What is suv in pet scan

Reference article, Radiopaedia. URL of Article. It is important to note that many infectious and inflammatory processes will also have high SUV. Nucl Med Commun. Nucl Med Commun link - Pubmed citation.

Promoted articles advertising. Loading more images Close Please Note: You can also scroll through stacks with your mouse wheel or the keyboard arrow keys. Loading Stack - 0 images remaining. By System:. Patient Cases. Contact Us. The role of the referring physician also comes into play here. 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. Metrics details. Interpretation requires integration of the metabolic and anatomic findings provided by the PET and CT components which transcend the knowledge base isolated in the worlds of nuclear medicine and radiology, respectively.

This encompasses how we display, threshold intensity of images and sequence our review, which are essential for accurate interpretation. For interpretation, it is important to be aware of benign variants that demonstrate high glycolytic activity, and pathologic lesions which may not be FDG-avid, and understand the physiologic and biochemical basis of these findings.

This is a modality with many patterns of structural, physiologic and biochemical abnormalities that transcend the boundaries previously isolated in the worlds of nuclear medicine or radiology in characterising pathological conditions, particularly including cancer. Future articles in this series will address the use of other tracers pertinent to other cancers.

Patient preparation is important in acquiring good quality studies and it is the responsibility of the PET specialist to ensure that appropriate protocols are in place to prevent non-diagnostic or suboptimal studies. Detailed discussion of acquisition parameters is beyond the scope of this review but includes preparation of diabetic patients, strategies to minimise brown fat activation, as well as prescription of the extent of the field-of-view and the positioning of the patient to address the clinical question.

For example, we position the patient with their arms down for head and neck malignancies but with their arms up for thoracic cancers. It is also important to determine the methodology to be used for CT acquisition. This varies widely according to local practice and our approach is discussed in further detail later in this manuscript.

An important aspect of interpretation is assessment of the technical adequacy of the study and ideally should be done before the patient leaves the department to enable repeat acquisition of any critical regions inadequately assessed on the initial examination.

Correct and consistent windowing is key to avoid both over- and under-interpretation of findings and to maintain the consistency required for accurate comparison of multiple studies. This also aids presentation of findings to referrers and patients. The primary data from PET has been traditionally displayed on a linear grey scale.

This is because the human eye is adept at discerning subtle differences in contrast from white through grey to black. The lower threshold of this display should be set at zero white while the upper threshold needs to be manipulated to obtain consistent display of physiological and pathologic uptake.

Consequently, the intensity of normal tissues should be within the lower-to-middle portion of the dynamic range while the upper range used to demonstrate the range of intensities that might exist in pathological processes characterised by high glycolytic activity.

By maintaining a reasonable spectrum of grey shades for display of normal tissues it is possible to detect faint lesions in areas of low background activity, such as the lung. Our preference is to have the most intense voxels in the normal liver appearing just below the middle of the grey scale range, which will be a light to mid-grey Fig. Use of a colour scale is required for superimposition of functional images over the CT. 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.