial therapy, whereas noninfectious, immune-mediated aortitis requires immunosuppressive therapy. However, in many instances, primarily because of the delay in diagnosis, surgical intervention is necessary to treat the associated anatomic and physiologic sequelae. Less definitive and more controversial is the role of inflammation in both primary and secondary accelerated atherosclerosis of the aorta and its modality of treatment.

18-fluorodeoxyglucose positron emission tomographic imaging in the detection and monitoring of infection and inflammation

During the past decade, 18-fluorodeoxyglucose (FDG) positron emission tomography (PET) has rapidly evolved from a pure research modality to a clinical necessity. FDG-PET was introduced to determine the state of brain function in physiologic and pathologic states. Its use as a powerful tool to diagnose, stage, and monitor patients with a variety of malignancies has been truly revolutionary. However, FDG is a nonspecific tracer and it has been found to accumulate at sites of infection and inflammation. It is becoming evident that PET imaging will play a major role in the treatement of patients with suspected infection and inflammation. PET has been shown to be particularly valuable in the evaluation of chronic osteomyelitis, infected prostheses, sarcoidosis, fever of unknown origin, and acquired immunodeficiency syndrome. Because of its ability to quantitate the rate of FDG uptake, PET may prove to be a powerful modality for the monitoring of disease activity and response to therapy. Novel PET tracers are being tested for imaging infection and inflammation that may further enhance the role of this technique in the appropriate clinical setting. PET imaging to detect and characterize infection and inflammation may become a major clinical indication in the day-to-day practice of medicine.