CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of U.S. Provisional Patent Application 61/204,574 to Gross, filed Jan. 7, 2009, entitled “Hat for hair loss treatment,” which is incorporated herein by reference. 
     
    
     FIELD OF EMBODIMENTS OF THE INVENTION 
       [0002]    The present invention generally relates to medical apparatus. Specifically, the present invention relates to an external medical apparatus for treating hair loss. 
       BACKGROUND 
       [0003]    Hair loss occurs most commonly on the head, but may affect any part of the body. Androgenetic alopecia is the most common type of hair loss, affecting about half of all men and 10 to 20% of women. Hair loss may develop gradually or suddenly. It results from hereditary factors, aging, local skin conditions, and diseases that affect the body generally (i.e., systemic diseases). Many drugs can also cause hair loss. 
         [0004]    Minoxidil, known under the brand name Rogaine®, is a drug approved by the FDA for treating hair loss. Rogaine® is applied directly to scalp skin where cessation of hair loss and stimulation of new hair growth is desired. Rogaine® is described as working by revitalizing shrunken hair follicles, thus increasing their size. When applied daily, hair follicles are described as increasing in size, and the growing phase becoming longer, producing longer, thicker hairs. Minoxidil&#39;s ability to stimulate hair growth and treat hair loss may be due to it having nitric oxide-related vasodilatory properties. 
         [0005]    U.S. Pat. No. 6,332,097 to Beder et al. describes a plurality of electrodes mounted within a hood positionable over a subject&#39;s head to form an array of concentric electrically conductive electrode rings. Beder et al. describe how the rings can be applied to an outer surface of an electrically insulating liner insertable within the hood. The array is described as preferably comprising five rings mounted within the hood to subtend a 90 degree arc on both sides of a central perpendicular axis of the hood. The four upper electrodes each subtend an arc of about 15 degrees, and the fifth (lower) electrode subtends an arc of about 6 degrees, with 6 degree arc gaps between each pair of electrodes on either side of the central perpendicular axis. A voltage pulse generator&#39;s output signal is described as being connected across the two upper electrode pairs, with alternate electrodes being connected to one of the two output terminals of the voltage pulse generator. A voltage divider applies a reduced voltage signal to the lower electrode. 
         [0006]    U.S. Pat. No. 5,344,440 to Stephen describes an improved method and apparatus for stimulating the growth and healing of living, especially human tissues, promoting the healing of wounds and skeletal fractures. Stephen describes an electrical apparatus that consists of a baseplate, made of lightweight nonconductive material, for encompassing all or a portion of a body member. A multiplicity of generally evenly spaced holes are provided in the baseplate and a probe adapter including a moveable electrically conductive probe is situated within the holes. An electric contact connects the interior of each adapter and the probe situated therein to a terminal on the baseplate. Each probe is described as being individually adjustable to contact the wearer&#39;s body part within the base member, regardless of the configuration of the body part, thus allowing treatment of all or a selected portion of the body part. 
         [0007]    U.S. Pat. No. 6,834,206 to Pitzen et al. describes a method for applying a therapeutic signal to a body portion of a subject to encourage hair growth. The apparatus is described as including a first electrode and a second electrode. The first electrode is secured in contact with the skin surface of the subject remote from the body portion, and the second electrode is positioned at the body portion. The therapeutic signal is provided at a conductive pod of the second electrode. The second electrode is manipulated by an operator to apply a circular motion to the body portion underlying the conductive pod. The circular motion is described as being repetitively applied as the conductive pod is moved across the body portion to loosen connective tissue at the body portion. 
         [0008]    U.S. Pat. No. 5,800,477 to Groux describes a method and apparatus for growing hair on a subject&#39;s scalp. The method includes pinching an area of a subject&#39;s scalp having hair bulbs for at least 2 seconds with a pair of electrodes. The electrodes are energized so that they pass a low voltage, low current and low frequency signal through the pinched area of the subject&#39;s scalp. The frequency of the signal is described as being preferably less than about 6 Hz and the current thereof is preferably between about 50 and 800 microamps. The Groux patent describes how the foregoing process is periodically repeated over several weeks, preferably months, to regrow or enhance the growth of hair on the treated area. The frequency and current of the signal are also described as being varied in each treatment for optimum results. 
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       SUMMARY OF EMBODIMENTS OF THE INVENTION 
       [0063]    For some applications of the present invention, a plurality of typically at least 24, for example, 24-100, electrodes are coupled to a housing configured to be placed on the scalp of a subject. A control unit is configured to stimulate hair growth by individually addressing subsets of one or more of the plurality of electrodes to apply a current into the scalp of the subject. Typically, the current is configured to induce nitric oxide production, which in turn enhances hair growth. 
         [0064]    The inventor has identified that when there is a large scalp area through which current can pass, the current does not uniformly pass through the area, but instead travels along one or more smaller paths of least resistance. By contrast, in these applications of the present invention, due to the alignment of the electrodes in the housing, the current is applied in many discrete, small regions, rather than across broad regions of the scalp. Application of the current in many discrete regions provides a more uniform distribution of the current, and therefore a more uniform pattern of hair regrowth. 
         [0065]    For some applications, the plurality of electrodes comprises a first and a second subset of two or more electrodes. In such an application, the control unit is configured to individually address the first and the second subsets of electrodes, by driving the current into the first and the second subsets of electrodes, in sequence, to apply the current to the scalp of the subject. 
         [0066]    In another application, the plurality of electrodes comprises a first, a second, a third and a fourth subset of two or more electrodes. In such an application, the control unit is configured to individually address the subsets, by driving the current into the subsets of electrodes in sequence, to apply the current to the scalp. 
         [0067]    Use of multiple subsets typically provides a more uniform distribution of current, and a more uniform pattern of hair regrowth. 
         [0068]    There is therefore provided, in accordance with some applications of the present invention, apparatus for stimulating hair growth of a subject, including: 
         [0069]    a housing configured for placement on a scalp of the subject; 
         [0070]    a plurality of at least 24 electrodes coupled to the housing; and a control unit configured to drive the plurality of electrodes to stimulate hair growth by driving the plurality of electrodes to apply a current to the scalp of the subject. 
         [0071]    For some applications, the plurality of electrodes includes 24 to 100 electrodes. 
         [0072]    For some applications, the control unit is configured to enhance nitric oxide production by tissue of the subject by driving the plurality of electrodes to apply the current. 
         [0073]    For some applications, at least 75% of the plurality of electrodes have a scalp-contact surface area of less than 10 mm2. 
         [0074]    For some applications, the plurality of electrodes are arranged in an array formation. 
         [0075]    For some applications, the control unit is configured to individually address subsets of two or more of the plurality of electrodes. 
         [0076]    For some applications, the control unit sets the current to have an amplitude that is between 100 uA and 4 mA. 
         [0077]    For some applications, the plurality of electrodes includes a first subset of two or more of the electrodes and a second subset of two or more of the electrodes, and the control unit is configured to individually address the first and second subsets by driving the first and second subsets of the electrodes, in sequence, to apply the current to the scalp. 
         [0078]    For some applications, the plurality of electrodes includes a first subset of two or more of the electrodes, a second subset of two or more of the electrodes, a third subset of two or more of the electrodes, and a fourth subset of two or more of the electrodes, and the control unit is configured to individually address the subsets by driving the subsets, in sequence, to apply the current to the scalp. 
         [0079]    For some applications, the plurality of electrodes includes a first and a second electrode, and the control unit is configured to: 
         [0080]    apply a first pulse of current to the scalp via the first electrode, 
         [0081]    subsequently, apply a second pulse of current to the scalp via the second electrode, and 
         [0082]    subsequently, apply a third pulse of current to the scalp via the first electrode, 
         [0083]    without applying a pulse of current to the scalp via the first electrode, between applying the first and third pulses. 
         [0084]    For some applications, the plurality of electrodes includes a first and a second electrode, and the control unit is configured to: 
         [0085]    apply a first pulse of current to the scalp via the first electrode, 
         [0086]    subsequently, apply a second pulse of current to the scalp via the first electrode, and 
         [0087]    subsequently, apply a third pulse of current to the scalp via the second electrode, 
         [0088]    without applying a pulse of current to the scalp via the second electrode, between applying the first and second pulses. 
         [0089]    For some applications, the control unit configures the current to have a frequency applied to at least one of the electrodes that is between 6 Hz and 20 Hz. 
         [0090]    For some applications, the control unit is configured to activate the plurality of electrodes in repeated waves of activation, in which at least two of the electrodes apply current to the scalp non-simultaneously, each of the electrodes applying its respective current at a respective frequency between 6 Hz and 20 Hz. 
         [0091]    For some applications, at least 75% of the plurality of electrodes are within 5 mm of another one of the electrodes. 
         [0092]    For some applications, at least 75% of the plurality of electrodes are within 1 mm of another one of the electrodes. 
         [0093]    There is additionally provided, in accordance with some applications of the present invention, a method for stimulating hair growth of a subject, including: 
         [0094]    placing a plurality of at least 24 electrodes on a scalp of the subject; and 
         [0095]    via the electrodes, driving into the scalp of the subject an electric current configured to stimulate hair growth. 
         [0096]    The present invention will be more fully understood from the following detailed description of embodiments thereof, taken together with the drawing, in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0097]      FIG. 1  is a schematic illustration of a device for treating hair loss, in accordance with some applications of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0098]    Reference is now made to  FIG. 1 , which is a schematic illustration of a hair loss treatment device  20 , in accordance with some applications of the present invention. Hair loss treatment device  20  comprises a plurality of at least 24, for example, 24-100, electrodes  24 , coupled to a housing  22 , such as a hat that fits securely to the head of a subject. A control unit  26  is configured to drive electrodes  24  to apply an electric current into the scalp of the subject configured to stimulate hair growth, typically by inducing nitric oxide production. Typically, control unit  26  is configured to individually address subsets of two or more of the plurality of electrodes  24 , to drive the subsets to apply the current into the scalp of the subject. 
         [0099]    Typically, at least 75% of electrodes  24  have a scalp-contact surface area of 0.2 mm2 to 15 mm2, or, less than 10 mm2. Typically, the scalp-contact surface of each of the electrodes is rounded. Typically, the plurality of electrodes are arranged in an array, such that at least 75% of the plurality of electrodes are within 5 mm, for example, within 1 mm, of another one of the electrodes. For some applications, at least 75% of the plurality of electrodes are within less than 1 mm of another one of the electrodes. 
         [0100]    Control unit  26  typically stimulates hair growth in the scalp of the subject by driving through each electrode an electric current with an amplitude between 100 uA and 4 mA, for example, about 1 mA, into a portion of the scalp of the subject. Typically, the electric current has a frequency between 6 Hz and 20 Hz. 
         [0101]    For some applications, a pulse (e.g., a pulse lasting 0.5 ms to 3 ms) is applied to the scalp via a first electrode pair, or a first electrode. Subsequently, a pulse is applied to the scalp via a second electrode pair, or single electrode, and so on. For some applications, having applied a current to the scalp via all of the electrodes, the cycle of applying the current to the scalp via respective electrode pairs (or electrodes) is then repeated. A time interval between the initiation of the first cycle and the initiation of the second cycle is typically about 10-200 ms, e.g., 15-45 ms (e.g., 30 ms) or 45-200 ms. In this manner, for any given electrode, the frequency of application can be a desired value, such as 6-20 Hz. For some applications, a 6-20 Hz train of pulses is applied to the scalp via a first electrode pair, or electrode, or set of electrodes. Subsequently, a train of pulses is applied to the scalp via a second electrode pair, or electrode, or set of electrodes. 
         [0102]    For some applications, device  20  comprises a first subset and a second subset of two or more electrodes  24  coupled to housing  22 . Control unit  26  is configured to individually address the first and the second subsets of electrodes  24 , by driving the first and the second subsets of electrodes  24 , in sequence, to apply the current to the scalp of the subject. The darkened pairs of electrodes in  FIG. 1  are an example of a first subset of electrodes, and in this embodiment are driven at the same time. The non-darkened pairs immediately to the right of the darkened pairs are an example of a second subset of electrodes  24 , and these non-darkened pairs are driven at the same time, but after the driving of the darkened pairs. Electrodes  24  in each subset apply a localized current to a local portion of the scalp. These localized currents generally travel along the path of least resistance through the scalp of the subject, between two electrodes, thereby stimulating hair growth. Typically, a large number of subsets of the electrodes are individually addressable, so as to provide current application to a large number of discrete regions of the scalp. 
         [0103]    For some applications, electrodes  24  are divided into a plurality of sub-arrays  28  of electrodes  24 . FIG. 
         [0104]      1 , for example, shows nine sub-arrays  28 , each sub-array containing nine pairs of electrodes  24 . Typically, one pair of electrodes  24  in each sub-array  28  is individually addressed by control unit  26  at any given time, so as to provide current application to a large number of discrete regions of the scalp at the same time. Subsequently, control unit  26  addresses another pair of electrodes  24  of each of the sub-arrays, in order to drive current into the portion of the scalp covered by the other pair. In sequence, the control unit then applies current into the scalp under each of the pairs of electrodes. (The pairs of electrodes that are addressed at any given time constitute a subset, as described above.) 
         [0105]    In another embodiment, the electrodes are not divided into sub-arrays, and the manner in which control unit addresses the electrodes is not related to an arrangement of sub-arrays of electrodes. Typically, in this case, the control unit causes a wave of activation by addressing each of the electrodes (or electrode pairs) in sequence, such that the current applied by a given electrode to the scalp has a desired frequency, such as 6-20 Hz. 
         [0106]    For some applications, only a portion of the scalp of the subject requires the use of hair loss treatment device  20 . In such an application, control unit  26  is configured to individually address only a subsection of electrodes  24  positioned local to this portion of the scalp of the subject. Alternatively or additionally, the electrodes are disposed within device  20  so as to reflect common hair loss patterns (e.g., male pattern baldness). Further alternatively or additionally, device  20  is removable from a hat and securable at a different site in the hat in order to allow treatment of a different portion of the scalp. 
         [0107]    It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. 
         [0108]    Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof that are not in the prior art, which would occur to persons skilled in the art upon reading the foregoing description.
Apparatus and methods are described for stimulating hair growth of a subject. A housing is placed on the subject's scalp, the housing having a plurality of at least 24 electrodes coupled thereto. A control unit drives the plurality of electrodes to stimulate hair growth by driving the plurality of electrodes to apply a current to the subject's scalp. Other embodiments are also described.