What are the advantages of 3D over 2D QCT?
Why should I buy a QCT system from Mindways instead of my scanner manufacturer?
Isn’t it better if the QCT software runs on my scanner computer?
One QCT system in the market does not require a calibration phantom. Isn’t this approach preferable?
Can your QCT system be used to measure the hip?
Is the radiation dose higher for a 3D study since more slices are needed?
Will the increased number of slices needed for a 3D exam decrease x-ray tube life?
In conventional QCT, 4 vertebral bodies are normally measured, but only 2 are measured for 3D QCT.
Does this compromise clinical accuracy?
We have been doing conventional QCT and scanning T1 through L3. If I scan only L1 and L2 now, will this have an adverse affect on longitudinal comparisons and precision?
Do I need a helical or spiral CT scanner to do 3D QCT?
Can I do 5×5 mm scans instead of 3×3 mm? One of your competitors claims your system uses an “old-style” liquid phantom.
What are the advantages of 3D over 2D QCT?
The primary advantages of 3D over 2D QCT are faster patient setup and scan time with 3D QCT. 3D QCT requires the acquisition of a simple set of evenly spaced, parallel planes encompassing two vertebral bodies. 2D QCT requires gantry tilt adjustments to acquire 3 or 4 axial scans through the mid planes of 3 or 4 vertebral bodies. An implication of faster patient setup and scan time is that there is less chance of problems induced by patient motion. 3D QCT bone volumes to be analyzed are determined retrospectively, while 2D QCT volumes are nearly completely determined at the time the axial data is acquired. Retrospective volume determination provides great latitude for handling common clinical situations, such as herniated disc, scoliosis or mild compression fractures, that may not be fully appreciated at the time the QCT data is acquired. A 2D QCT analysis provides limited options for reducing measurement errors induced by such clinical realities, while a 3D analysis provides much greater latitude in choosing the volume of bone to be analyzed so that measurement errors can be minimized. You can measure the hip. Clinically, the advantages of 3D QCT result in increased patient through-put, and improved measurement precision, which can result in better diagnostic accuracy, relative to 2D QCT.
Why should I buy a QCT system from Mindways instead of my scanner manufacturer?
If QCT is of interest to you, then finding a system that meets your QCT needs should be your goal. The supplier is much less important than the product capabilities. QCT is the primary business interest of Mindways, and it is our goal to provide a broad range of products that can be tailored to effectively meet the clinical needs of any institution with a CT scanner and a desire to do QCT. Our QCT products can be easily distinguished from other products on the market by attention to details that matter to our customers. Details such as sophisticated analysis techniques to give you the best measurement precision possible with your system, thorough QA procedures to verify the operational integrity of your QCT system, clear and concise printed exam reports, database tools to facilitate management and reporting of your QCT patient records, extensive documentation and published literature for your reference use when interpreting your QCT results. And at Mindways we know that someday you are going to upgrade your CT scanner, and that you would like to be able to access and use patient QCT measurements from your old scanner when interpreting QCT exams acquired with your new scanner.
Isn’t it better if the QCT software runs on my scanner computer?
It may be more convenient to have your QCT software run on your CT scanner console, but this “convenience” does have its disadvantages. QCT packages that run on CT consoles are often times manufacturer and even model-specific—if you upgrade to a different scanner model or manufacturer, your QCT system and QCT patient database may become obsolete. And a new CT system also often implies new QCT phantoms, as well as new QCT software on top of the inaccessibility to prior exam records. Mindways QCT products are designed to work with all modern whole-body CT scanners. There are no database portability concerns. The same phantoms can be used with any scanner. There is no need to learn how to use and interpret results from a new QCT package. And our QA procedures include normalization procedures that facilitate comparisons of results between various CT scanners.
One QCT system in the market does not require a calibration phantom. Isn’t this approach preferable?
The theory behind the “phantomless” QCT system is good—it assumes that the CT number of fat, muscle, and peak CT number of bone can be used to calibrate the scan. Unfortunately, patients do not always adhere to the theory. Fat varies among patients because of variable vasculature and cellularity; muscle CT number depends on the amount of intermixed fat and the hydration status of the patient; peak bone CT number depends on the porosity of the bone and the resolution of the CT scanner. The phantomless method gives a precision of about 5%. It is useful for diagnosis of osteoporosis or other low bone-mass conditions, but a 5% measurement precision may not be adequate for monitoring of patients.
Can your QCT system be used to measure the hip?
Yes. CTXA which produce a DXA-equivalent measurement is now available.
Is the radiation dose higher for a 3D study since more slices are needed?
The overall x-ray exposure from a 3D QCT exam is about 20% higher than for a conventional 2D QCT exam. About one-half of the dose from a QCT exam is delivered by the localizer, with the other half by the axial images. Typical QCT exam effective does are in the range of 3 to 6 mRem. This dose compares to 40-50 mRem for a mammogram or 5 mRem for a chest x-ray.
Will the increased number of slices needed for a 3D exam decrease x-ray tube life?
Only very slightly. All QCT BMD studies are done at x-ray tube loadings much lower than those used for conventional CT body or head exams. Low tube loading implies that tube wear and tube cooling are not issues relative to more common CT examinations. So while it is true that more axial images are required for 3D QCT than are necessary for 2D QCT, in most clinical situations the primary burden on the x-ray tube is induced by non-QCT studies, and differences between tube wear between 2D QCT and 3D QCT studies is very small.
In conventional QCT, 4 vertebral bodies are normally measured, but only 2 are measured for 3D QCT. Does this compromise clinical accuracy?
No, if it is assumed that clinical accuracy is limited by BMD measurement precision. Published studies have consistently reported better measurement precision for 3D QCT spine BMD measurements relative to 2D QCT spine BMD measurements. The quality of these types of measurements are influenced by factors such as accuracy of the localizer, patient motion between localizer and CT scan, errors introduced by image streaks and noise, and x-ray beam hardening. Generally 3D QCT fairs better with these issues than does 2D QCT because of reduced patient setup and scan times, relative insensitivity to exact axial slice locations, smaller slice thickness, and retrospective determination of the bone volume to be analyzed associated with 3D QCT analyses.
We have been doing conventional QCT and scanning T1 through L3. If I scan only L1 and L2 now, will this have an adverse affect on longitudinal comparisons and precision?
There may be some adverse affect on longitudinal studies when using two different QCT BMD techniques. However, it has been observed clinically that the average BMD of L1/L2 is almost exactly the average BMD of T12/L1/L2/L3. QCT BMD shows a slight but consistent decrease going from T12 to L3. For consistency, the Mindways QCT PRO BMD modules only compare measurements of vertebral bodies in common between all serial exams. Thus, for example, QCT PRO would compare BMD measurements of L1/L2 from a 3D study with L1/L2 from a 2D study even though the 2D study might include results from T12/L1/L2/L3. This method of analysis better accommodates comparisons between other vertebral body pairs, for example T12/L1 or T12/L2, as may be necessary when vertebral abnormalities inhibit measurements in L1 or L2. That is, this serial analysis method favors comparison accuracy at the expense of some comparison precision.
Do I need a helical or spiral CT scanner to do 3D QCT?
No. 3D QCT can be done with any scanner that can do at least 5 mm contiguous slices. Helical studies are generally faster, giving a better 3D data set due to the reduced possibility of patient motion, but at a slight decrease in longitudinal resolution. However, helical scans should be done at a pitch of 1.0 and a slice thickness of 4 mm or less.
Can I do 5×5 mm scans instead of 3×3 mm?
Mindways suggests that 3 mm thick scans every 3mm should be used for 3D QCT. However, published clinical results indicate contiguous scans of 4×4 or 5×5 mm can be used successfully with only minor loss of precision. Results also indicate that slice thicknesses greater than 5 mm, or helical scans greater than 4 mm or with a pitch greater than 1.0, significantly degrade positioning reproducibility in the 3D analysis.
One of your competitors claims your system uses an “old-style” liquid phantom.
The competitor is wrong. Mindways has developed not only a new solid phantom but also a revolutionary calibration method that allow the Mindways solid phantom to used with the de facto standard UCSF normal database without errors and/or correction factors.
Osteoporosis and BMD
What is osteoporosis?
Osteoporosis is a disease where bones break even though you are not doing anything out of the ordinary. These so-called “fragility fractures” happen when the amount of bone is not enough to withstand the pressures from simple tasks, such as picking up a bag of groceries or a grandchild, or when you slip and fall and your wrist or hip breaks, where it would not have broken when you were younger. While spine, wrist and hip fractures receive the most attention in osteoporosis, many people believe that if you simply fall down and break any bone, then you have or are at risk for having osteoporosis.
How do I know if I have osteoporosis?
If you have had a broken bone recently from a minimal trauma, such as falling down or bending over to lift something up, you probably have osteoporosis. If you broke your ankle skydiving, you probably don’t have osteoporosis. Not everybody who is at risk of breaking their bones actually does so it usually takes at least a little fall or injury to break the bone, and some people are more careful than others. However, just because you haven’t broken a bone in the last year doesn’t mean that it couldn’t happen. Just like a person with very high cholesterol levels has a high risk of heart attack, it might not happen to all of them in the next month, or year, or 5 years, but eventually it usually does. People with osteoporosis have an increased risk of having a fracture, even if it doesn’t happen right away. One way to identify these people is to measure how much bone they have.
Why is a bone density test useful?
A bone density test measures how much bone you have. The size and density of a bone influences strongly whether or not it will break, so measuring the density of a bone can be used to estimate its risk of breaking. However, there is no need to measure the density of every bone in the body. Osteoporosis is a global disease that affects the whole skeleton, some parts more than others, but all to some extent, so that measuring any one bone helps to estimate your overall risk for fracture.
Can osteoporosis be diagnosed without a bone density test?
If you have a fracture from a simple fall, that is a good indicator that you have osteoporosis. But you don’t want to wait until you have a fracture to find out if you might be at risk. There are many factors that increase your risk of having osteoporosis—if your mother or grandmother had it, if you smoke, if you have low body weight, or if you had low estrogen levels or low dietary calcium intake earlier in life—but a measurement of low bone density is the single most predictive factor for osteoporosis.
If I don’t get a mammogram, I could die from breast cancer, but I can’t die from osteoporosis, can I?
More women in the US die from osteoporosis and its complications each year than from breast, uterine, and cervical cancer combined. It’s not the fall and broken hip that kills, it’s the pneumonia after being laid up for months, or the infection after surgery, or the disability that leads to other complications. Osteoporosis is a preventable disease, and if detected early can be treated successfully.
Why are some bone density tests done in the heel or wrist and some at the spine or hip?
Any bone density test can be useful, but the bone measured and the preferred method depend on how the results of the test are going to be used. Heel or wrist bone density measurements are usually done with special portable machines, and are generally more available and less expensive than spine or hip measurements. Because osteoporosis is usually generalized throughout the skeleton, a simple measurement of bone density in the heel or wrist helps to determine if a person has low bone density relative to what they might have had when they were younger. These methods give a better indication of overall skeletal status in women over age 65 than for women early after menopause. For younger women, a measurement at the spine is the most sensitive way to determine if they have osteoporosis. Also, because the spine changes fastest with therapy or with low estrogen levels, it is usually the best site to measure for women who are starting therapy, or those who might want to delay taking hormone or other therapy until they see how their bones may be changing. Bone density measurements at the hip are most useful in older women and men who may be at higher risk of hip fracture, because a hip measurement gives the best estimate of the risk for hip fracture in these people. If a person is on therapy, however, spine measurements are still more useful than hip or wrist measurements to determine if the therapy is working.
How accurate are bone density tests in determining if I have osteoporosis?
All bone density tests approved by the FDA are considered to give some useful information. A measurement of the spine or the hip is considered the most definitive, and they are mentioned in the Medicare guidelines as the preferred bones to measure. The World Health Organization has also come up with some guidelines for defining who has osteoporosis, based on a bone density measurement. While these guidelines are still being debated, they are one of the best ways we have at this time to determine who may need to be treated for osteoporosis. These guidelines are based on comparing your bone density to the average bone density for young adults, and results are given as a “T-score” (the “T-score” is determined by the range of bone density values in young adults, with 95% of normal young adults having a T-score between -2 and +2). A T-score of -1 or higher is considered “normal” by the WHO guidelines, from -1 to -2.5 is considered “osteopenia,” and below -2.5 is considered “osteoporosis.” It is important to note that these are just guidelines, and that the numbers are intended to be used in the overall evaluation of a patient, and not for a definitive diagnosis, that is, a woman with a T-score of -1.5 who has other risk factors could be considered osteoporotic, while one with a T-score of -2 but no other risk factors might not be a candidate for treatment.
If a bone density measurement in my heel gives a T-score value of -1.5, will this be the same for my spine?
Not necessarily. Measurements made in different bones and with different instruments can give T-score values that differ by as much as 1 or 1.5 units. Most of the time, T-scores that are low for heel or wrist will also be low for spine or hip, but if the heel or wrist is only slightly low, you can still have osteoporosis in the spine. This is especially true in women soon after menopause, because bone is lost faster from the spine than from the wrist, hip, or heel. Because of these differences, many clinicians feel that if the wrist T-score is between -1 and -2, it is important to do a followup measurement in the spine or hip to confirm the diagnosis of low bone density. In these cases, Medicare will reimburse both for the initial wrist or heel measurement, and the followup spine or hip measurement.
If I start therapy, do I need any special bone density tests?
The Medicare guidelines say that central measurements are the most effective in monitoring bone changes in response to therapy. The two methods used for central bone density measurements are quantitative computed tomography, or QCT, for the spine, and dual energy x-ray absorptiometry (DXA) for the spine or the hip. Because the spine is the first to change, it is the preferred site to measure bone changes, and Medicare guidelines say that measurements every 2 years are allowed for coverage. The guidelines also say that in special cases, more frequent measurements may be covered, for example in patients who are taking high doses of corticosteroids for asthma.
If I am already being treated for osteoporosis or taking hormone replacement therapy, why should I have a bone density test?
Not everyone responds to therapy for osteoporosis in the same way. In the past, only hormone replacement therapy was available for preventing or treating osteoporosis, but some women do not want to take HRT, and in some cases it does not prevent bone loss from occurring even in women taking estrogen. In the past couple of years, new therapies have been approved for osteoporosis. Alendronate (Fosamax) is the first of a class of new drugs called bisphosphonates that can be used to prevent or treat osteoporosis. Selective Estrogen Receptor Modulators (SERMs) is another class of “designer estrogens” that can be used, with raloxifene (Evista) the first of these to be approved. Calcitonin nasal spray is also an approved treatment for osteoporosis. All of these treatments are alternatives to HRT, all are more expensive than HRT, and all have some side effects, so it is important to make sure that they are working to prevent bone loss. Bone density tests, especially at the spine, are the most accurate way to detect if a treatment is preventing bone loss.
Do bone density tests use x-rays?
Almost all bone density tests use small amounts of x-rays to measure the amount of bone. The exception to this are the new ultrasound machines that measure bone at the heel or in the leg, but these are only used for a “peripheral” bone test and are not used to monitor changes in the bone with therapy. The amount of x-rays used by all other bone density tests are less than chest x-rays or dental x-rays, and substantially less than for a mammogram or conventional x-rays of the spine.
Do men get osteoporosis?
Yes. While osteoporosis is often considered a “woman’s disease,” men also get osteoporosis. After age 70 or 75, about one-third of hip fractures are in men. Osteoporosis in men may have some different risk factors than in women, but as men live longer the chances of them having a fracture increase just like for women. There is not as much information about bone density and osteoporosis in men as in women, but most experts consider that bone density measurement in men is useful, especially in those over 65 and with other risk factors.
How do we interpret QCT results?
QCT, like any bone density measurement, is used to compare a patient to normal control data or to an absolute reference value, and to measure the change in bone density with time in a given patient. Researchers have established a “fracture threshold” level for all bone density methods; patients with bone density above this level are rarely seen with osteoporotic fractures, while below it the prevalence of patients with fractures rises. This level is about 100–110 mg/cm3 for QCT. As the value decreases below this the fracture prevalence increases, so that below 50 mg/cm3 most patients seen already have spinal fractures. The QCT value for a patient, when added to other diagnostic information, can be helpful in deciding an approach to treatment. Serial QCT measurements can establish the rate of change of bone mineral density in both treated and untreated patients, but the sensitivity of the method depends on how well the technique is done at a given hospital. In most cases, a change of 8–10 mg/cm3 can be significant or at least indicate a trend, and several serial measurements all changing the same way improve confidence in the result. Women within 1–3 years after menopause average 7 mg/cm3/yr loss, so yearly measurements can be helpful. Bone loss may be slower in older individuals. The frequency for each patient will depend on other diagnostic and treatment factors, and it is important to interpret the bone density results within the context of each individual’s clinical status.
DICOM
What is DICOM?
DICOM is an abbreviation for Digital Imaging and COmmunications in Medicine. DICOM is an accepted standard for transmitting medical images and associated information between devices in a medical environment.
Who developed DICOM?
DICOM is the result of a joint committee, with members from ACR (American College of Radiology) and NEMA (National Electrical Manufacturers Association), tasked to develop a standard for digital imaging and communications in medicine. DICOM was developed in liaison with other Standardization Organizations including CEN TC251 in Europe and JIRA in Japan, and with review by other organizations including IEEE, HL7 and ANSI in the USA.
What implications does DICOM have on me?
DICOM was developed with input from a broad range of international organizations concerned with the development of a standard that would be accepted world-wide by medical device manufacturers. DICOM is an open standard that can be used by any medical device manufacturer with a need to transmit and/or receive medical images and associated information from other devices—including devices made by other manufacturers. Eliminating dependencies on proprietary data formats and communication protocols makes it possible for devices such as printers, image archives, and specialized image display and analysis workstations to interface and work with data from a broad range of medical imaging devices. This often results in reduced cost, greater reliability and a better choice of devices for consumers.
How do I know that two DICOM devices will work together?
An important aspect of the DICOM standard is that manufacturers of DICOM compliant devices must prepare a “DICOM Conformance Statement” for each compliant device. Conformance statements must be made available to any interested party; this includes consumers and other device manufacturers. Compatibility of two DICOM devices is established by comparing the DICOM capabilities of each device to make sure that a consistent set of capabilities are supported by both devices so that the two devices can communicate.
What is a DICOM Conformance Statement?
The DICOM standard is extensive. It defines numerous methods for representing data and communicating that data between devices. Few, if any, medical devices need to support all aspects of the DICOM standard in order to perform the operations intended by the device manufacturer. Thus, the DICOM standard includes the definition of methods for constructing a “DICOM Conformance Statement” for each device. A conformance statement defines the DICOM services provided by a particular device as well as the DICOM services required of other DICOM devices in order for them to operate properly with the particular device.
Should I ask for copies of DICOM Conformance Statements?
Yes. It is always a good idea to obtain DICOM Conformance Statements for DICOM devices that you own or are considering purchasing. These provide you with documentation of the specific capabilities of particular devices, and it allows you to check that two particular DICOM devices should be able to communicate. Alternatively, copies of conformance statements for devices that you own can be provided to device manufacturers for a more complete evaluation of the level of compatibility between their device and your devices.