Collimation

Collimation, or specifically collimation refers to beam size alterations. Gamma ray collimation employs a brute force method of beam size reduction, namely; lead in the way of the beam (at least part of it).

I have noted that gamma ray collimation is a variable in all three dimensions: x, y and z. Z, in this case, is determined by thickness of the absorbing material, typically lead, while X and Y are basically designed as beam stoppers.

A few texts suggest that beam stopping should be in the vicinity of 99% efficient. By this it is meant that virtually all gamma rays employ the absorber. This is quite impossible to achieve regardless of expectations and or specifications. Gamma ray absorption is a probability factor and not an absorption value. Typically, a useful unit of measure is the half value layer. This means that the gamma ray beam at 100 kev will be reduced to half at 0.12 mm of lead. For purposes of these assumptions we will consider our typical gamma ray energy to approximate 100 kev.

At 100 kev the beam thickness in lead is 0.12 mm. This means that 50% of the beam has been absorbed. That also means that 50% of the beam passes straight on through.

0.12mm lead reduces the beam to 50% value, therefore, an additional 50% is reduced by an additional 0.12 mm lead. The original beam of X-rays is now down to 25% beam strength.

What this means is that all body parts outside of the collimated field will receive a radiation dose equal to 25% of the raw beam. That seems to be a somewhat careless determination.

By measurement of transmitted beam it has been determined that some collimators in clinical use produce one half layer of beam absorption or deliver a radiation dose at half that of raw beam. Others that have been tested reduce that be another factor of two with 25% of original beam intensity passing through the patient.

I suggest that collimation should be improved to reduce the incident beam strength to approximately 12.5%. Beyond that it seems unnecessary to increase absorption.

I intend to look into collimation improvements to that 12.5% level.

Good News: We’re moving, bigger and better.

We are happy to announce that Ann Arbor Digital Devices (A2D2) is in the process of moving into a new and larger facility in Dexter, Michigan. We are expanding our space almost three-fold and will be able to add to our work-force. Dexter, Michigan is a town away from Chelsea and somewhat closer to Ann Arbor.

This is another banner year for us with additional growth in sales and product features. We are also in the process of introducing the latest Model 128i podiatry system with improved functionality and features. Prices remain the lowest in the industry with a step up in performance.

We will be in our new location in Dexter starting November 1st, 2014 with expanded office space and more modern facilities. Thanks to Michigan X-Ray setting up our X-Ray equipment the transition into our new facility should go smoothly. Between the two of us we can boast of the latest digital X-ray technology in the nation, if not the world.

A training room will now become available so that customers and dealers alike can benefit from our newest technology. With accommodations within a short drive and a collection of fine restaurants nearby, we welcome our dealers and customers to visit.

SINGLE PHASE V HIGH FREQUENCY X-RAY

In general it is best to use high frequency X-ray systems to maximize image quality and to minimize patient exposure time. Older X-ray machines may be limited to low power such as 100 MA and 100KVp. These systems will stress the ability to record good quality images due to patient girth limitations.

What happens is that power limitations such at that listed above require that the patient be limited to a modest size, small physical girth, or else a multi-second exposure will be required. A long exposure time will require that the patient be as motionless as possible to avoid motion artifact.

Experience has shown that any time in excess of one second will require the patient to be as motionless as possible. This rarely works and image quality suffers.

Stress Fracture Indications

Stress Fracture Indications

A stress fracture is not an easy injury to identify. The difference between a sore foot and a stress fracture can convert a few patient visits into almost a $1,000 increase in revenue. Of greater importance is the degree of improvement in patient care and the optimizing of diagnostic data interpretation. These factors are essential to both doctor and patient.

A stress fracture can be difficult to diagnose because the fracture site may obscure viewing of the fracture site itself. Frequently, a stress fracture is characterized by pain, possible swelling and little else. Sometimes a faint fracture line may be present but seeing it is not always easy. A hurried look may lead the doctor into missing the details of the fracture.

Additional views are sometimes helpful in making this diagnosis. Unfortunately, additional views may be equally difficult to discern so there may be little help for seeing what is actually there. In this case, it may be helpful to lower the KVp and try another exposure. Lower KVp, softer X-rays, may help in seeing a slightly stressed bone more easily than if using a harder beam of X-rays.

Using the ROI option can help in seeing stress fractures because the area under question can be optimized for Contrast and Brightness. The ROI area to be examined should include not much more than the joint where a suspicious spot may exist.

Frequently, a stress fracture can be accompanied by a rise in temperature and this can frequently be seen by thermography. Deep stress fractures may be obscured by the thickness of the foot itself thereby causing attenuation in temperature levels. An increase in temperature of 0.5 degrees C can be helpful in identifying where a hotter spot is located.

George’s Line

GEORGES LINE

   In 1921 A. George published “A Method for More Accurate Study of Injuries to the Atlas and Axis”. This is a significant work because the only way to make this determination, especially at that time, was to take two films, one at full extension and the other at full flexion, and measure both extremes. The sum of the differences, if exceeding 3.5 mm, indicated excessive stretching of the ligaments. The George rule is that once stretched to that extent the ligaments would remain stretched. There was no going back to a more compressed condition.

   George had managed to make this observation concerning the extremes of Motion without being able to observe Motion. It required just two films and significant observational skills to make this determination. It is no wonder that this technique was not as popular as hoped for.

   However, now that Motion studies are readily available the ability to observe aberrant motion should be simple and extremely helpful.

George's Line

   Note that the distance starting at C 4 has caused an offset between the two sides of the cervical spine. These two distances sum thus indicating that stretching has occurred. If the stretching sum exceeded 3.5 cm the damage was considered to be permanent.

BONE EVALUATION

A2D2 Bone Evaluation
A2D2 Bone Evaluation

   Patient bone evaluation (BE) can be a sensitive method for the determination if therapy is needed to restore bone strength. Until the present, a Bone Density test has been necessary to make such a determination. This test can be expensive and somewhat intrusive. On the other hand, a bone evaluation test can be made utilizing the raw data contained within a standard AP view of the foot.

   Classic bone densitometry compares the absorption properties of the vertebra of the lumbar spine with soft tissue surrounding the spine. On occasion, a similar measurement is made in the human wrist where the radius and ulna bone absorption is compared to soft tissue surrounding the wrist. This is normally performed while the wrist is immersed in water. Immersion in water is used to adjust for fat content that may surround the wrist and bias the soft tissue contribution.

   The standard AP view of the foot produces an image of the foot while the body is stressed by the weight of the entire body. The foot is as flat as possible which results in any fat contained within to be spread over the entire area of the foot. The resultant image shows data that is located in the web of the big toe that is adjacent to the bone of the big toe.

   The bone evaluation (BE) calculation is made by a simple ratio of bone absorption vrs soft tissue absorption. This measurement is relative with the first test but absolute when the second test is administered. A sample area of approximately 60 by 180 pixels is used in order to avoid great variations in sample area. It is recommended that several measurements be made to avoid positional area variations. As in all cases of bone densitometry, position variances can influence test results and this has been especially true with wrist measurements.

   This is much less so in the case when dealing with the AP view of the foot. A record is made within the patient chart for each measurement made. This allows for variations over time.