Mammogram Imaging

Proper positioning and techniques

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Figure 1: Right CC – (1) PNL line (Olive Peart, MS, RT(R)(M))

Figure 2: Left CC

Figure 3: Right MLO – (2) PNL line, (3) Inframammary crease

Figure 4: Left MLO – (4) Pectoralis major muscle

Obviously, compression is very important in mammography imaging. It allows a uniform density of glandular tissue to be imaged, but it also reduces dose to the breast by reduced tissue thickness, separates superimposed areas and brings lesions closer to the film for more accuracy when evaluating size. Compression will also decrease unsharpness, due to motion and increase contrast because of the reduction in the amount of scattered radiation.

The amount of compression is regulated by the MQSA and should not exceed 40 pounds (200 Newton) of pressure. The patient should not be in pain, but the breast must be taut to fingertip contact. There is also a minimum requirement of 25 pounds (111 Newton).

CC Projection of the Breast

In imaging the breast in the CC projection, the first priority is the position of the image receptor (IR). It is important that the IR be positioned at the level of the raised inframammary crease. The patient should stand with feet slightly apart and head turned away from the side being examined. The arm closest to the breast being examined hangs by the patient's side, while the other arm is raised and holding on to the machine for support.

The central ray (CR) in mammography is fixed, directed to the center of the IR. The patient should be advised to stop breathing during the exposure but without first taking a deep breath, as this action sometimes pulls breast tissue out of the compression.

Both medial and lateral aspects of the breast must be included in the collimated field, and the image should be centered with the nipple in the profile. There should be no motion, and all dense areas of the breasts should be well penetrated. MQSA requires appropriate positioning markers, and labeling should conform to the MQSA's requirements to include the date, facility's address, patient's name and identifier and the technologist's initials.

The pectoral muscle is often seen on approximately 20 percent of all CC projections, but, more importantly, the posterior nipple line (PNL) must measure within 1 cm of the PNL of the MLO projection.

MLO Projection of the Breast

In imaging the mediolateral oblique (MLO) breast, the tube angulation should depend on the angle of the patient's pectoral muscle. In general, angulations could range from 30 degrees to 70 degrees, depending on the patient's size, with thin patients requiring steeper angulations than heavier patients. The patient's arm closest to the breast under examination is draped over the top of the IR with the IR placed in the patient's armpit. Compression must be carefully applied in the MLO to support the anterior breast tissue in order to prevent sagging and distortion of the ductal architectures.

As compression is applied, mammographers can use one hand to support the anterior breast tissue and the other hand to adjust the skin over the sternum and clavicle to reduce any unnecessary pulling sensation to the upper thorax.

The image should show a convex pectoral muscle to the level of the nipple, and again should include appropriate patient identification and positioning markers. On the MLO, the inframammary crease should be open and the image should not include portions of the abdomen.

— Olive Peart, MS, RT(R)(M), is the clinical instructor of the radiology program at Stamford Hospital in Connecticut, as well as an editorial consultant for and regular contributor to RT Image. Questions and comments can be directed to editorial@rt-image.com.