SPECT-CT Scanning

Back and neck pain is one of the most common reasons people see a doctor, yet it is also one of the hardest problems to pin down. The trouble is rarely a lack of findings on a scan — it is usually the opposite. By the time most adults reach middle age, ordinary scans of the spine show all sorts of changes: worn discs, bony spurs, narrowed joints, and signs of general wear and tear. The difficulty is that many of these changes are completely painless. They are simply the spine showing its age, in the same way grey hair or a few wrinkles are part of getting older.

This creates a real puzzle. If someone has lower back pain and a scan shows worn discs at three different levels and arthritis in several joints, which one is actually causing the pain? Often, none of the changes that look the most dramatic are to blame, and sometimes the genuine source barely shows up at all. Standard scans are very good at showing what the spine looks like, but they struggle to show what is actually hurting.

This matters enormously, because treatment depends on getting the answer right. An injection, an operation, or a course of targeted therapy only works if it is aimed at the correct spot. Picking the wrong level, or treating several levels "just to be safe," tends to lead to bigger procedures, more recovery, and disappointing results. A scan that can tell the active troublemaker apart from the harmless background noise is therefore extremely valuable — and that is exactly what a spine SPECT/CT scan is designed to do.

A SPECT/CT scan is essentially two scans combined into one appointment. The two halves answer two different questions, and it is the combination that makes the test so useful.

The first half, the SPECT, is a picture of activity. It shows where the bones and joints of your spine are working hard — repairing, reacting, remodelling, or responding to stress and inflammation. Busy areas show up brightly, almost as if they are glowing. Quiet, settled areas stay dim.

The second half, the CT, is a detailed picture of structure. It is a clear, three-dimensional map of the bones, joints, and any metal implants in your spine, showing their exact shape and position.

On their own, each picture is only part of the story. The activity picture can show that something is busy but cannot always say precisely which bone or joint it is. The structure picture can show the anatomy in fine detail but cannot tell whether a worn-looking area is actually inflamed and painful. A computer lines the two pictures up so precisely — typically to within a few millimetres — that each bright "active" spot can be matched to the exact bone or joint underneath it. The result is a single fused image that shows not only what a part of your spine looks like, but whether it is the spot that is genuinely causing trouble.

Before the scan, you are given a small injection of a substance called a radioactive tracer. The most common one used for bone and joint imaging is a compound that seeks out active bone. After it is injected into a vein, it travels through your bloodstream and gradually settles into the skeleton. Crucially, it gathers most strongly in places where bone is actively building or repairing itself — the very places where there is likely to be a problem.

The reason it behaves this way comes down to bone biology. Bone is not a dead, static material; it is living tissue that constantly renews itself. Specialised cells are forever laying down new bone and clearing away old bone, and this turnover speeds up wherever the bone is under strain, healing, inflamed, or reacting to a nearby problem. The tracer binds to the mineral surface of bone exactly where this fresh activity is happening. So an area of high turnover collects a lot of tracer and shows up brightly, while a quiet area collects little and stays dim.

Timing is part of the design. In the first moments after the injection, the tracer is mostly still in the blood vessels, and in the minutes that follow it spreads into the soft tissues. It is only after a couple of hours that it has properly concentrated in the skeleton, which is why there is a waiting period built into the appointment. By the time the scanner takes its pictures, the tracer that has not stuck to bone has largely been cleared by the kidneys, leaving a clean image dominated by the skeleton. (This is also why you may be asked to drink plenty of fluid and empty your bladder — it helps clear the unused tracer and improves the picture.)

When the scanner runs, a special camera rotates slowly around you, building up the three-dimensional activity image. At the same time, or just before or after, the CT part captures the detailed anatomy. Software then merges the two into the fused image your specialist will read. The whole approach means structure and activity are captured in one sitting, without you having to move between machines, so the two pictures line up reliably.

To understand why this combination is so powerful, it helps to compare it with the scans most people have already had.

X-rays and CT scans are excellent at showing bones, alignment, and hardware, but they show only the physical structure. They can reveal that a joint is worn or a disc space has narrowed, but they cannot tell whether that worn joint is actually inflamed and painful right now.

MRI is superb for soft tissues — discs, nerves, ligaments, the spinal cord — and is the test of choice for many problems, especially anything involving nerve compression. But MRI shares the same core limitation when it comes to ordinary back pain: it is so sensitive that it picks up a great many age-related changes, and studies have shown again and again that a large proportion of these changes are present in people with no pain at all. A "dark disc" or a worn facet on an MRI is not proof that it hurts.

SPECT/CT adds the missing ingredient: activity. By showing which structures are metabolically busy and pinning that information onto precise anatomy, it helps separate the changes that are merely old from the ones that are actively part of the problem. It does not replace MRI — the two are complementary, and many people sensibly have both — but in the specific situation of trying to identify the source of bony or joint-related pain among several suspects, it can provide the deciding piece of information.

A SPECT/CT scan can be focused on any region of the spine, and the principle is the same wherever it looks.

The neck, or cervical spine, can be examined for neck pain and for problems in the small joints and bones of the upper spine. The mid-back, or thoracic spine, can be assessed in the same way. The lower back, or lumbar spine, is the area scanned most often, because it is by far the most common site of back pain and the place where multiple worn levels make it hardest to identify the real culprit. The base of the spine and the pelvis can also be examined, including the joints that link the spine to the pelvis — a frequently overlooked source of lower back and buttock pain that we will come to shortly.

This is where a SPECT/CT scan really earns its place. Below are the main situations in which it is used, explained in everyday terms.

The facet joints are small joints at the back of the spine, one pair at each level, that guide and limit movement. Like other joints in the body, they are lined with cartilage and can develop arthritis, becoming inflamed and painful. Pain coming from these joints is one of the more common forms of mechanical back and neck pain. It is often a deep ache that is made worse by leaning or arching backwards, and it is thought to be a significant contributor in a sizeable share of people with long-standing low back pain — depending on the study, somewhere between roughly one in six and four in ten.

The problem is that facet arthritis is extremely common on ordinary scans, and the joints that look the most worn are not necessarily the ones causing pain. This is precisely the kind of puzzle a SPECT/CT scan can help with. By showing which facet joints are metabolically active, it can highlight the joint or joints most likely to be responsible, even when many joints look worn on a CT or MRI. This information can then be used to target a diagnostic injection or a nerve-deactivation procedure (radiofrequency treatment) at the right level, rather than working through several joints by trial and error.

It is important to be honest about the limits here, because the research is genuinely mixed. Several studies have found that activity on the scan does not always line up neatly with where a person's symptoms are, and sometimes the scan and other imaging point to different joints. For this reason, a hot facet joint on a SPECT/CT scan is usually treated as a strong lead rather than a final verdict. Good practice is to confirm the suspected joint with a targeted diagnostic injection before committing to longer-term treatment. Used this way — as a guide that narrows the field and is then confirmed — the scan can make injection and denervation treatments more accurate.

The discs between the vertebrae act as cushions and allow the spine to bend and twist. When a disc degenerates, tiny tears and inflammation can develop, and this can become a source of pain in its own right, separate from any pinched nerve. Pain coming from the disc is thought to account for a large proportion of chronic low back pain — by some estimates around four in ten cases. It typically feels like a deep, dull ache that is worse with sitting and loading the spine and eased by lying down.

Diagnosing disc pain is notoriously difficult. History and examination alone are unreliable, and although MRI is the best tool for looking at the discs themselves, the link between how degenerate a disc looks and how much it hurts is far from clear. An older, invasive test called discography exists, but it is controversial, carries risks, and can produce misleading results.

SPECT/CT offers a different angle. Rather than looking at the disc directly, it looks at the bone of the vertebral endplates — the bony surfaces immediately above and below each disc. When a disc is actively inflamed, these endplates often become metabolically busy, and that activity shows up on the scan. Research has linked this endplate activity to specific inflammatory changes seen on MRI (known as Modic changes), and has shown that endplates with the most active type of these changes very often light up on SPECT/CT. In practice, this can help point to which disc level is the active pain generator, which in turn can guide a decision about focused treatment at that level.

Again, the picture is not perfect. Some people with genuine disc pain show no increased activity at all — possibly because the disc can cause pain before the neighbouring bone reacts — while some people with no pain show activity from long-standing, burnt-out changes. So a SPECT/CT result is best interpreted alongside MRI and the clinical picture rather than in isolation.

In younger people, and especially in athletes, a different problem is common: a stress injury or small fracture in a part of the vertebra called the pars interarticularis. This injury, known as spondylolysis, is typical of sports that involve repeated arching backwards — gymnastics, diving, fast bowling, weightlifting, and similar activities — and it most often affects the lowest level of the lumbar spine. It is a frequent cause of back pain in adolescents and young adults.

This is an area where SPECT/CT is particularly valuable, for two reasons. First, it is very sensitive to early bone stress, sometimes detecting a developing injury before it becomes a clear crack on other scans. Catching it early matters, because a fresh, active stress injury has a real chance of healing fully with rest and a period of reduced activity — whereas a missed injury can progress to an established, non-healing break. Second, the scan helps distinguish an active, recent injury from an old, settled one. An active injury is metabolically busy and shows up brightly; a long-standing, non-healing defect is quiet and may not show up at all. That distinction guides treatment: an active injury is worth resting and protecting in the hope of healing, while a chronic, inactive defect calls for a different approach.

Research comparing young athletes scanned with the older activity-only technique against those scanned with the combined SPECT/CT has suggested that the combined scan can shorten the delay before the right treatment is started, simply because it pins down the problem more precisely and confidently. The one caveat is that the scan relies on there being active healing to detect; in a fully established, non-healing break, it may not show anything, and its role in people who have a defect but no symptoms is not well defined.

In older adults, particularly those with thinning bones (osteoporosis), the sacrum — the large triangular bone at the base of the spine — can develop small stress fractures without any major injury. These are called sacral insufficiency fractures, and they are a treatable but frequently missed cause of lower back and buttock pain. They are more likely in people with osteoporosis, those who have taken steroids long-term, those who have had radiotherapy to the pelvis, and people who have had a long spinal fusion ending at the sacrum, because that concentrates stress on the bone below.

On a SPECT/CT scan, these fractures often produce a very recognisable pattern of activity across the sacrum, sometimes described by its shape (an "H" or "Honda" sign). This can make the diagnosis clear even when the fracture is subtle on other scans. While MRI remains the standard test for this problem, SPECT/CT is a genuinely useful alternative when MRI is not available, is difficult to perform, or cannot be done for other reasons.

Another common problem in older people with fragile bones is a compression fracture, where a vertebra partially collapses. These can be painful and disabling and can cause a stooped posture. The challenge is often telling a fresh, active fracture (which may benefit from treatment) from an old, healed one that is no longer the source of pain. MRI is the usual tool for making this distinction, but studies have shown that SPECT/CT is comparably good at identifying recent and still-active fractures, because a fresh fracture is metabolically busy while an old one has quietened down.

There is an added benefit here. For people being considered for a procedure in which bone cement is injected to stabilise and relieve a painful fracture, a SPECT/CT scan can help predict who is likely to respond. If the fracture is still active on the scan, the chances of good pain relief from the procedure appear better, and the scan can sometimes reveal additional active levels that also need attention.

The sacroiliac joints sit where the base of the spine meets the pelvis, one on each side. They are the link between the spine and the legs, and they rely on a complex arrangement of ligaments and muscles to stay stable and transfer load smoothly. When this stabilising system fails — sometimes after pregnancy and childbirth, when hormones loosen the ligaments, and sometimes after trauma such as a fall onto the buttocks or a twisting injury in a car accident — the joint can move abnormally and become a genuine source of lower back and buttock pain.

This condition is notoriously underrecognised and easy to dismiss. The pain overlaps heavily with other causes of low back pain, the joint is hard to examine, and — importantly — ordinary scans, including MRI, very often look completely normal. As a result, many people with this problem have been told nothing is wrong, or worse, have been wrongly suspected of exaggerating their symptoms. One of the striking findings from research in this area is that the great majority of affected patients had normal MRI scans, which is part of why the condition has been so easily overlooked.

SPECT/CT can change that. It can reveal a characteristic pattern of activity in and around the joint — including in the ligaments behind it — that is specific to this kind of mechanical dysfunction. In one large study, the scan was able to identify this pattern with very high accuracy, reliably distinguishing genuine sacroiliac joint dysfunction from ordinary, non-specific low back pain. The reason it succeeds where MRI struggles seems to come down to the nature of the injury: it is a long-standing, repetitive strain on the ligaments that leads to subtle bone and ligament reactions, which the activity scan detects but which produce little of the signal MRI relies on. There is also some evidence that the intensity of the activity tracks with how severe the problem is, which may help guide how aggressively to treat it. Confirming the joint as the source of pain in this way can open the door to specific treatments, from targeted physiotherapy and injections through to, in selected cases, surgery.

Some people are born with a slightly unusual vertebra at the junction between the lumbar spine and the sacrum, where the lowest level has features partway between a normal lumbar vertebra and part of the sacrum. This is called a lumbosacral transitional vertebra, and it is surprisingly common — present in roughly a fifth of people. In some of these cases, an enlarged piece of bone forms a false joint with the sacrum or pelvis. When this false joint becomes a source of pain, the condition is known as Bertolotti syndrome.

The difficulty is that simply having this anatomical variation on an X-ray does not prove it is causing pain — plenty of people have it and feel nothing. So the key question is whether the false joint is actually active and symptomatic. SPECT/CT answers exactly this question. It can show intense activity precisely at the false joint, confirming that this is where the trouble is coming from rather than some other level. In a reported case, a person with many years of unexplained lower back pain, normal previous investigations, and no lasting benefit from injections was found on SPECT/CT to have an active false joint; once it was confirmed as the source and treated with a minimally invasive procedure, the pain resolved. This is a good example of how the scan can rescue a diagnosis that has eluded other tests, and crucially, it can also tell an active, painful false joint apart from one that has degenerated quietly without causing symptoms.

Spinal fusion is an operation that joins two or more vertebrae together to stop painful movement, usually with metal screws and rods. It helps many people, but a proportion — by some estimates around one in ten to one in five — continue to have, or go on to develop, back pain afterwards. Working out why is one of the hardest problems in spine care, partly because the metalwork itself interferes with ordinary scans: CT images can be degraded by streaks around the metal, and MRI can be distorted by it too.

There are several different reasons pain can persist after a fusion, and they call for different solutions. The screws or rods may have loosened. The fusion may have failed to take, so the bones never fully knitted together — a situation called pseudarthrosis. Or the levels immediately above or below the fusion may be taking extra strain and wearing out faster, because fusing one part of the spine changes how the neighbouring parts move and load. Telling these possibilities apart matters, because loosening, a failed fusion, and a problem at the next level each lead to a different plan.

SPECT/CT is well suited to this task. By combining activity with detailed anatomy, it can localise exactly where the bone is reacting and match it to the hardware or the bone next door. Studies have shown that adding the combined scan to older activity-only imaging changes the working diagnosis in a substantial share of cases — in one series, nearly half the suspicious areas were reclassified once the fused images were available, often shifting between "failed fusion," "loose hardware," and "problem at the adjacent level." That kind of reclassification can be the difference between the right operation and the wrong one. The scan can flag a failed fusion through intense activity at the fusion site, can help identify loosening, and can show when the real problem is actually the segment next to the fusion.

A sensible note of caution applies. A loose-looking or broken screw is not always the source of pain — a broken screw that is stable within solid bone may show no activity at all — and the scan is not perfect at confirming a failed fusion. Because of this, specialists are careful not to rely on a SPECT/CT scan alone to decide on repeat surgery. It is used as one important piece of evidence, weighed together with the clinical picture, examination, blood tests, and other imaging.

A related and promising use is helping to predict who will actually benefit from a fusion operation in the first place. One of the long-standing frustrations in spine surgery is that even when imaging shows degeneration, it is hard to know whether operating on a particular level will relieve someone's pain. Early research suggests that when surgery is targeted at the levels that are active on a SPECT/CT scan, a good proportion of carefully selected patients report meaningful pain relief afterwards. In several studies, most patients whose treatment was guided by the scan saw significant improvement. This evidence is still developing and needs to be confirmed in larger, more rigorous studies, but it points to a genuinely useful role: using activity to choose the right target before committing to an operation.

Less commonly, back pain can be caused by an infection in the bones or discs of the spine. These infections are becoming more frequent, often affect older or unwell people, and can be slow to diagnose because they can look like ordinary degenerative change on early scans. Delays in diagnosis can be serious. SPECT/CT, sometimes using specialised tracers designed to highlight infection, can help confirm an infection and show exactly where it is, including whether it has spread into the nearby soft tissues — information that can change how it is treated. MRI remains the main test for suspected spinal infection, but the combined scan can be a valuable additional tool.

Knowing how the appointment runs can take away a lot of the uncertainty.

When you arrive, you will be given the tracer through a small injection into a vein, usually in the arm — much like having a blood test. This is the only needle involved, and the scan itself is completely painless. You may be encouraged to drink fluids, as staying well hydrated helps clear the unused tracer and improves the quality of the images.

After the injection there is a waiting period, often a couple of hours or so, while the tracer settles into the bones. You can usually relax during this time, and in many units you are free to sit comfortably, read, or step away as advised. This waiting is not wasted time — it is what allows the tracer to concentrate in the skeleton so the picture is clear.

When it is time to scan, you will lie still on a bed while the camera moves slowly around the area being examined. Lying still is important for a sharp image, but there is nothing to feel, and the scanning portion is relatively quick. Because of the waiting period, though, it is wise to set aside a longer-than-usual appointment overall and to plan your day around it.

A SPECT/CT scan is a routine, well-established test that has been used safely for many years. Like many medical scans, it does involve a small amount of radiation, from both the tracer and the CT part, but the CT is usually performed at a low dose, and the overall exposure is generally considered low and acceptable when there is a real diagnostic question to answer. As with any test that uses radiation, it is recommended when the value of getting a clear answer outweighs that small exposure, and your care team will only suggest it when it is likely to be genuinely helpful.

If you are pregnant, think you might be, or are breastfeeding, it is important to tell your care team before the scan so they can advise you, as different precautions may apply. If you have significant kidney problems, mention this too, since the unused tracer is cleared by the kidneys.

A SPECT/CT scan brings together several advantages that no single conventional scan offers on its own. It answers two questions at once — what a part of your spine looks like and whether it is active. It can separate harmless, age-related changes from the spot that is genuinely contributing to your pain. It often makes a difficult diagnosis clearer and gives your specialist more confidence about where the problem lies. And by pinpointing the active source, it can make treatment more precise — guiding an injection, a nerve-deactivation procedure, or surgery to the right place, and helping to avoid larger, less focused operations.

No scan is perfect, and a SPECT/CT scan is no exception. To use it well, it helps to understand the two ways it can point in the wrong direction — and, importantly, why this happens. The key thing to hold onto is this: the scan does not measure pain. It measures bone and joint activity. Most of the time, activity and pain go together, but not always, and the gaps between the two are where misleading results come from.

A false positive is when the scan lights up an area that turns out not to be the source of your symptoms. This is common, because plenty of things make bone busy without causing pain.

The most frequent reason is everyday wear and tear. Arthritic joints and degenerating discs are often metabolically active simply because the body is constantly remodelling them, whether or not they hurt. Research that scanned people with no back pain at all found that a meaningful proportion still had active, "hot" areas in the spine — for example, increased activity at the bony edges of the discs in people who felt perfectly well. In those individuals, the activity reflects long-standing, settled change that the body is quietly maintaining, not a live problem. The same can happen with the small facet joints: studies comparing scans with symptoms have found that the joint lighting up is not always the joint causing trouble, and that the scan and other tests sometimes disagree about which side or which level is responsible.

After surgery, a similar trap exists. Bone around screws and rods can stay mildly active for many months as part of normal healing, and a screw that looks loose or even broken may be perfectly stable within solid bone and completely painless — yet still draw the eye on a scan. There can also be a purely technical cause: the brightness threshold a reporter chooses, and the reference point they compare against, can change how many "hot spots" appear, so a borderline area can be counted as active in one reading and normal in another.

The practical consequence of a false positive is the risk of treating the wrong place. If a bright but innocent spot is mistaken for the pain source, an injection or operation aimed at it will not help — and may even cause harm or delay the real diagnosis. This is exactly why a hot spot is treated as a lead to be confirmed, not a verdict.

A false negative is the opposite: a genuine source of pain that the scan misses because it is not metabolically active enough to show.

The clearest example is timing. A problem can hurt before the bone reacts. With disc pain in particular, the disc itself can be inflamed and painful while the neighbouring bone has not yet become active — so the scan can look normal even though there is a real pain generator. In studies of people with ongoing low back pain, a sizeable minority showed no increased activity at all, almost certainly for this reason. Chronicity works the same way in reverse: a long-standing injury that has stopped trying to heal can go quiet. An established, non-healing stress fracture of the pars, for instance, may appear "cold" precisely because the active healing phase is over, even though the defect is still there and still causing symptoms.

Some problems never produce much bone activity in the first place. Pain coming mainly from soft tissues — muscles, nerves, or some ligament injuries — may not register on a scan that is designed to detect bone turnover. And around metalwork, the CT and the activity image can both be degraded, so a genuine problem can be partly hidden by the hardware itself.

The practical consequence of a false negative is false reassurance. A normal-looking scan does not prove there is nothing wrong; it may simply mean the problem is one this particular test cannot see. That is why a normal SPECT/CT scan is never used on its own to tell someone their pain is not real or to stop looking for a cause.

Both kinds of error come from the same root: the scan shows where bone is active, and active bone is only an indirect signpost to pain. Activity can be present without pain (old, settled change), and pain can be present without activity (early, soft-tissue, or burnt-out problems). Understanding that single idea explains almost every misleading result.

Because of everything above, the scan is only half of the answer. The other half is you — your symptoms, where exactly it hurts, what makes it better or worse, and what the examination shows.

A bright spot on the scan only counts for something if it matches your clinical picture. If the activity sits at the level and on the side where your pain actually is, and fits the way your pain behaves, it becomes a strong, usable clue. If it sits somewhere that has nothing to do with your symptoms, it is most likely one of those harmless, incidental hot spots and should not be chased. In other words, the scan is interpreted through your symptoms, not instead of them.

This is why specialists insist on what is called clinical correlation, and why the most reliable approach often adds one more confirming step. When a scan and a person's symptoms both point to the same facet joint or the same sacroiliac joint, a targeted diagnostic injection into that exact spot can test the theory directly: if numbing that one area takes the pain away, the source is confirmed; if it does not, the search continues. Matching the scan to the symptoms, and then confirming where it matters, is what turns a picture of activity into a genuine diagnosis — and protects you from being treated at the wrong level on the strength of a misleading spot alone.

This also shapes how you should read your own result. A "positive" scan is not an automatic reason for surgery, and a "normal" scan is not proof that nothing is wrong. Both only make sense in the context of your story and your examination, which is why your specialist will always weigh the images together with everything else they know about you.

For all its strengths, a SPECT/CT scan is not a crystal ball, and being clear about its limits is part of using it well.

It is not perfectly accurate. Some genuinely painful problems do not light up, and some bright spots are not the source of pain. An active area is a strong clue, not absolute proof, which is why findings should always be read together with your symptoms, your examination, and your other scans rather than treated as the last word.

It is not the right test for every situation. Where the question is telling a spinal infection apart from inflammatory disc changes, for example, other scans may serve better. And it does not replace MRI for soft tissues, nerves, or the spinal cord.

It is more expensive than a standard X-ray, CT, or MRI, and it takes longer because of the waiting period. For these reasons it is used selectively — typically when simpler tests have left the diagnosis unclear, when there are several possible pain sources to choose between, or when previous surgery makes the picture complicated — rather than as a routine first step.

Finally, the science behind some of its uses is still maturing. The evidence is strongest in certain areas and more preliminary in others, and good specialists will weigh a SPECT/CT result as one valuable input among several, not as an automatic instruction to inject or operate.

A SPECT/CT scan is most useful not as an end in itself but as a guide to action. Once an active level or joint has been identified, that information can be used to target a diagnostic injection to confirm the source, to plan a precise nerve-deactivation or other interventional treatment, or to focus surgery on the level most likely to be responsible — making procedures smaller and more targeted than they might otherwise be. In some cases it can help decide whether a particular treatment, such as cement stabilisation of a fracture or a focused fusion, is likely to help. In every case, the aim is the same: to replace guesswork with a clearer picture, so that treatment is aimed where it has the best chance of working.

Is a SPECT/CT scan better than an MRI? Neither is simply "better" — they do different jobs and are often used together. MRI is the best test for soft tissues, nerves, the spinal cord, and many disc and nerve problems. SPECT/CT is better at showing active bone and joint problems and at pinpointing the source of pain among several worn areas. In some conditions, such as certain sacroiliac joint problems where MRI often looks normal, SPECT/CT can succeed where MRI cannot.

Will the scan hurt? No. The only needle is the small tracer injection at the start, similar to a blood test. The scanning itself is completely painless — you simply lie still while the camera moves around you.

How long will I be there? The scanning part is relatively quick, but you should plan for a longer overall appointment because of the waiting period after the injection, which is usually a couple of hours. It is sensible to keep the rest of your day flexible.

Can it really find the cause of my back pain? It is very good at highlighting active, metabolically busy areas that tend to correspond to where pain is coming from. That is precisely why it is so useful when other scans have shown lots of changes but have not made clear which one matters. It is not infallible, so the results are always considered alongside your symptoms and other tests, but in the right situation it can provide the deciding piece of the puzzle.

Why has my doctor suggested this when I have already had an MRI? This is common. An MRI may have shown several possible problems without making clear which is responsible, or it may have looked normal despite ongoing pain, or previous surgery may have made it hard to interpret. A SPECT/CT scan adds the missing layer — activity — and can help resolve exactly these situations.

This page is general information to help you understand the scan and the situations in which it is used. It is not medical advice, and it cannot tell you what is causing your own symptoms. Your results must always be interpreted by your doctor or specialist, alongside your history, examination, and other tests, and any decisions about treatment should be made with them.

• —NICE — Low Back Pain and Sciatica in Over 16s (NG59)
• —NHS — Spinal Conditions
• —British Association of Spine Surgeons (BASS)

This information is for general patient education and is not a substitute for an individual consultation. Always seek personalised advice from a qualified spinal specialist.