Radt 251 Orthoroentgenography & Bone Densitometry

Orthoroentgenography

radiography of long bones w/ minimal magnification using a ruler

Leg Length Discrepancies

Indications

Adults: may cause back pain

Children: developmental growth, more common in lower limbs

Corrections: Epiphysiodesis- premature fusion of epiphysis that retards growth, Leg Lengthening

Procedure

• Both limbs imaged for comparison

• Bell Thompson ruler used, taped to table

• Possible unilateral images if lower limb discrepancy is more than 1" difference

• 70-80 kV

• Bucky on all images

• 14 X 17" IR/ 3 views

• Shielding/Close collimation

• No movement of patient or ruler between images

Views

Lower limb: AP hip- CR to neck of femur; AP knee- ¾" distal to apex of patella; AP ankle- midway between malleoli

Upper Limb: AP Shoulder- CR 2" inferior & medial to lateral border of shoulder; AP elbow- CR to mid elbow; AP- wrist Mid wrist (only unilateral)

Alternate Imaging Modalities

CT scanograpm

Bone Densitometry

Specialty diagnostic modality to evaluate bone mineral density for diagnosis of osteoporosis

History of Bone Densitometry

• Before bone densitometry, standard radiographs of the dorsal and lumbar spine were used to determine bone density

• Loss of 30%-50% of trabecular bone will produce first visible changes on radiographs

• Osteoporosis not detectable until later portions of the disease• First indicator is a bone break

• Thoracic "hump" is a sign of advance stage osteoporosis

• Bone densitometry equipment is the best method for evaluating bone density

Bone cells

Osteoblast - builds new bone and bone repair

Osteoclast - breakdown and reabsorption of old bone

Osteocyte - mature bone cell

Bone Mineral Content vs Bone Mineral Density

BMC - quantity measured in gram

BMD - ratio of BMC in an area of bone

Purpose

To measure bone mineral density

To detect bone loss

To establish diagnosis of osteoporosis

To assess risk of fracture

To assess response of patient response to osteoporosis therapy

To perform vertebral fracture assessment

Indications of bone densitometry

Gender, Family history, ethnicity, body habitus, lifestyle, nutritional deficiency, sedentary lifestyle, frequent falls, alcohol/tabacco abuse, hhyperparathyroidism, GI conditions, medications

Most common: advanced age/estrogen deficiency

Steroid use: Rheumatoid arthritis

BMD & Fx Risk

• PROXIMAL FEMUR IS BEST TO DETERMINE RISK FACTORS FOR HIP

• Low BMD risk for fragility fx

• Age adjusted relative risk for fx approx. 2.7 for each of 1 standard deviation (SD) in BMD

• More accurate to use BMD & clinical risk factors to predict future fractures (Ex: In BMD of hip-this means that a woman whose BMD is 2 SD below the mean for her age is more than 7x (2.7 X 2.7) more likely to have a fx than a woman of the same age whose BMD is equal to the mean)

T-SCORE

the # of SDs the individual's BMD is from the mean BMD of a young normal population of the same sex & ethnic background

Z-SCORE

The # of SDs the individual's BMD is from the mean BMD of age-appropriate individuals. Used for premenopausal women and men younger than 50.

Osteoporosis Management- Drugs

Inhibit bone resorption: estrogen, SERMs (selective estrogen receptor modulators, calcitonin, bisphosphonate

Stimulate bone formation- Parathyroid hormone

Contraindications for Bone Densitometry

QC procedures not updated to ensure accurate results

Bone mass too low/body part too thick

Anatomic malformations (Scoliosis/kyphosis)

Previous fx or metallic prosthesis

New procedures (vertebroplasty/kyphoplasty)

Pregnant patient

Patient Prep

1.Loose clothing or gown

2.No dense objects such as belts or zippers

Dual-Energy X-Ray Absorptiometry (DXA)

-Technique that is commonly used in current practice that incorporates the use of a high and low x-ray energy beam to determine the mass of tissue

-This is done by using an energy switching system or rare earth filter

-The site of interest is analyzed and a bone mineral report is taken.

Quantitative Computed Tomography (QCT)

Unique to QCT. It can measure both trabecular and cortical bone. It also allows three dimensional or volumetric analysis of data

Quantitative Ultrasound (QUS)

-This uses a non-ionizing technique in peripheral site

-Most common site is the os calcis(heel)

-For people that are excessively over weight

Radiation Safety

• For this examination the benefits should always outweigh the risks

• The effective dose from a bone density exam of both spine and hip is less than 5 micro Sv

• The dose range for quantatative computed tomography (QCT) is at approximately 30 micro Sv

• Most protocols call for re-examinations every 18 months to evaluate change

• Technologist should always practice the ALARA principle for both themselves and the patient

Site Selection and Method

• Bone mineral analysis can be performed in various locations of the body or through whole-body scan acquisition

• The site selected is determined by the patients history and associated risk factors

• Central/axial is the most common measured site

• QCT is the only technique that provides 3D analysis, which gives a true volumetric measurement

• Peripheral site selection may be performed with single-energy x-ray absorptiometry, Central Densitometry (DXA), or QUS

Positioning

Spine: Patient is placed in a supine position with MSP midline of table. Region included should be from T12 to L4

Hip: MSP with midline of table and the legs are positioned for a true AP projection of the hip with feet rotated inward

Forearm: Only scanned when spine or hip scans are not obtainable (ex. Wheelchair confinement, obesity, inability to lie down)

Body Habitus

technologist must be aware of the body habitus and soft tissue variations of each patient to ensure that an appropriate amount of soft tissue is available for an adequate scan analysis

Precision

Also known as "reproducibility"

Ability of a quantitative measurement technique to reproduce the same numerical result when repeatedly performed in an identical fashion

Influenced by a combination of short-term and long-term variability of scanner, patient motion, body habitus, and technical factors

Good measurement precision is essential for detecting changes in bone mass density (BMD)

Accuracy

How well the measured value reflects the true or actual value of the object

Compared between the true and measured values expressed and percentage values

Typical accuracy of a DXA unit +/- 10% and is sufficient for clinical assessment of fracture risk and diagnosis of osteoporosis

Vertebral Fracture Assessment

New method using software to diagnosis current and potential vertebral fractures

During assessment the thoracolumbar spine is performed in a lateral projection

Measures vertebral heights and compares them with reference values