Dual time point imaging of FDG PET/CT in a tuberculous spondylodiscitis
1 Discipline of Medical Radiations, School of Medical Sciences, RMIT University, Melbourne, Victoria, Australia.
2 Medical Imaging Department, Faculty of Health
Sciences, University Technology MARA, Selangor, Malaysia.
3 Radiology Department, Serdang Hospital, Selangor, Malaysia.
4 Nuclear Imaging Unit, Faculty of Medicine and
Health Sciences, University Putra Malaysia, Selangor, Malaysia.
Dual Time Point Imaging (DTPI) technique is a specialised
protocol adopted in 18F-Fluorodeoxyglucose (FDG) Positron Emission
Tomography (PET) imaging. This technique is claimed to be useful in
differentiating malignant and infective lesions. The authors adopted this
technique in a patient diagnosed with tuberculous spondylodiscitis and psoas
abscess which demonstrated higher Maximum Standardized Uptake Value (SUVmax)
during initial scans as compared with those obtained on delayed scans. The
SUVmax changes between the two time points are believed to be a valuable finding
for chronic granulomatous infective lesions such as tuberculosis. � 2010
Biomedical Imaging and Intervention Journal. All rights reserved.
Keywords: Tuberculosis; Positron Emission Tomography/Computed
Tomography; FDG; Dual Time Point Imaging
In recent decades, there has been a massive evolvement in
the nuclear medicine field with the advent of new integrated functional imaging
modality, Positron Emission Tomography/Computed Tomography (PET/CT). 18F-Fluorodeoxyglucose
(FDG) is the most commonly used tracer for PET/CT imaging, especially on cancer
diagnosis. Unfortunately, the uptake of FDG has been found to be non-exclusive
to malignant tissues alone. Previous report has found that lesions with high
concentration of inflammatory cells, such as neutrophils and activated
macrophages, will show an incremental uptake of FDG, which potentially can
result in false-positive interpretation .
Routine diagnostic work-out for spine infection commonly
employs a multimodality imaging approach; in particular, magnetic resonance
imaging (MRI) and nuclear medicine studies including FDG PET [2, 3].
Current FDG PET/CT protocol for infectious/inflammatory
investigation is the same as oncology cases . To the authors� knowledge,
Dual Time Point Imaging (DTPI) using FDG in PET/CT for tuberculous
spondylodiscitis with psoas abscess has not been previously described. The aim
of this study was therefore to investigate the changes occurring over these two
A 26-year-old woman presented with history of backache for
the past several months and increasing in severity. This was associated with
low-grade fever and lethargy. Routine physical examination and investigations
including total white count, sputum test and urine examination were all
negative for tuberculosis (TB) infection, and there was no evidence of lung
infections. Other imaging studies including the ultrasonography examination
demonstrated that there was an abscess found in her left psoas muscle. Whole
body FDG PET/CT examination was done to localise the lesion and identify the
extension of the infection. She was confirmed for TB through response to
anti-TB treatment where there was a complete metabolic remission upon repeating
follow-up PET/CT scanning after six months following completion of the
A DTPI approach was applied during the scanning session.
All imaging studies were performed on a dual-modality PET/CT system (Biograph
2, Siemens Medical Solutions�). Transmission and emission imaging (Examination
1) started 58 min after intravenous injection of 336.7 MBq (equivalent to 9.1
mCi) of FDG. Total acquisition time for the initial whole body PET/CT was about
30 min. Using the same parameters, a delayed PET/CT imaging (Examination 2) was
obtained about 128 min after FDG injection (about 2 hours delay).
Image analysis and semi-quantitative evaluation
PET image datasets were reconstructed iteratively using CT
data sets for attenuation correction calculation, creating fusion PET/CT image
sets. All co-registered images were reviewed on a workstation in transaxial,
coronal and sagittal planes along with Maximum Intensity Projection (MIP)
images. The CT images were set in the soft tissue window setting as for general
image interpretation. These image analyses were visually and semi-quantitatively
interpreted by two experienced nuclear medicine physicians. The evaluating
physicians were aware of the patients� clinical history, including the results
of radiological examinations.
The degree of FDG uptake activity in the lesion was
visually scored using a 4-point grading system: normal background uptake (Grade
1), mild uptake as in liver or spleen (Grade 2), higher uptake than liver or
spleen (Grade 3) and very high uptake with equal or more than brain/bladder
uptake (Grade 4). Grade 3 or 4 was considered to represent significantly high
FDG uptake. For semi-quantitative analysis, a volume of interest (VOI) was
carefully drawn around the site of suspected lesions using the transaxial
images. The size of FDG avid lesions was measured on high-resolution CT scan
images. For the comparison of initial and delayed images, both images were
displayed simultaneously using the same windowing and levelling.
On fusion PET/CT images, there was a huge area detected
with high FDG uptake found at lumbar vertebrae region. This finding was highly
suspected to be a tuberculous spondylitis with psoas muscle involvement (Figure
1a). The SUVmax values were obtained on axial PET image (Figures 1b to 1e). For
third lumbar-fourth lumbar (L3-L4) intervertebral disc and psoas muscle, the
SUVmax1 values were 10.2 and 9.7, respectively, whereas, both lesions were
declined on delayed imaging i.e. SUVmax2 were 8.3 and 7.3.
FDG PET/CT was performed on a confirmed tuberculous
spondylodiscitis patient; at the level of her lumbar region. Based on the
authors� observation, the intensity of FDG uptake of the lesions changed with
time following injection. Several studies have reported that tuberculosis can
produce high FDG uptake during PET scanning [5, 6], which potentially can cause
false positive findings. In overcoming the difficulties in the diagnosis of
spine infections, FDG PET offers better imaging features as compared with other
imaging modalities. It was possible to clearly differentiate between infections
of vertebrae and adjacent soft tissue infections by using FDG PET [2, 3].
Furthermore, this modality is also capable of demonstrating the extent of the
DTPI protocol allows comparison between the two sets of
images acquired at two different points in time. The characteristic appearance
of the lesion and the differences on the intensity of FDG uptake within the
studied lesion were recorded. SUVmax values were used to estimate these
differences as DTPI protocol has been utilised by others [7, 8]. A recent study
by Suga et al.  reported that the combination of early SUVmax of more than
3.0 or delayed SUVmax of more than 4.0 was an optimal parameter in
differentiating metastatic and benign lymph nodes of the thoracic region. This
finding was supported by the fact that FDG uptake in malignant tumours was
increased up to several hours after the injection time, and vice versa for
benign lesions . Therefore, the utilisation of DTPI protocol may improve the
sensitivity and specificity of PET/CT imaging modality .
The SUVmax values of the lesions in this case showed a
relatively high FDG uptake, up to 10.2 during the first scan. A previous study
also found that the SUVmax value of a positive tuberculous spondylodiscitis was
as high as 18.1 . In an earlier animal study, Yamada et al.  found that
inflammatory tissue gradually reached peak FDG uptake for about 60 min after
injection, slowly decreasing over time. Therefore, the high FDG uptake value
during the first scan with slight reduction on second scan in this case is
In conclusion, the results of the present study provide
further evidence that DTPI protocol of FDG PET/CT appears to be a useful and
non-invasive method in the detection of tuberculous spondylodiscitis. Further
investigation in a larger group of patients is warranted.
Figure 1 (a) Coronal plane of fusion PET/CT image; showing avid FDG uptake at L3-L4 region affecting the left paravertebral muscle (white arrow); (b) and (c) axial PET images of Examination 1; (d) and (e) axial PET images of Examination 2.
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|Received 11 November 2009; received in revised form 14
February 2010, accepted 15 February 2010
Correspondence: Head of Nuclear Imaging Unit, Faculty of Medicine and Health Sciences, University Putra Malaysia, Serdang 43400, Selangor, Malaysia. E-mail: firstname.lastname@example.org (Abdul Jalil Nordin).
Please cite as: Abdul Razak HR, Abdul Rahim N, Nordin AJ,
Dual time point imaging of FDG PET/CT in a tuberculous spondylodiscitis, Biomed Imaging Interv J 2010; 6(2):e18