What does intense fdg uptake mean

They need to provide specialty radiologists with any lab work or other scans performed, as well as general clinical information about how the patient is feeling. FDG PET scans have great potential to guide patients and their doctors through the diagnostic and management stages of cancer. But accurately interpreting PET scans is complex - more so than other types of imaging. My advice is to make sure that all your medical imaging is interpreted by the appropriate specialist. There are a lot of radiologists who, after completing a short training, start reading PET scans.

Another reader might be able to offer a different insight that might help clarify the clinical status better. Providing second opinions through DocPanel, I've found that, oftentimes, patients have a lot of questions.

Being able to help people understand their scan gives them the confidence they deserve to have before going into treatment. It's also a great way to get peace of mind that current therapy is indeed working. Nuclear medicine imaging uses small amounts of radioactive material called a tracer to examine physiology cells, molecules, chemical interactions, etc. Before the scan is performed, a small amount of fluorodeoxyglucose FDG is injected into the patient.

The FDG tracer produces color-coded images of the body that show both normal and cancerous tissue. What capabilities does it have that other radiology scans lack? In terms of diagnosis, PET helps us pick up on abnormal behavior and figure out that something is a problem, even when it appears to be normal. Let me explain that in a little more detail. After that, the patient can begin treatment. Other times, cancer might not be so detectable. In some cases, cancer may be hidden inside of what looks like normal tissue.

We prefer to use the "rainblow" colour scale that has low activity regions displayed in the blue-green range and higher intensity regions in the orange-red spectrum. With this colour scale, the liver will generally appear blue with flecks of green with adjusgment if not Fig. This corresponds to an upper SUV window threshold of 8—10 and will usually achieve an appropriate contrast, except in very large patients in whom this may make the liver too dark. This is because adipose tissue contributes to the weight correction of administered activity, which is used for SUV calculation, but does not itself take up FDG.

This means that more FDG is available for uptake in other tissues, including the liver. However, this may be counteracted by deposition of fat in the liver in obese subjects. This will usually be apparent by virtue of increased relative uptake in the spleen, which is generally marginally less intense than the liver.

The brain will usually be nearly black with this scaling. This is unless cortical glycolytic activity is reduced by metabolic processes, especially by hyperglycaemia, or neurological conditions such as dementia. In children requiring general anaesthesia during the uptake and scanning procedure, cortical activity can also be significantly reduced. There are also changes in the brain during childhood maturation [ 2 ]. The PET window intensity is adjusted so that the liver appears light to mid-grey on the grey scale, corresponding to flecks of green in the liver on the rainbow colour scale.

Despite the difference in SUVmax of the liver secondary to differences in weights of the two patients a and b , the liver intensity this appears the same in both patients.

Under fasting conditions, glucose and its analogue, FDG, have facilitated uptake into the liver and therefore generally this organ has significantly higher activity than the blood. By definition, any structure with uptake more intense than that in the liver must also have facilitated FDG uptake and trapping.

The advantage of using the liver as a reference tissue is also aided by this organ having rather low variability in metabolic activity [ 3 ]. It is, however, inappropriate to threshold for liver uptake if it is not deemed normal due to diffuse malignant infiltration, sarcoidosis, or fatty infiltration. This can be detected visually if there is marked discrepancy between liver and spleen intensity, although with sarcoidosis or lymphoma both can be increased.

Our practice of thresholding the grey and colour scale to liver as detailed above results in similar image intensity to a fixed upper SUV threshold of 8 to When the liver is abnormal and cannot be used as a reference organ, we use the default SUV setting of an upper SUV threshold of 8. The same SUV threshold as that used for the whole body study should be applied when additional separate series are acquired e. Since some disease processes can have extremely high SUV values, it may be necessary to increase the upper threshold to appreciate the dynamic range of glycolytic activity.

This is particularly important in diseases where there can be considerable heterogeneity in disease. Standard thresholds provide a good representation of the extent of disease but using a higher upper threshold to display the images can help to identify the regions of likely transformation or different disease biology and can aid biopsy site selection Fig.

This patient presented with suspected metastatic nasopharyngeal cancer. Initial workup with endoscopic ultrasound and biopsy of the subcarinal node was non-diagnostic with necrotic tissue. The findings suggest a different tumour biology at this site with necrosis. When feasible, we recommend biopsy of the most FDG-avid lesion which likely represents the site of most aggressive disease and least likely to be non-diagnostic.

In summary, the PET study windowed narrowly is primed for sensitivity whereas a wider window enables superior characterisation. It is also a psychologically intuitive scheme with blue-green shades being cool colours whereas yellow-orange colours denote caution and reds, danger.

Like a traffic light, we teach our referrers that these spectrums usually represent benign, equivocal and pathological findings, respectively. Clearly, this is an oversimplification, but it enables one to eyeball the PET image and decide if the uptake is of low, moderate or high metabolic activity.

We often see studies, particularly from practices that have more experience with CT than PET, that have clearly had the threshold altered to render them red, or not, depending on whether the reader considers them more, or less, likely to be malignant based on the CT characteristics. While this might be a reasonable approach to communicate the site of a lesion, it diminishes the power of PET to characterise disease based on the degree of its metabolic activity.

To avoid the risks associated with this scale, some manufacturers set the default colour scale to a dichotomous range, such as blue-yellow or brown-gold see Fig. This does not carry the psychological power of the rainbow scale but can be useful for displaying sites of presumed disease against the background of CT while reducing the risk of false-positive results due to use of an inappropriate display threshold.

Patient with metastatic colorectal carcinoma and hepatic metastasis. The fused image is presented in different colour scales. The human eye is very sensitive in detecting differences of intensity within a grey scale but not so good within a single colour spectrum.

Moreover, the highest intensity on this scale is sometimes white, which is essentially uninterpretable when superimposed on a grey scale CT image.

Standardised windows have been developed that set upper and lower levels for Hounsfield units that optimally display the range of densities pertinent for a particular tissue. We routinely review soft tissue, lung and bone windows but in appropriate situations will use other specialised windows. Just as the profession has imposed certain discipline in the use of standardised windows for use on CT, we believe that there should be greater harmonisation of display of PET images.

Initial review of the images blinded to patient history or indication is valuable as it enables an unbiased assessment. The black-and-white cine maximum intensity projection MIP is foremost in this initial review. The reconstruction method of these images tends to suppress noise and highlight regions of increased activity. Furthermore, the brain can appreciate these images as being volumetric, especially when rotating. This particularly aids recognition of the shape of regions increased activity, and particularly whether they are spherical, tubular or geographic.

With experience, key findings are often established within seconds by review of this series. By definition, this image is relatively insensitive to regions of reduced activity. It is important to review these images on a workstation that has capacity to triangulate findings in axial, coronal and sagittal planes.

We find the coronal images particularly helpful for detecting small abnormalities, particularly within the lungs and subcutaneous tissue. Any lesions identified on the PET are then correlated with the CT images, reviewing soft tissue, lung and bone windows as appropriate to the location of the abnormality. We selectively review the non-attenuation corrected NAC series when there is uncertainty about possible reconstruction artefacts due to metallic objects or patient movement between PET and CT components.

Finally, it is important to widen the PET window in order to review the brain, otherwise easily discernible abnormalities can be missed see Fig. Patient with diffuse large B cell lymphoma. This corresponded to a MRI abnormality which was not reported prospectively but identified following targeted review after the PET scan.

Changing the PET window so that abnormalities can be identified above physiologic brain activity should be a routine component of image review. This is often the preferred method of experienced radiologists who are sometimes more comfortable reviewing the CT than looking at stand-alone PET images.

Those disposed to this method will also generally prefer to obtain a full diagnostic CT as part of the examination. The advantages and disadvantages of these differing methods will be discussed subsequently. As a final pass, we review the CT images sequentially on soft tissue, lung and bone windows to identify structural abnormalities not previously identified on PET review. Interpretation of structural abnormalities that are not associated with metabolic abnormality requires particular care and can give significant insights into the nature of pathological processes.

The reader is directed to the initial article in this series, which details many of the principles that we use in formulating an impression of a scan, in reporting its findings and reaching a conclusion. When high metabolic activity is present, one of the primary aims is to ascertain if the aetiology is malignant, benign or inflammatory. In early PET literature focusing on analysis of solitary pulmonary nodules, some researchers defined malignancy based on a SUV max threshold of greater than 2.

We contend that SUV analysis has virtually no role in this setting. Far more important than the SUV max is the pattern rather than intensity of metabolic abnormality and the correlative CT findings. Our number one rule is that tumours grow as spheres, whereas inflammatory processes are typically linear and track along soft tissue boundaries such as pleural surfaces or fascial planes see Fig. This patient had suspicion of pelvic recurrence in the setting of prior surgical excision for rectal carcinoma.

There was intense uptake in the known pre-sacral soft tissue thickening a and c red arrow with SUVmax of The linear morphology on the coronal image b suggested this was more likely inflammatory than malignant. A separate linear tract of metabolic activity was also seen green arrow extending from the pre-sacral abnormality to the peri-anal region not shown. All abnormalities resolved following antiobiotic therapy confirming inflammatory aetiology.

Occam's razor teaches us to look for a single cause that will explain all the findings on a particular study. Many benign and inflammatory processes are also associated with high glycolytic activity. Whilst some require further investigation, many have characteristic appearances that enable confident characterisation. A variety of potential pitfalls are detailed in Table 1 , most of which do not require further investigation.

Recognition of other pitfalls requires knowledge of the typical pattern of the various malignancies but is beyond the scope of this review. Patient with prior lung malignancy presents for surveillance. The study demonstrates a typical appearance of inflammatory change post talc pleurodesis with intense multi-focal uptake evident throughout the pleural surface a.

Such change can persistent for many years after pleurodesis. Patient with non-small cell lung cancer treated with curative intent radiotherapy.

Follow-up CT 9 months later demonstrated enlargement of multiple mediastinal nodes considered likely to represent malignant aetiology. Given the symmetry of distribution in hilar and mediastinal nodes the aetiology was considered inflammatory, which was confirmed by resolution on follow-up.

Thresholding the PET with a SUV threshold of 5 h — i might lead to erroneous description of intense uptake and interpretation as malignant in aetiology. Appearance of physiologic adnexal uptake observed mid-cycle. However, the gastroesophageal junction may show normal uptake. Homogenous low uptake within the stomach wall is relatively common. If the stomach is contracted, this may appear as a round focal area of moderate activity.

Small intestinal uptake is variable and usually of low grade. Colonic activity may be quite marked, particularly in the caecum and rectosigmoid junction. In general, uptake is highest in the colon, followed by the small bowel, with the stomach showing uptake of lowest intensity. Bowel uptake can be diffuse but not focal. Testicular uptake in a male is normally seen and is symmetrically diffuse. However, in the female, ovarian uptake is not usually seen.

If ovarian uptake is seen in a post-menopausal patient, malignancy must be ruled out. Faint uterine activity is common. Uptake in the uterus has been reported during menstruation and ovulation in pre-menopausal women and in relation to fibroids, but in practice it is an uncommon finding Figure 7. Activity is seen in the endometrial cavity in this patient who was menstruating arrow. A common area for interpretative pitfall is related to FDG uptake in active skeletal muscle. In relaxed and rested patients, no significant skeletal muscle uptake is noted.

Muscular imbalance, e. Most skeletal muscle activity can easily be recognised as such. There is increased activity seen in the neck and shoulder muscles. Brown fat is most prominent in newborns and diminishes with age. Unlike white adipose tissue it has the capacity to generate heat. It is stimulated by several factors, including exposure to cold. The incidence of tracer uptake in brown fat also increases in women. Areas in which prominent tracer uptake into brown fat is seen are in the supraclavicular regions followed by the axillae, mediastinum, intercostal, paravertebral, and perinephric regions Figure 9.

Even when recognised as a benign variant, the degree of uptake can easily obscure malignant lymphadenopathy in the region. It is essential to be aware of the clinical correlation of other sites of uptake or absence of uptake that may be of no significance. These include healing fractures less than three months and healing surgical incision sites, sites of previous radiation therapy no or low uptake , joint prosthesis not infected , degenerative joint disease, stoma sites colostomy, ileostomy, tracheostomy , chest tube drainage site, biopsy sites and porta-cath sites.

Adequate patient preparation is necessary to minimise the appearance of potential artefactual uptake patterns that make interpretation difficult.

Exercise should be avoided on the day of scanning to avoid muscle uptake. Patients need to be totally relaxed and kept warm. If the patient is cold and nervous, clenching their hands will increase muscle activity in the forearms, resulting in increased tracer uptake. Stress-induced muscle tension is often seen in the trapezius and paraspinal muscles. Those known to have muscle spasms may be administered benzodiazepines before the FDG injection. This minimises uptake by normal skeletal muscles, particularly the proximal muscles, which would make neck and supraclavicular nodal evaluation difficult.

Patients are advised to avoid talking, chewing and swallowing too much to reduce accumulation of tracer into muscles of mastication and the larynx. Brown fat has the capacity to generate heat.

It is known to increase glucose uptake when the sympathetic nervous system is activated by cold stimulation. Therefore, keeping the patient warm may be helpful in reducing uptake into brown fat. For oncological indications, an extended body survey is usually acquired, typically including images from the skull base to the proximal thighs.

The typical acquisition time is less than a minute for the CT scan. The CT component is performed as a non contrast low radiation dose scan. It is performed primarily for attenuation correction and anatomical correlation.

Next, without the patient moving or changing position, a PET scan encompassing the same imaging field is performed. Many of the problems with regard to pitfalls and areas of normal uptake described above are solved with the use of PET CT imaging.

PET CT imaging will reduce diagnostic uncertainty with respect to physiologic activity by allowing more confident interpretation related to areas of anatomically normal structures. It merges anatomic and molecular data with the aim of producing one integrated diagnosis.